Radiopurity studies of a rock sample from the Aut region

TL;DR

This study assesses the radiopurity of a rock sample from the Aut tunnel in India, revealing significantly lower potassium-40 levels and comparable neutron backgrounds, supporting its suitability for underground physics experiments.

Contribution

It provides the first detailed radiopurity analysis of Aut rock, comparing it with BWH, and evaluates its potential for low-background physics research.

Findings

Aut rock has 1000 times lower $^{40}$K than BWH.

Lower $^{232}$Th impurity in Aut rock.

Similar neutron background levels at Aut and BWH.

Abstract

Efforts are underway to set up an underground laboratory in India for rare event studies like double beta decay, dark matter, etc. For such experiments, mitigation of radiation background is of paramount importance and understanding ambient background at the site, originating from the rock, is one of the crucial factors. With this motivation, the radiopurity studies of a rock sample from the potential laboratory site in the Aut tunnel of Himachal Pradesh (India) have been carried out using the TIFR low background experimental setup (TiLES). The concentration of $^{40}$K in Aut rock is observed to be lower by a factor of ~1000 as compared to the samples from BWH (Bodi West Hill), Tamil Nadu (India), current designated site for India-based Neutrino Observatory. The natural radioactive trace impurity $^{232}$Th is lower in the Aut rock, while $^{238}$U is somewhat higher than the BWH rock. Overall, the ambient gamma ray background at Aut is expected to be lower than the BWH, while ambient neutron background is expected to be similar. Further, to assess the neutron-induced long lived activity, fast neutron activation studies have been carried out on the both Aut and BWH rock samples at the Pelletron Linac Facility, Mumbai.