Measurement result and performance parameters are presented for fast neutron detectors exploiting the scintillation of natural helium at high pressure. This detection medium has a very low electron density, minimizing the sensitivity to gamma radiation and thus enabling neutron detection also in high gamma radiation environment. Contrary to proportional counters, scintillation detection enables fast (nanosecond) timing and pulse shape discrimination, a technique that enables a lower neutron detection threshold. In this work, the basic principles of the detector are described, followed by a study of gamma rejection capabilities. Methods to calibrate the detector are discussed. Finally, a brief description of a 4 He scintillation based detector system including data acquisition electronics is given.

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He NE-213 Scintillation Gamma-rays Fast neutrons Pulse-shape discrimination a b s t r a c t A first comparison has been made between the pulse-shape discrimination characteristics of a novel 4 He-based pressurized scintillation detector and a NE-213 liquid-scintillator reference detector using an Am/Be mixed-field neutron and gamma-ray source and a high-resolution scintillation-pulse digitizer. In particular, the capabilities of the two fast neutron detectors to discriminate between neutrons and gamma-rays were investigated. The NE-213 liquid-scintillator reference cell produced a wide range of scintillation-light yields in response to the gamma-ray field of the source. In stark contrast, due to the size and pressure of the 4 He gas volume, the 4 He-based detector registered a maximum scintillationlight yield of 750 keV ee to the same gamma-ray field. Pulse-shape discrimination for particles with scintillation-light yields of more than 750 keV ee was excellent in the case of the 4 He-based detector. Above 750 keV ee its signal was unambiguously neutron, enabling particle identification based entirely upon the amount of scintillation light produced.

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In this paper we report the experimental study of high-pressure xenon used as a scintillator, in the context of developing a gamma ray detector. We measure a light yield near 2 photoelectrons per keV for xenon at 40 bar. Together with the light yield, we also measured an energy resolution of ∼9% (FWHM) at 662 keV, dominated by the statistical fluctuations in the number of photoelectrons.