Study of Radiation Levels in the Building Materials of a Historic Monument of Narnaul, Haryana, India

Naturally occurring radioactive materials (NORMs) in building materials can elevate background gamma radiation and pose potential health risks. Establishing baseline radiation levels in historically significant areas is therefore important for both public health and heritage conservation. This study aimed to assess the activity concentration of radionuclides (²²⁶Ra, ²³²Th, and ⁴⁰K) and associated radiological hazards in two historical monuments located in Narnaul, Haryana, India—Jal Mahal and Chor Ghumbad and the survey initiated in April 2024. Samples of building materials such as marble, soapstone, brick, and lime were collected from both sites. Each sample was dried, powdered, homogenized, and sealed prior to analysis. Gamma spectrometry using a NaI(Tl) detector was employed to measure activity concentrations, and radiological indices including radium equivalent activity (Raeq), absorbed dose rate (ADR), annual effective dose (AED), excess lifetime cancer risk (ELCR), activity utilization index (AUI), gamma index (Iγ), and annual gonadal dose equivalent (AGDE) were calculated.The mean activity concentration of NORMs was 518.08 Bq/kg in Jal Mahal and 632.99 Bq/kg in Chor Ghumbad, both higher than the world average of 420 Bq/kg (UNSCEAR). The mean Raeq values were 130.78 Bq/kg and 149.87 Bq/kg for Jal Mahal and Chor Ghumbad, respectively, well below the recommended safety limit of 370 Bq/kg. Similarly, the mean ADR values (60.63 nGy/h and 69.57 nGy/h) were slightly above the global average of 59 nGy/h, while the AED, ELCR, and other indices remained below international safety thresholds. In conclusion, although both monuments exhibit higher NORM activity concentrations than the global average, For some values the radiological risk indices confirm that the sites are not so hazardous. Continuous monitoring is recommended to ensure long-term safety and preservation of these cultural heritage structures.