Activation analysis of tibetan coins and thermal neutron flux measurement at the VR-1 training reactor

The VR-1 training reactor of Czech Technical University in Prague serves mostly to train students; however, owing to the presence of the experimental channels, it can be utilized for particular research tasks such as irradiation experiments, neutron radiography, and neutron activation analysis (NAA). Within the presented experiments, eight samples of historical Tibetan coins were irradiated in the experimental channel at maximum power, and the amount of the copper, silver, gold, and zinc was investigated using the NAA. The irradiated samples were repeatedly measured by the calibrated semiconductor HPGe detector; saturated activities were obtained by means of the gamma-ray spectrometry, and subsequently the composition of the samples was determined. In investigated Tibetan coins, the determined concentration of silver ranged from 47.9% to 54.5%, concentration of copper ranged from 13.5% to 99.3%, concentration of zinc ranged from 0.6% to 4.0%, and abundance of gold was 0.03-0.2%. Moreover, the activation measurement of neutron field parameters using the dosimetry foils was performed, and the reaction rates in the vertical experimental channel were determined utilizing the bare and cadmium covered gold foils. Afterwards, the thermal neutron flux for the relevant position was extracted employing the Westcott formalism and activation cross-section from the ENDF/B-VII.1 database. The results presented in this paper show clearly that the low-power VR-1 training reactor (ca. 80 W) is suitable for the neutron activation analysis of historical samples containing the noble metals.