The present study reports the anomalous behaviour of Radon isotope pairs (222 Rn, 220 Rn) in different soil depths at Mat fault, Mizoram (India). The measurement was taken for six occasions between November 2017 and April 2018 under dry soil condition in majority of the occasions. The Radon isotope pair's data were generated in situ online at depths of 5 cm, 50 cm and 1 m from ground surface in nine selected grid locations at Mat fault. At the same time, to identify geophysical phenomena Radon data were generated at Mizoram University (MZU) in a continuous monitoring station (CMS), located about 57 km from Mat fault. A ZnS/Ag scintillation-based continuous Radon monitor (Model: SMARTRnDuo, BARC, India) was deployed for monitoring Radon at Mat fault as well as in MZU. Correlation study shows that 222 Rn data at 5 cm and 50 cm depths of Mat fault region vary in the same manner with 222 Rn data at the CMS during all geophysical and non-geophysical process as identified by the CMS 222 Rn data. However, 222 Rn data at 1 m depth in the fault region does not show any definite correlation with CMS data. The variation of 220 Rn data at 50 cm depth in Mat fault also match the CMS 220 Rn data but deviated from it at 5 cm and 1 m depth. The influence of meteorological parameters on 222 Rn and 220 Rn data monitor at the CMS and Mat fault was also reported, and comparison was made with observation reported by other authors in the region.

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The study investigates radon and thoron concentrations in soil and water at one of the most prominent faults in Mizoram state, India. The obtained isotope pair data were consequently used for estimating the uranium and thorium content of the region. An indigenously developed and calibrated ZnS(Ag) alpha based scintillation counter (Model: SMARTRnDuo, BARC, India) was deployed for assessing radon and thoron data. Thoron concentration was found to be higher than radon concentration in both soil and water. The isotope pair and their parent nuclei concentration in water were found to be higher than in soil. The uranium and thorium content in soil were estimated to be 17.5 and 22.6 Bqkg-1 respectively, but in water, they were estimated to be 41.6 and 124.8 Bqkg-1 respectively. Comparisons with global averages were also presented in detail and no radiological risk has been observed for the region. A continuous radon data was generated at Mizoram University, Aizawl, Mizoram (India) for cross-analysis with data at Mat fault. It was observed that radon data of the two locations behave similarly during geophysical phenomena, indicating that the region was seismically active. No geophysical properties of thoron were observed.