3He Neutron Spectrometer Using Pulse Risetime Discrimination

Abstract

A 3He filled proportional counter can be used for neutron detection in the range 100 keV to 8 MeV by using the 3He(n,p)T reaction. The major limitation as a neutron spectrometer is that the 3He recoil distribution, arising from the elastic scattering of the higher energy neutrons present, masks the 3He(n,p)T peaks due to lower energy neutron groups. Since a 3He recoil and a proton of equal energies have difference specific ionizations and, therefore, different ranges in the counter filling, one thus has a means to distinguish between pulses from the 3He(n,p)T and 3He(n,n)3He reactions. For appropriate operating conditions the risetime of the pulses for these two events will be different. By converting this risetime to a pulse height and only accepting pulses with long risetimes [which correspond to protons from the 3He(n,p)T reaction], one has a neutron spectrometer useful in an energy interval between the maximum neutron energy present and that energy for which the proton range equals the range of the maximum energy 3He recoil. Spectra of monoenergetic neutrons obtained with a 3He filled proportional counter and the pulse risetime discrimination are presented to illustrate the energy range over which this detector may be used as a neutron spectrometer. Under typical operating conditions, spectra of the 24Mg(d,n)25Al, 28Si(d,n)29P, 32S(d,n)33Cl reactions were obtained to illustrate the performance of the spectrometer.

Fast-neutron spectrometry using a 3He ionization chamber and digital pulse shape analysis

“…[19] With the implementation of pulse shape discrimination prior work 8 with analog pulse analysis circuitry has been shown capable of achieving up to 60% acceptance for 6.3-MeV 9 neutrons and up to 80% acceptance for 8.1-MeV neutrons. [1] Knowing that the ENG was operated with an 10 accelerating voltage of 90 keV and that the accelerated ion beam was mostly diatomic, we estimate that the energy 11 of these neutrons was approximately 2.47 MeV. [30] Analysis of the DD neutron spectrum was used to determine an 12 absolute starting-point energy calibration for the system, using the epithermal peak (at 0.764 MeV) and the center of 13 the DD neutron peak.…”

Measurement Of The Neutron Spectrum Of A DD Electronic Neutron Generator

“…[8] Neutron capture in 3 He is exothermic with a Q-value of 0.764 MeV; the amplitude of signal pulses resulting from neutron capture corresponds to the sum of this energy plus the incident neutron's energy. These detectors are very sensitive to microphonic noise and electromagnetic interferences but under ideal conditions neutron energy measurements have been made with a resolution of <15 keV, which is the limiting factor for the low-energy range of spectrometry for these detectors.…”

“…[3,12,14,15] Until recently most measurements systems used with C-S spectrometers used analog pulse analysis techniques to execute the rise-time pulse shape analyses. Continued development of laboratory electronics has also lead to the use of high-speed waveform digitizers has presented new options for collecting and analyzing this data.…”

“…[3][4][5][6][7] Detectors based on this approach are frequently referred to as Cuttler-Shalev (C-S) spectrometers.…”

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Abstract.A Cuttler-Shalev (C-S) 3 He proportional counter has been used to measure the energy spectrum of neutrons from a portable deuterium-deuterium electronic neutron generator. To improve the analysis of results from the C-S detector digital pulse shape analysis techniques have been used to eliminate neutron recoil artifacts in the recorded data.

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