Further evidence on the origin of trapped gases in the meteorite Khor Temiki

A concentration profile for the trapped gases in the grains of the Khor Temiki meteorite was established by removing the surface layer of individual grains in a homogenous grain size fraction with hydrofluoric acid and measuring the remaining rare gas contents. The profile shows a strong enrichment of the trapped gases in the surface layer (outermost 5000 A) of the grains. This result is in agreement with the recently established anticorrelation between grain size and trapped gas content. The most likely emplacement mechanism leading to such a pronounced surface effect is ion bombardment. From our experiments, an upper limit of 100 kev is deduced for the energy of the incident He4 ions.