Keywords: NE213, scintillator, pulse shape discrimination.

NE213 scintillation detectors are excellent tools for use in a mixed gamma and neutron field due to its established pulse shape discrimination ability. With proper pulse shape discrimination, gamma or neutron responses may be obtained in a mixed radiation field. The neutron response needs to be deconvolved from the detector response function to obtain an energy spectrum. To perform unfolding of neutron spectra, mono-energetic responses are needed and the responses may be obtained via experiment or simulation of the NE213 detector. In this work, response functions were tested with the unfolding of a Cf-252 spectrum. Particularly, experiments were performed at the Los Alamos National Laboratory where Cf-252 spectra were obtained. During the experiment, different pre-amplifier set-ups were tested. Namely, the pulse shape discrimination ability of the system using 50 ohm, 500 ohm, and 1000 ohm termination resistors were compared. However, linear system responses were not observed with the different settings. Thus, the Amoeba Simplex fitting routine was used to augment the charge integration pulse shape discrimination technique to separate the neutron and the gamma signals. Furthermore, a new figure of merit scheme was explored to quantify the pulse shape discrimination ability of the said non-linear system. Alongside the Cf-252 spectra experimental measurements, the program Scinful was used to generate mono-energetic neutron responses needed for unfolding. Consequently, both the Cf-252 neutron spectra and the Scinful responses were used with the program FERD-PC for unfolding. Among the different termination resistors compared with the new figure of merit scheme, the 50 ohm resistor setting was observed to be superior. The resultant unfolded spectrum using the 50 ohm termination resistor shows excellent agreement between 2-10 MeV. However, even with the Amoeba Simplex method, results below 2 MeV are not accurate due to the poor pulse shape discrimination limit of the sys.

A comparison study of pulse-shape analysis techniques was conducted for a BC501A scintillator using digital signal processing (DSP). In this study, output signals from a preamplifier were input directly into a 1 GHz analog-to-digital converter. The digitized data obtained with this method was post-processed for both pulse-height and pulse-shape information. Several different analysis techniques were evaluated for neutron and gamma-ray pulse-shape discrimination. It was surprising that one of the simplest and fastest techniques resulted in some of the best pulse-shape discrimination results. This technique, referred to here as the Integral Ratio technique, was able to effectively process several thousand detector pulses per second. This paper presents the results and findings of this study for various pulse-shape analysis techniques with digitized detector signals.

Authoritative reference providing the principles, practical techniques, and procedures for the accurate measurement of radioactivity.

Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.