Performance of Compton suppression system (CSS) and applicability in food matrices

Abstract

As a non-destructive and multi-element tech- nique, with high-level metrological properties, instrumental neutron activation analysis (INAA) has an important role to determine chemical elements in food. However, its use may be limited when looking for mass fractions near the detection limits. The Compton scattering of higher energy gamma-rays raised the spectrum baseline thus impairing the determination of several elements. Therefore, the gamma-ray spectrometry with Compton suppression becomes an alternative for improving the performance of INAA, since it can reduce the uncertainty of measurements and the detection limits by increasing the proportion between photopeak area and base- line. Here the performance of a Compton suppression system set by Ortec, with 50% relative efficiency and 2.04 keV res- olution (FWHM) for the 1,332 keV photopeak, was evaluated for food analysis. Samples of beans, chickpeas, lentils, peas, and rice were irradiated with neutrons and measured in the suppression system. Detection limits calculated from sup- pressed and unsuppressed spectra were compared. The sup- pression factor achieved by the system for 137 Cs was 5.88 ± 0.11 (n = 20) in the plateau region (358 to 382 keV), which was stable along a 20 week period and similar to the data provided in literature for other systems. Amongst fifteen elements determined, the detection limits for Br, Co, La, Na, Sc, and Se were not improved by the use of Compton sup- pression. On the other hand, the variable improvement obtained for As, Ca, Cd, Cr, Fe, Hg, K, Rb, and Zn corrobo- rated the idea that the performance of the Compton suppressor must be individually assessed for each type of sample.