Measurements of radiation exposure of dentistry students during their radiological training using thermoluminescent dosimetry.

Exposure among dentistry students has not been assessed or regulated in Mexico. This work assessed the average exposure of 35 dentistry students during their training with the aid of LiF:Mg,Cu,P+PTFE thermoluminescent dosimeters. For the students in the roles of dentist and observers, maximum accumulated equivalent dose obtained was 2.59±0.11 and 4.64±0.39 mSv, respectively. Students in the role as patients received a maximum accumulated effective dose of 28.41±0.31 mSv. If compared to occupational dose limits, this latter value is 56% of the recommended value of 50 mSv in any year. It was found that in all cases, values of equivalent dose to the women breasts were equal to the background dose. Results are discussed and compared to previous published work. Suggested recommendations were given to authorities in order to minimize exposure of the students in the role as patients.

Uranium removal from water using cellulose triacetate membranes added with activated carbon.

Ultrafiltration removal of uranium from water, with composite activated carbon cellulose triacetate membranes (AC-CTA), was investigated. The filtrate was provided by uraninite dissolution with pH=6-8. Removal efficiencies were calculated measuring solutions' radioactivities. Membranes were mainly characterized by microscopy analysis, revealing iron after permeation. Uranyl removal was 35±7%. Chemical speciation indicates the presence of (UO(2))(2)CO(3)(OH)(3)(-), UO(2)CO(3), UO(2)(CO(3))(2)(2-) and Fe(2)O(3)(s) as main compounds in the dissolution, suggesting co-adsorption of uranium and iron by the AC during filtration, as the leading rejection path.

Evolution of chemical species during electrodeposition of uranium for alpha spectrometry by the Hallstadius method.

The morphology and composition of uranium alpha sources with co-deposited platinum have been investigated by scanning electron microscopy (SEM) with energy dispersive X-ray fluorescence analysis (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) studies. Combined SEM and EDX measurements reveal the effect of porous platinum on the morphology of the sources which in turn affects their alpha-spectral resolution. The XPS analysis suggests that the presence of platinum initially increases the concentration of hydroxyl species in the deposits, which then act as centres for subsequent preferential uranium precipitation. XPS and XAFS analysis also provide for first time an indication of oxidation states of uranium present in the sources prepared by the Hallstadius method. These results are in line with Hansen's theory of electrodeposition of actinides.

Natural radioactivity in groundwater and estimates of committed effective dose due to water ingestion in the state of Chihuahua (Mexico).

The activity concentration of 222Rn, 226Ra and total uranium in groundwater samples collected from wells distributed throughout the state of Chihuahua has been measured. The values obtained of total uranium activity concentration in groundwater throughout the state run from <0.03 up to 1.34 Bq l-1. Generally, radium activity concentration was <0.16 Bq l-1, with some exceptions; in spring water of San Diego de Alcalá, in contrast, the value reached approximately 5.3 Bq l-1. Radon activity concentration obtained throughout the state was from 1.0 to 39.8 Bq l-1. A linear correlation between uranium and radon dissolved in groundwater of individual wells was observed near Chihuahua City. Committed effective dose estimates for reference individuals were performed, with results as high as 134 microSv for infants in Aldama city. In Aldama and Chihuahua cities the average and many individual wells showed activity concentration values of uranium exceeding the Mexican norm of drinking water quality.

Radon concentrations in ground and drinking water in the state of Chihuahua, Mexico.

This paper reports (222)Rn concentrations in ground and drinking water of nine cities of Chihuahua State, Mexico. Fifty percent of the 114 sampled wells exhibited (222)Rn concentrations exceeding 11Bq/L, the maximum contaminant level (MCL) recommended by the USEPA. Furthermore, around 48% (123 samples) of the tap-water samples taken from 255 dwellings showed radon concentrations over the MCL. There is an apparent correlation between total dissolved solids and radon concentration in ground-water. The high levels of (222)Rn found may be entirely attributed to the nature of aquifer rocks.

Uranium-238 and thorium-232 series concentrations in soil, radon-222 indoor and drinking water concentrations and dose assessment in the city of Aldama, Chihuahua, Mexico.

High-resolution gamma spectrometry was used to determine the concentration of 40K, 238U and 232Th series in soil samples taken from areas surrounding the city of Aldama, in Chihuahua. Results of indoor air short-time sampling, with diffusion barrier charcoal detectors, revealed relatively high indoor radon levels, ranging from 29 to 422 Bq/m3; the radon concentrations detected exceeded 148 Bq/m3 in 76% of the homes tested. Additionally, liquid scintillation counting showed concentrations of radon in drinking water ranging from 4.3 to 42 kBq/m3. The high activity of 238U in soil found in some places may be a result of the uranium milling process performed 20 years ago in the area. High radon concentrations indoor and in water may be explained by assuming the presence of uranium-bearing rocks underneath of the city, similar to a felsic dike located near Aldama. The estimated annual effective dose of gamma radiation from the soil and radon inhalation was 3.83 mSv.

Calibration of diffusion barrier charcoal detectors using a semi-empirical expression.

Several calibration settings of diffusion barrier charcoal canister (DBCC) detectors for measuring radon concentration in air were studied. A set of functions and graphs were developed for relations between radon concentration in air and adsorbed activity in DBCC, when calibrated in small chambers. Both the integration time for 10% of DBCC of a batch, and the radon adsorption coefficient for the activated charcoal used in these detectors, were determined. Thus, a semi-empirical expression for detector calibration was applied.

Radioactivity in bottled waters sold in Mexico.

Measurements of gross alpha and beta activities were made on 21 domestic and international brands of bottled (purified and mineral) water sold in the Mexican market to assess its radiological quality. Alpha and beta activities were determined using a liquid-scintillation detector with pulse-shape analysis feature. All the purified water had values of beta activity lower than the limit for potable drinking water (1.0 Bq/l), while three brands surpassed the limit of alpha activity (0.1 Bq/l). The limit for alpha radioactivity content was exceed by three mineral waters; the results show a correlation between radioactivity content and mineral salts, which are related with the origin and treatment of the waters.

Characterization of ophiolites from northern Havana-Matanzas petroleum fields using instrumental neutron activation analysis.

Concentrations of 16 elements from 14 serpentinitic samples from Basilio and Cantel petroleum fields were obtained by instrumental neutron activation analysis (INAA): Cr, Co, Ni, La, Nd, Sm, Eu, Gd, Tb, Ce Yb, Lu, Rb, Cs, Hf and Th. Relative INAA was performed using certified reference materials and laboratory standards. Average elemental concentrations showed that the ophiolites have a basic character, suggesting the use of a well-logging method designed for volcano-sedimentary petroleum fields.

Instrumental neutron activation analysis of rocks from Cayajabos petroleum ore.

The relative INAA method under statistical control was used to measure the concentrations of Sb, La, Eu, Co, Rb, Tb, Cs, Hf, Th, Cr, Lu, Yb, Ce, Sm, Gd, Nd. Rare earth element (REE) Chondrite-normalized patterns are presented. The La(cond)/Lu(cond) normalized concentration ratios obtained confirm the carbonaceous character of the rocks.