Gamma (γ)-Ray Activity as a Tool for Identification of Hidden Ejecta Deposits Around Impact Crater on Basaltic Target: Example from Lonar Crater, India

Geophysical techniques based on radioactivity measurements are not generally used for exploration of asteroid impact craters. Our studies on the field and laboratory measurements of radioactivity on samples from the Lonar crater, India, show that this technique could be an important method for mapping the distribution of ejecta around the deeply excavated impact craters particularly when these structures are formed on relatively old target rocks/palaeosol. The Lonar ejecta shows ~1.3 times higher γ-ray count rates in the field on average compared to the underlying palaeosol and ~1.9 times higher values over the target basalt while measured by a portable Geiger–Müller pulse counter. The absorbed γ-dose rate (D) of the Lonar samples, computed from 232Th, 238U, and 40K abundances in these samples, also show that the ejecta has distinct bulk dose rates (average ~8.42 nGy h−1) as compared to those of the palaeosol (~18.34 nGy h−1), target basalt (~11.97 nGy h−1), and the impact-melts and spherules (~14 nGy h−1). Therefore, radioactivity mapping of the terrestrial and planetary impact craters by direct methods has importance in mapping ejecta distributions around these structures.