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The radioactivities of 37Ar (35‐day half‐life) and 39Ar (270‐year half‐life) were measured in the separated iron phase and in whole‐rock samples of the Lost City meteorite. Two samples of magnetic phase were dissolved in acid, thus releasing the argon radioactivities. Those radioactivities were concordant. After the calcium and potassium contributions to the argon radioactivities were removed, the average values of the 37Ar and 39Ar from the iron and nickel at the time of fall were 11.7±0.9 dpm/kg and 24.6±0.9 dpm/kg, respectively, and the 37Ar/39Ar ratio for the iron and nickel was 0.48±0.04. This low 37Ar/39Ar ratio cannot be explained solely by the modulation of cosmic rays at the time of fall. Since the orbit of the Lost City meteorite is known, the 37Ar/39Ar ratio can be interpreted in terms of a variation in the cosmic‐ray flux along its orbit. A positive radial gradient for the flux of cosmic rays of energies greater than 400 Mev is required. The gradient is (62±17)% per AU for the long‐term (∼500 year) average flux. In the whole rock, the tritium and argon radioactivities were measured as a function of depth along a 10.0‐cm bar. The tritium varied from a maximum of 358±5 dpm/kg to a minimum of 260±10 dpm/kg. The tritium activities, together with the low 60Co activity, indicate that between 4 and 11 cm of material was ablated from one end of the bar, and between 10 and 23 cm of material was ablated from the other end.

A production rate of 0. 065 ± 0. 003 Ar atom/kg min of K at 2-mwe depth below sea level was measured by sweeping argon from potassium solutions. This rate is unaffected by surrounding the solution by paraffin and is attributed to negative-muon captures and the electromagnetic interaction of fast muons, and not to a nucleonic cosmic-ray component. The 37 39 Ar yield from K by the stopping of negative muons in a muon beam of the SREL synchrocyclotron was measured to be 8. 5 ± 1. 7%. The stopping rate of negative cosmic-ray muons at 2-mwe depth below sea level from these measurements and an estimated 17% electromagnetic production is 0.63 ± 0.13 |_i /kg min. Previous measurements on the muon stopping rate vary by a factor of 5. Our value is slightly higher but is consistent with two 37 previous high values. The sensitivity of the Ar radiochemical method for the detection of muons is considerably higher than that of the previous radiochemical methods and could be used to measure the negative-muon capture rates at greater depths. IntroductionUntil the experiments of the Utah cosmic-ray group [Bergeson et al., 1967], it was universally believed that cosmic-ray muons result solely from the decay of secondary pions and kaons from cosmic-ray interactions in the atmosphere. The Utah experiment raised the possibility for an additional source of muons. An explanation [Bjorken et al., 1969] of the Utah experiment has been proposed that requires an anomalous absorption of muons of negative helicity and unusual shape for the sea-level muon energy spectrum. This spectrum is often inferred from stopping rate versus depth measurements near sea level. Although the muon stopping rate has been 111-098 measured by three different methods, measurements by even the same method often disagree. Stopped muon rates have mainly been measured with nuclear emulsions and with scintillators at depths to 300 mwe (meters of water equivalent). Recent measurements by Bergamasco [1970] are a factor of 2-5 higher than previous ones. Additional measurements of the stopped negative-muon rate might be helpful in determining whether cosmic muons result solely from the decay of secondary IT and K mesons.Until now, because of restricted sensitivity, radiochemical methods for detection have yielded positive results to a depth of only 0.2 mwe. Winsberg [1956] Cl from rainwater produced by the Ar (|jt , v n) reaction. Rama and Honda [1961] extracted gold radioactivities from mercury at sea level and state that their result is 59 consistent with Winsberg's. Takagi and Tanaka [1969] observed a Fe radioactivity of 0. 35 ± 0.14 atom/kg min induced by cosmic-ray muons in cobalt at sea level. This is a lower limit for the stopping of negative muons because the yield of the reaction was not determined. A more sensitive radiochemical method with a measured yield is needed. -37The K ([i , v 2n)Ar reaction offers the possibility for extremely high sensitivity because it is possible to extract argon with almost 100% efficiency from large 37 volumes of potassium ...

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The 37Ar and 39Ar radioactivities were measured in a dissolved and in a melted sample of Haverö. The 37Ar in the metal was 12.4 ± 2.6 dpm/kg (Fe + Ni). The 39Ar in the metal was 49.3 ± 5.5 dpm/kg (Fe + Ni). The 37Ar activity is within 30 percent of that in the Lost City meteorite, while the 39Ar activity is a factor of two higher than in Lost City. The similarity in the 37Ar activities of the metal of the two meteorites indicates that these two bodies had similar preatmospheric sizes. The higher 39Ar activity in the metal of Haverö indicates that the aphelion of Haverö's orbit was at least 4.3 A.U. The 3H radioactivity in Haverö was measured to be 415 ± 30 dpm/kg. The 3H activity combined with the 3He content gives a 3He/23H exposure age for Haverö of (29.5 ± 2.5) X 610 years.