Speakers
Description
Precision and accurate measurements with neutron beams require a monochromatic, background-free, variable-energy neutron source. Also, the accuracy of absolute normalization of the neutron flux is essential. We are working towards developing a neutron source that meets these criteria. This is also in support of the mandates D1, D3 of the CUPAC-NE Collaboration$^{[1]}$. In particular, IUAC-PAC has approved two precision measurements by our collaboration$^{[2,3]}$.
For example, Nuclear Astrophysics reactions have very low cross-sections. These reactions proceed through emissions of photons, neutrons and/or charged particles. These background radiations introduce uncertainties in reaction rate measurements. For photon detection, this is circumvented by constructing the accelerator and detector facility in deep underground environments (LUNA$^{[4]}$, JUNA$^{[5]}$). The Indian Neutrino Observatory proposal is also towards this direction. However, this technique isn’t optimum for neutron beam measurements, since alpha emitters like Th in surrounding rocks produce neutrons through ($ \alpha $,n) reactions. The accelerator itself also contributes background neutrons, and achieving “perfect neutron shielding” is highly challenging. Our efforts are aimed at mitigating these effects, and progress made towards this is reported.
Our background suppression method relies on a similar technique used in leading nuclear astrophysics facilities, like ERNA (Italy), St. George (USA), Dragon (Canada), etc. In these, an RMS is used in inverse kinematics and coincidence is imposed between signals in the detector and the recoils detected at the RMS focal plane. Our method will use the HIRA-RMS facility at IUAC in inverse kinematics$^{[6]}$.
Finally, the neutron beam production method is similar to “The Orsay neutron source” at IPN, France$^{[7]}$. In this, p($^{7}\text{Li}$,$^{7}\text{Be}$)n was used in inverse kinematics and kinematic focusing was used to get neutron flux as high as 10⁷ n/s/sr (100nA beam-current). The main constraints according to the authors were: (i) Damage to the production target by incident beam, (ii)Compromise of the key monochromatic character of the neutron beam above E($^{7}\text{Li}$)=16.513 MeV,and (iii)Impracticality of the technique for E($^{7}\text{Li}$)>25.726 MeV. These pose serious limitations on the utility of the “neutron source” for fundamental research. We will use the 15-UD Pelletron accelerator at IUAC, identical to the one used at IPN-Orsay, but optimized to overcome the limitations stated by them. In addition, our method also addresses the issue of the “absolute normalization of neutron flux”.
A 4 MHz $^{7}\text{Li}$ pulsed beam from the IUAC 15-UD pelletron will be used for neutron production using p($^{7}\text{Li}$,$^{7}\text{Be}$)n reaction in inverse kinematics. The available neutron beam energy range will be 300 keV-12 MeV with $\Delta E$~100 keV. The source of backgrounds, the scattered and/or secondary neutrons and photons, will be suppressed by demanding that the neutron and the $^{7}\text{Be}$ originate from the same event.
We have performed a preliminary ion optics simulation for HIRA RIB mode. Fig.(2) presents the simulation results for a 32 MeV $^{7}\text{Li}$ beam and 16.73 MeV $^{7}\text{Be}$ ions, after target loss. The results obtained matches closely with those documented during the commissioning of the RIB facility$^{[8]}$. Table-1 lists the ion optical parameter from the simulation. This is a preliminary simulation up to first-order. Further optimization is required for better output.
Acknowledgement: We extend our heartfelt gratitude to Prof. G. C. Wary, Prof. M. Patgiri, Dr. V. M. Datar, HIRA group, Dr. S. Santra and Dr. P. C. Rout for their constant guidance and unwavering support.
References:
1 G. C. Wary et al., “Developing a Discovery Class Particle Accelerator Facility at Cotton
University by CUPAC- North East Collaboration,” Proc. DAE SNP, 65, G4, 760 (2021).
2 J. J. Das et al., “Production and slowing down of fast neutron beam produced using 15-UD Pelletron accelerator and HIRA facility for AD-BNCT investigations at IUAC Delhi,” IUAC AUC-71368, 2021.
3 J. J. Das et al., “Measurement of s process neutron source strength in AGB stars by time reversal method,” AUC-75328, 2024.
[4] H Costantini et al.,“LUNA: a Laboratory for Underground Nuclear Astrophysics,” Rep. Prog. Phys. 72 086301, 2009, doi: 10.1088/0034-4885/72/8/086301
[5]Hao Ma et al., “Status and prospect of China Jinping Underground Laboratory”, J. Phys.: Conf. Ser. 2156 012170, 2021, doi: 10.1088/1742-6596/2156/1/012170
[6] A. K. Sinha et al.,“Heavy ion reaction analyzer (HIRA): a recoil mass separator facility at NSC,”NIM A 339 (1994) 543-549, https://doi.org/10.1016/0168-9002(94)90191-0
[7] M. Lebois et al., “Development of a kinematically focused neutron source with the p($^{7}\text{Li}$,$^{7}\text{Be}$)n inverse reaction,” NIM A 735 (2014) 145-151, https://doi.org/10.1016/j.nima.2013.07.061
[8] J. J. Das et al., “Development of a radioactive ion beam facility using 15 UD tandem accelerator at NSC,” J. Phys. G: Nucl. Part. Phys. 24 (1998) 1371–1375, doi:10.1088/0954-3899/24/8/009
[9] https://web-docs.gsi.de/~weick/gicosy/
