Validation of Performance Measurements of The Penn State Compton Suppression System PDF Download

Author: Sarah Sarnoski
Publisher:
ISBN:
Category : Gamma rays
Languages : en
Pages :

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Book Description
Compton suppression is a measurement technique that reduces the intensity of the Compton continuum, which is composed of the partial energy depositions created via Compton scattering of gamma rays in the detector material. The Compton continuum from a high-energy gamma ray can obscure the full-energy gamma ray photopeaks of isotopes with lower energy gamma ray emissions. The reduction from the Compton suppression system enables a more accurate identification of these low-energy gamma rays with energy peaks located within the Compton continuum. The Penn State Compton suppression system (CSS) uses a high purity germanium (HPGe) detector and a cylindrical and plug sodium iodide (NaI(Tl)) guard detector to negate the effect of partially deposited gamma rays on the gamma spectrum produced when measuring a sample. The Penn State CSS negates the effect of partially deposited gamma rays on the overall gamma spectrum, therefore producing a more accurate spectrum with fewer overall counts and reduced background interference. The research performed in this thesis used the Penn State CSS to validate earlier sample measurements obtained prior to the dismantling and reconstruction of the CSS. The Penn State CSS has produced superior results when compared with published literature, and it is important that it continues to perform at this level after reconstruction. 137Cs, 60Co, and irradiated National Institute of Standards and Technology (NIST) standard reference materials were measured in the CSS. A suppression factor (SF) is a comparison of suppressed to unsuppressed peak to Compton ratios, a further explanation and definition is provided in section 6.3 of this thesis. The suppression factor (SF) for the 137Cs calibrated gamma ray spectrum was 9.21, similar to the previous SF measurement of 9.97. These values are approximately 28% larger than most SFs recorded in literature, demonstrating the superior ability of the Penn State CSS. Using the calibrated Penn State CSS, two NIST standard reference materials, SRM 1570 Spinach Leaves and SRM 1571 Orchard Leaves, were measured after irradiation in the Penn State Breazeale Reactor (PSBR). Bare and cadmium covered gold wires were also irradiated in the PSBR to characterize the neutron flux shape of the current core design of the reactor. Peak and average neutron fluxes were determined for each of the irradiation locations, and the axial positions where peak neutron fluxes occurred were determined. The reference materials were irradiated both in the PSBR dry tubes and using the PSBR pneumatic transfer system. The dry tube irradiation of SRM-1570 produced a SF of 3.30 and the pneumatic transfer irradiation of SRM-1570 produced a SF of 3.27±0.21; these values are functionally equivalent. The pneumatic transfer irradiation of SRM-1571 produced a suppression factor of 4.2±0.10, approximately 10% greater than a previous measurement of 3.80. This work irradiated and measured the standard reference materials in triplicate, providing a more accurate evaluation of the CSS capabilities than previous work, which used a single reference material measurement. This thesis further improved upon previous Penn State CSS characterization efforts by clarifying the contributions of two isotopes to a single photopeak: a photopeak that was identified as 56Mn in 2008 was shown to be a combination of two energy peaks with contributions from 56Mn and 27Mg. This distinction was more apparent in the suppressed spectrum. The improved measurements and evaluation of the Penn State CSS validates its performance by producing suppression factors that are consistent to those obtained prior to the dismantling and reconstruction of the CSS. Furthermore, these suppression factor results remain among the highest reported in the literature.