HELIUM ION-IMPLANTATION INTO MINERALS

We implanted rock-forming minerals (olivine, magnetite, ilmenite, and rutile) with a 3.6 keV helium ion beam, which simulates solar wind α-particles, and analyzed implanted helium. A total fusion experiment shows that nearly 100% of impinging helium ions is trapped in a target at smaller doses, while the concentration of trapped helium tends to be saturated above a helium ion dose of ∼ 1016 ions/cm2. There is no appreciable difference in the concentration of trapped helium among minerals. A stepwise heating experiment shows that implanted helium is retained more firmly in magnetite and rutile than in olivine. On the basis of the experimental results, a high degree of loss of implanted helium out of IDPs is suggested. This may be attributed to decomposition of helium-bearing minerals in IDPs during their entry into the earth's atmosphere. © 1990.