Abstract:
Background Gamma and thermal neutron imaging are important non-destructive testing methods, which are complementary in many aspects. The thermal neutron and gamma bimodal imaging can combine the advantages of both. Compared with single beam imaging, the bimodal imaging has the ability to identify different substances and the sensitivity to both nuclides and elements simultaneously.
Purpose Utilizing the reaction between protons and target material producing neutrons and gamma together, based on the 18 MeV cyclotron accelerator being developed by the China Institute of Atomic Energy, this paper presents a design of a bimodal imaging neutron source by simulation.
Methods Beryllium with a high (p, n) reaction cross-section is selected as the neutron target to generate neutrons. To obtain thermal neutrons with higher flux, polyethylene is used as the neutron moderator and reflector. By the different spatial distributions of thermal neutrons and gamma, these two types of radiation are separately extracted from different directions. Besides, by designing the neutron and gamma exits on polyethylene, high neutron flux and gamma beams are simultaneously obtained.
Results After simulation optimization, the thermal neutron flux at the thermal neutron outlet can reach 1.78×1010 n/（cm2·s） , and the gamma dose at the gamma outlet can reach 2.23×104 rad/h.
Conclusions This paper presents a design of a neutron source for thermal-neutron-gamma imaging based on the 18 MeV/1 mA cyclotron accelerator. The design efficiently extracts thermal neutron flux and gamma flux from a single target, implementing a single-target-dual-source configuration.
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