Article

Estimation of radiation hazard indices from syenite building rocks in the South-western region of Cameroon

¹ Nuclear Physics Laboratory, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
² National Radiation Protection Agency, P.O. Box 33732, Yaoundé, Cameroon

^* Corresponding author: bajeanfelix@yahoo.fr

Received: 3 August 2016
Accepted: 7 July 2017

Abstract

Radium equivalent (Ra_eq) and external hazard index (H_ex) were estimated based on ²²⁶Ra, ²³²Th and ⁴⁰K measurements in syenite building rocks collected from various sampling sites of Lolodorf area, South-western region of Cameroon to assess the radiation hazards due to the use of these rocks in dwellings construction. The analysis has been carried out by γ-ray spectrometry using a high purity germanium (HPGe) detector. Ra_eq varied from 186 ± 4 to 2564 ± 24 Bq · kg⁻¹, while H_ex varied from 0.5 ± 0.01 to 6.93 ± 0.06. The corresponding mean values are 1463 ± 930 Bq · kg⁻¹ and 3.95 ± 2.51 in Awanda subdivision while in Madong subdivision, these values are 683 ± 553 Bq · kg⁻¹ and 1.84 ± 1.49, respectively. Absorbed dose rate ranged from 98 ± 2 to 1171 ± 11 nGy · h⁻¹ while annual effective dose ranged from 0.60 to 7.18 mSv · year⁻¹. The average absorbed dose rates are 670 ± 420 nGy · h⁻¹ and 313 ± 245 nGy · h⁻¹ in Awanda and Madong, respectively. These average values give rise to a mean annual effective dose of 4.11 mSv · year⁻¹ and 1.92 mSv · year⁻¹. All syenite building rocks have shown Ra_eq activity concentrations higher than the limit set in the Organization for Economic Cooperation and Development (370 Bq · kg⁻¹), equivalent to external gamma dose of 1.5 mSv · year⁻¹. The obtained values of the annual external effective dose in Awanda and Madong are higher (nine-fold and four-fold, respectively) than the worldwide mean annual effective dose (0.48 mSv · year⁻¹). The syenite rocks in the corresponding localities can be considered as high radiation's material not recommended for dwellings construction.