Assessment of some characteristics of a multi chamber alpha spectrometer with PIPS detectors

Purpose This study aims at assessing the resolution and the efficiency of a high-resolution multi-chamber alpha spectrometer and to understand the contribution of alpha PIPS spectrometers to the generation of outliers obtained during IAEA proficiency tests by assessing the influence of the source detector distance (SDD) to the trueness and precision in activities measurements of alpha emitting nuclides. The knowledge of those characteristics is necessary to avoid inaccurate measurements in alpha spectrometry.
Methods The assessment of several parameters of a high-resolution multi-chamber alpha spectrometer is performed using Alpha standard electro-deposited disc source containing four nuclides, ²³⁸U, ²³⁴U, ²³⁹Pu and ²⁴¹Am. The parameters assessed are the resolution, the efficiency, the trueness and the precision at different SDDs. A Monte Carlo simulation software named AASI was also used to generate theoretical efficiencies values for comparison with experimental values. The assessment of the precision is done using two parameters, the precision coefficient and the precision ratio.
Results The efficiencies obtained from measurements are lower than those obtained using the Monte Carlo simulation software AASI. Though the lowest resolution for ²⁴¹Am equal to 15.8 keV was measured at a SDD of 41 mm, the lowest average resolution equal to 17.77 keV was measured at a SDD of 25 mm. The trueness was found to be independent of SDD. Though the precision coefficient increases linearly as the SDD increases, the precision ratio which is the second parameter used for the assessment of the precision was found to be independent of the SDD. Increasing the number of measurements at any SDD improves the trueness and the precision of the activities measured. The results obtained show the necessity when analyzing a sample by alpha spectrometry to rely on several measurements instead of one single measurement to avoid inaccurate results. From our study it appears that to avoid precision outliers during interlaboratory comparisons one should preferably perform activities measurements at low SDDs.