15th Nordic Meeting on Nuclear Physics

5 May 2026, 08:00 → 8 May 2026, 14:00 Europe/Stockholm

Gotland, Visby

Ali Al-Adili, Andreas Ekström

Welcome to the 15th edition of the Nordic Meeting on Nuclear Physics, organized by Uppsala University and Chalmers University of Technology. The meeting will take place from May 5th to 8th, 2026, in the picturesque medieval city center of Visby, a UNESCO World Heritage Site nestled on the island of Gotland, Sweden. This continues a tradition of Nordic Nuclear Physics Meetings held regularly since the 1970s, rotating among Denmark, Finland, Norway, and Sweden. The 14th Nordic Meeting was organized in Longyearbyen, Svalbard, in 2018.

The Nordic Meeting offers a forum for the Nordic nuclear physics community to strengthen their collaborations, present new results, and provide opportunities for young researchers. The scientific program will consist of invited talks and contributed talks showcasing forefront applied, experimental, and theoretical developments on topics focusing on energy and medical applications, accelerators and instrumentation, nuclear and hadron structure physics, heavy-ion physics, and fundamental symmetries.

The scientific program will start in the morning on Tuesday 5 May, and end at lunch on Friday 8 May.

The program features a mix of invited and contributed presentations covering a broad range of topics in nuclear physics. Invited talks are scheduled for 20 + 5 minutes, and we are planning for contributed talks  12 + 3 and 15+5 minutes, and 5+2 flash talks.

Invited Speakers:

Gillis Carlsson, Lund University, Sweden
Andreas Heinz, Chalmers University of Technology, Sweden
Erik Jensen, Chalmers University of Technology, Sweden
Anu Kankainen, University of Jyväskylä, Finland
Henna Kokkonen, University of Jyväskylä, Finland
Arjan Koning, IAEA, Austria
Maria Markova, University of Oslo, Norway
Wanja Paulsen, University of Oslo, Norway
Stéphane Pietri, GSI, Germany
Johan Rathsman, Lund University, Sweden
Mikael Reponen, University of Jyväskylä, Finland
Karsten Riisager, Aarhus University, Denmark
Sunniva Siem, University of Oslo, Norway
You Zhou, Niels Bohr Institute, Denmark

Indico-website: 

https://indico.global/e/15thNordicMeeting

 Important dates 

• First circular, October, 2025
• Extended abstract submission deadline, January 23, 2026
• Notification of talk presentation, January 30, 2026
• Pre-book accommodation, February 15, 2026
• Registration deadline, March 15, 2026
• Conference, May 5-8, 2026

 

Local organizing committee 
• Ali Al-Adili, Department of Physics and Astronomy, Uppsala University
• Andreas Ekström, Chalmers University of Technology
Nordic organizing and program committee
• Paul Greenlees, University of Jyväskylä
• Hans Fynbo, Aarhus University
• Vetle Wegner Ingeberg, University of Oslo
• Ann-Cecilie Larsen, University of Oslo
• Stephan Pomp, Uppsala University
• Sunniva Siem, University of Oslo

Region Gotland

Tuesday 5 May

08:30 Registration

1 Welcome

Welcome to the 15th Nordic Meeting on Nuclear Physics

Speakers: Ali Al-Adili, Andreas Ekström

Energy, Data, and Society: I

Convener: Ali Al-Adili

2 From nuclear models to nuclear data

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Speaker: Arjan Koning (IAEA)

3 The Norwegian Nuclear Research Centre

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Speaker: Sunniva Siem (University of Oslo)

4 Cross-Section and Isomeric Yield Ratio Measurements at En= 14 MeV Using the NESSA D-T Neutron Facility for Reactor Dosimetry Applications

Reactor dosimetry relies on accurate nuclear cross-section data. Activation foils are often the only practical way to measure neutron flux inside a reactor core or near structural components where active detectors cannot survive. Threshold reactions with different energy sensitivities allow unfolding of the neutron spectrum. The high-energy tail is particularly relevant for fusion-fission hybrids, D-T-driven subcritical assemblies, and damage studies in reactor pressure vessels where the 14 MeV component matters such as any future fusion reactors. For reactions leading to isomeric states, the isomeric yield ratio directly affects how foil activity translates to flux. Experimental validation at 14 MeV is therefore needed to benchmark the evaluated libraries and nuclear model codes used in reactor calculations.
NESSA (NEutron Source in UppSAla) is a facility at Uppsala University built around a sealed-tube D-T neutron generator, at present producing up to 5 × 10⁸ n/s at 14.1 MeV. The facility is being developed in phases and recently commissioned with the Sodern Genie 16 generator in December 2025. A higher yield generator of strength 1 x 1010 n/s is scheduled to be commissioned by December 2026. Samples can be placed as close as 3 cm from the target, giving fluence rates of the order of 2.5 x 10⁶ n/cm²/s. Real-time beam monitoring is done with ²³⁵U and ²³⁸U fission chambers, which record the neutron yield throughout irradiation and allow correction for flux variations. The facility is designed to support cross-section measurements, detector testing, electronic damage studies and other work relevant to reactor physics and radiation protection.

As a preliminary study, we have irradiated indium and niobium foils to study several reactions of interest to reactor dosimetry. From indium activation, we observe products from multiple channels: ¹¹³In(n,2n)¹¹²In and ¹¹³In(n,2n)¹¹²ᵐIn (threshold ~9 MeV), ¹¹⁵In(n,n′)¹¹⁵ᵐIn (threshold ~0.5 MeV), ¹¹⁵In(n,α)¹¹²Ag, ¹¹⁵In(n,p)¹¹⁵Cd, ¹¹⁶In via the ¹¹⁵In(n,γ) capture reaction, and ¹¹³In(n,n′)¹¹³ᵐIn. From niobium foil irradiation, we measure the ⁹³Nb(n,2n)⁹²ᵐNb reaction, along with ⁹⁰Y produced via the (n,α) channel. The gamma spectra were acquired with an HPGe detector whose efficiency was determined from FLUKA simulations, and multiple sequential measurements allowed tracking of different decay components.
Cross-section determination requires corrections for neutron self-shielding, gamma-ray self-absorption, and where applicable—feeding from metastable to ground states via isomeric transitions, treated using the Bateman equations. For the ¹¹³In(n,2n)¹¹²In reaction, an additional complication arises from the ¹¹⁵In(n,α)¹¹²Ag channel which produces a 617 keV gamma line overlapping with ¹¹²ᵍIn; the different half-lives (3.13 h for Ag-112 versus 14.88 min for In-112g) allow separation through time-resolved measurements. We have extracted individual cross-sections for both ¹¹²ᵐIn (4⁺, T₁/₂ = 20.67 min) and ¹¹²ᵍIn (1⁺, T₁/₂ = 14.88 min) from the 156.6 keV and 617.5 keV gamma lines respectively. The preliminary results are encouraging—the isomeric ratio σₘ/σg falls in the range 3–4, consistent with TALYS calculations using various level density models and with the expectation from spin statistics that favours population of the higher-spin metastable state. Additionally, activation analysis based on a realistic neutron spectrum at the sample position has been performed using PHITS Monte Carlo simulations, providing an independent check on the expected product yields and helping to validate the experimental methodology.
These first measurements demonstrate that the NESSA facility can produce activation data relevant to reactor dosimetry. The close source-to-sample geometry provides adequate fluence rates, and real-time fission chamber monitoring ensures reliable flux determination. In the presentation, we will report cross-sections and isomeric yield ratios for the reactions studied, compare with evaluated data libraries and TALYS predictions, and discuss the measurement uncertainties achievable with the present setup. Future work will extend to additional dosimetry foils and spectrum-averaged cross-section measurements for reactor and fusion neutron spectra.

Speaker: Sandipan Dawn (Uppsala University)

10:30 Coffee

Nuclear Structure, Spectroscopy, and Decay: I

Convener: Andreas Ekström

5 From nuclear DFT to spectra and reaction observables

Accurate nuclear data are essential for simulations of new types of reactors and to deepen our understanding of the cosmos. The nuclear density-functional theory (DFT) has been developed to provide high accuracy binding energies and bulk properties of nuclei all over the nuclear chart. The quest to move from bulk properties to detailed spectroscopic information and reaction observables presents a challenge for the theory community. Overcoming the challenges involves development of improved formalism [1] and efficient methods [2] to make the connection from DFT to a fully quantal description of the nucleus. Our approach is based on employing a low-energy effective Hamiltonian that captures the response of an underlying energy density functional to external fields [2]. The resulting many-body problem is then solved using symmetry restoration in combination with the Generator-Coordinate method (GCM), using a procedure that allows it to account for both collective and single-particle excitations. This combination of low-energy interactions and GCM is a versatile many–body framework capable of describing both light and superheavy deformed nuclei [3,4]. The nuclear structure part have been integrated with dynamics within a consistent framework, enabling predictive simulations of neutron cross sections across a wide range of isotopes [5]. In this talk I discuss the recent progress of this line of research.
1. B.G. Carlsson and J. Rotureau, Phys. Rev. Lett. 126, 172501 (2021)
2. J. Ljungberg, B.G. Carlsson, J. Rotureau, A. Idini and I. Ragnarsson, Phys. Rev. C 106, 014314 (2022)
3. A. Såmark-Roth et al., Phys. Rev. Lett. 126, 032503 (2021).
4. J. Ljungberg et al., J. Phys.: Conf. Ser. 2586, 012081 (2023).
5. J. Boström , J. Rotureau , B.G. Carlsson , A. Idini, Phys. Rev. C 112, L051602 (2025)

Speaker: Gillis Carlsson (Matematisk fysik, Lunds Universitet)

6 Shape coexistence in mid‑shell of Pb isotopes and beyond

Shape coexistence is a phenomenon in which multiple shapes occur within the same nucleus. Although this phenomenon has been proposed to exist in various regions of the nuclear chart [1], neutron‑deficient Pb isotopes near the N=104 mid‑shell have been a primary focus of study for several decades. Notably, the neutron‑deficient $^{186}$Pb isotope exhibits three distinct shapes [2–5] at low excitation energy. In the shell‑model picture, these three shapes are associated with 0p–0h (spherical), 2p–2h (oblate), and 4p–4h (prolate) multiproton–multihole configurations. Performing fusion–evaporation experiments beyond the mid‑shell becomes increasingly challenging due to the decreasing production cross‑sections and the rising fission cross‑section.

The most recent results at Jyväskylä focused on $^{184}$Pb, utilising the recoil‑decay‑tagging method in conjunction with the JUROGAM II germanium‑detector array [6]. This experiment led to the identification of non‑yrast structures in $^{184}$Pb for the first time. Observing non‑yrast structures in this nucleus is currently at the limit of experimental feasibility. The systematic behaviour of structures in neutron‑deficient Pb isotopes will be discussed.

Another topic of this presentation concerns the mid‑shell nucleus $^{186}$Pb, studied using the combined gamma‑ray and conversion‑electron spectrometer SAGE. The results of this experiment enabled an assessment of the mixing between yrast and non‑yrast configurations and revealed the $2_1^+\rightarrow0_2^+$ collective transition.

This presentation will focus on the most recent results for $^{184}$Pb [6], as well as findings from combined gamma‑ray and conversion‑electron spectroscopy of $^{186}$Pb [5], and will compare these results. Both experiments were performed at the Accelerator Laboratory of Jyväskylä. Future prospects will also be outlined in this presentation.

Speaker: Joonas Kalervo Ojala (University of Jyvaskyla (FI))

7 The quadrupole moments of the $2^{+}_{1}$ state in the even neutron deficient Sn isotopes

Recent Monte Carlo Shell Model (MCSM) calculations made by T. Togashi et. al. [Phys. Rev. Lett. 121, 062501 (2018)] attempt to account for discrepancies observed between measurements and previous theoretical calculations of the reduced transition probability B(E2;$2^{+}_{1}->0^{+}_{1}$) in the neutron deficient Sn isotopes. One of the predictions of the MCSM calculation is that a shape change should occur for the $2^{+}_{1}$ state between ${}^{108}$Sn and ${}^{110}$Sn. In this work we present the first experimental results for the quadrupole moment for this state in ${}^{110}$Sn, along with preliminary results for ${}^{106}$Sn and ${}^{108}$Sn in order to address this question. The measurement results were obtained through a safe Coulomb excitation experiment at HIE-ISOLDE, using the Miniball setup. A novel analysis approach combining GOSIA and GOSIA2 codes with a DSAM measurement was used to calculate both diagonal and transitional matrix elements. Preliminary results are compared to MCSM calculations and observations regarding a shape change in the $2^{+}_{1}$ state are discussed.

Speaker: Rafael Antonio Lopez (Lund University)

8 The evolution of triaxiality in the mass 110 region

Strong triaxiality is rare in the nuclear chart, and such nuclei can serve as useful tests of theoretical predictions. The breaking of axial symmetry also enables phenomena which cannot occur in symmetrically deformed nuclei, making it an interesting phenomenon to study. The neutron rich region around mass 110 presents several cases of strong tiaxiality, namely in the ruthenium, molybdenum and palladium chains. Ruthenium especially is considered one of the best examples of strong triaxial deformation near the ground state in the entire nuclear chart.
This contribution presents new results from an experiment performed at GANIL to measure lifetimes of excited states in this region with the recoil distance Doppler-shift method. The studied nuclei were populated in a fusion-fission reaction, and identified event by event in the Variable Mode Spectrometer (VAMOS++). The Advanced Gamma Tracking Array (AGATA) provided high resolution gamma spectra of the decaying fission fragments.
We present new B(E2) values for transitions in ^108–112Ru, and compare them with phenomenological triaxial rotor predictions and fully microscopic symmetry conserving configuration mixing calculations. Triaxiality is shown to be increasing from ¹⁰⁸Ru to ¹¹²Ru, with the latter exhibiting near maximum triaxiality. The results are consistent with a simultaneous transition from γ soft to γ rigid deformation. New results for molybdenum and palladium isotopes will also be presented.

Speaker: Johannes Sørby Heines (Nuclear Physics Group, University of Oslo)

9 Recoil-decay tagging studies of neutron-deficient actinium nuclei at JYFL-ACCLAB

Since December 2020 a series of four experiments has been conducted to probe systematically the structure of all odd-A neutron-deficient actinium isotopes from $^{207}$Ac to $^{213}$Ac. In this campaign both recoil separators, RITU and MARA, of the Accelerator Laboratory of University of Jyväskylä, Finland (JYFL-ACCLAB) were employed. These experiments used fusion-evaporation reactions to produce the nuclei of interest, and the events associated with actinium isotopes were identified through very selective recoil-decay tagging method (RDT). In this talk a brief introduction will be provided to the RDT studies at JYFL-ACCLAB, followed by a discussion on the results of this campaign, some of which has been recently published [1], and some will be published in near future [2]. The main outcome of these experiments is that the structure of the studied actinium nuclei resembles strongly that of the underlying even-even radium core of a given isotope. The odd h$_{9/2}$ proton of actinium ground states appear to systematically act as a “passive spectator” and it contributes very little to the lowest exited states. Similar effect has been observed previously in nearby francium and astatine nuclei, see, for example Refs. [3-4] and references therein.

[1] J. Louko et al., Phys. Rev. C 110 (2024) 034311.
[2] H. Kokkonen et al., Under review in Phys. Rev. C
[3] U. Jakobsson et al., Phys. Rev. C 87 (2013) 054320.
[4] K. Auranen et al., Phys. Rev. C 91 (2015) 024324.

Speaker: Kalle Auranen (University of Jyväskylä)

12:30 Lunch

Facilities, Accelerators, and Instrumentation: I

Convener: Andreas Solders

10 New isotopes search experiments at GSI and prospective for FAIR

By 2023 a totality of 3337 nuclides have been discovered by mankind [1] of which 445 have been discovered at GSI in its various experimental areas (FRS, SHIP, TASCA, Online Mass Separator etc..) which ranks it as a second place in worldwide discoveries. Continuing this tradition, we report in this paper of an experiment performed at the GSI in FAIR Phase-0 where new isotopes were identified with the FRagment Separator [2] using an high intensity, high duty cycle 208Pb beam fragmentation on a beryllium target. The experiment, part of the scientific program of the Super-FRS Experimental collaboration [3], focused in the neutron rich region between terbium and rhenium, close to the N=126 line. This region is of particular interest for the NUSTAR collaboration [4] and close to the third waiting point of the r-process. As such, we used the reported experiment as a benchmark for the production of heavy ions in this region for further studies during the FAIR phase 0 NUSTAR program.
This paper will present current results of the experiment and mention last development on new isotope search during the phase 0 program of FAIR as well as presenting the possibility the new Super-FRS facility will enable starting from 2028.

[1] Discovery of Nuclides Project: https://people.nscl.msu.edu/~thoennes/isotopes/
[2] H. Geissel et al., Nucl. Inst. Meth. B 70, 286 (1992)
[3] J. Äystö et al. Nucl. Inst. Meth. Phys. Res. B 376, 111 (2016)
[4] N. Kalantar-Nayestanaki, A. Bruce, Nucl. Phys. News, 28, 5 (2018)
[5] W. R. Plaß et al., Nucl. Inst. Meth. Phys. Res. B. 317, 457 (2013)
[6] R. Kummar et al. Nucl. Inst. Meth. Phys. Res. A. 598, 754 (2008)

Speaker: Prof. Stephane Pietri (GSI Helmholtzzentrum für Schwerionenforschung, Germany)

11 Gamma-neutron program for structure nuclear and reactions with γ-ray beams at ELI-NP

The Extreme Light Infrastructure – Nuclear Physics (ELI-NP) facility is a major European nuclear physics facility for high-power laser beamlines and a projected high-brilliance γ-ray beams with energy up to 20 MeV and a very narrow bandwidth. The scientific focus of the γ beam system will cover a broad range of topics from nuclear astrophysics to applications to basic science. One of the research directions is the scientific program on photonuclear reactions and nuclear properties in the continuum and quasi-continuum, to be studied via the giant dipole resonance (GDR) and the pygmy dipole resonance (PDR). For this purpose, the ELI Gamma Above Neutron Threshold (ELIGANT) instrumentation has been developed. This suite of instruments consists of a spectroscopic setup with large-volume LaBr$_{3}$:Ce and CeBr$_{3}$ scintillator detectors, liquid scintillators and lithium glass scintillators called ELIGANT-GN [1], and a setup for (γ,n) cross-section measurements for basic science and applications using a moderated neutron counter called ELIGANT-TN [2]. Here we will discuss the instrumentation, commissioning, and some initial results from these instruments in experiments with spontaneous fission sources [3] and (α,n) reaction cross-sections from low-energy particle beams [4].

[1] P.-A. Söderström, et al. Nucl. Instrum. Methods Phys. Res. A, 1027:166171, 2022.
[2] P.-A. Söderström, et al. Nucl. Instrum. Methods Phys. Res. A, 1084:171229, 2026.
[3] D. Choudhury, et al. in manuscript
[4] R. Roy, et al. Phys. Rev. C, 112:044613, 2025; R. Roy, et al., in manuscript

This work was supported by the ELI-RO program funded by the Institute of Atomic Physics, Măgurele, Romania, contract numbers ELI-RO/RDI/2024-002 (CIPHERS), ELI-RO/RDI/2024-007 (ELITE) and the Romanian Ministry of Research and Innovation under research contract PN 23 21 01 06.

Speaker: Pär-Anders Söderström (ELI-NP)

12 Recent Developments and Measurements at the JYFLTRAP Mass Spectrometer

High-precision mass measurements of radioactive isotopes play a key role in advancing our understanding of nuclear structure and nuclear astrophysics. Nuclear masses provide direct access to binding energies and are essential inputs for testing nuclear models and studying shell evolution far from stability. Accurate masses are indispensable for modeling nucleosynthesis pathways, such as the rapid neutron-capture (r-) process, where reaction rates and decay energies strongly depend on precise input [1]. Penning-trap mass spectrometry has established itself as a powerful technique for achieving the required precision.
The IGISOL (Ion Guide Isotope Separator On-Line) facility [2] in Jyväskylä provides a versatile approach to produce exotic nuclei. Reaction products from fusion, fission, or multi-nucleon transfer reactions are stopped in a gas cell, extracted, bunched and delivered to various experimental setups. The JYFLTRAP double Penning-trap mass spectrometer [3], located downstream of IGISOL, is dedicated to high-precision mass measurements. It combines a purification trap for isobaric cleaning with a precision trap where cyclotron frequencies are measured using time-of-flight ion-cyclotron-resonance [4] and phase-imaging techniques [5]. In this contribution, I present recent developments and measurements of the Penning trap setup such as its recommissioning following a quench of the superconducting magnet and results of double-beta decay studies in the A = 150 region.

[1] M. Mumpower, et al., Prog. in Part. and Nucl. Phys. 86, 86–126 (2016).
[2] I.D. Moore et al., Nucl. Inst. Meth. Phys. Res. B 317 (2013) 208.
[3] T. Eronen et al., European Physical Journal A 48, 46 (2012).
[4] König et al., Int. J. Mass Spectrom. Ion Process. 142, 95 (1995).
[5] D.A. Nesterenko et al., Eur. Phys. J. A 54, 154 (2018).

Speaker: Simon Rausch (University of Jyväskylä)

13 Physics highlights from the SEC station of HIE-ISOLDE

The XT03 beamline at the HIE‑ISOLDE facility is a highly versatile station designed for a wide range of non‑permanent reaction experiments. At its focal plane, a large reaction chamber (SEC) is installed, capable of accommodating various internal detection setups. This article presents an overview of the first ten years of operation, highlighting key physics results achieved at the station.

Speaker: Olof Tengblad (Consejo Superior de Investigaciones Cientificas (CSIC) (ES))

15:30 Coffee

Fundamental Symmetries

Convener: Hans Fynbo (Aarhus University (DK))

14 Exploring light Z´-bosons and neutron skin with Coherent Elastic neutrino Nucleus Scattering at the ESS

Coherent Elastic neutrino Nucleus Scattering at spallation sources such as the ESS, offer new exciting possibilities to study fundamental physics in a small scale experiment. There is an ongoing effort at Lund and Uppsala universities to explore these possibilities in more detail. I will present the theoretical background for CEvNS and as examples, I will describe the possibility to search for the X17 - a hypothetical light Z´-boson, that can explain observations in Be8* -> Be8 decays made by the ATOMKI experiment, as well as possibilities to observe the neutron distribution in nuclei and exploring the neutron skin effect. I will present how the nuclear recoil spectrum would be modified for these two cases and discuss the prospects for studying them in more detail in an experiment at the ESS using a Germanium detector.

Speaker: Johan Rathsman (Lund University)

15 Experimental aspects of a potential program in neutrino physics at ESS.

This presentation will discuss the possibility of starting a program in fundamental physics at the European Spallation Source, under construction on Lund, with a specific focus on neutrino physics. One the one hand some experimental aspects of starting a program based on Decay-at-Rest (DAR) neutrinos that are produced in the ESS spallation target without any further adjustments of the facility itself will be presented. The specific challenge, when using DAR neutrinos for experiments that rely on Coherent elastic neutrino-nucleus scattering (CEvNS), is the need to reach very low-energy thresholds for detection of the nuclear recoil. A few different technologies for such experiments will be presented with a focus on low-noise and low-threshold HPGe detectors for CEvNS experiments. In the second part of the presentation I will show some results from the now completed Conceptual Design Report of a possible long-baseline neutrino facility at the ESS, ESSnuSB, funded by the EU via the Horizon 2020 program and also touch on the work done in the follow-up project ESSnuSB+.

Speaker: Joakim Cederkall (Lund University (SE))

16 High-Precision Searches for Baryon Number Violation using HIBEAM

The European Spallation Source (ESS) under construction in Lund, Sweden, is set to become the brightest cold spallation neutron source in the world. Neutrons are produced by a 2 GeV proton beam hitting a tungsten target and moderated in cold and thermal moderators.
The HIBEAM/NNBAR program is a proposed two-stage experiment at the ESS to search for baryon number violation [1]. The primary goal of the program is to produce new insights into the origins of baryogenesis by performing searches for neutron–antineutron oscillations and conversions of a neutron into a sterile neutron. The first stage of the program, HIBEAM (High-Intensity Baryon Extraction and Measurement) represents the first search for neutron to antineutron oscillations at a spallation source [2] and will be able to provide the most stringent limit of the free neutron-antineutron oscillation time to date.
In this talk, an overview over the planned beamline and detection systems will be given and the current status of development will be discussed. The neutron optics system as well as the radiation shielding have been designed and optimized using Monte Carlo simulations. The beamline is also being designed so that the magnetic field inside it can be controlled, as the processes intended to be studied are highly sensitive to external fields.
The HIBEAM annihilation detector must be able to identify the multi-pion state created by the annihilation of an antineutron in a carbon target. The planned design consists of a TPC surrounded by the WASA electromagnetic calorimeter [3] as well as scintillation detectors used to veto cosmic background. The performance of this detector has been evaluated in simulations and detector prototypes have been constructed. A first in-beam test of these prototypes was performed at the Cyclotron Centre Bronowice in Krakow, Poland. Elastic scattering of 190 MeV protons from a CD2 target was measured. First results from this experiment will be presented.

[1] Addazi et al. “New high-sensitivity searches for neutrons converting into antineutrons and/or sterile neutrons at the HIBEAM/NNBAR experiment at the European Spallation Source”, J.Phys.G: Nucl. Part. Phys. 48 (2021) 7, 070501
[2] Santoro et al. “The HIBEAM Instrument at the European Spallation Source”, J. Phys. G: Nucl. Part. Phys. 52 (2025) 040501
[3] Bargholtz et al. “The WASA Detector Facility at CELSIUS“ , Nucl.Instrum.Meth. A594 (2008) 339-350

Speaker: Matthias Holl (Lund University)

17:45 Nordic Football Tournament

Wednesday 6 May

Nuclear Structure, Spectroscopy, and Decay: II

Convener: Paul Greenlees

17 Beta-decays in (exotic) light nuclei

Beta decay increases in importance as a probe of nuclear structure as one moves towards the proton and neutron driplines. The decay energies increase so that more of the beta strength is available, and separation energies decrease leading to an increasing number of beta-delayed decay modes. I shall present an overview of which types of information have been extracted in light nuclei, here somewhat arbitrarily taken to be nuclei up to 40Ca.

Precision studies of the weak interaction often employs nuclei in this region. This is also where cluster structures and the halo structure have been probed in detail. More exotic beta-delayed decay modes (i.e. beyond emission of one nucleon or an alpha particle) can be studied here in detail. I shall give examples of all of this with a special focus on the role (for proton-rich nuclei) on the Isobaric Analogue State, as well as on the practical issues met when broad levels (with widths approaching the MeV scale) are populated. A discussion of how such decays may be described will lead to the suggestion that beta decays may proceed directly to continuum states.

Some material on these topics can be found in M. Pfützner et al, Rev. Mod. Phys. 84 (2012) 567 and my paper on beta decay of halo nuclei in Handbook of Nuclear Physics, eds I. Tanihata, H. Toki, T. Kajino.

Speaker: Karsten Riisager (Aarhus University)

18 The beta decay of 8He

The $\beta$-decay of $^8$He creates a significant background in antineutrino detectors based on the inverse $\beta$-decay mechanism due to the fact that it has $\beta$-delayed neutron final states and can be created by cosmic rays impinging on carbon. By providing excitation spectra and branching ratios for the $^8$He $\beta$-decay, this background can be quantified.

$^8$He is the most neutron-rich bound helium isotope and has the largest neutron-to-proton ratio of any bound nucleus. The diverse range of final states ($\gamma$+$^8$Li, n+$^7$Li, n+$\gamma$+$^7$Li and $\alpha$+n+t) for the decay provides a probe into the structure of $^8$Li excited states, a nucleus which is reachable by few-body quantum models.

Our experiment, performed at the ISOLDE Decay Station, is for the first time sensitive to every branch of the decay of $^8$He. In my talk I will present a holistic analysis of the decay of $^8$He, the challenges in extracting physics and the results of this effort.

Speaker: Jeppe Schultz Nielsen (Aarhus University (DK))

19 Fixing the isospin mixing of the 2+ doublet in 8Be populated via 8B beta-decay

The beta decay of 8B into 8Be is of interest both from nuclear structure and astrophysical point of view. For astrophysics, the 8B decay is the main source of solar neutrinos with energy higher than 2 MeV mainly coming from the intense (88%) beta branch of the 8B decay to the 3 MeV state of 8Be.

From the nuclear structure point of view, the 2+ 8B ground state is the only well-established proton halo state known. Its +/EC decay can give access to the 2+ doublet at 16.6 and 16.9 MeV in 8Be observed in reaction studies more than fifty years ago [1]. These states have dominant configurations as 7Li+p and 7Be+n, respectively and constitute the highest mixed isospin doublet known as stated in [2]. This assumption is able to describe well the experimental reaction data, however direct determination is missing. The beta decay of 8B feeding the 2+ states of 8Be offers a valuable avenue for probing the isospin composition of the doublet by the determination of the selective Fermi and Gamow-Teller (GT) components. However, resolving the feeding to the 2+ doublet poses challenges due to the low beta feeding.

We have performed an experiment at the ISOLDE-CERN facility's decay station to study the 8B decay. Thanks to relevant target development we achieved high statistics, allowing for first time a good separation of the population of the doublet. In this contribution, a comprehensive description of the results of experiment IS633 will be presented. We apply two methods to deduced the Fermi and GT strengths to the doublet. From these two analyses, the isospin mixing of the doublet is determined [3].

[1] C. P. Browne et al., Phys. Lett. 23 (1966) 371.
[2] P. von Brentano, Phys. Rep. 264 (1996) 57.
[3] D. Fernandez Ruiz et al., submitted.

Speaker: Prof. Maria Jose G. Borge (Instituto de Estructura de la Materia, CSIC, Serrano 113bis, E-28006, Madrid, Spain)

20 Data-driven approaches to learning about nuclear structure

The teaching of nuclear physics has traditionally followed a rather rigid pedagogical perspective offering a chronological view of the evolution of the topic. Theoretical perspectives are emphasised such as the independent-particle shell model, moving on to collective models such as the rotational model. Comparison of model predictions with experimental data is frequently limited leaving the student unclear about the limitations of the different models.

We argue for an alternative pedagogical perspective on the subject, starting with the data and seeing how the patterns observed necessarily lead to concepts such as nuclear rotation. Indeed, rotational behaviour in nuclei seems to emerge as the one paradigm strongly supported by data while evidence appears scarce, for example, in the case of true independent-particle motion behaviour. Moreover, the data points to emerging complexity in nuclear structure even in systems we might expect to be simple such as doubly-magic nuclei. Indeed, shape coexistence appears to be a ubiquitous perspective although historically this has been confused with different naming conventions in different mass regions such as “islands of inversion” and “fission isomers”.

A new approach to nuclear physics teaching starting with data has been outlined in a trilogy of electronic textbooks written by the presenter and John Wood. The first book, Nuclear Data: A Primer, provides an introduction to nuclear structure with the two later volumes, Nuclear Data: A Collective Motion View and Nuclear Data: An Independent-Particle Motion View focussing on more specific topics in nuclear structure. Through video-based tutorials and exercises, these books encourage the reader’s independent explorations making use of the contents of databases such as ENSDF. Indeed, the time is ripe to apply recently developed data science techniques to this data and discover further hidden trends. This presentation will highlight some of the key approaches found in this text book series.

Speaker: David Jenkins (University of York)

10:30 Coffee

Energy, Data, and Society: II

Convener: Sunniva Siem (University of Oslo)

21 Neural-network–enabled passive localization of multiple sources in radioactive waste

In the Swedish nuclear industry, characterization of legacy radioactive waste, produced before contemporary standards, remains a significant challenge. These waste packages often involve added complications, including concrete shielding, varying origins and lacking documentation. Because of this, traditional approaches to passive characterization may struggle.

We introduce a custom convolutional neural network approach designed to estimate the locations of radioactive soures within concrete-lines waste containers. Because of the complexities of this type of waste, experimental training data is difficult to obtain. The network is therefore trained on synthetic data produced via Monte Carlo-simulations to learn to map complex signal patterns to three-dimensional spatial coordinates for bounding boxes containing the sources.

The neural network model is designed to handle varying detector geometries and emission spectra, provided that it has been trained on the corresponding type of data, as it is independent of sensor position information. Preliminary testing on multi-source scenarios demonstrates the model's ability to detect both the quantity and location of the sources within the waste containter volume. These findings suggest that automated machine learning methods can serve as a valuable tool for characterization in complex waste scenarios.

Speaker: Vivian Peters (KTH Royal Institute of Technology)

22 Scalability of Heat-Pipe cooled Reactors for Remote and Autonomous Applications

Heat-Pipe cooled Reactors (HPRs), which were originally intended for space applications, are of particular interest for remote/autonomous operations as their designs are simple, compact, and transportable. Historically most HPR designs produce only limited thermal power in the kilowatt range and/or utilize highly enriched fuel. This work investigated how reactor design principles can be used to scale up HPRs to higher nominal powers while using less-enriched fuel and without exceeding material limits. The effective core height, number of fuel assemblies, and heat-pipe parameters were used to constrain the design parameter of the final HPR core. The open-source particle transport code OpenMC was used to determine the average volumetric heat rate of a fuel pin, which was coupled with an iterative finite-difference scheme to determine local temperature distributions in the reactor core. These were used to set new material temperatures in the neutronics model, and the process was repeated until the neutron multiplication factor had converged within a tolerance of 50 pcm. The design was simulated at thermal power levels between 5 and 20 MWth, and peak material temperatures were calculated and compared.

Speaker: Baltasar Johannes Hemmerle (University of Oslo)

23 Development of an Automated Uncertainty Quantification Pipeline in Nuclear Data Evaluation

Reliable nuclear data and well-characterized uncertainties are crucial for predictive reactor physics modeling, safety analysis, criticality assessment, and the design of advanced nuclear systems. Nuclear data uncertainties, arising from experimental measurement errors, theoretical model deficiencies, and evaluation procedures, often introduce uncertainty in key integral parameters such as the effective multiplication factor. Quantifying, reducing, and transparently propagating these uncertainties is therefore a cornerstone of next-generation reactor analysis.

We present a reproducible and automated nuclear data evaluation pipeline being developed at Uppsala University that addresses the uncertainty propagation in nuclear cross-section data through structured integration of experimental data, nuclear reaction modeling, and statistical inferences [1]. The pipeline is designed as a modular workflow to facilitate systematic evaluation of neutron-induced cross sections, focusing on the fast neutron energy range above the resolved resonance region. Reproducibility and ease of deployment are achieved via containerized execution, enabling consistent environments across computational platforms and facilitating collaborative development and system independent output.

The core concept of the pipeline combines the TALYS [2] nuclear model parameters with differential experimental data, primarily sourced from EXFOR nuclear database, to quantify uncertainty in cross-section predictions. A tailored Levenberg-Marquardt optimization algorithm is employed to calibrate non-linear model parameters against experimental observations [1], embedding sensitivity to both statistical and systematic data uncertainties within the calibration process. A particular emphasis of the pipeline lies in the explicit treatment of model defects, especially where smooth theoretical predictions diverge from unresolved resonance-like structures present in experimental data. This is addressed through the inclusion of heteroscedastic Gaussian process models that adaptively characterize energy-dependent deviations between model and experiment [3]. The result is evaluated cross-sections with integrated uncertainty descriptions that reflect both measurement limitations and theoretical modeling uncertainty.

In this contribution, we will outline the design and methodological development of the nuclear data evaluation pipeline, including data ingestion, uncertainty analysis, and covariance matrix generation. We illustrate its relevance to reactor physics applications by discussing how the evaluated data can be leveraged in uncertainty studies for generation IV reactor concepts.

References:
[1] G. Schnabel et al., Nuc. Data Sheets 173, 239 (2021).
[2] A. J. Koning and D. Rochman, Nucl. Data Sheets 113, 2841 (2012).
[3] A. Göök et al., EPJ Web Conf. 294, 04005 (2024).

Speaker: Dr Jinti Barman (Uppsala University)

24 Multi-coincidence set-up for nuclear forensics with Si-strip and Compton-suppressed HPGe detectors

A radiation detection system combining a single-sided Si strip detector
and a HPGe-COMPEX detector module together with its anti-Compton shield was set up at Lund University for environmental sample measurements. This system enables high sensitivity alpha-beta-gamma-coincidence analysis, enhancing the identification level of radionuclides in environmental samples. A comprehensive multi-coincidence data acquisition system was implemented for optimal signal readout. It was demonstrated using a real environmental filter sample containing traces of radionuclides from the Th-232 natural decay chain. A set of calibrated IAEA samples with different sources has been identified using a single-blind study.

Speaker: Luis Gerardo Sarmiento Pico

25 Multi-MOX: Facilitating plutonium multi-recycling in the French PWR fleet

The findings of a study published in Annals of Nuclear Energy, June 2025, will be presented (DOI: https://doi.org/10.1016/j.anucene.2025.111641).

This study examines the novel Multi-MOX (MMOX) strategy for plutonium multi-recycling in PWRs using the CLASS fuel cycle simulation tool with assembly-level calculations. MMOX facilitates the multi-recycling of used nuclear fuel by mixing reprocessed plutonium from various sources to create viable fresh nuclear fuel. The strategy significantly curtails the growth of the plutonium inventory, but does not stabilize it entirely in the long term. Although lower fuel burnup reduces plutonium build-up, it increases the production of minor actinides. Comparing MMOX with non-recycling and mono-recycling scenarios, we find that it reduces plutonium inventory by 35% and 19%, respectively. Despite a higher level of minor actinide production, MMOX decreases overall transuranic element production. Additionally, MMOX reduces the need for interim spent fuel storage by a factor of ten compared to non-recycling and by two-thirds compared to mono-recycling, while substantially lowering the age of stockpiled used nuclear fuel.

Speaker: Gulla Torvund (Department of Physics, University of Oslo)

12:30 Lunch

14:00 Networking Activities

Energy, Data, and Society: III

Convener: Sunniva Siem (University of Oslo)

26 The Historical Economics of the US Nuclear Fleet

Between the 1960s and early 1980s, the United States undertook the world’s largest nuclear power construction program. Early projects benefited from declining construction costs, making nuclear power economically competitive with fossil alternatives. From the early 1970s and onward, however, overnight construction costs (OCC) escalated rapidly, coinciding with regulatory tightening, high inflation and interest rates, and increasing project size and complexity. This cost escalation ultimately ended the U.S. nuclear build-out and has since been extensively studied. Most existing analyses focus on construction costs alone, leaving unresolved the question of whether nuclear investments were economically successful over their full operating lifetimes.
This paper addresses that gap by evaluating the historical economics of the U.S. nuclear fleet using lifetime performance metrics rather than construction costs alone. By combining reactor-specific OCC data with detailed operational, fuel, and financial data, the study reconstructs Levelized Cost of Electricity (LCOE) and Net Present Value (NPV) for U.S. nuclear reactors over their initial operating lifetimes.

Fuel costs are estimated using a physics-based model of the uranium fuel cycle calibrated to historical reported fuel cost reporting, while O&M costs are reconstructed using plant-specific data supplemented by fleet-level benchmarks.
The results contribute a long-missing perspective to nuclear cost studies by evaluating whether the U.S. nuclear build-out was economically successful when judged on realized lifetime performance rather than construction outcomes alone. The findings offer empirical insights for current nuclear investment debates, particularly regarding optimal reactor size, project complexity, and the economic lessons relevant for future nuclear deployment.

Speaker: Vala Valsdottir (University of Oslo)

27 SFI SAINT - The Future of Nuclear Maritime

This presentation will introduce SFI SAINT, an NTNU-led research project funded for the next 8 years.

"SFI SAINT will conduct research on nuclear power as a zero-emission technology for shipping, with the goal of developing, testing and scaling solutions for commercial use. The center will work on regulations, adaptation to maritime operations, energy efficiency, integration into ships, training, education, risk management and business models. Industrialization and interdisciplinary collaboration will be central. The ambition is to contribute to demonstrating solutions on Norwegian ships in the 2030s.

NTNU will collaborate with the University of Bergen, Department of Energy Technology STI, SINTEF, the Norwegian Defence Research Agency, 13 Norwegian companies, two partners from the public sector, four foreign companies and three foreign research institutions."

Speaker: Jessica Chow (NTNU)

16:40 Coffee

Flash talks: I

Convener: Andreas Ekström

28 Neutronic Analysis of a Hybrid Fuel Cycle Between Maritime and Terrestrial Fluoride-salt-cooled High-temperature Reactors

This study computationally evaluates a hybrid nuclear fuel cycle in which partially depleted fuel pebbles from a compact maritime Fluoride-salt-cooled High-temperature Reactor (FHR) are transferred to a larger terrestrial FHR for continued utilization. Neutronic behavior is analyzed using a high-fidelity Monte Carlo framework: the Hyper-Fidelity (HxF) tool models detailed depletion in the maritime reactor, while the Search Equilibrium tool determines the equilibrium steady-state fuel composition in the terrestrial core. Results indicate that the hybrid approach significantly enhances total energy extraction per unit mass of heavy metal compared to independent single-reactor operation. While a conventional once-through cycle achieves an average burnup of 148 MWd/kgHM, transferring pebbles at burnup of 47.5 MWd/kgHM enables a subsequent burnup of 110 MWd/kgHM in the terrestrial core, yielding a total of 157.5 MWd/kgHM, a 6.4% increase. Additionally, performance improves further at lower transfer burnups, with 35 MWd/kgHM transfers achieving total burnups up to 163 MWd/kgHM. These results demonstrate that sequential burning of pebbles in spectrally different reactor environments can outperform the energy extraction limit of single-core operation, providing a potential path toward improved fuel utilization and reduced waste generation for advanced FHR fleets, and potentially other TRISO fueled reactors.

Speaker: Mr Josef A. H. Hisanawi (Department of Physics, University of Oslo)

29 FREYA as a fission fragment generator in the TALYS nuclear reaction code

The need for accurate nuclear data is crucial for the nuclear power industry, and with the Swedish plans to invest in new Gen IV nuclear power plants, there is a further need for new nuclear data regarding the processes involved in these new reactor concepts. Together with experimental data, simulated nuclear data is an important tool for nuclear research. The nuclear reaction code TALYS has a wide range of capabilities, from medical and astrophysical applications, to the simulation of the nuclear fission process. Currently, TALYS has the option of using simulated fission fragment yields from four different fission codes, which are then de-excited using a sophisticated Hauser-Feshbach model to produce data for fission observables, such as average multiplicities and average energies for prompt neutrons and prompt gammas. The TALYS model can be used as a common tool to de-excite simulated fission fragments in order to benchmark different fission codes against each other, which makes it possible to investigate the effects of different models assumptions, such as fission fragment yield distributions and excitation energy sharing between fragments and how these effects the results for the fission observables. This work investigates the possibility of introducing the nuclear fission code FREYA as an additional fission fragment generator in TALYS by using simulated fission fragment yield files from FREYA in the TALYS evaporation process. The standalone results for the fission observables from the FREYA model are compared to those of the GEF and HF3D models and the results for the fission observables from the TALYS model using FREYA, GEF and HF3D as fission fragment generators are investigated.

Speaker: Peter Karlsson (Uppsala university)

30 Total Monte Carlo approach to geometric uncertainty propagation in mesh-based geometries

In nuclear engineering, a criticality event is an instance in which a chain reaction reaches a state of self-sustenance. Criticality safety involves preventing inadvertent criticality events by managing factors such as material composition, geometric configuration, and neutron interactions. Thus, the quality and success of criticality safety analyses inherently depend on how well nuclear data, material distribution, and geometric parameters are known. Uncertainty propagation is therefore fundamental to the field of criticality safety. In this work, we demonstrate the Total Monte Carlo approach to geometric uncertainty propagation (the GTMC method) using mesh-based geometries. The method is implemented using the RINGEN (Random INput file GENerator) tool, which was previously used to propagate geometrical uncertainties in location and size within constructive solid geometry (CSG). The current work extends the capabilities of the RINGEN tool to incorporate mesh-based geometries, allowing it to handle other forms of geometric uncertainties such as localized deformations, shape variations, and surface roughness. We evaluate this new approach across three benchmark cases, comparing results against both adjoint-based perturbations and the original CSG-based RINGEN implementation. The GTMC method with mesh-based geometries reproduces equivalent results when modeling equivalent uncertainties, while offering vastly improved scope and fidelity for modeling intricate geometric uncertainties beyond the reach of traditional CSG. Finally, the future outlook of the GTMC method and the RINGEN tool is discussed.

Speaker: Amit Hasan Arpon (Uppsala University)

31 The ELIFANT Array: Selected Physics Results

Extreme Light Infrastructure – Nuclear Physics, Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, 30 Reactorului Street, 077125 Magurele, Romania

In the period 2022-2025, four experimental campaigns were carried out at the 9 MW tandem accelerator of IFIN-HH using the large-volume LaBr$_3$:Ce and CeBr$_3$ detectors of the ELIGANT-GN array, which were placed in the anti-Compton shields of the ROSPHERE [1]. As a result, a highly efficient spectrometer, ELIFANT, was assembled for the detection of high-energy gamma rays. The ELIFANT experimental program included measurements of weak γ-ray decay branching ratios in $^{10}$B [2-6], the precise radiative decay of the Hoyle state in $^{12}$C [7,8], the search for extra PDR strength at high nuclear temperature in $^{56,60,62}$Ni, the so-called HOT-PDR mode [9,10], isospin mixing in the $^{72}$Kr via GDR decay [11], and measurements of γ-strength functions in $^{112,114}$Sn and level densities of $^{128}$Te in the PDR region and the nuclear quasi-continuum [12,13].

This program will be extended to studies of the structure of the PDR in different nuclei at the N = 28 neutron shells, and the Z = 28 proton shell in (d,pγ) reactions using the ELIFANT array, and their comparison with excitations using other probes.

In this contribution, I will describe the performance of the spectrometer, and some selected results from the experimental campaigns will be presented.

References:
[1] S. Aogaki, et al., Nucl. Instrum. Methods Phys. Res. A, 1056, 168628 (2023).
[2] A. Kuşoğlu, D. L. Balabanski, Quantum Beam Sci., 7(3), 28 (2023)
[3] A. Kuşoğlu, et al., Phys. Rev. Lett. 133, 072502 (2024)
[4] A. Kuşoğlu et al., Nuovo Cim. C, 47, 47 (2024)
[5] A. Kuşoğlu, Sci. Bull. 69, 3303-3304 (2024)
[6] A. Kuşoğlu et al., EPJ Web of Conf. 311, 00020 (2024)
[7] K. Sakanashi et al., EPJ Web of Conf. 306, 01047 (2024)
[8] K. Sakanashi et al., Phys. Lett. B, 139893 (2025)
[9] O. Wieland et al., Nuovo Cim. C, 47, 24 (2024)
[10] O. Wieland et al., Acta Phys. Pol. B Proc. Suppl. 18, 2-A33 (2025)
[11] A. Giaz et al., Phys. Lett. B 868, 139653 (2025)
[12] P. A. Söderström et al., Phys. Rev. C, 112, 024327 (2025)
[13] P. A. Söderström et al., Phys. Scr. 100, 075301 (2025)

Acknowledgment: This work was supported by the Romanian Ministry of Research and Innovation under research contract PN 23 21 01 06, and the ELI-RO program funded by the Institute of Atomic Physics, Măgurele, Romania, contract numbers ELI-RO/RDI/2024-002 CHIPHERS and ELI-RO/RDI/2024-007 ELITE.

Speaker: ASLI KUŞOĞLU (ELI-NP/IFIN-HH)

32 Field Theory for Neutronics

Recent research suggests that neutron fluctuations in combination with feedback effects might have a non-negligible impact on the neutron distribution in nuclear reactors. This phenomenon can be analysed with statistical physics by using methods from quantum field theory. In this presentation, I will give an overview of previous research and our plan for how to improve the theoretical model. Preliminary results might be included, depending on our progress.

Speaker: Jacob Persson (Uppsala universitet)

33 Root2ebye - Using simulations to mimic DAQ output

As experiments often are complex, simulations are a helpful tool in
designing experimental setups and subsequent analysis. There already
exists many Monte Carlo simulation programs to simulate the physics.
However, a method to convert the simulated data to mimic the DAQ
output removes the need to use measured data to test the analysis
software. This makes it possible to prepare the analysis tools before
the setup phase of an experiment, which was done last year for an
experiment at ISS. We can also use the same analysis tools to directly
compare simulations of certain aspects of our experiments with the
measured data. This is currently being worked on to be used for an
experiment at FRIB.

Speaker: Björn Johansson (Aarhus University (DK))

Thursday 7 May

Nuclear Astrophysics, and Reactions

Convener: Eda Sahin

34 Precision mass measurements for nuclear astrophysics

Nuclear masses are key inputs for r-process calculations. With JYFLTRAP double
Penning trap at the IGISOL facility in the JYFL Accelerator Laboratory, we have recently
determined masses for dozens of neutron-rich nuclei and their isomeric states, see e.g.
[1-6]. With the phase-imaging ion-cyclotron resonance technique, it is possible to
resolve long-lived isomeric states with low excitation energies, leading to better
accuracy for the ground-state masses. The measurements directly improve the
precision of astrophysical reaction-rate calculations for neutron captures but also
serve important testing points for current mass models used for the experimentally
inaccessible r-process nuclei. In this contribution, I will present an overview of our
recent results from JYFLTRAP.
References
[1] A. Jaries et al., Phys. Rev. C 110, 045809 (2024).
[2] A. Jaries et al., Phys. Rev. Lett. 134, 042501 (2025).
[3] M. Hukkanen, W. Ryssens, et al., Phys. Rev. C 107, 014306 (2023).
[4] M. Hukkanen, W. Ryssens et al., Phys. Lett. B 856, 138916 (2024).
[5] J. Ruotsalainen et al., Phys. Rev. C 111, 044314 (2025).
[6] L. Canete et al., Phys. Lett. B 853, 138663 (2024).

Speaker: Anu Kankainen (University of Jyväskylä)

35 TBD

na

Speaker: wanja paulsen (university of Oslo)

36 The Pygmy Dipole Resonance and its evolution across the Sn mass region

The pygmy dipole resonance (PDR) is commonly associated with excess $E1$ strength superimposed on the low-energy tail of the giant dipole resonance (GDR), near the neutron-separation energy in both stable and unstable heavy nuclei. Although its detailed structure, properties, and origin remain under debate, the neutron-skin oscillation picture still prevails, suggesting a dependence of the PDR strength on neutron excess. Recent experimental studies, however, have challenged this interpretation [1, 2]. To further elucidate its structure, systematic investigations across isotopic chains, both of the PDR and the low-lying $E1$ strength in general, are of highly desired.

This work presents the most recent update on a consistent systematic study of the low-lying electric dipole strength and the potential PDR in stable and unstable Pd, Cd, In, Sn, and Sb isotopes with the Oslo method [3]. This method exploits the compound-nucleus mechanism to extract dipole $\gamma$-ray strength functions and nuclear level densities below the neutron threshold from particle–$\gamma$ coincidence data obtained in light-ion–induced reactions at the Oslo Cyclotron Laboratory. The most recent ($p,p^{\prime}\gamma$) and ($\alpha,p\gamma$) experiments have been performed with a new array of 30 LaBr3(Ce) scintillator detectors (OSCAR) with an improved energy resolution and timing properties for the selection of particle-$\gamma$ events as compared to the earlier experiments done with the NaI(Tl) detector array CACTUS. All previously published GSFs of Cd [3] and Pd [4] isotopes have been re-analysed to provide a more consistent analysis of the strengths in the Sn mass region.

With a wide range of isotopes, from neutron-deficient $^{109}$In to neutron-rich $^{127}$Sb, these dipole strengths provide an excellent basis for investigating the evolution of the PDR with increasing proton–neutron asymmetry. By combining these data with available $(\gamma,n)$ cross sections and dipole strengths from (p,p$^{\prime}$) Coulomb excitation experiments, we extract the low-lying $E1$ component of the total dipole strength in each case. This component is found to exhaust approximately $1$–$3\%$ of the classical Thomas–Reiche–Kuhn (TRK) sum rule, remaining nearly constant along the Sn isotopic chain and showing only a weak increase with neutron number in Cd and Pd isotopes. This behavior contradicts most theoretical approaches, such as relativistic quasiparticle random-phase and time-blocking approximations, which predict a strong, steady increase in low-lying $E1$ strength with neutron number. Moreover, a possible isovector component of the PDR is identified for $^{118-122,124}$Sn. Particular attention in this work will be given to the most neutron-deficient case, $^{109}$In, recently studied at OCL, which exhibits little to no excess $E1$ strength below the neutron threshold and thus stands out among neighboring isotopes. An interpretation of this observation within the random-phase time-blocking approximation framework will be discussed.

References
1. P. von Neumann-Cosel \textit{et al.}, Phys. Rev. Lett. \textbf{133}, 232502 (2024).
2. M. Markova \textit{et al.}, Phys. Lett. B \textbf{860}, 139216 (2025).
3. A. C. Larsen \textit{et al.}, Phys. Rev. C \textbf{83}, 034315 (2011).

Speaker: Dr Maria Markova (University of Oslo)

10:20 Coffee

Fission

Convener: Stephan Alois Pomp (Uppsala University (SE))

37 Fission in inverse kinematics – history, status and outlook

The use of radioactive beams in inverse kinematics has a strong impact on nuclear physics research and nuclear fission is no exception. Nuclear fission is a quite complex process with a large number of observables, such as fission fragment charge and mass distributions, multiplicities and energies of evaporated neutrons and gamma-rays, released total kinetic energy, fission cross sections and more. It is an experimental challenge to measure as many of those observables as possible in coincidence to obtain a clear picture of the evolution of a fissioning nucleus from the ground state to the eventual formation of the fission fragments.
Inverse kinematics turned out to be a game-changer, as it dramatically increased the number of fissioning isotopes, which could be accessed to study low-energy fission at small angular momenta. Such fission reactions are strongly influenced by shell effects and pairing and offer a unique perspective into the evolution of cold nuclear matter at extreme deformations. Experiments in inverse kinematics contributed to the revival of this field of research in the past twenty years, as did a renewed interest from nuclear astrophysics. In this presentation the ongoing volution of fission experiments in inverse kinematics will be discussed, while physics results from this approach will be highlighted. Finally, an outlook toward future experiments will be given.

Speaker: Andreas Heinz (Chalmers University of Technology)

38 Isomeric yield ratios and angular momenta of fission fragments in proton induced fission

Isomeric yield ratios (IYRs) are key observables in nuclear fission, as they provide insight into the angular-momentum distribution of primary fission fragments. Accurate IYR data are also essential for modeling the r-process in stellar nucleosynthesis and for determining the antineutrino mixing angle from reactor spectra. In addition, IYRs play a role in nuclear-energy applications, including β-delayed neutron emission and decay-heat calculations. Nevertheless, experimental data remain scarce, and evaluations therefore rely heavily on model estimates, such as those from the Madland–England approach.

In a recent study, a large set of IYRs was measured in proton-induced fission of ^{238}U. The experiment was performed at the IGISOL facility using the Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique, which enables separation of ground-state and excited-state isomers at mass differences down to a few tens of keV. The analysis included newly developed procedures to correct for detector efficiency and decay losses.

The measured IYRs, together with 12 ratios from an earlier experiment, were compared with predictions from the Madland–England model and the GEF fission code. The results show that the Madland–England model is too crude to describe the population of long-lived states, and that GEF also fails to reproduce many of the ratios, partly due to limited proton-induced fission data and simplified de-excitation modeling. To mitigate the latter, a hybrid approach combining GEF with the reaction code TALYS was evaluated. Overall, the comparisons indicate that while spin configurations of the populated states account for part of the trends, additional effects—such as the state of the fissioning system and the configuration of the complementary fragment—are also important.

To estimate fragment angular momenta from the measured IYRs, a surrogate model based on GEF was developed to generate average properties of primary fragments. By varying the four model parameters, including the fragment angular momentum, and using TALYS to compute the relative isomer populations, average angular momenta with uncertainties were extracted from 24 of the measured ratios. The results reveal a mass-dependent trend consistent with earlier observations in other fissioning systems.

Speaker: Andreas Solders

39 Upcoming Fission Program at the Oslo Cyclotron Laboratory

The Oslo Cyclotron Laboratory (OCL) at the University of Oslo is developing a comprehensive experimental program focused on advancing our understanding of nuclear fission. Leveraging the existing cyclotron infrastructure and state-of-the-art detection systems such as OSCAR [1, 2], this program aims to investigate prompt fission gamma emission and the interplay between nuclear structure and fission mechanisms in the actinide systems.

A central component of the program is the development of a fission chamber setup equipped with newly developed scintillation-based fission fragment detectors [3, 4] and the detection of gamma rays in coincidence with fission fragments. The available beams of p, d, and alpha particles at the OCL provide the opportunity to perform particle-induced fission reactions. A study performed with conventional fission gas detectors in the past highlighted the capability to study structural features in PFGS and their evolution with excitation energy [5], which was possible to measure using the charged particle setup SiRi [6]. In a significant advancement, the highly segmented S2 detectors will be used to detect charged particles with even better precision, enabling further enhancement in the resolution of the excitation energy of the fissioning system. By combining multi-detector arrays with advanced data acquisition and analysis frameworks, we aim to constrain theoretical models of fission and improve predictive capabilities relevant for both fundamental nuclear science and applied domains.

This presentation will outline the scientific goals of the OCL fission program, describe the experimental setups under commissioning, and discuss preliminary results from pilot studies. In addition, we will highlight planned collaborations within the Nordic research community and opportunities for joint activities that can enhance the collective research impact on emerging questions in fission.

References
[1] F. Zeiser, et al., Nucl. Instrum.Meth. A 985, (2021) 164678.
[2] V. W., Ingeberg et al., Under production and soon to be submitted.
[3] M. Hunyadi et al., Adv. Photonics Res. 2025, 2400217.
[4] M. Hunyadi et al., Adv. Funct. Mater. 2022, 32, 2206645
[5] D. Gjestvang et al., Phys. Rev. C 103, (2021) 034609.
[6] M. Guttormsen et al., Nucl. Instrum. Methods Phys. Res. A 648, (2011) 168–173.

Speaker: Neeraj Kumar (Norwegian Nuclear Research Centre (NNRC), University of Oslo)

40 Transfer-induced fission at the ISOLDE Solenoidal Spectrometer

The study of nuclear fission remains a critical area of research, not only for advancing our understanding of fundamental nuclear processes but also for its implications in the synthesis of heavy elements in astrophysical environments. In the context of r-process nucleosynthesis, fission plays a pivotal role by limiting the mass of nuclei that can be produced. However, data on the fission barriers of neutron-rich nuclei are still scarce. Investigating these fission barriers is crucial for understanding the impact of nuclear structure on fission dynamics.

The ISOLDE Solenoidal Spectrometer (ISS) introduces a novel approach to studying fission probabilities of neutron-rich actinides through (d,pF) reactions using Radioactive Ion Beams. This method employs an innovative setup designed to enhance detection efficiency for fission fragments, which are detected in coincidence with transfer-like protons in a solenoidal magnetic field. This optimised technique enables access to the fission probability as a function of the excitation energy. Furthermore, complementary $\gamma$-ray measurements provide valuable information on the total energy and multiplicity of $\gamma$-rays emitted during fission.

As an initial step to establish this new approach, the fission barrier of $^{233}$U has been measured. This data is not only important for our understanding of nuclear fission but could also have relevance for the thorium fuel cycle. In this presentation, the experimental setup will be introduced, and preliminary results will be discussed, emphasizing its potential to enhance our understanding of fission processes. Beyond this specific study, this method could be extended to explore even more exotic nuclei further from the valley of stability, offering new opportunities to investigate fission in regions of the nuclear chart that have previously remained experimentally inaccessible.

Speaker: Maria Vittoria Managlia (Chalmers University of Technology)

41 Very asymmetric fission yields of U-233(n,f) at LOHENGRIN

In this work we report on a fission yield experiment done with the LOHENGRIN recoil mass spectrometer. Understanding the dynamics of nuclear fission requires accurate knowledge of the charge and mass distributions of fission fragments, particularly in rare and poorly studied regions. We present a dedicated investigation of the assymetric fission yields in 233U(n$_{th}$,f), targeting fragment masses below A = 70, a region previously unexplored for this system. A particular focus is on confirming an expected enhancement of the yields of fragments near mass 70, potentially indicative of a super-asymmetric fission mode influenced by nuclear structure effects, such as the Z = 28 major shell closure. The experiment employed the LOHENGRIN recoil mass spectrometer in combination with a ΔE/E Frischgrid ionization chamber. This allows the identification of the mass of light fission fragments. The far asymmetric mass region will serve for benchmarking theoretical models and improving our understanding of shell effects in fission.

During the presentation, we discussed the necessary correction steps during the analysis, including digital signal processing, scanning ionic charge and kinetic energy distributions, and target burn-up. Moreover, we discuss a comparison of different foil stacks that can be used as passive attenuators in the next beam-time campaign. Preliminary results from this work suggest a yield enhancement in the studied region, implying that the fissioning system U234* may exhibit a similar effect like the heavier systems. We finish by discussing the outlook and preparations for upcoming beam times at ILL.

Speaker: Marius Torsvoll (University of Oslo)

12:30 Lunch

Nuclear Structure, Spectroscopy, and Decay: III

Convener: Gillis Carlsson (Matematisk fysik, Lunds Universitet)

42 Imaging-By-Smashing: New Frontiers of Nuclear Structure from MeV to TeV

One of the central challenges in nuclear physics is achieving a precise understanding of the structure of the atomic nucleus. Recent developments have shown that relativistic nuclear collisions at RHIC and the LHC can complement low‑energy nuclear experiments by providing a snapshot of the nuclear shape at the moment of collision, offering a sensitive probe of nuclear structure.

In this talk, I will present our latest advances in nuclear structure studies using the imaging‑by‑smashing technique, which connects final‑state collective expansion to the initial geometry of colliding nuclei at relativistic energies. I will demonstrate how this approach constrains the quadrupole deformation and triaxiality of $^{129}$Xe and highlight new opportunities to explore nuclear shape phase transitions in Xe–Xe collisions at the LHC. Furthermore, I will discuss recent collective‑flow measurements designed to probe $\alpha$-cluster structures in $^{16}$O and $^{20}$Ne through O–O and Ne–Ne collisions at the LHC. These developments form a crucial step toward bridging low‑energy nuclear physics at the MeV scale with high‑energy heavy‑ion physics at the TeV scale.

Speaker: You Zhou (Niels Bohr Institute (DK))

43 Decay spectroscopy studies on the two new isotopes of astatine

Decay properties of two new astatine isotopes, $^{188}$At and $^{190}$At, were studied in the Accelerator Laboratory of University of Jyv\"askyl\"a, Finland. The nuclei were produced in fusion-evaporation reactions, and those were subsequently separated from the primary beam using the gas-filled recoil separator RITU (Recoil Ion Transfer Unit). Decay spectroscopy studies resulted with a proton emission from $^{188}$At, presenting the observation of the heaviest known proton-emitting nucleus to date. The proton is suggested to be emitted from a prolate deformed (2$^-$) state, with a dominant $s_{1/2}$ proton component in the wavefunction. The interpretation was based on the non-adiabatic quasiparticle model which was expanded to treat nuclei in the beyond-lead region. The one-proton separation energy deviates from the systematics, and a possible source for this effect will be discussed in this presentation. The $\alpha$-decay properties for the second lightest known astatine isotope, $^{190}$At, were measured and compared to the systematics. In addition, the possible presence of proton emission from this nucleus is discussed. In this presentation, the experimental details and the results of already published $^{188}$At [1] and $^{190}$At [2] isotopes will be presented.

[1] H. Kokkonen, K. Auranen et al., Nat Commun 16, 4985 (2025)
[2] H. Kokkonen, K. Auranen et al., Phys. Rev. C 107 064312 (2023)

Speaker: Henna Kokkonen (University of Jyväskylä)

44 Neutron reactions from Hamiltonian solutions in deformed nuclei

A microscopic and coherent description of nuclear structure and reactions is crucial to extend the predictivity of scattering observables, particularly for exotic nuclei that have not yet been discovered [1]. Optical potentials provide an effective way to decouple the nuclear structure many-body problem from the nuclear reaction few-body problem by constructing a projectile–target interaction.
We have developed a generator coordinate method (GCM) model based on an effective Hamiltonian [2]. Using this framework, we have calculated low-energy scattering properties for Mg and Cr isotopes, as reported in [3] and in an upcoming publication. This method provides the first viable way to calculate nuclear reaction observables from a microscopic structure model in heavy and deformed nuclei.
In this talk, I will illustrate the steps involved in constructing an optical potential for deformed nuclei from microscopic wavefunctions obtained with the projected GCM built on a Hartree–Fock–Bogoliubov basis.

References
[1] C. Hebborn et al., J. Phys. G 50, 060501 (2023)
[2] J. Ljungberg et al., Phys. Rev. C 106, 014314 (2022)
[3] J. Boström et al., Phys. Rev. C 112, L051602 (2025)

Speaker: Andrea Idini (Lund University)

45 Probing exotic silver and palladium isotopes beyond the N=50 shell closure near tin-100

The different configurations of the atomic nucleus form a landscape of over 3000 known isotopes. However, even more than 100 years since its discovery
by Ernest Rutherford, the complexity of the nucleus continues to elude a global theoretical description. To drive theory development, new experimental data
are required from unexplored reaches of the chart of nuclei. A key area for new data is the immediate region below the heaviest bound self-conjugate nucleus,
tin-100. This proton-rich region past the shell closure has been and continues to be the subject of intense experimental and theoretical research [1]. However,
only limited information is available for the ground-state properties in the region, mainly due to challenges in producing these isotopes with sufficiently high
yields. Recently, new ultra-sensitive measurement techniques developed at the University of Jyväskylä Accelerator Laboratory opened the immediate vicinity
of tin-100 to optical spectroscopy and mass spectrometry studies [2,3]. Here I will present our most recent result on mass and optical studies on
silver [4] and palladium isotope chains, culminating on the masses of isotopes 94-Ag and 92-Pd which we recently accessed at the IGISOL facility. I will also give an overview of ongoing developments with a brief view to the near future.

[1] Magdalena Gorska. “Trends in the Structure of Nuclei near 100Sn”. en.
In: Physics 4.1 (Mar. 2022). Number: 1
[2] M. Reponen et al. “An inductively heated hot cavity catcher laser ion
source”. In: Review of Scientific Instruments 86.12 (Dec. 2015), p. 123501.
[3] M. Reponen et al. “Evidence of a sudden increase in the nuclear size
of proton-rich silver-96”. en. In: Nature Communications 12.1 (July 2021), p. 4596.
[4] Z. Ge et al. High-precision mass measurements of neutron deficient silver isotopes probe the robustness of the = 50 shell closure. Phys. Rev. Lett. 133, 132503, (2024).

Speaker: Mikael Reponen (University of Jyvaskyla (FI))

15:30 Coffee

Flash talks: II

Convener: Ali Al-Adili

46 Hyperon-Hyperon Interaction Studies Close to Threshold with CBM at FAIR

on behalf of CBM and "QCD at FAIR"

The strong interaction between baryons at low energies is a key ingredient for understanding the emergence of nuclear matter from Quantum Chromodynamics (QCD). Among other topics, the “QCD at FAIR” program at FAIR aims to explore strongly interacting matter with versatile experimental setups, e.g. CBM and HADES, using hadronic and electromagnetic probes, with particular emphasis on strangeness as a tool to access short-range QCD dynamics. Future measurements will provide unique opportunities to constrain baryon-baryon interactions beyond the nucleon-nucleon sector, which are essential for nuclear structure and astrophysical applications.

This contribution focuses on the determination of low-energy scattering parameters such as scattering lengths and effective ranges in baryon–baryon systems using short-ranged production reactions such as $pp\mapsto \Lambda\Lambda K^+K^+$ in the low-GeV energy regime ($\sqrt{s}$=3.6 GeV). Near-threshold hadronic reactions provide indirect but powerful access to final-state interactions in channels where direct scattering data are scarce or unavailable, notably for hyperon–nucleon and hyperon–hyperon systems. This talk addresses the methodological aspects and experimental requirements for such studies with CBM within the “QCD at FAIR” program based on feasibility studies using Monte Carlo simulations, thus highlighting their role in establishing a systematic description of baryon-baryon forces with strangeness. These measurements constitute a key step toward a quantitative understanding of non-perturbative QCD in the baryonic sector and provide essential input for modelling nuclear matter.

Speaker: Gandharva Appagere (Stockholm University)

47 Search for Axion-Like Particles at the European Spallation Source

The European Spallation Source (ESS), currently under construction in Lund, Sweden, will provide the most intense pulsed neutron beam in the world. To make use of this unique infrastructure, the two-stage HIBEAM/NNBAR program [1,2] proposes to use neutron beamlines for precision studies of fundamental symmetries. While one of its principal goals is the first search in more than three decades for free neutron-antineutron oscillations, the HIBEAM beamline is envisioned for a broader program that also includes a newly proposed search for ultralight axion-like particles (ALPs) [3].

With the support of the Swedish Foundation for Strategic Research and Swedish Research Council, the collaboration is developing a 10-meter long dual-layer mumetal magnetic shield along with a coil system for Ramsey interferometry. In parallel, ongoing efforts aim to optimise the neutron optics, polarisation system and neutron detector for improved experimental performance and operational reliability. Informed by finite-element magnetostatics simulations and spin dynamics simulations, the design of the magnetic shield and its mechanical support is nearing completion, while ensuring consistency with ESS engineering and radiation safety constraints. Therefore, the procurement phase is commencing and the shield will thereafter be characterised and used in fundamental physics experiments.

In this talk, I will review the physical motivation behind searches for dark matter and axion-like particles. I will then describe the experimental setup in detail and outline the ongoing work on beamline design, with emphasis on magnetic field control, detector design and simulation-driven performance studies.

[1] V. Santoro et al. J. Phys. G: Nucl. Part. Phys. 52, 040501 (2025).
[2] V. Santoro et al. JNR 25(3-4):315 (2024).
[3] P. Fierlinger et al. Phys. Rev. Lett. 133, 181001 (2024).

Speaker: Linus Persson (Lund University)

48 Radiative Neutron-capture Rates on the Exotic $^{132}\mathrm{I}$ Isotope for the Intermediate Neutron-capture Process on $^{130}Te(\alpha, p\gamma)^{133}\mathrm{I}$ Data Using the Oslo Method

The nucleosynthesis of elements heavier than iron remains an open question in nuclear astrophysics. In the last decade, the intermediate (i) neutron-capture process has attracted attention as a potential explanation for observed abundance patterns in for example the old halo stars in our Galaxy, that cannot be reproduced by the slow and rapid processes. Understanding the i-process requires reliable neutron-capture reaction rates for nuclei away from stability, which motivates the present work.
The work presents an experimental study performed at the Oslo Cyclotron Laboratory (OCL) where a $^{130}\mathrm{Te}$ target was irradiated by an alpha beam to populate excited states in $^{133}\mathrm{I}$ through the $^{130}\mathrm{Te}(\alpha, p\gamma)^{133}\mathrm{I}$ reaction. The emitted protons and $\gamma$ rays are measured by the SiRi and OSCAR detectors. By applying the Oslo method on the particle-$\gamma$ coincidence data, the nuclear level density and $\gamma$-ray strength function of $^{132}\mathrm{I}$ is extracted and used as input to nuclear reaction codes like TALYS to provide astrophysical reaction rates on the radiative neutron-capture reaction $^{132}\mathrm{I}(n, \gamma)^{133}\mathrm{I}$ of importance for the i process.

Speaker: Claudia Grieg (Department of Physics, University of Oslo)

49 Indirect measurement of the $^{132}$I(n,$\gamma$)$^{133}$I neutron-capture rate on the exotic $^{132}$I for the intermediate neutron-capture process

The nucleosynthesis of elements heavier than iron remains an open question in nuclear astrophysics. In the last decade, the intermediate (i) neutron-capture process has attracted attention as a potential explanation for observed abundance patterns in for example the old halo stars in our Galaxy, that cannot be reproduced by the slow and rapid processes. Understanding the i-process requires reliable neutron-capture reaction rates for nuclei away from stability, which motivates the present work.

The work presents an experimental study performed at the Oslo Cyclotron Laboratory (OCL) where a $^{130}$Te target was irradiated by an alpha beam to populate excited states in $^{133}$I through the $^{130}$Te($\alpha$, p$\gamma$)$^{133}$I reaction. The emitted protons and $\gamma$ rays are measured by the SiRi and OSCAR detectors. By applying the Oslo method on the particle-$\gamma$ coincidence data, the nuclear level density and $gamma$-ray strength function of $^{132}$I is extracted and used as input to nuclear reaction codes like TALYS to provide astrophysical reaction rates on the radiative neutron-capture reaction $^{131}$I(n, $\gamma$)$^{132}$I of importance for the $i$ process.

Speaker: Claudia Grieg

50 An investigation into the scissors mode in well deformed Sm isotopes using the Oslo method

The samarium isotopic chain provides us with an opportunity to study how the statistical properties, such as the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF), are effected by deformation.

In 2018, an experiment was carried out at the Oslo Cyclotron Laboratory where we studied the $^{152}$Sm$(p,p^\prime\gamma)^{152}$Sm and $^{154}$Sm$(p,p^\prime\gamma)^{154}$Sm reactions. The NLD and $\gamma$SF were extracted using the Oslo method for these reactions. The $\gamma$SFs were plotted together with data from $(\gamma,n)$ experiments in order to distinguish several resonances which are seen in $^{152,154}$Sm.

In this work, a resonance compatible with the Scissors Mode was found in both isotopes. Finally, the strength of the scissors resonance, $B_{SR}(M1)$, for both $^{152}$Sm and $^{154}$Sm were extracted. These $B_{SR}(M1)$ values will be compared with other available samarium isotopes to see how this changes with deformation.

Speaker: Lauren Bell (University of Oslo)

51 Ground-state properties of exotic silver isotopes in the immediate vicinity of tin-100

The atomic nucleus exhibits a vast variety of configurations, and despite over a century of study since its discovery, a unified theoretical description of nuclear structure remains incomplete [1]. Progress in this field relies critically on new experimental data from regions of the nuclear chart that remain largely unexplored. One such key region lies in the immediate vicinity of the doubly magic nucleus tin-100, the heaviest bound self-conjugate (N=Z) system, where strong shell effects and proton-neutron correlations are expected to show [2]. The purpose of this research is to investigate the ground-state properties of proton-rich isotopes below tin-100, with particular emphasis on silver isotopes such as silver-95. These nuclei provide a sensitive probe of the robustness of the N=50 shell closure and the evolution of the nuclear structure approaching the N=Z line [3]. Precise measurements of masses, charge radii, and magnetic moments in this region, enabled by newly developed optical spectroscopy and mass spectrometry techniques at the University of Jyväskylä Accelerator Laboratory [4], put to test modern nuclear theories, such as Density Functional Theory (DFT), and could establish a benchmark for future theoretical developments.
I will present the status of magnetic moment measurements performed with in-source resonance ionization spectroscopy on exotic silver isotopes up to silver-95, and give a picture of the the nuclear charge radius below the N=50 shell closure in silver isotopes.

[1] R. Li et al. “Measured proton electromagnetic structure deviates from theoretical predictions”. en. In: Nature (2022).
[2] M. Konieczka et al. “Gamow-Teller response in the configuration space of a density-functional-theory–rooted no-core configuration-interaction model”. In: Physical Review C 97.3 (2018). Publisher: American Physical Society, p. 034310.
[3] J. Karthein et al. “Electromagnetic properties of indium isotopes illuminate the doubly magic character of 100Sn”. In: Nature Physics 20 (2024), p. 1719–1725.
[4] M. Reponen et al. “Evidence of a sudden increase in the nuclear size of proton-rich silver-96”. en. In: Nature Communications 12.1 (2021), p. 4596.

Speaker: Natalia Ambrosio Macias (University of Jyväskylä)

52 Microscopic study of the low-energy enhancement in the gamma-decay strength of $^{50}$V

The low-energy enhancement (LEE) of the dipole γ-ray strength function has been observed in many nuclei, yet its microscopic origin remains debated. We investigate the LEE in $^{50}$V using large-scale shell-model calculations that treat electric and magnetic dipole transitions consistently within a single framework. Calculations are performed in a sd–pf–sdg valence space with a $1\hbar\omega$ truncation, employing the SDPFSDG-MU interaction and the KSHELL code. The model space yields several thousand eigenstates and nearly two million individual E1 and M1 transitions.

Benchmark comparisons demonstrate excellent agreement with experimental data: low-lying levels are reproduced within 300 keV, the calculated level density matches Oslo-method data up to $E_x\!\approx\!7.5$ MeV, and the dipole γ-strength function follows the measured shape over the full experimental γ-energy range, including the LEE. By separating electric and magnetic contributions, we show that the enhancement in $^{50}$V is entirely of magnetic dipole origin. Both spin and orbital components of the M1 operator are essential, with constructive interference between them providing a significant additional enhancement at low γ energies.

Analysis of one-body transition densities identifies $0f_{7/2}\!\rightarrow\!0f_{7/2}$ proton transitions as the dominant microscopic mechanism driving the LEE, while transitions between different orbitals govern the higher-energy M1 strength. These results establish a direct link between specific shell-model configurations and emergent statistical properties of γ decay, providing a quantitative microscopic explanation of the LEE in this mass region.

Speaker: Jon Kristian Dahl (University of Oslo)

19:00 Dinner

Friday 8 May

Nuclear Structure, Spectroscopy, and Decay: IV

Convener: Joakim Cederkäll (Lund University)

53 TBD

na

Speaker: Erik Jensen (Chalmers University of Technology)

54 Coulomb Dissociation of 17B

The neutron halo is one of the most intriguing features in systems with a large excess of neutrons compared to protons, providing valuable information about weakly bound many-body systems near the neutron drip line. $^{17}$B has long been regarded as a two-neutron halo nucleus based on various experimental observations. However, recent studies suggest otherwise due to a dominant $d$-wave configuration of the valance neutrons and due to the presence of a thick neutron skin.
In this work, we report the first measurement of electric dipole ($E1$) excitation of $^{17}$B. A kinematically complete measurement was performed at RIBF, RIKEN, using the SAMURAI spectrometer. A $^{17}$B beam at 270MeV/u was impinged on a Pb target causing Coulomb dissociation (CD), and the breakup fragments $^{15}$B and two neutrons were detected in coincidence. From this measurement, the differential CD cross section $d\sigma_{\mathrm{CD}}/dE_x$ and the $E1$ strength distribution $dB(E1)/dE_x$ were extracted.
The observed $E1$ strength distribution indicates that $^{17}$B has a weakly developed halo. These results provide important structural information on $^{17}$B and they contribute to setting the criteria required for neutron halo formation.

Speaker: Hyeji Lee (University of Oslo)

55 Study of isomers in 165W and 169W

The level structures of two tungsten isotopes, $^{165}$W and $^{169}$W, have been experimentally well known up to high spin since over 30 years ago. However, in both cases, these structures were not connected to the ground states of the two nuclei. The reason for this, as it turns out, is the presence of an isomeric state preventing the observation of all transitions down to the ground state. These nuclei have now been studied using fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä (JYFL). The connections between the floating levels and their respective ground states have been probed using the recoil-decay tagging method. The experimental setup at JYFL included the recoil-separator MARA, JUROGAM 3 Ge-detector array, and several detectors at the focal plane.The observed isomeric states have been assigned spin-parities of $(13/2^+)$ in $^{165}$W and $(9/2^+)$ in $^{169}$W and half-lives of $7.4(2)$ µs and $7.4(5)$ µs, respectively, have been measured. In this presentation, I will describe the setups in detail and how these results were extracted from unexpected sources of data - produced on the side in a calibration measurement of an experiment and during a competition for high-school students.

Speaker: Henna Joukainen (Chalmers University of Technology)

56 Impact of octupole deformation on the nuclear electromagnetic response

Reflection-symmetry-breaking nuclear octupole deformation is a phenomenon of significant interest due to its connection with fundamental symmetry considerations ($\mathcal{C}$, $\mathcal{P}$, and $\mathcal{T}$) and its relevance in nuclear structure studies. Substantial experimental evidence indicates that a few nuclei exhibit a pear-like octupole deformation [1], whereas global theoretical studies predict the existence of a dozen or even more such nuclei [2]. Meanwhile, the nuclear electromagnetic response can provide insight into the collective properties of the nucleus, such as deformation [3,4]. However, the impact of octupole deformation on the nuclear electromagnetic response remains less studied and is the focus of the present work.

We have studied the effect of octupole deformation on the nuclear electromagnetic response using nuclear density functional theory (DFT) combined with linear response theory. We employed the Skyrme-Hartree-Fock-Bogoliubov (HFB) model to determine two distinct deformed ground-state solutions for the studied nuclei: one with conserved and the other with broken reflection symmetry. Based on these two HFB ground-state solutions, we performed finite amplitude method (FAM) [5] calculations to solve quasiparticle random phase approximation (QRPA)-type equations and obtain transition strength functions. In the calculations, zero-energy linear and rotational momentum spurious modes associated with the broken translational and rotational symmetries, respectively, were removed where relevant. The resulting transition strength functions and selected sum rules were then compared between the two deformed HFB solutions.

We calculated electric and magnetic transition strength functions for different multipolarities ($E1$, $E2$, $E3$, and $M1$) of expected octupole-deformed even-even nuclei around the actinide region. Our results indicate three key aspects of the effect of octupole deformation on the nuclear electromagnetic response. Firstly, octupole deformation appears to have only a modest impact on the transition strengths in the resonance region. Secondly, at low excitation energies (< 8 MeV) of $M1$ transitions, especially around the expected scissors resonance [4], octupole deformation has a stronger impact on transition strengths. This effect even leads to a violation of the expected correlation [4] between the non-energy weighted sum rule and the quadrupole deformation parameter. Thirdly, our analysis confirms that octupole-deformed solutions can exhibit a significant rotational spurious contribution to the isoscalar $E3$ transition strength (its $K=1^-$ mode), which is consistent with the non-conservation of parity in these solutions. Therefore, both the rotational and linear-momentum spurious modes were removed from the calculated isoscalar $E3$ transition strengths. These results motivate further investigation into the impact of octupole deformation on low-energy $M1$ transitions and highlight the importance of accounting for spurious mode contributions arising from broken parity symmetry.

[1] P. A. Butler. Proc. R. Soc. A 476, 20200202 (2020).
[2] Y. Cao et al. Phys. Rev. C 102, 024311 (2020).
[3] B. L. Berman and S. C. Fultz. Rev. Mod. Phys. 47, 713 (1975).
[4] K. Heyde, P. von Neumann-Cosel, and A. Richter. Rev. Mod. Phys. 82, 2365 (2010).
[5] P. Avogadro and T. Nakatsukasa. Phys. Rev. C 84, 014314 (2011).

Speaker: Manu Kanerva

10:15 Coffee

Facilities, Accelerators, and Instrumentation: II

Convener: Vetle Wegner Ingeberg (University of Oslo (NO))

57 Fragmentation Cross-section Measurements at FRS Using the Uranium Beam

Projectile fragmentation is universal and very powerful tool for production of exotic nuclei, including neutron-deficient species. The yield estimates of neutron-deficient trans-Pb nuclei lack benchmark against experimental data in terms of production cross sections. Therefore, measurements of projectile fragmentation cross-sections using the 1 AGeV ²³⁸U primary beam on a beryllium target have been carried out at the GSI Fragment Separator (FRS) in FAIR Phase-0 programme.

Gathering cross-section data towards and beyond the borders of known nuclei is important for tests and further development of fragmentation models. It is also important for planning of future experiments at FAIR Super-FRS. Most of the existing data originate from a measurement of ²³⁸U at 1 AGeV on a proton target [1]. Another study [2] measured fragmentation cross section of ²³⁸U + ⁹Be reaction at 1 AGeV. This study provides the possibility compare to theoretical models down to cross section of about 1 nb, but is limited to Th and Pa isotopes. There is a large mismatch when comparing the cross-section predictions of the EPAX or ABRABLA codes with scarce data. This is profound especially for the trans-Pb neutron-deficient nuclei.

To provide a reliable dataset of fragmentation reaction cross sections, measurements at FRS are presented. These data contain a comprehensive set of cross sections of neutron-deficient isotopes ranging from Pb to U. In the present contribution, the methodology and results will be presented. The measurements form a part of larger programme at FRS to map production cross sections in projectile fragmentation.

[1] Taïeb et al., Nucl. Phys. A 724 (2003) 413
[2] Kurcewicz et al., Nucl Phys A 767 (2006) 1

Speaker: Tuomas Grahn (University of Jyvaskyla (FI))

58 Designing coincidence gamma-ray spectrometers with optimized minimum detectable activity

Coincidence gamma-ray spectrometers are promising detector systems in numerous circumstances, thanks to their improved minimum detectable activity (MDA) compared to conventional single-detector systems. In the field of radionuclide monitoring, coincidence gamma-ray spectrometers have the potential to lower detection thresholds and improve the ability to verify compliance with treaties that ban the detonation of nuclear weapons, such as the Comprehensive Nuclear-Test-Ban Treaty (CTBT). In the CoSpeR collaboration between Uppsala University and the Swedish Defence Research Agency (FOI), the design of coincidence gamma-ray spectrometers is optimized to achieve low MDAs of key CTBT-relevant nuclides that emit gamma-rays in coincidence. Simulations with the Geant4 toolkit are used to evaluate the MDA of detector concepts and are used for parametric detector design studies. This presentation will discuss the simulation approach behind the parametric design study, show preliminary results, and describe the future path towards high-sensitivity gamma-ray detector systems.

Speaker: Elias Arnqvist

59 First measurements of the (n,Xp)Fe-nat cross sections with the Medley setup at GANIL

Light-ion emission from neutron-induced reactions remains crucial for enhancing our understanding of the theoretical models governing these nuclear reactions, as well for a wide range of practical applications. Despite advances in recent decades, models such as those implemented within codes like TALYS, still strongly rely on experimental data to constrain free parameters. Accurate measurements are essential for better model prediction, specially at the 20 MeV - 40 MeV range, where pre-equilibrium processes dominate the emission processes and nuclear effects are gradually washed out.

This knowledge also directly impacts our comprehension on how structural materials respond to radiation damage under longer periods of irradiation, proving to be a fundamental aspect of fusion-relevant materials development, which will be extensively explored in facilities such as in the International Fusion Materials Irradiation Facility - Demo Oriented NEutron Source (IFMIF-DONES) facility, under construction in Granada, Spain.

This project presents the first results for proton emission measurements from natural iron (Fe-nat), carried out in the Neutrons for Science (NFS) facility, part of the Grand Accélérateur d'Ion Lours (GANIL), in France. The facility provides a neutron beam from 40 MeV deuterons impinging on a Beryllium converter. The Medley setup, conceived and built by Uppsala University, was used to provide large angular coverage and optimal particle identification capability.

The results are compared with TALYS calculations using different configurations, as well as other available measurements. A key strength of this experiment is its ability to provide high-quality nuclear data across a wide energy and angular range, contributing to improve the knowledge of nuclear reaction mechanisms and pavementing the way for more accurate predictions on the radiation damage caused by neutron fields to structural materials.

Speakers: Lucas De Arruda Serra Filho (Uppsala University / Université de Caen-Normandie / Grand Accélérateur d'Ions Lourds (GANIL)), Diego Tarrío

60 Hadron physics at Belle II

The Belle II experiment at the SuperKEKB electron–positron collider provides a high-luminosity environment uniquely suited for precision studies of hadron physics. Although primarily designed for flavor physics, Belle II offers powerful opportunities to address key questions in non-perturbative QCD that are of direct interest to nuclear physics.
In this talk, I will present recent Belle II measurements and near-term prospects relevant to hadron spectroscopy, hadronization, and the internal structure of hadrons.
Belle II measurements of exotic hadron candidates provide improved information on masses, widths, quantum numbers, and decay modes.
Analyses of semi-inclusive hadron production in electron–positron annihilation yield differential cross sections, azimuthal asymmetries, and transverse-momentum distributions that can directly constrain TMD fragmentation functions and spin–momentum correlations.
Furthermore, Belle II measurements of meson and baryon time-like electromagnetic form factors can probe hadron structure in a kinematic regime complementary to space-like experiments.
These existing and future results demonstrate the capability of Belle II to deliver high-impact hadron-structure measurements and its complementarity with ongoing and future nuclear physics experiments.

Speaker: Bianca Scavino (Uppsala University)

61 Belle II Tracking and Optimisation of Hit Finding

Reliable track reconstruction is vital for the success of the Belle II experiment, especially as detector conditions evolve. The full tracking chain in the Belle II Analysis Software Framework combines Central Drift Chamber (CDC)-seeded and Silicon Vertex Detector (SVD)-seeded tracking stages, which are merged and cleaned to produce final tracks using a Combinatorial Kalman Filter (CKF). We focus on optimising the SVD-seeded CKF extension into the CDC, where SVD-only tracks are extrapolated to attach CDC hits. This step is sensitive to CDC inefficiencies caused by ageing electronics and inactive wires. A grid search is used to tune key CKF hyperparameters—such as allowed layer skips—using a F1 score built from hit efficiency and hit purity as the optimisation objective. The resulting parameter set, which yields the highest F1 score, is integrated into the full tracking chain, thereby improving tracking robustness and performance under degraded detector conditions. In this task, a description of the Belle II tracking chain and results from the optimisation will be presented.

Speaker: Mr Adeel Akram

62 Closing

Speakers: Ali Al-Adili, Andreas Ekström