Production rates of cosmogenic helium‐3, neon‐21, and neon‐22 in ordinary chondrites and the lunar surface

The production of 3 He, 21 Ne, and 22 Ne in meteoroids of various sizes and in the lunar surface was investigated. The LAHET code system, a purely physical model for calculating cosmic- ray particle fluxes, was used to simulate cosmic-ray particle interactions with extraterrestrial matter. We discuss the depth and size dependence of the shielding parameter 22 Ne/ 21 Ne, which is used for reconstruction of pre-atmospheric sizes, depth, and exposure histories. The 22 Ne/ 21 Ne ratio decreases with increasing depth or pre-atmospheric size but then increases with depth in very large objects. This increase with depth in the 22 Ne/ 21 Ne ratio means that this ratio is a poor indicator of shielding in some large objects. The dependence of 3 He/ 21 Ne as function of 22 Ne/ 21 Ne was also calculated, and differences between the calculations and the Bern line are discussed.