Concentration levels of gamma radioactivity on superficial soils of municipalities of Guadalupe and Zacatecas

A study on inside of municipalities of Guadalupe and Zacatecas in Zacatecas, Mexico was realized, with the purpose of determine the concentration levels of radionuclides 232Th, 238U, 40K and 137Cs, distributed on superficial soils. For this work was obtained a total of 44 samples of superficial soils nearby to 10 communities more populated of each one of municipalities; those that were prepared and placed on containers Marinelli type of 500 m L. The samples were measured in a gamma rays spectrometry system based on a germanium detector hyper pure, and was utilized the photo pick of 609 KeV of the 214Bi for to measure the activity of 226Ra, of 666 KeV for to measure the activity of 137Cs, of 911 KeV of the 228Ac for to measure the activity of 232Th, and of 1461 KeV for to measure the activity of 40K. The calculations to optimize the detector operation as much in efficiency as in energy were realized, and it was determined a time specifies for to obtain a relative error on the activity measurement smaller to 5%. Was found a minimum perceptible activity of 1.7 Bq·kg-1 for 226Ra, 0.96 Bq·kg-1 for 137Cs, 3.7 Bq·kg-1 for 232Th and of 6.8 Bq·kg-1 for 40K; these values were below those measured in the samples with the exception of 12 cases of the total for 137Cs. The average and concentration range in activity of soils of Guadalupe were of 22.3±1.5% (11-31.3) Bq·kg-1 for 226Ra, of 2.7±6% (0.95-5.5) Bq·kg-1 for 137Cs, of 28.2±2.5% (11-41.8) Bq·kg-1 for 232Th and of 540.5±0.6% (339.8-782.6) Bq·kg-1 for 40K. The average and concentration range in activity of soils of Zacatecas were of 24.8±1.4% (8.3-34.4) Bq·kg-1 for 226Ra, of 3.5±1.2% (1.1-7.7) Bq·kg-1 for 137Cs, of 35.1±2% (10.4-56.8) Bq·kg-1 for 232Th and of 625.2±0.5% (279.5-1278.3) Bq·kg-1 for 40K. These values are inside the world ranges reported by UNSCEAR and they do not represent a risk to population of municipalities in study; although the results can be used as reference from the exposure to population and environment. (Author)