Study on the gamma rays and neutrons energy response optimization of a scintillating fiber detector for EAST with Geant4

A new scintillating fiber detector inside magnetic shielding tube was designed and assembled for use in the next round of fusion experiments in the experimental advanced superconducting tokamak to provide D-T neutron yield with time resolution. In this study, Geant4 simulations were used to obtain the pulse height spectra for ideal signals produced when detecting neutrons and gamma rays of multiple energies. One of the main sources of interference was found to be low-energy neutrons below 10-5 MeV, which can generate numerous secondary particles in the detector components, such as the magnetic shielding tube, leading to high-amplitude output signals. To address this issue, a compact thermal neutron shield containing a 1-mm Cd layer outside the magnetic shielding tube and a 5-mm inner Pb layer was specifically designed. Adverse effects on the measurement of fast neutrons and the shielding effect on gamma rays were considered. This can suppress the height of the signals caused by thermal neutrons to a level below the height corresponding to neutrons above 4 MeV because the yield of the latter is used for detector calibration. In addition, the detector has relatively flat sensitivity curves in the fast neutron region, with the intrinsic detection efficiencies (IDEs) of approximately 40%. For gamma rays with energies that are not too high (< 8 MeV), the IDEs of the detector are only approximately 20%, whereas for gamma rays below 1 MeV, the response curve cuts off earlier in the low-energy region, which is beneficial for avoiding counting saturation and signal accumulation.