Attenuation correction for the collimated gamma ray assay of cylindrical samples.

The Hybrid Monte Carlo (HMC) method developed earlier for attenuation correction of non-collimated samples [Agarwal et al., 2008, Nucl. Instrum. Methods A 597, 198], has been extended to the segmented gamma ray assay of cylindrical samples. The method has been validated both experimentally and theoretically. For experimental validation, the results of HMC calculation have been compared with the experimentally obtained attenuation correction factors. The HMC attenuation correction factors have also been compared with the results obtained from literature available near-field and far-field formulae at two sample-to-detector distances (10.3cm and 20.4cm). The method has been found to be valid at all sample-to-detector distances over a wide range of transmittance. On the other hand, the literature available near-field and far-field formulae have been found to work over a limited range of sample-to detector distances and transmittances. The HMC method has been further extended to circular collimated geometries where analytical formula for attenuation correction does not exist.

Isotopic ratio correlation for the isotopic composition analysis of plutonium in Am-Pu mixed samples having high americium content.

Interference of high amount of americium in the plutonium isotopic composition analysis has been studied by simulating gamma-ray spectra for Am-Pu samples over a wide composition range (5-97% (241)Am) for both power and research reactor grade plutonium. An alternate way for isotopic composition analysis has been proposed by correlating the isotopic ratios available in our old database with the experimentally obtained (241)Pu/(239)Pu isotopic ratio. The proposed method has been validated using simulated spectra of known isotopic compositions.

Attenuation correction for the assay of uranium(VI) solutions in large cylindrical containers by gamma ray spectrometry.

The Hybrid Monte Carlo method developed for attenuation correction has been extended for 500 ml cylindrical geometry. The method has been experimentally validated. Absolute efficiency studies for 500 ml aqueous, air and point source has been carried out using Monte Carlo simulation. It has been observed that point source efficiency is a good estimate of 500 ml source beyond sample-to-detector distance of 15 cm. It has been found that while HMC method for attenuation correction is valid at all sample-to-detector distances and over all transmittance range, the far-field and near-field formulae available in literature are valid only over a very narrow range of sample-to-detector distance.