Nuclear Instruments and Methods in Physics Research A 578 (2007) 528–536 A system for simultaneous beta and gamma spectroscopy A.T. Farsoni à , D.M. Hamby Department of Nuclear Engineering and Radiation Health Physics, Radiation Center, Oregon State University, Corvallis, OR 97331 5902, USA Received 22 January 2007; received in revised form 18 May 2007; accepted 18 June 2007 Available online 21 June 2007 Abstract A state-of-the-art radiation detection system for real-time and simultaneous spectroscopy of beta-particles and gamma-rays has been developed. The system utilizes a triple-layer phoswich detector and a customized Digital Pulse Processor (DPP) designed and built in our laboratory. The DPP board digitally captures the analog signal pulses and, following several digital preprocessing steps, transfers valid pulses to the host computer for further digital processing. A resolving algorithm also was developed to digitally discriminate beta and gamma events, and reconstruct separate beta and gamma-ray energy spectra with minimal crosstalk. The spectrometer has proven to be an effective tool for recording separate beta and gamma-ray spectra from mixed radiation fields. The system as a beta–gamma spectrometer will have broad-ranging applications in nuclear non-proliferation, radioactive waste management, worker safety, systems reliability, dose assessment, and risk analysis. r 2007 Elsevier B.V. All rights reserved. PACS: 29.30.h; 29.40.n; 29.40.Mc Keywords: MCNP; Beta spectroscopy; Gamma spectroscopy; Phoswich detector 1. Introduction Generally, detectors designed to measure beta-particle energy distributions possess an inherent sensitivity to gamma-ray interactions that result in distortions of the measured distributions [1]. The design of a beta spectro- meter depends largely on the measuring task [2–4]; if a beta spectrum is to be measured in a mixed beta/gamma field, a separation of the beta energy from that of the gamma rays has to be carried out [5]. In an attempt to compensate for this potential interference, a general technique of data collection has evolved over the years whereby two separate energy distributions are measured for each mixed beta/ gamma source [6,7]. The first measurement provides the spectrometer ‘‘open window’’ response to both beta particles and gamma rays. A filter, of sufficient thickness to stop incident beta particles, is then placed around the spectrometer and the gamma-ray response is measured. The incident beta-particle energy distribution is determined by stripping the second measured distribution from the first. The disadvantages of this method are that the ambient gamma-ray field must remain constant during the measurement of the two distributions, the method doubles the time required to collect data, and instabilities in the spectrometer can lead to discrepancies between the two gamma-ray-induced pulse-height distributions. In the same way, a gamma detector is not immune to beta interference or ‘‘crosstalk’’ when the detector is exposed to a mixed beta/gamma field. Although gamma- rays and beta particles undergo different initial interaction mechanisms, the gamma-ray energy will be absorbed in the form of energetic electrons. Because of this similarity, difficulties arise in attempting to separate energy deposition events originating from beta or gamma interactions. To address these problems, and based on previous measurements and the Monte Carlo N-Particle (MCNP) [8] analyses of a prototypic detector [9], we have designed, modeled, and constructed a triple-layer phoswich detector for beta and gamma spectroscopy. The instrument, in conjunction with our customized digital pulse proces- sor (DPP), data acquisition software, and controlling ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2007.06.020 à Corresponding author. Tel.: +1 541 737 9645; fax: +1 541 737 0480. E-mail address: tavakola@onid.orst.edu (A.T. Farsoni).