Speaker
Description
At high-energy electron accelerator facilities, neutron shielding is one of the main considerations in radiation shielding due to the generation of secondary neutrons by the interactions of primary and secondary particles with surrounding materials. Neutrons produced from these interactions will have wide-energy spectrum based on the incident particle energy. Higher part of neutron energy contributes significantly to the neutron dose equivalent. Therefore, neutron energy spectrum after shielding is important to properly address radiation shielding in such facility.
This study aims to confirm the exposed dose contribution from high energy neutron component at high-energy electron accelerator facility. In this study, neutron spectrum and its dose at klystron gallery in KEK injector linac were measured. KEK injector linac provides the positron beam and electron beam. To produce positron beam, tungsten target were hit by 3.3 GeV electron beam. At this target, neutron dose is at its highest.
Conventional moderator-based survey instruments are not sufficient to perform neutron measurement at this facility due to limited energy range until 20 MeV. By using extended range survey instrument such as FHT 762 WENDI-2, neutron dose up to 5 GeV can be measured. By using these two types of survey instruments, a significant amount of neutron contribution above 15 MeV has been measured at injector linac after shielding. Monte Carlo code, Particle and Heavy Ion Transport code System (PHITS) simulation for this measurement was also performed.
To measure neutron energy spectrum, a dose and spectrum monitoring system applicable to neutrons, photons, and muons over wide range of energy (DARWIN) has been used. DARWIN use liquid scintillation detector and capable to measure neutron doses from thermal energy to 1 GeV. To estimate energy spectrum, DARWIN uses the unfolding technique based on the maximum entropy deconvolution (MAXED) code.
By performing neutron dose and spectrum measurement, coupled with Monte Carlo code calculation, the contribution of the high energy component at high-energy electron accelerator were confirmed.