Solar composition noble gases in the Washington County iron meteorite

A sample of the Washington County iron meteorite is analyzed for its light noble gases by a combustion technique in two steps at 1160 C. The ratio of trapped to spallogenic noble gases in the sample was high enough to allow the resolution of trapped and spallogenic components in both combustion steps. The He:Ne:Ar elemental ratios in the trapped component are comparable to present-day solar-wind ratios. The (Ne-20)/(Ne-22) ratio, while subject to some uncertainty due to possible variation in either the spallation or the trapped component between the two steps, is in the range 13.3 + or 0.5, also comparable to present-day solar wind. Unless the Washington County iron formed by some unique process in a solar-wind-irradiated regolith, the fact that the trapped gas is of solar composition has implications with regard to the compositional history of the solar wind, to conditions in the early solar nebula during grain formation or accretion, and to primordial helium in the earth.