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

Digital pulse shape analysis (dPSA) has been used with a Cuttler–Shalev type 3He ionization chamber to measure the fast-neutron spectra of a deuterium–deuterium electronic neutron generator, a bare 252Cf spontaneous fission neutron source, and of the transmitted fast neutron spectra of a 252Cf source attenuated by water, graphite, liquid nitrogen, and magnesium. Rise-time dPSA has been employed using the common approach for analyzing n +3He→1H+3H ionization events and improved to account for wall-effect and pile-up events, increasing the fidelity of these measurements. Simulations have been performed of the different experimental arrangements and compared with the measurements, demonstrating general agreement between the dPSA-processed fast-neutron spectra and predictions. The fast-neutron resonance features of the attenuation cross sections of the attenuating materials are clearly visible within the resolution limits of the electronics used for the measurements, and the potential applications of high-resolution fast-neutron spectrometry for nuclear nonproliferation and safeguards measurements are discussed.

► We show the use of digital pulse shape analysis techniques with a helium-3 proportional counter. ► The technique has been used in fast neuron spectrometry of bare and shielded fission sources. ► Neutron-transport simulations and measurements are in agreement, helping with interpretation. ► Relevance and applications for nuclear nonproliferation and safeguards are discussed.