In situ natural radioactivity and radiological hazard assessments of granite gneiss outcrops in parts of the Southwestern Basement Complex of Nigeria

Öz

Radioactive emission (gamma ray) emanating from rock materials constitutes threats to humans and their environment. Hence, the natural radioactivity and radiological hazard indices of some granite gneiss outcrops with their residual soils from two different localities within the Southwestern Basement Complex of Nigeria were assessed using Gamma-ray spectrometry. The study aimed at determining the natural radiation levels of granite gneissic rocks and associated radiological threats to people living in the study area from gamma ray exposure. Data were collected along six geophysical traverses of 200 m each with station spacing of 5 m using the portable hand-held Gamma-ray Spectrometer. The results of weighted mean values of the elemental and activity concentrations for ⁴⁰K, ²³⁸U, and ²³²Th are 2.00 ± 1.43%, 3.13 ± 0.90 ppm, 12.32 ± 4.99 ppm and 629.28 ± 447.29, 38.58 ± 11.02, 49.96 ± 20.23  respectively. The obtained mean concentration ratios of 1.32 for U/Th and 2.14 for Th/U were higher than 0.26 and lower than 3.5 global standard ratios respectively. The increase in activity concentrations and concentration ratio may have suggested the enrichment of radioactive minerals in the granite gneissic rocks. The annual outdoor and indoor effective doses of gamma ray exposure for people living in the study area were below the world permissible standard of 1 , thus, the area is radiologically safe. However, increase in estimated mean of AGDE and ELCR; 525.620  and 1.273  above the world permissible standards of 300  and  respectively does not translate to significant radiological threats. Therefore, control measure by constant monitoring of the radioactivity levels of the area and rocks should be practiced.

Anahtar Kelimeler

• Ground Radiometric Survey,Gamma-Ray Spectrometry,Natural Radioactivity,Granite Gneiss,Akunu-Akoko,Ayere

Nijerya'nın Güneybatı Temel Kompleks Bölgesinde Yüzeye Çıkan Granit Kayaların Doğal Radyoaktivite ve Radyolojik Tehlikelerinin Yerinde Değerlendirilmesi

Öz

Kaya materyallerinden kaynaklanan radyoaktif emisyon (gama ışını) insanlara ve çevresine tehdit oluşturur. Bu nedenle, Nijerya'nın Güneybatı Temel Kompleksi'nde iki farklı bölgeden yüzeye çıkan granit kayalar ile bunların kalıntısı olan toprakların doğal radyoaktivite ve radyolojik tehlike endeksleri Gamma-ray spektrofotometre kullanılarak değerlendirilmiştir. Bu çalışmada, granit yapıdaki kayaların doğal radyasyon düzeylerinin ve bağlantılı radyolojik tehlikelerin çalışma alanında yaşayan ve gama ışınına maruz kalan insanlar üzerindeki etkilerinin belirlenmesi amaçlanmıştır. Veriler, taşınabilir Gamma-ray Spektrometresi kullanılarak her biri 200 m’lik altı jeofizik travers boyunca 5 m’lik istasyon aralığı ile toplanmıştır. ⁴⁰K, ²³⁸U ve ²³²Th için temel ve aktivite konsantrasyonlarının ağırlıklı ortalama değerlerinin sonuçları sırasıyla %2.00 ± 1.43, 3.13 ± 0.90 ppm, 12.32 ± 4.99 ppm ve 629.28 ± 447.29, 38.58 ± 11.02, 49.96 ± 20.23  dir. Elde edilen U/Th (1.32) ve Th/U (2.14) ortalama konsantrasyon oranları, sırasıyla, genel standart oranları olan 0.26’dan yüksek ve 3.5’tan düşüktür. Aktivite konsantrasyonları ve konsantrasyon oranlarındaki artış, yüzeye çıkan granit kayalarda radyoaktif minerallerin zenginleştiği anlamına gelebilir. Çalışma alanında yaşayan insanlar için gamma ışını maruziyetinde uygulanan yıllık dış ve iç etkili dozları dünyanın izin verilen 1  standardının altında olduğundan, alan radyolojik olarak güvenlidir. Bununla birlikte, AGDE ve ELCR'nin tahmini ortalamaları olan 525.620  ve 1.273 x10^-3 değerlerindeki artışın, izin verilen 300  ve 0.29 x10^-3 standart miktarların üzerinde olması da ciddi radyolojik tehditler anlamına gelmemelidir. Bu nedenle, alanın ve kayaların radyoaktivite seviyesinin sürekli izlendiği kontrol önlemleri tatbik edilmelidir.

Anahtar Kelimeler

• Akunu-Akoko,Ayere,Yer Radyometrik Araştırması,Gama-Işını Spektrometresi,Doğal Radyoaktivite,Metamorfik Granit Kaya

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