Neutron detectors based upon nuclear-optical
conversion in gas media

S.P.Melnikov
All-Russia Scientific Research Institute of Experimental Physics (VNIIEF)
June 26, 2002

Abstract:
VNIIEF has studied the feasibility of neutron detectors based on nuclear-optical conversion. These studies investigated the spectral and time-amplitude characteristics of luminescence for rare gases and their mixtures. For these purposes, a prototype neutron detector based upon the nuclear-optical converter (NOC) concept was produced. In this detector gas mixtures are excited by uranium fission fragments escaping from a thin U235 layer within the detector after interaction with neutrons. The GIR2 and VIR-2M pulse reactors were used as a neutron sources to study the performance of the prototype detector.

Information on the intensity of 146 spectral lines in the 350-875 nm spectral range which belong to transitions of HeI, NeI, ArI, ArII, KrI, KrII, XeI, and XeII was obtained. Comparison of neutron and luminescent pulses shows that luminescence power depends linearly on neutron flux density for the majority of studied gas media. This circumstance allows use of NOC for measurement of neutron flux. NOC calibration for the Ne-Kr mixture in the range of neutron flux densities of 1e8 to 1e16 cm-2-s-1 and time durations from 3 ms to 200 s was carried out.

To produce long-lived neutron detector based on NOC, it is necessary to solve some auxiliary problems (besides of choosing an optimal gas media): 1) stability of gas mixture composition; 2) development of methods for deposition of radiation-stable uranium layers on substrates; 3) choosing of radiation-stable fibers for transmission of luminescent light with minimal losses.