ENHANCED RADIOACTIVE CONTENT OF 'BALANCE' BRACELETS

During a routine whole body counting measurement of a worker at the Nuclear Research Center Negev, abnormal activities of (232)Th and (238)U were measured. After a thorough investigation, it was found that the radioactivity was due to a rubber bracelet ('balance bracelet') worn by the worker during the measurement. The bracelet was counted directly by an high pure germanium gamma spectrometry system, and the specific activities determined were 10.80 ± 1.37 Bq g(-1) for (232)Th and 5.68 ± 0.88 Bq g(-1) for natural uranium. These values are obviously high compared with normally occurring radioactive material (NORM) average values. The dose rate to the wrist surface was estimated to be ∼3.9 µGy h(-1) and ∼34 mGy for a whole year. The dose rate at the centre of the wrist was estimated to be ∼2.4 µGy h(-1) and ∼21 mGy for a whole year. The present findings stresses a more general issue, as synthetic rubber and silicone products are common and widely used, but their radioactivity content is mostly uncontrolled, thus causing unjustified exposure due to enhanced NORM radioactivity levels.

A statistical model for reconstruction of historical internal doses for uranium workers

Uranium workers are monitored for their internal doses mainly by urine measurements. During the years before the early nineties, urine samples were analysed using a fluorimetric system, and the lower limit of detection of the urine samples was relatively high, thus most of the urine measurements were recorded as below threshold. A model was developed for the reconstruction of doses to workers at uranium facilities during these years. The model is based on the assumption that the results of urine measurements are log-normally distributed and that a normalised log-normal distribution with a constant geometric standard deviation characterises the results distribution in all the uranium workplaces for workers throughout their occupational work. Therefore, the average of the urine results can be calculated from the general normalised distribution. The intake and dose can be evaluated from the reconstructed average urine concentration by assuming a constant chronic intake regime throughout the whole period of monitoring.

Determination of the solubility and size distribution of radioactive aerosols in the uranium processing plant at NRCN

Inhalation is the main route of internal exposure to radioactive aerosols in the nuclear industry. To assess the radiation dose from the intake of these aerosols, it is necessary to know their physical (aerodynamic diameter distribution) and chemical (dissolution rate in extracellular lung fluid) characteristics. Air samples were taken from the uranium processing plant at the Nuclear Research Center, Negev. Measurements of aerodynamic diameter distribution using a cascade impactor indicated an average activity median aerodynamic diameter value close to 5 microm, in accordance with the recent recommended values of International Commission on Radiological Protection (ICRP) model. Solubility profiles of these aerosols were determined by performing in vitro solubility tests over 100 d in a simultant solution of the extracellular fluid. The tests indicated that the uranium aerosols should be assigned to an absorption between Types M and S (as defined by the ICRP Publication 66 model).