Simulation and Development of a Transportable Neutron Activation Analysis System for the Assessment of Aluminum In Vivo
Aluminum is present throughout the environment and in many industrial processes and consumer goods. While very useful in everyday lives, it has no inherent biological functions in humans. High quantities in the human body can be toxic, resulting a range of skeletal, neurological, and hematopoietic effects. A system has been developed to analyze aluminum using the neutron activation analysis (NAA) technique in vivo. NAA was performed with a transportable neutron generator as a neutron source and a high purity germanium (HPGe) detector for spectroscopy. The neutron generator and HPGe detector were completely modelled in MCNP6. Measurements were carried out to evaluate the accuracy of the MCNP6 simulations and to determine the detection capabilities of the system for aluminum. Simulations were also conducted to determine the acceptability of radiation dose to subjects undergoing analysis. The detection limit for the system was evaluated using skeletal bone as a long-term aluminum biomarker. The detection limit was determined to be 3.41 x 101 μg of Al per g of dry bone for an irradiation time of six minutes. This detection level is below a point at which physiological effects have been observed in humans. A lower detection level was demonstrated to be possible with a longer irradiation time. The radiation absorbed dose was determined to be 7.30 mGy for an irradiation of six minutes. The system can therefore be utilized as a potential screening and monitoring tool for high skeletal burdens of aluminum that may lead to physiological effects.
The simulation and calculation techniques developed herein were applied to a set of human subject data that were acquired for a purpose other than evaluating aluminum. The human subject data included both bone Al from NAA and fingernail Al from mass spectrometry measurements. No significant aluminum signals were observed when assessing the in vivo NAA spectra data. Through simulation and calculation, it was demonstrated that the NAA experimental parameters resulted in an elevated detection limit for aluminum that is above Al skeletal loads observed in healthy individuals. The elevated detection limit prevented the in vivo detection of aluminum in a healthy population, thus confirming the NAA results.