Modelling the response of semiconductor based thermal neutron detectors with MCNP 6.2 and PHITS

This paper describes the experimental characterization and Monte Carlo (MC) modelling of developed thermal neutron detectors based on p-i-n silicon diodes covered with micrometric layers of 6LiF, called TNPD (Thermal Neutron Pulse Detector). TNPDs are routinely manufactured at INFN-LNF for a variety of neutron measurement applications. TNPDs with different 6LiF thickness, in the range 10–60 μm, were manufactured and thoroughly modelled using two independent Monte Carlo transport codes: MCNP6.2 and PHITS. The simulations were focussed on determining the pulse height distribution induced in the detectors when exposed to thermal neutrons. A validation experiment was performed in the HOTNES thermal neutron calibration facility (ENEA/INFN Frascati, Italy). The simulated pulse height distributions matched very well the experimental ones in terms of both shape and energy-integrated quantities. No scaling factors were needed. This work is an important milestone for the INFN-LNF detector-manufacturing laboratory. In addition, it provides guidance for others who need to accurately predict the response of similar detectors in a wide range of applications.