Radioactivity, radiogenic heat production and environmental radiation risk of the Basement Complex rocks of Akungba-Akoko, southwestern Nigeria: insights from in situ gamma-ray spectrometry

Abstract

The Basement Complex rocks of Akungba-Akoko, southwestern Nigeria, typically migmatites (M), biotite gneisses (BGN), granite gneisses (GGN), charnockites (Ch), biotite granites (BG) and pegmatites (P), were assessed using ground gamma-ray spectrometry (GRS). This study aimed at determining rocks' radionuclides concentration, alterations, radionuclides mobilization, radiogenic heat production (RHP) rate (first report for the area) and environmental radiation risk to humans. The results of this study were integrated with previous data on the petrography and geochemistry of these rocks, for detailed interpretation. The results of average elemental and activity concentrations for Akungba-Akoko rocks, were 2.66%, 3.16 ppm and 13.98 ppm, and 831.35, 39.01 and 56.77 for 40 K, 238 U and 232 Th, respectively; with increasing rock order of Ch < M < GGN < BGN < P < BG. High radionuclides concentration in the rocks, with exception of charnockites, were determined by high fraction of K-feldspar, plagioclase, biotite and accessory minerals -zircon and monazites. On the other hand, the low radionuclides concentration in the rocks, especially in Ch and M, were aided by the variability of the naturally occurring radioactive elements (NORMs) caused by alterations and mobilization during metamorphism and crystallization processes as suggested by radioelements composite, K/eTh ratio and F-parameter of Efimov analyses. RHP average of 2.03 µ above the crustal average range of 0.8 -1.2 µ may have significantly contributed to the heat flux in the studied area; however, the RHP of charnockites are lower than the crustal range. The absorbed dose rate average of 87.98 was within the permissible range, and other estimated radiological parameters, namely annual effective doses, hazard indices, gamma activity and activity utilization index, were all far below the permissible limit of 1 for these rocks. However, annual gonad dose equivalent (618.874) and excess life cancer risk (1.511 10 ) were above their permissible limits. Due to the high gamma radiations from the pegmatitic and biotite-rich rocks in the studied area, their high usage should be reduced. Hence, periodic monitoring of the study area is advised.

Radiogenic heat production estimation towards sustainable energy drive in northeastern Nigeria

“…However, the average RHP values of the granitic rocks found in the present research is higher than the average crustal granite value of 1.48 [ 24 ]. Moreover, the average granitic RHP values obtained in the present study is greater than the 2.40 , and 2.03 values reported for Gebel Duwi, Egyptian granites, and south western Nigerian granites by [ 24 ], and [ 7 ] respectively ( Table 3 ).…”

“…Therefore, a higher resolution data requires a higher acquisition cost and vice-versa. The intensity of radiation being emitted in an area depend on the quantity of the naturally occurring radioactive minerals present in the rock [ 7 ]. Hence, the geology and tectonics of an area is a significant factor in radiometric exploration.…”

An Alternative Approach to the Excess Lifetime Cancer Risk and Prediction of Radiological and Cancer Risks Caused by Terrestrial Radiation, Case of Isparta/Turkey

“…Many studies, especially on volcanic rocks, show that gamma radiation is considerably higher than the values given in UNSCEAR (2000) (e.g. Chiozzi et al 1998; Uyanık et al (2010;2013a;2015a;2015b;2022); Rosianna et al 2020; Cinelli et al 2020 Akingboye et al 2021). In addition, many studies have obtained very high gamma radiation in the soil, which is formed as a result of the disintegration and transport of these volcanic rocks (e.g.…”

Geohydraulic characteristics and groundwater vulnerability assessment of tropically weathered and fractured gneissic aquifers using combined georesistivity and geostatistical methods

“…Far to the west, the rock is extensively deformed and migmatized, forming migmatite with an ENE-WSW trend. In addition, intrusions such as quartz veins, pegmatite, aplite, basic dykes, and sills characterized the granite gneisses in the area [3,21,27,29]. The tropical climatic conditions and the metamorphic activities in the Akungba-Akoko Basement Complex terrain have assisted in the weathering and fracturing of the subsurface geology.…”