Radioactivity Levels of 226Ra, 232Th and 40K in Limestone, Clay, Sand, Magnesium-oxide, Pozzolana, and their Cement Products

Abstract

This study was to determine the radioactivity levels of 226Ra, 232Th and 40K in limestone, sand, clay, magnesium-oxide, pozzolana and their cement products. Raw material samples were collected from areas of Western, Eastern and Northeastern Uganda whereas cement samples were collected from hardware stores in Kampala city. Cement is incorporated with natural radionuclides since its raw materials are extracted from the earth’s crust. Therefore its use in the construction of houses results into radiation exposure to the public. To assess the radiological hazard associated with the collected samples, the specific activity concentration of each of these radionuclides was determined using a Sodium Iodide scintillation detector.

The average specific activity concentration values of 226Ra, 232Th and 40K in cement raw material (limestone, clay, sand, magnesium-oxide and pozzolana) samples from Western Uganda used by Hima cement limited were 94.9 Bq kg−1, 97.1 Bq kg−1 and 484.8 Bq kg−1 respectively. The average specific activity concentration values of 226Ra, 232Th and 40K in cement raw material (Limestone, Clay and Pozzolana) samples from Eastern and Northeastern Uganda used by Tororo cement limited were 30.2 Bq kg−1, 58.7 Bq kg−17 and 557.5 Bq kg−1, respectively. The average specific activity concentration values of 226Ra, 232Th and 40K in Hima cement samples were 65.6±1.8, 108.7±1.9, and 445.8±6.9 Bq kg−1, respectively. The average specific activity concentration values of 226Ra, 232Th and 40K in Tororo cement samples were 43.1±1.5, 57.7±1.5, and 451.6±7.0 Bq kg−1, respectively. The average radium equivalent activity value of cement raw material samples from Western and, Eastern and Northeastern Uganda were 271.0 Bq kg−1 and 157.1 Bq kg−1, respectively. The average radium equivalent activity value for Hima and Tororo cement samples was 255.3 Bq kg−1 and 160.4 Bq kg−1 respectively. Each of these values was less than the limit of 370 Bq kg−1 for building materials. The average external and internal hazard index values were 0.7 and 1.0, respectively for cement raw material samples from Western Uganda used by Hima cement limited. The average external and internal hazard index values were 0.4 and 0.5, respectively for limestone, clay and pozzolana samples from Eastern and Northeastern Uganda used by Tororo cement limited. The average external and internal hazard index values for Hima cement samples were 0.7 and 0.9, respectively. The average external and internal hazard index values for Tororo cement samples were 0.5 and 0.6, respectively. Each of these values was within the safe limit of unity suggested by EC (1999).

The average outdoor absorbed gamma dose rate value for cement raw material samples from Western and, Eastern and Northeastern were 122.7 nGyh−1 and 72.3 nGyh−1, respectively. Each of these values was greater than the world average value of 59 nGyh−1. The average indoor absorbed gamma dose rate value for Hima and Tororo cement samples were 215.8 nGyh−1and 139.2 nGyh−1 respectively. Each of these values was greater than the world average value of 84 nGyh−1.

The average outdoor annual effective dose value for raw material samples from Western Uganda used by Hima cement was 0.15 mSvy−1whereas the average value for raw material samples from Eastern and Northeastern Uganda used by Tororo cement limited was 0.09 mSvy−1. The average indoor annual effective dose value for Tororo cement samples was 0.7 mSvy−1. Each of these average annual effective dose values was less than the limit of 1 mSvy−1 as per ICRP (2019). The average indoor annual effective dose value for Hima cement samples was 1.1 mSvy−1which was slightly greater than the permissible limit of 1 mSvy−1.

Since the average values for radium equivalent activity, external and internal hazard indices, and annual effective doses for limestone, clay, sand, magnesium-oxide, pozzolana and Tororo cement samples were within the safe recommended limits, we were led to conclude that these samples posed no significant radiological hazard to both miners and the public. However, for Hima cement samples, the average indoor effective dose value was slightly greater than the permissible limit for public exposure hence these samples may pose a significant radiological hazard when solely used to construct houses.