Gamma Ray Survey Reveals Hidden Radioactivity in the Soils of India’s Gurugram District

Beneath the glass towers and expressways of Gurugram, one of India’s fastest-growing urban centers, the ground itself is quietly radioactive. Not in any alarming sense, but in the way all soil is: every handful of earth contains trace amounts of naturally occurring radionuclides that have been part of the planet’s crust since its formation. A new study published in Environmental Monitoring and Assessment has now put hard numbers on this background radiation for District Gurugram in the state of Haryana, offering one of the most detailed radiological portraits yet of a district whose population has swelled alongside its skyscrapers. The research, led by Bhupender Singh of IIMT College of Engineering, Greater Noida, together with colleagues from Amity University, Shri Krishna Ayush University, Gurugram University, and Maharshi Dayanand University, combined high-precision gamma ray spectrometry with a battery of statistical tests to map and interpret the natural radioactivity locked in local soils.

The team collected thirty-eight soil samples from across the district, preparing them under controlled laboratory conditions before analysis. The measurement technique of choice was gamma ray spectrometry using a high-purity germanium detector, an instrument prized in radiation science for its exceptional energy resolution. Unlike simpler sodium iodide detectors, high-purity germanium crystals can separate the closely spaced gamma ray lines emitted by different radionuclides, allowing researchers to identify and quantify specific isotopes with confidence. In this study, the detector was calibrated and used to measure the activity concentrations of three radionuclides that dominate the natural radiation environment: potassium-40, thorium-232, and radium-226, the latter serving as a proxy for the uranium decay chain in soil.

The results reveal a clear hierarchy among the three isotopes. Potassium-40, a long-lived isotope that makes up a tiny fraction of all natural potassium, showed the highest activities, ranging from 342 plus or minus 10 to 760 plus or minus 16 becquerels per kilogram, with an average of 568 becquerels per kilogram. Thorium-232 activities ranged from 35 plus or minus 1.0 to 83 plus or minus 3.4 becquerels per kilogram, averaging 55 becquerels per kilogram, while radium-226 ranged from 48 plus or minus 1.9 to 90 plus or minus 3.7 becquerels per kilogram, with a mean of 65 becquerels per kilogram. These values sit within the ranges typically reported for soils worldwide, though the upper end of the potassium-40 distribution is notable, reflecting the mineralogy of the local geological formations from which the soils derive.

What makes the study more than a simple catalog of numbers is its statistical treatment of the data. Because environmental radioactivity measurements are frequently skewed by outliers and by the heterogeneous nature of soil, the authors first applied the Shapiro-Wilk test to assess whether the activity distributions followed a normal distribution. This test, widely regarded as one of the most powerful normality tests for moderate sample sizes, informs which subsequent statistical tools are appropriate. The researchers then employed the Spearman rank correlation test, a non-parametric method that measures monotonic relationships without assuming linearity or normality, to probe whether the three radionuclides vary together across sampling sites. Strong positive correlations between radionuclides can indicate a shared mineralogical origin, for example when uranium, thorium, and potassium-bearing minerals are concentrated together in the same parent rocks and weathering products.

To investigate whether the underlying geology, or lithology, exerts a measurable influence on radionuclide levels, the team turned to the Kruskal-Wallis test, a non-parametric analysis of variance that compares multiple groups without requiring normally distributed data. Gurugram’s geology is diverse, with the Aravali hill range skirting the district and alluvial plains covering much of its area, so differences in radionuclide concentrations between zones with different geological character are scientifically expected. The combination of these tests, descriptive statistics, normality assessment, rank correlation, and group comparison, represents a methodologically rigorous framework that is increasingly standard in environmental radioactivity studies, allowing researchers to distinguish genuine geological signals from random spatial variation.

Beyond characterizing the distribution of radionuclides, the study translated its measurements into quantities that matter for human health. From the measured activity concentrations, the authors calculated the absorbed gamma dose rate in air, which describes the energy deposited by gamma radiation per unit mass of air at ground level, and from that the annual effective dose rate for both indoor and outdoor exposure scenarios. Indoor doses are typically weighted more heavily in radiological assessments because people spend the majority of their time inside buildings, where gamma rays from construction materials derived from soil add to the outdoor background. The comparison of these derived doses with reference values established by international agencies such as the United Nations Scientific Committee on the Effects of Atomic Radiation provides the practical yardstick for judging whether the measured levels pose any concern to the public.

The team also computed two widely used screening indices. The gamma index, which ranged from 0.48 to 0.95 across the sampled soils, is designed to flag materials whose gamma radiation could become significant if used in building construction; values below unity are generally considered acceptable under international guidance. The alpha index, which ranged from 0.24 to 0.45, serves as a screening tool for potential radon inhalation hazards associated with radium-226 content, since radon-222 is a radioactive gas in the uranium decay chain that can accumulate in enclosed spaces. Both indices remained below their conventional thresholds across all thirty-eight samples, indicating that the natural radioactivity of Gurugram’s soils falls within the range considered safe for ordinary exposure and typical construction use.

The Gurugram survey is the latest entry in a growing body of work on natural radioactivity across northern India, much of it involving overlapping research groups. Previous studies by the same lead author and collaborators have examined radon and thoron exhalation from Gurugram soils, radionuclides in the soils of neighboring Palwal district, seasonal and geological influences on gamma radiation in Faridabad, and radon doses from groundwater in the same region. Parallel investigations elsewhere in Haryana and Punjab, including assessments of Rohtak, Jind, Bathinda, and Sirsa, and geospatial surveys of urban soils in Chennai, contribute to a national picture in which terrestrial gamma dose varies principally with local geology rather than with human activity. Such baseline datasets are valuable not only for radiation protection but also as reference points against which any future anthropogenic contamination, whether from industrial activity, construction, or accidents, could be detected and quantified.

For the residents of Gurugram, the practical message of the study is reassuring: the natural radioactivity of the district’s soils, from the potassium-rich alluvium to the thorium-bearing sediments near the Aravalis, produces radiation doses that international agencies would classify as within normal background levels. But the scientific significance runs deeper. As urbanization transforms land use across the National Capital Region, soils that once lay undisturbed are being excavated, processed into building materials, and incorporated into the homes and offices of millions. Understanding the radiological properties of that raw material, and the geological factors that control its variability, is a quiet but essential piece of public health infrastructure. With rigorous measurement, transparent statistics, and comparison against international standards, this study demonstrates how even an invisible, omnipresent hazard can be brought into sharp, quantifiable focus.

Subject of Research: Measurement of natural radionuclides and radiological hazard assessment in soils of Gurugram district, India

Article Title: Monitoring of natural radionuclides in soil of District Gurugram, Haryana (India), by gamma spectrometry and statistical analysis

Article References: Singh, B., Gupta, U., Kant, K., Yadav, S., & Tanwer, N. (2026). Monitoring of natural radionuclides in soil of District Gurugram, Haryana (India), by gamma spectrometry and statistical analysis. Environmental Monitoring and Assessment, 198(10), Article 1106. https://doi.org/10.1007/s10661-026-15925-7

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15925-7

Keywords: natural radioactivity, gamma spectrometry, potassium-40, thorium-232, radium-226, soil, Gurugram, Haryana, radiation dose, gamma index, statistical analysis, environmental monitoring