Cosmogenic radionuclides in the Lost City and Ucera meteorites

A 416-gram slice of the first Lost City fragment (9.825 kg) was analyzed nondestructively in a gamma-gamma-coincidence counting system. The first measurement was started about eight days after fall, permitting detection of 5.7-day 52Mn. Analysis of several measurements yields the following cosmogenic radioactivities, in disintegrations per minute per kilogram of meteorite: 22Na, 74±2; 26Al, 62±1; 46Sc, 12±1; 48V, 11±1; 51Cr, 71±23; 52Mn, 34±11; 54Mn, 85±42; 56+58Co, 14±6; 57Co, 9±1; 60Co, 1.9±0.4. The location of this sample within the recovered fragment, supported by the high 26Al activity, the low 22Na/26Al ratio, and the low (Fe-normalized) 54Mn activity, indicates a mean depth for this sample of at least 10 cm from the preatmospheric surface. At such a depth the very low 60Co activity requires an initial radius (for a spherical body) of less than about 25 cm, equivalent to a stony mass of less than 200 kg. The radioactivities found in Ucera are: 22Na, 60±4; 26Al, 43±3; 46Sc, 9±4; 54Mn, 61±4; 60Co, 5.5±1.6. The 22Na, 26Al, and 54Mn (normalized to per cent Fe) activities closely resemble the concentrations found in Harleton, suggesting that Ucera was, like Harleton, a small body in space.