Determination of the HPGe detector efficiency in measurements of radioactivity in extended environmental samples.

A combination of experimental measurements and Monte Carlo (MC) calculations was used to determine the full-energy peak efficiency of a HPGe detector employed in environmental measurements. The manufacturer-provided parameters of the detector were corrected by comparing measured values of the efficiency with those obtained by MC simulations. After the adjustment of the active volume of the detector, the simulated and experimentally measured efficiencies agreed within 1%. A full-energy peak efficiency curve for a new distance was obtained by simulation. The efficiency curve for volumetric samples in the 53-1408keV energy range was determined using the efficiency transfer method. Geometric and self-absorption correction factors were estimated by experimental measurements, MC calculations or a combination of the two. In addition, the density of two sediment samples was estimated by a transmission measurement experiment and data simulation. Finally, concentrations of 238U and 232Th in two sediment samples from the Caetité region of Brazil were determined with relative uncertainties of about 5%.

Evaluation of uranium incorporation from contaminated areas using teeth as bioindicators--a case study.

The Southwest region of the Bahia state in Brazil hosts the largest uranium reserve of the country (100 kton in uranium, only), plus the cities of Caetité, Lagoa Real and Igaporã. In this work, aim was at the investigation of uranium burdens on residents of these cities by using teeth as bioindicators, as a contribution for possible radiation protection measures. Thus, a total of 41 human teeth were collected, plus 50 from an allegedly uranium free area (the control region). Concentrations of uranium in teeth from residents of 5- to 87-y old were determined by means of a high-resolution inductively coupled plasma mass spectrometer (ICP-MS). The highest uranium concentration in teeth was measured from samples belonging to residents of Caetité (median equal to 16 ppb). Assuming that the uranium concentrations in teeth and bones are similar within 10-20% (for children and young adults), it concluded that uranium body levels in residents of Caetité are at least one order of magnitude higher than the worldwide average. This finding led to conclude that daily ingestion of uranium, from food and water, is equally high.

Long-term accumulation of uranium in bones of Wistar rats as a function of intake dosages.

Groups of Wistar rats were fed with ration doped with uranyl nitrate at concentration A ranging from 0.5 to 100 ppm, starting after the weaning period and lasting until the postpuberty period when the animals were sacrificed. Uranium in the ashes of bones was determined by neutron activation analysis. It was found that the uranium concentration in the bones, as a function of A, exhibits a change in its slope at approximately 20 ppm-a probable consequence of the malfunctioning of kidneys. The uranium transfer coefficient was obtained and an analytical expression was fitted into the data, thus allowing extrapolation down to low doses. Internal and localized doses were calculated. Absorbed doses exceeded the critical dose, even for the lowest uranium dosage.

Shielding analysis of the Microtron MT-25 bunker using the MCNP-4C code and NCRP Report 51.

A cyclic electron accelerator Microtron MT-25 will be installed in Havana, Cuba. Electrons, neutrons and gamma radiation up to 25 MeV can be produced in the MT-25. A detailed shielding analysis for the bunker is carried out using two ways: the NCRP-51 Report and the Monte Carlo Method (MCNP-4C Code). The walls and ceiling thicknesses are estimated with dose constraints of 0.5 and 20 mSv y(-1), respectively, and an area occupancy factor of 1/16. Both results are compared and a preliminary bunker design is shown.