Abi T. Farsoni

A Phoswich Detector With Compton Suppression Capability for Radioxenon Measurements

A phoswich detector with Compton suppression capability has been developed and tested for measuring xenon radioisotopes via a beta-gamma coincidence measurement technique. The phoswich detector has been designed with three scintillation layers. Beta-gamma coincidence events from radioxenon isotopes are identified when a coincidence energy absorption is detected in the first (BC-400) and second (CsI(Tl) crystal) scintillation layers. To identify and reject scattered photons from the CsI(Tl) crystal, the crystal is surrounded by a BGO scintillation layer. Our measurements show that the Compton suppression mechanism reduces the Compton continuum from 662 keV photons by 20-50% in the low-energy region of spectrum. Our beta-gamma coincidence measurements with 135Xe and 133Xe radioisotopes show energy resolutions (FWHM) of 13%, 46% and 24% for 250 keV, 30 keV and 80 keV gamma-ray peaks, respectively. In this paper, the detector design, assembly steps, digital pulse shape discrimination technique, and our recent measurements with radioactive lab sources and xenon radioisotopes are discussed.

A compton-suppressed phoswich detector for gamma spectroscopy

A phoswich detector with two scintillation layers has been designed and assembled at Oregon State University. This detector is able to identify and reject Compton events and ultimately reduce the Compton continuum in gamma energy spectra. In this detector, CsI(Tl) crystal is used to primarily detect photoelectric events. The CsI(Tl) crystal is partially surrounded by a BGO crystal layer to capture and identify Compton-scattered photons. Both crystals are optically coupled to a single photomultiplier tube. A real-time, FPGA-based digital pulse shape analysis was developed to discriminate and reject Compton-induced pulses from the CsI(Tl) crystal. All the digital pulse processing functions including pulse shape discrimination analysis, pile-up rejection and energy measurement were implemented in an on-board FPGA device. In this paper, the results of recent measurements using radioactive lab sources will be presented and discussed.

A CZT-based radioxenon detection system in support of the Comprehensive Nuclear-Test-Ban Treaty

In this work, a prototype radioxenon detection system was designed, developed and tested at Oregon State University to study the response of CdZnTe (CZT) detectors to xenon radioisotopes for monitoring nuclear explosions. The detector utilizes two coplanar CZT detectors and measures xenon radioisotopes through beta–gamma coincidence detection between the two detection elements. The CZT-based detection system offers excellent energy resolution and background count rate compared with scintillator-based beta–gamma coincidence detectors currently in operation at the IMS stations. In this paper, we briefly discuss the detector design and report our recent measurement results with 131mXe, 133mXe, and 133Xe produced in the TRIGA reactor at OSU.

A radioxenon detection system using CdZnTe, an array of SiPMs, and a plastic scintillator

This paper presents the design and characterization of a prototype compact beta–gamma radioxenon detection system that utilizes a coplanar CdZnTe crystal, an array of SiPMs, and a plastic scintillator. The detector is directly mounted on a custom PCB. The system provides the advantage of room-temperature operation, while being compact, low noise, and with simple readout electronics. Preliminary measurements using 137Cs, 135Xe, and 133/133mXe were conducted to optimize various system parameters to achieve optimal resolution of key photopeaks. The purpose of this research was to explore the potential of these radiation detection elements for use in beta–gamma coincidence applications.

A Compton-suppressed phoswich detector for radioxenon measurements

A phoswich detector with Compton suppression capability has been developed and assembled for measuring low concentration of xenon radioisotopes in the atmosphere. The phoswich detector has been designed with three scintillation layers. Beta-gamma coincidence events from radioxenon isotopes are identified when a coincidence energy absorption is detected from the first (BC-400) and second (CsI(Tl) crystal) scintillation layers. To identify and reject scattered photons from CsI(Tl) crystal, the crystal is surrounded by a BGO scintillation layer. In this paper, detector assembly steps and our recent measurements with lab sources and radioxenon isotopes produced in the Oregon State Universitys TRIGA reactor will be discussed.