Assessment of natural and artificial radionuclides in Mission (Texas) surface soils

Application of gamma spectrum analysis techniques for natural radioactivity measurements using NaI(Tl) detector

Sodium iodide (NaI(Tl)) scintillation detector is commonly used for gamma-ray spectrometric evaluations in airborne surveys and geophysical well logging. However, the applications related to environment monitoring are often encountered with challenges of low-level counting (LLC), demanding a high-resolution spectrometry system, such as a high purity germanium (HPGe) system. HPGe systems are expensive and cannot be used continuously due to the necessary supply of liquid nitrogen. In this paper, the possibility to use relatively poor resolution NaI(Tl) detector for measuring low-level radioactivity due to principal nuclides by spectrum unfolding has been explored. We quantified the activities of principal radionuclides, 232Th, 238U, and 40 K, in soil samples from NaI(Tl) spectral measurements by spectrum decomposition (SD) and matrix deconvolution (MD) techniques. The specific activities of radionuclides were statistically characterized with respect to the measurements made with HPGe detector. The comparison suggests that activities determined with NaI(Tl) detector were underestimated in the majority of cases. However, the activity of 238U measured with the MD method was overestimated. The results of SD were closer to the HPGe detector measurements as compared to the MD method. Considering the normal distribution of measurements from both detectors, correlation coefficients were computed that led to the development of linear regression models to numerically transform NaI(Tl) measurements to HPGe equivalent activities within statistically acceptable bounds. Thus, a low-resolution but high-efficiency NaI(Tl) detector provides a cost-effective and time-saving alternative to HPGe measurements for the routine environmental radioactivity surveys, since it offers continuous operation and provision for carrying in fields as well, which facilitates sample characterization and thereby quick assessment of radiological hazards.

Assessment of radiation hazard indices due to naturally occurring long-life radionuclides in the coastal area of Barra de Valizas, Uruguay

The Uruguayan east coast has several mineral resources, which include black sand ores in the Barra de Valizas-Aguas Dulces area. Cancer in Uruguay shows non-homogeneous geographical distribution, with the highest standardized mortality ratio (SMR) in the northeast and east region, which includes the aforementioned area and the town of Barra de Valizas. The activity concentration of natural radionuclides (226Ra, 232Th and 40 K) in Barra de Valizas´soil was determined by gamma spectrometry in order to evaluate the radiological hazard for inhabitants and tourists. The outdoor annual effective dose (AEDE), excess lifetime cancer risk (ELCR), and annual gonadal dose equivalent (AGDE) were evaluated for inhabitants with a life expectancy of 77.7 years, a 0.2 and 0.5 occupancy factor, and using the conversion coefficients recommended by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The annual effective dose was also evaluated for both summer and fortnight tourists. The radiological hazard indices for Barra de Valizas inhabitants are higher than the worldwide mean and recommended values. This may contribute to Rocha's higher SRM value, although a direct correlation cannot be assured with the epidemiological information currently available. Social, medical and anthropological studies will be carried out in future to provide data and verify this correlation.

Vertical distribution and radiological risk assessment of 137Cs and natural radionuclides in soil samples

The aims of this study were to investigate the vertical distributions of natural radionuclides 232Th, 226Ra and 40K as well as anthropogenic radionuclide 137Cs in soil samples and to analyze the correlation among the radioactivity of these radionuclides and the physiochemical characteristics of soil samples namely pH, grain size, carbonate content and organic matter. Risk assessment of the radiological hazard has also been estimated. Forty-four soil samples were collected from eleven locations in Qatar at four depth levels from 0 to 16 cm. The average concentrations of 232Th, 226Ra, 40K and 137Cs in the soil depth of 16 cm were 10, 17, 201 and 4 Bq/kg, respectively, which were within the reported world mean. The external absorbed gamma dose rate, the annual effective dose, the mean radium equivalent activity, the external hazard index and the lifetime cancer risk were 22 nGy/h, 0.027 mSv/y, 47 Bq/kg, 0.125 and 0.096 × 10-3, respectively. These values were far below the minimum recommended international values. The level of radioactivity concentrations in the soil was affected by the physiochemical characteristics of the soil. The positive correlation with highest R2 value was found among the radioactivity concentrations of 232Th and 40K and the soil clay content. Total organic carbon was also positively correlated for 226Ra and 137Cs activity concentrations, whereas, carbonate content was negatively correlated with the radioactivity concentrations of 232Th and 40K. As far as soil moisture content is concerned, the positive correlation with highest R2 value was obtained for 226Ra activity concentrations.

Natural radioactivity assessment of surface sediments in the Yangtze Estuary

The activities of the natural radionuclides (²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K) of the surface sediments in the Yangtze Estuary were determined and used to evaluate radiation hazards in the study area. The of activities of ²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K ranges from 14.1 to 62.3, 26.1 to 71.9, 13.7 to 52.3, and 392 to 898Bqkg^-1, respectively, which were comparable to values of other regions in China. The activities of ²³²Th, ⁴⁰K and ²²⁶Ra were clearly different from the global recommended values. The radium equivalent activity was less than the recommended limit of 370Bqkg^-1; therefore, the sediment in this area can be safely used for reclamation. The external hazard index values were less than one. The average absorbed gamma dose rate and annual effective dose equivalent values were slightly greater than the world average value. ²²⁶Ra/²³⁸U and ²³²Th/²³⁸U ratios could potentially be applied for tracing sediment source.