Abstract
A gamma spectrometric analysis of rock samples collected from the Precambrian Oban Massif, southeastern Nigeria, was performed to determine some primordial radioelements’ activity concentrations: U-238, Th-232, and K-40, and their associated radiological hazards. The mean activity of the primordial radionuclides was determined to be 1073.06 ± 0.65, 160.74 ± 1.32, and 250.76 ± 0.91 Bq·kg−1 for 40K, 238U, and 232Th, respectively, showing that they are inhomogeneously distributed, with activity changing with the rock type and location. The activity concentrations are highest in biotite garnet schist, quartz diorite, and biotite gneiss rock domains. The mean values of the radiological hazards are 0.08 Bq·kg−1 (alpha index), 2.15 Bq·kg−1(gamma index), 2.06 Bq·kg−1(internal) and 1.63 Bq·kg−1 (external4.30 Bq·kg−1(representative level index6), 602.23 Bq·kg−1, (radium equivalent), 780 nGy·h−1 (total absorbed dose rate), 270.91 nGy·h−1 (indoor), 509.78 nGy·h−1 (outdoor), 624.99, 1329.07 and 1954.06 mSv·yr−1 (outdoor, indoor and total annual effective dose equivalent, respectively), 6448.40 (cumulative excess lifetime cancer risk) and 248.94–3761.47 Bq·kg−1 (annual gonadal dose equivalent). These results are higher than their various permissible limits (except at Ako Community) and suggest that rocks in the area may be unsuitable for constructing dwelling places. It is strongly advised that basic safety standards and precautionary measures recommended by the European Commission should be strictly adhered to while dealing with these rocks.
Highlights
Fifteen undisturbed rock samples collected from locations within the study area (Figure 2) were analyzed and used in this study
The activity concentrations of the primordial radionuclides vary from 182.22 ± 0.08 (Ekong Community) to 1924.29 ± 134.63 (Aking Community), with a mean of 1073.06±0.65 Bq·kg−1 for 40K, 22.01 ± 0.38 to 545.61 ± 97.46 (Mfamosing Community), with a mean of 160.74 ± 1.32 Bq·kg−1 for 238U, and 27.13 ± 0.20 (Ako Community) to 661.51 ± 65.78 (Betem Community), with a mean of 250.96±0.91 Bq·kg−1 for 232Th
The activity concentration was used to map the spatial spread of the radionuclides and infer the radiation-induced challenges that direct and indirect interaction with these rocks may pose to life
Summary
Different types of rocks, which are usually mined, crushed into various aggregates, and used for the construction of assorted dwelling places and other civil engineering works, exist in high quantities in the different geological terrain of the world Most of these materials, comprising sands, gravels, limestones, marls, slag, clays, and laterites, are used mainly to reinforce and strengthen composite materials [1]. These materials are used to construct civil engineering structures such as septic drain fields, rail tracks, foundations, retaining walls, drains, road construction, and roadside edge drains in the construction industries. The resulting situation has caused miners to resort to crushing basement rocks to satisfy rising demands, those of public service infrastructure-provisioning agencies
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