Cosmogenic and trapped rare gases in Luna-24 drill core samples

The elemental and isotopic composition of noble gases in six samples from different depths of the Luna-24 drill core soil column, obtained by mass spectrometric analyses, are presented and the results are compared with those obtained by others for additional samples from the same drill core. The elemental ratios of²²Ne/¹³²Xe, seem to indicate a low degree of maturity for the majority of the samples in this soil column. A detailed study of the cosmogenic isotopes, particularly²¹Ne, in samples from different depths suggests that the entire soil column could be divided into two zones. Most of the samples in the upper zone fit to a regolith deposition model where about a meter of material got rapidly deposited and was irradiated as a single slab for a period of about (500±100) m. y. The samples from the lower zone, however, show cosmogenic²¹Ne_c contribution due to predepositional irradiation.