A review of electrodeposition methods for the preparation of alpha-radiation sources.

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

Uranium-series isotopes transport in surface, vadose and ground waters at San Marcos uranium bearing basin, Chihuahua, Mexico

Determining ionizing radiation in a geographic area serves to assess its effects on a population’s health. The aim of this study was to evaluate the spatial distribution of the background environmental outdoor gamma dose rates in Chihuahua City. This study also estimated the annual effective dose and the lifetime cancer risks of the population of this city. To determine the outdoor gamma dose rate in air, the annual effective dose and the lifetime cancer risk, 48 sampling points were randomly selected in Chihuahua City. Outdoor gamma dose rate measurements were carried out by using a Geiger-Muller counter. Outdoor gamma dose rates ranged from 113 to 310 nGy·h−1. At the same sites, 48 soil samples were taken to obtain the activity concentrations of 226Ra, 232Th and 40K and to calculate their terrestrial gamma dose rates. Radioisotope activity concentrations were determined by gamma spectrometry. Calculated gamma dose rates ranged from 56 to 193 nGy·h−1. Results indicated that the lifetime effective dose of the inhabitants of Chihuahua City is on average 19.8 mSv, resulting in a lifetime cancer risk of 0.001. In addition, the mean of the activity concentrations in soil were 52, 73 and 1097 Bq·kg−1, for 226Ra, 232Th and 40K, respectively. From the analysis, the spatial distribution of 232Th, 226Ra and 40K is to the north, to the north-center and to the south of city, respectively. In conclusion, the natural background gamma dose received by the inhabitants of Chihuahua City is high and mainly due to the geological characteristics of the zone. From the radiological point of view, this kind of study allows us to identify the importance of manmade environments, which are often highly variable and difficult to characterize.

Lifetime Effective Dose Assessment Based on Background Outdoor Gamma Exposure in Chihuahua City, Mexico

The present study aims to use the a-spectrom- etry, at NMA. A radiochemical technique (1, 2) for analysis of U-isotopes was carried out for some granite samples from Gabal Gattar and El Missikat localities and also for some reference soil samples of IAEA. Several steps of sample preparation, radiochemical separation, and source preparation were performed before analysis. The concerned sample was leached by HNO3, HF and H2O2 acids after ashing. The ashed sample was spiked with uranium tracer ( 232 U) for chemical yield and activity calculation. Then uranium was extracted from the matrix elements with tri- octylphosphine oxide (TOPO) and stripped with 1 M NH4F/0.1 M HCl solution. The uranium fraction was purified by co-precipitation with LaF3 to ensure complete removal of thorium and traces of resolution degrading elements. This was followed by a final clean-up step using an anion exchange. The pure uranium fraction was elec- trodeposited on a stainless steel disc from HCl/oxalate solution. The obtained results from the soil reference samples indicate general similarities between the tech- niques of a-spectrometers of NMA, EAEA and IAEA for analysis of U-isotopes. The U-isotopes in the granite samples of high radioactivity levels need more attempts after dilution process to be in the limit detection of a-spectrometry.

Use of alpha spectrometry for analysis of U-isotopes in some granite samples

Como parte de un proyecto cientiﬁco sobre actividad alfa en agua subterranea de consumo humano en la ciudad de Chihuahua, se ha desarrollado la caracterizacion de las rocas fuentes de la radiactividad en el valle de Chihuahua. Se determino tambien la actividad de muestras de agua subterranea y de sedimentos. La actividad de los isotopos de las series radiactivas en las rocas se obtuvo usando espectroscopia gamma de alta resolucion. Algunos valores representativos son 50 Bq/kg para el valor medio de la actividad del Bi-214 y 121.5 Bq/kg para el valor mas alto al oeste de la ciudad. La actividad de los sedimentos extraidos durante la perforacion de pozos para agua potable, se determino usando un detector de NaI(Tl). En la formacion montanosa de San Marcos se localizo un deposito de uranio no publicado. Sus aﬂoramientos se encuentran dentro de la cuenca del valle Chihuahua-Sacramento y se realizo la caracterizacion de su radiactividad. Se determinaron actividades por espectrometria alfa de agua, plantas, sedimentos y peces extraidos en emplazamientos cercanos a los aﬂoramientos de minerales de uranio. La actividad del agua en la presa de san Marcos llego a 7.7 Bq/L. La actividad de pescados de la misma presa alcanza 0.99 Bq/kg. Se obtuvieron conclusiones sobre la contaminacion del agua subterranea al norte de la ciudad de Chihuahua.

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T. Crespo

Papers

Characterization of source rocks and groundwater radioactivity at the chihuahua valley