Graph of Correlation between Background Gamma Radiation and Radon Concentration in Soil of Meidum and Zanlawn Oil Exploration Areas in Mizoram

Abstract

Background gamma radiation on earth surface and radon concentration at different depth beneath the ground surface of oil exploration areas the oil exploration areas of Meidum(MD) and Zanlawn(ZL) in Mizoram, are studied. The main instrument utilized for the study was RnDuo machine devised to survey Radon 222 (222Rn) connected to soil probe of 1mtr long to be baptized at different depth. Background gamma radiation survey at ground level is conducted with Russian base Gamma Survey Meter (PM 1405). The background gamma radiation at ground level varies from 177 nSv/hr at MD-3 to 202 nSv/h at MD-1 location with an average of 186.5 nSv/h. An in-situ measurement of soil gas was carried out at three different spots at four different depths each namely 10cm, 30cm, 50cm and 70cm. The radon gas concentration beneath the soil, within the study area ranges from 0.10 kBq/m3 at MD-3 to 1.31 kBq/m3 at MD-1 location. A correlation graph between ground level gamma radiation and the radon concentration in soil at different dept shows that the correlation coefficient is highest at 10cm with R2=0.466 and lowest at 70cm with R2=0.175. The Radon gas concentration obtained in these areas are below the worldwide average of 35-40 kBq/m3 .(UNSCEAR 2000).

Introduction

This study investigates the radon concentration in soil gas at different depths and its relationship with background gamma radiation in two oil exploration areas—Meidum and Zanlawn—located in Mizoram, India. Natural soil contains radioactive elements such as uranium, thorium, radium, and potassium, which contribute to background radiation. Among these, radon (^222Rn), a decay product of uranium (^238U), is a significant source of natural radiation exposure to humans. Radon concentration in soil is influenced by factors such as soil porosity, geological structures, faults, fractures, and depth, with previous studies showing that radon levels generally increase with increasing soil depth.

The primary objective of this research was to measure radon concentration at four different soil depths (10 cm, 30 cm, 50 cm, and 70 cm) and examine its correlation with ground-level gamma radiation in the selected oil exploration sites.

The study was conducted in the Meidum and Zanlawn oil fields near the Assam–Mizoram border. Background gamma radiation was measured using a PM-1405 Gamma Survey Meter, while in-situ soil gas radon concentration was measured using the Smart RnDuo instrument equipped with a stainless-steel probe. Six sampling locations (three in each area) were selected, and radon measurements were taken at each depth. Four readings were recorded at 15-minute intervals, and the average value was used for analysis.

The results showed that radon concentration consistently increased with soil depth in both study areas. In Meidum, radon concentration ranged from 0.10–0.22 kBq/m³ at 10 cm to 0.15–0.31 kBq/m³ at 70 cm. In Zanlawn, concentrations increased from 0.12–0.15 kBq/m³ at 10 cm to 0.16–0.21 kBq/m³ at 70 cm. Ground-level gamma radiation measurements ranged from 175 to 202 nSv/h across the sampling sites.

Measurements were conducted during January 2020, when weather conditions were dry and there had been no rainfall for approximately one month. The absence of soil moisture minimized environmental influences on radon migration, providing more reliable measurements.

Correlation analysis between ground-level gamma radiation and radon concentration at different depths was performed using Pearson’s R², indicating the relationship between natural gamma radiation and subsurface radon levels.

Conclusion

The Radon concentration in soil gas of Meidum and Zanlawn oil exploration areas in Mizoram is studied. An in situ measurement was taken at four different depth such as 10cm, 30cm, 50cm and 70cm with the help of a Smart RnDuo and a stainless steel probe. The study was carried out during winter season in the month of January 2020. The soil has no moisture content. It has been observed that the concentration of radon gas increases as we baptize the soil probe deeper and deeper. This means that for every spot chosen, the radon gas concentration at 10cm deep is lowest and the radon gas concentration at 70cm is highest and the concentration at 30cm and 50 cm lie in between. But, the correlation coefficient (R2) obtained from the graph was highest at 10cm with R² = 0.466 while it is maximum at 70cm deep with R² = 0.175. This indicates that the gamma radiation had a better correlation close to the surface. The correlations observed are not that good. The possible reason for this poor correlation may be due to the contributing factor. Whereas the radon concentration at different baptism depth is contributed by Uranium 238; on the other hand, the background gamma radiation at ground level is contributed by many cosmic and terrestrial sources like Uranium, potassium, thorium etc. The radon gas concentration obtained in these locations are far below the world average of 35-40 kBq/m3 (UNSCEAR 2000).

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Copyright

Copyright © 2026 Lalmuanawma Chhangte, Remlalsiama , Lalnunpuia . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.