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 similar to 1.3 times higher gamma-ray count rates in the field on average compared to the underlying palaeosol and similar to 1.9 times higher values over the target basalt while measured by a portable Geiger-Muller pulse counter. The absorbed gamma-dose rate (D) of the Lonar samples, computed from Th-232, U-238, and K-40 abundances in these samples, also show that the ejecta has distinct bulk dose rates (average similar to 8.42 nGy h(-1)) as compared to those of the palaeosol (similar to 18.34 nGy h(-1)), target basalt (similar to 11.97 nGy h(-1)), and the impact-melts and spherules (similar to 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.