Large Area Radiation Monitor Project

Radiation detector systems based on 6LiF:ZnS are good alternative technology to 3He neutron detectors. Thermal neutron absorption in 6LiF:ZnS emulsion is well characterized but detection efficiency is likely to depend upon the light collection efficiency. For large area system this is particularly important as light attenuation and uniformity across the active area can be large.

We developed in 2012 a segmented large area system (2 m x 0.3 m x 0.12 m) made of 16 neutron sensitive strips (1.62 m long) with embedded wavelength shifting fibres read out by MPPCs. The MARS detector design is flexible and truly scalable. The volume segmentation gives additional position sensitivity not possible with more monolithic designs. The ZnS scintillating properties provides high discrimination against γ-ray fluxes ensuring a good operation in mixed field of neutrons and other radiations.

This system was succesfully validated at the Physical National Laboratory in Teddington with calibrated source of neutrons and gamma-rays. These measurements demonstrated a neutron efficiency of 3.05 n/s/ng of 252Cf at 2 m and a GARRn of 1.01. Various studies on the stability of the efficiency, position resolution, directionally of the source and static drive-by test were also conducted.