Speaker
Description
We started a program [1] at the RIKEN Radioactive Isotope Beam Factory (RIBF) aiming to measure the spin-isospin responses of light nuclei along the neutron drip line. There is no available data on spin-isospin collectivity for nuclei with large isospin asymmetry factors, where (N−Z)/A>0.25 [2]. We investigated this unexplored region up to (N−Z)/A=0.5.
The spin-isospin responses of $^{11}$Li and $^{14}$Be drip-line nuclei were measured in charge-exchange $(p,n)$ reactions at around 180 MeV/nucleon beam energies. These reactions in inverse kinematics, at intermediate beam energies (E/A>100 MeV) and small scattering angles can excite Gamow-Teller (GT) states up to high excitation energies in the final nucleus, without Q-value limitation [3,4].
The combined setup [5] of our new, digital-readout-based low-energy neutron spectrometer, PANDORA (Particle Analyzer Neutron Detector Of Real-time Acquisition) [6] and the SAMURAI large-acceptance magnetic spectrometer [7] together with a thick liquid hydrogen target allowed us to perform the SAMURAI30 experiment with high luminosity. In this setup, PANDORA was used for the detection of the recoil neutrons with kinetic energy of 0.1–5 MeV, while the SAMURAI was used for tagging the decay channels of the reaction residues. It was proven, in our first (p,n) experiment on $^{132}$Sn [8], that using such setup we can take data on unstable nuclei with quality comparable to those on stable nuclei.
In this talk, details of experimental setup as well as the intelligent digital-pulse processing for neutron-gamma discrimination with PANDORA will be presented. We successfully identified 15 different decay channels of the $^{11}$Be reaction product. Preliminary result of the reconstructed excitation-energy spectrum and B(GT) distribution up to 40 MeV, including the Gamow-Teller (GT) Giant Resonance region in $^{11}$Li, will be reported. Our observation, that GT peak occurs below the Isobaric Analog State in $^{11}$Li, will be discussed in connection with the variation of residual spin-isospin interaction in exotic nuclei.
[1] L. Stuhl et al., RIKEN Accelerator Progress Report 48, 54 (2015).
[2] K. Nakayama, et al., Phys. Lett. B 114, 217 (1982).
[3] M. Sasano et al., Phys. Rev. Lett. 107, 202501 (2011).
[4] M. Sasano et al., Phys. Rev. C 86, 034324 (2012).
[5] L. Stuhl et al., Nucl. Instr. Meth. B 463, 189 (2020).
[6] L. Stuhl et al., Nucl. Instr. Meth. A 866, 164 (2017).
[7] T. Kobayashi, et al., Nucl. Instr. Meth. B 317 294 (2013).
[8] J. Yasuda et al., Phys. Rev. Lett. 121, 132501 (2018).
| Topic | Experiment |
|---|
