No abstract

The 35‐day Ar37 and the 270‐year Ar39 isotopes were measured in the iron‐ataxite meteorite Alandroal, which fell on November 14, 1968, and in two recently fallen stony meteorites, Allende, which fell on February 14, 1969, and Sprucefield, which fell on April 25, 1969. The Ar37/Ar39 ratio in Alandroal is 0.50±0.03, which is considerably lower than that measured in previous iron meteorites and a factor of 2 lower than the ratio of 1.09±0.05 expected if the high‐energy (>300 Mev) cosmic rays were constant. In the autumn of 1968, the high‐energy cosmic‐ray flux near 1 AU was 0.46±0.07 of the flux during the previous several hundred years near the apogee of the orbit of Alandroal (probably near 4 AU). The Ar37/Ar39 ratio in the iron phase of Sprucefield is 0.90±0.09, which requires that the high‐energy cosmic‐ray flux in the spring of 1969 near 1 AU be approximately the same as the flux near the apogee of the orbit of Sprucefield (probably near 1 AU) during the previous several hundred years. A small orbit for Sprucefield is also indicated by the loss of spallation He3 and Ne21 and of radiogenic He4 and Ar40, which indicate solar heating. From the Ar37/Ar39 ratio in Alandroal, a lower limit of +15% per AU is obtained for the average gradient of the cosmic‐ray flux with distance from the sun. In the Allende whole rock and in the stone phase of Sprucefield, the Ar37 is produced almost entirely by secondary neutrons. The radioactivities, H3, Na22 + Al26, Co60, and the stable rare‐gas isotopes were also measured, and exposure ages were determined. The radioactivities and stable rare gases were also measured in the stony meteorite Ankobar, which fell on July 7, 1949. No argon radioactivities were detected in the iron ataxite Deep Springs, which indicates that it landed more than 2000 years ago.

No abstract