Dual glass sensor in a mixed gamma and neutron radiation field

Abstract

Cerium-activated lithium glass with highly enriched 6Li dopant is very useful in detecting low-energy neutrons. The neutrons are identified by pulse height separation; however, in a mixed gamma and neutron field a simple pulse height separation severely degrades the gamma rejection ratio for the sensor. By using a glass element doped with natural 7Li that is exactly the same as the cerium-activated glass, the ambient gamma response can be obtained. 7Li does not show any thermal neutron response. Therefore, the pulse height spectrum due to net neutrons can be obtained by subtracting the pulse height response of the 7Li-doped glass from that obtained from a 6Li-doped glass element. The pulse height peaks at 1.3 MeV (electron equivalent) with a full width half maximum (FWHM) resolution of 15.5%. A prototype dual counter for gamma and neutron radiation has been built and operationally tested to be linear in the dose rate range of 0 to 1 mrem/hr. A simple conversion formula relating gamma or neutron counts to the corresponding dose rates contains non-significant second-order correction terms. For small hand-held detectors, GS-20 and GS-30 combination glass scintillators have performed well by increasing the effective gamma rejection ratio from neutron counting while increasing the gamma sensitivity (by addition of counts from two similar scintillators).