GROUND RADIOMETRIC INVESTIGATION IN THE SOUTHERN PART OF THE KERRI–KERRI FORMATION, GOMBE STATE, NORTHEASTERN NIGERIA
GROUND RADIOMETRIC INVESTIGATION IN THE SOUTHERN PART OF THE KERRI–KERRI FORMATION, GOMBE STATE, NORTHEASTERN NIGERIA
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Date
2016-06
Authors
YUSUF, DAVID BACHAMA
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Abstract
The first ground radiometric investigation has been carried out in the present study to confirm the occurrences or otherwise of uranium, thorium and potassium mineralization and also to assess the risks associated with human exposure to these radiations in the southwest of the Kerri–Kerri Formation. Total count readings were taken randomly with a portable ground scintillometer “Exploranium GR-101A”. From the analysis of the scintillometric data, an area 2.25 km2 was identified with higher gamma ray activity (40–60 cps) situated northeast of Tumu in the southwest of the study area bounded by latitudes 10º 00ʹ 14ʺ N to 10º 01ʹ 19ʺ N and longitudes 11º 00ʹ 58ʺ E to 11º 02ʹ 04ʺ E. Further ground spectrometric survey was carried out with a “Pico Envirotec Portable Ground Information System Gamma Ray Spectrometer” (PGIS–SP/Model GIS-15), in the area identified with higher gamma ray activity. Rocks samples were also collected in the study area for laboratory gamma spectrometer analysis which was carried out at the Centre for Energy Research and Training (CERT), Ahmadu Bello University (A.B.U.), Zaria. Results from map analysis of both the PGIS-SP data and rock samples indicate the concentration of potassium in the northwestern part of the study area consisting of high alluvium and low level elevation, while uranium and thorium are more concentrated in the central and southern parts of the area consisting of highly weathered ironstones (i.e. hematite). The equivalent thorium image map shows the concentration of thorium in the southwest, southeast and southern end of the area. The mean activity concentration of 238U, 232Th and 40K for the PGIS-SP data are respectively 5 ppm, 16 ppm and 0.6 % while their standard deviations are: 2 ppm for 238U, 6 ppm for 232Th and 0.2 % for 40K. The correlation coefficients between (238U and 232Th), (238U and 40K) and (232Th and 40K) are respectively 0.30, 0.31 and 0.24. For the rock samples, the mean concentrations of 238U, 232Th and 40K are respectively 2 ppm, 15 ppm and 0.3 % while their standard deviations are 1 ppm for 238U, 4 ppm for 232Th and 0.3 % for 40K. For the rocks, a good correlation (r = 0.50) exists, between 232Th and 40K while a very weak correlation (r = 0.05) exists, between 238U and 40K. The correlation between 238U and 232Th is good but negative (r = - 0.63) which indicates the absence of significant accessory minerals in the study area. There is uniformity in the concentrations of the radionuclides as their standard deviations are lower than their mean values. The resulting low eTh/K and eU/K ratios are good indicators of preferential enrichment of potassium to thorium and uranium in the rocks of the area. Results from statistics and map analysis revealed that the concentration of uranium in the study area were far below 250 times the average content in normal rocks and in addition their ratios did not reflect preferential enrichment of uranium to the others. The mean absorbed dose rate for the PGIS-SP data is 15.646 nGyph-1 while that of the rocks is 53.6930 nGyph-1 both of which are lower than the world average value of 60 nGyph-1. Radiations from the rocks of the area are therefore not harmful to humans and the environment. This study has also revealed that the radiometric anomaly observed on the ternary image map of Gombe Sheet 152 S.W. in the study area is mostly due to potassium radiation.
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A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD
OF A
DEGREE OF DOCTOR OF PHILOSOPHY IN APPLIED GEOPHYSICS
DEPARTMENT OF PHYSICS
FACULTY OF SCIENCE
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
Keywords
GROUND RADIOMETRIC INVESTIGATION,, SOUTHERN,, KERRI–KERRI FORMATION,, GOMBE STATE,, NORTHEASTERN NIGERIA,