Verification of He-3 proportional counters’ fast neutron sensitivity through a comparison with He-4 detectors

Abstract

In the field of neutron scattering science, a large variety of instruments require detectors for thermal and cold neutrons. Helium-3 has been one of the main actors in thermal and cold neutron detection for many years. Nowadays, neutron facilities around the world are pushing their technologies to increase the available flux delivered at the instruments; this enables a completely new science landscape. Complementary with the increasing available flux, a better signal-to-background (S/B) ratio enables to perform new types of measurements. For instance, in neutron reflectometry, the time resolution for kinetic studies is limited by the available S/B. An improved S/B opens the possibility of sub-second kinetic studies. To this aim, this manuscript reexamines the background sensitivity of today's "gold standard" neutron detection. Fast neutrons and gamma rays are the main background species in neutron scattering experiments. The efficiency (sensitivity) of detecting fast neutrons, cosmic rays and gamma rays, for a Helium-3-based detector is studied here through the comparison with Helium-4 counters. The comparison with Helium-4 allows to separate the thermal (and cold) neutron from the fast neutron contributions in Helium-3-based counters which are otherwise entangled, verifying previous results from an indirect method. A relatively high sensitivity is found. Moreover, an estimate for the cosmic neutron fluence, also a source of background, at ground level at ESS is presented in this manuscript.

Transmutation of Palladium at Electrochemical Interfaces: Experimental and Theoretical Validation with Second Order Perturbation Theory

“…In our system, fast neutrons as well as thermal neutrons were detected. In addition, the plot of neutron count vs time, obtained using gas filled 3 He detectors, 13 was found to be linear (Fig. 3F), indicating thermal neutrons emission increased as a function of time after thermalization through high density polythene sheets.…”

Multi-Blade detector with VMM3a-ASIC-based readout: installation and commissioning at the reflectometer Amor at PSI

“…A full detector characterization was performed along with specular and off-specular reflectivity measurements on several samples. Moreover, background studies, in particular the response of this detector to fast neutrons [23][24][25] and gamma-rays [4], has been carried out at the Source Testing Facility (STF) at the Lund University in Sweden. During 2019-2020, a Multi-Blade demonstrator has been tested for an entire year at the Amor reflectometer at PSI (CH), serving the instrument as the main detector [5].…”

Conformal chemical vapor deposition of boron carbide thin films

“…Neutron detectors are classified into three types, scintillators, proportional counters 8 , and solidstate detectors 9 . Scintillators sense neutrons by detecting photons produced during the neutron interaction with hydrogen or during a neutron capturing event.…”

“…10 Whereas in proportional detectors, the ionization caused by neutron interaction with a gaseous medium is amplified by secondary ionization with an external voltage bias to get the signal output. 8 Solid-state neutron detectors convert neutrons into energetic detectable ions in a solid conversion layer. 11 These energetic ions further reach a semiconductor medium and create electron-hole pairs causing an electric output signal through a device, such as a PiN diode.…”