Simulation of neutron detection performance of a boron-coated ionization chamber with FLUKA

[Background]: At present, the existing online dose monitoring instruments have the problems of no response and dose leakage in measurements of mixed pulse radiation field generated by ultra-short and ultra-intense laser facilities. Hence, developing radiation monitoring instruments, which are suitable for the surrounding environment of laser facilities, is of great significance. [Purpose]: This study aims to achieve high-sensitivity neutron dosimeter with robust anti-interference capability in pulsed neutron-dominated radiation environments. [Methods]: A boron coated current type ionization chamber structure based on the A-B rem meter was proposed. The optimization process of the detector was realized based on FLUKA simulation. Firstly, the neutron detection efficiency was simulated under different boron thicknesses of the detector from 0.4 to 4.2 μm. Secondly, neutron sensitivity over a wide energy range under the thickness of polyethylene from 7.75 to 10.75 cm was simulated by fixing the thickness of the coated boron to 4.2 μm. Finally, the neutron and photon fields of the Station of Extreme Light (SEL) at Shanghai HIgh repetitioN rate XFEL and Extreme light facility (SHINE), were utilized as the radiation source terms for testing the response performance and n-γ resolving ability in the specific radiation field. [Results]: The results show that if the thickness of polyethylene is chosen to be 7.75 cm, the neutron detection efficiency will be 5.29% with boron thickness of 1.4 μm. The neutron sensitivity is up to 4.2 × 10-14 A/(n·cm-2·s-1) within the energy range of 0.025 eV ~ 200 MeV. Under the mixed neutron and γ radiation field conditions at the SHINE-SEL, the equivalent energy response of the detector to the neutron field with a dose rate of 71.2 μSv/h is 0.022 pA/(n·cm-2·s-1), which is three orders of magnitude higher than that to the photon field with a dose rate of 151.2 μSv/, and it has a good resistance to γ interference. [Conclusions]: This study demonstrates the feasibility of applying the boron-coated ionization chamber detector for high-sensitivity radiation dose monitoring in pulsed neutron fields.