Brian D. Rooney

Library of radioisotope identifier spectra

We have measured spectra with good statistics from many common industrial and medical radioisotopes by using a variety of commercially available radioisotope identifiers and have assembled them into a comprehensive computer library. The identifiers used included the ORTEC Detective and ORTEC Detective EX, Target identiFINDER (LaBr<inf>3</inf> and NaI), SAIC Exploranium GR-135, and Thermo Electron Interceptor. A library of spectra is useful, for example, when an identifier algorithm is unable to correctly identify the isotope(s) present with high confidence, and manual analysis is therefore required. An identifier may not be able to correctly identify an isotope because of problems like unresolved peaks, pileup, backscatter peaks, Compton edges, and incorrect calibration, and we discuss and compare some of these features in specific identifiers. Sources in our library include ¹³³Ba, ¹⁰⁹Cd, ⁵⁷Co, ⁶⁰Co, ¹³⁴Cs, ¹³⁷Cs, ¹⁵²Eu, ¹⁵⁴Eu, ¹⁵³Gd, ^166mHo, ¹³¹I, ^177mLu, ⁵⁴Mn, ²²Na, ²²⁶Ra, ¹¹³Sn, ²²⁸Th, ⁸⁸Y, and ⁶⁵Zn, but new sources and identifiers are continually added as they become available. The library contains measurement parameters such as the calibration parameters, run time, live time, source strength, and source-to-detector distance. Spectra are saved in the international standard format. SPE, which can be read by many commercial multichannel analyzer software programs. Spectra from the library can be visually compared with an unknown spectrum using these software programs to manually identify the radioisotope. This library of spectra is expected to become a valuable asset for the identifier community.

Temperature dependency analysis of light output from an NE-213 liquid sintillator

NE-213 liquid scintillation detectors are currently used in radiation fields consisting of both gamma rays and fast neutrons and are an excellent tool for differentiating between each type of radiation via their respective interactions. In this experiment, an analysis was performed on an NE-213 liquid scintillation detector to investigate the effects of temperature changes on the light output. The two effects measured were the amount of the individual light decay components have to the total pulse height and the total gain of the system as a function of temperature.

Evaluation of digitizer properties on pulse shape discrimination in a gelled NE213 cell

The figure-of-merit for a gelled NE213 scintillator cell from Bubble Technology Industries is determined for a variety of digitizing speeds and vertical resolutions using the digital-charge-integration-comparison method for pulse shape discrimination. If a digitizing board allows for an increase in the vertical resolution at the expense of the digitization rate, then there is an optimal combination of the two. For the Gage Board 82G, a board that does allow this tradeoff to be made, the best pulse shape discrimination occurred for digitization rates and vertical resolutions of 1 GS/s and 8 bits, 500 MS/s and 9 bits, and 250 MS/s with 9 bits.

Electron and photon responses of Gd/sub 2/SiO/sub 5/(Ce/sup 3+/) and BaF/sub 2/

Gd/sub 2/SiO/sub 5/(Ce/sup 3+/) (GSO) and BaF/sub 2/ electron responses were characterized using the Compton Coincidence Technique (CCT). The CCT has been used previously to characterize several scintillators and has proven to be an accurate and reliable technique. The GSO measured electron response was observed to increase by 28% as the electron energy increased from 5 keV to 445 keV. BaF/sub 2/ measured electron response increased by 22% as the electron energy increased from 18 keV to 436 keV. The observations made with GSO and BaF/sub 2/ in this study are consistent with the general trend reported for previously characterized non-alkali halide scintillators. The GSO and BaF/sub 2/ measured electron responses were further used to calculate their respective photon responses. MCNP4C together with simplified electron cascade sequences for GSO and BaF/sub 2/ were used in these photon responses calculations. Calculated photon responses for both crystals are in good agreement with measured photon responses. This agreement confirms the accuracy of the GSO and BaF/sub 2/ measured electron responses.