A new neutron area monitor with extended energy range

Abstract

Radiation protection monitoring in installations producing high-energy neutrons requires dedicated instrumentation, called extended range neutron area monitors (ERNAM). With the main purpose of increasing the sensitivity of this class of instrument, while keeping a good degree of isotropy, a new portable device called neutron extended counter for high energy (NECH) was prototyped. NECH is based on a Helium-3 proportional counter placed in the center of a cylindrical polyethylene moderator with truncated cone ends, embedding a lead insert to promote the detection of neutrons above 20 MeV. NECH responds nearly isotropically, in terms of ambient dose equivalent H*(10), up to GeV neutrons. Its sensitivity is about three times larger than common commercial instruments of the same class. This novel instrument was fully simulated with Monte Carlo N-Particle (MCNP) and calibrated in radionuclide-based reference neutron fields at IRSN Cadarache and ENEA Frascati. Workplace testing was performed around the ENEA Frascati Neutron Generator operating at 2.5 MeV and, for the high-energy domain, at the CERN-EU high-energy Reference Field facility (CERF). This work presents the instrument, the simulated and measured dose equivalent response and the results of the workplace testing. The performance is compared with that of commercial ERNAMs.