Impact of diorites and feldspars on soil radioactivity: Evidence from university city of the Universidad Nacional Mayor de San Marcos and the National Institute of Neoplastic Diseases

Abstract

This study represents the first systematic measurement of environmental radiation in the University City of the Universidad Nacional Mayor de San Marcos (UNMSM) and the National Institute of Neoplastic Diseases (INEN) in the city of Lima, Peru, conducted between July, December 2022, and January 2023. Natural radioactivity levels and absorbed dose rates in soil samples were determined by using gamma spectroscopy with a high purity germanium detector (HPGe) semiconductor detector with 150 % efficiency. At UNMSM, the following results were obtained for the activity concentrations (A) of the four main naturally occurring radioactive materials NORM (238U, 226Ra, 232Th, and 40K): AU238 = 24.2 ± 3.4 Bq kg− 1, ARa226 = 28.8 ± 0.7 Bq kg− 1, ATh232 = 39.4 ± 1.2 Bq kg− 1 and AK40 = 539 ± 7 Bq kg− 1. We find the absorbed dose rate of 57.5 nGy h− 1 and an annual effective dose equivalent of 0.28 mSv y− 1. On the other hand, at INEN, the following activity concentrations of NORM were found: AU238 = 26.0 ± 3.4 Bq kg− 1, ARa226 = 27.9 ± 0.8 Bq kg− 1, ATh232 =42.1 ± 1.6 Bq kg− 1 and AK40 = 559 ± 7.8 Bq kg− 1. We found the annual absorbed dose rate of 60.7 nGy h− 1 and an annual effective dose equivalent of 0.30 mSv y− 1. Additionally, the equivalent activity in radium (Req) and the risk indices for both indoor and outdoor environments were also determined. The higher than global average values of 40K activity concentrations are due to the greater presence of diorites and feldspars in the alluvial soils of Lima. These findings highlight the geological influence on local environmental radioactivity and are essential for future risk assessments. Nonetheless, the levels of environmental radioactivity found in this study are safe for the population in urban areas of academic and medical importance.