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- Author or Editor: J. Kalef-Ezra x
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We investigated the spatial dependence of the sensitivity of nitrogen measurement with a prompt gamma neutron activation analysis (PGNAA) system for small animals and developed an analysis procedure that permits the reduction of systematic errors due to that dependence. The analysis procedure is based on neutron and photon transport calculations performed using the MCNP code in order to evaluate the sensitivity of the PGNAA facility. The system can be calibrated experimentally using a small number of phantoms of known size and composition. The calculation approach can then be used to predict responses for animal body sizes and shapes relatively to those experimentally determined and to include the effect of tissue inhomogeneities. Our calculations were verified by experimental measurements performed for a set of cylindrical inhomogeneous phantoms. The calculated to experimental ratios observed were within 6%.
A large sample neutron activation analysis (LSNAA) facility is under development at GRR-1 research reactor, NCSR ‘Demokritos’, to perform multi-element, non-destructive, contamination-free analysis of large volume samples. Correction algorithms have been derived to account for thermal neutron and gamma-ray self-attenuation in macroscopically homogeneous samples, as well as the photon detection efficiency to voluminous samples, based on no prior knowledge of the sample matrix composition. In the present study Monte Carlo simulations were performed to estimate the influence of inhomogeneities of major (matrix) and trace element on the accuracy of the technique. Types of inhomogeneities that can lead to severe errors in the analysis were depicted. The potential of including inhomogeneity tests in the measuring procedure to ensure the method’s applicability was examined.
Serum aluminum levels were determined by instrumental neutron activation analysis in 31 patients undergoing long-term haemodialysis. Aluminum-28 1.778 MeV (T 1/2=2.24 min) γ-rays produced by the thermal neutron reaction27Al(n,γ)28Al were detected. Successive irradiation of the samples at epithermal neutron fluence was performed to correct for the interference from the fast neutron reaction31P(n,α)28Al. Serum aluminum level in this group of subjects was adequately represented by a lognormal distribution with a mean and variance of 16.5 μg/l and 16.8 μg/l, respectively. The results obtained were found to be in agreement with serum aluminum determination performed by electrothermal atomic absorption spectrophotometry (r 2=0.97). Instrumental neutron activation can provide a rapid technique to routinely monitor long-term haemodialysis patients in order to identify individuals at greater risk to develop aluminum toxicity.