A negative muon beam from the Carnegie Tech synchrocylotron was stopped in a six-inch propane bubble chamber. Since the hydrogen does not form $\mu$-mesonic atoms in the presence of carbon, the pictures yield information on the interaction of stopped muons with carbon. About 30 000 pictures of stopping muons were taken with the bubble chamber kept sensitive for ∼20 msec after the beam pulse in order to observe the beta decay of any bound ${\mathrm{B}}^{12}$ nuclei resulting from $\mu$ absorption by carbon. The chamber was photographed right after the beam pulse to determine whether a given stopped muon decayed, or was absorbed. Another photograph was taken about 15 msec later to determine if the absorption had led to a nucleus which had beta decayed. A count of $\mu -e$ decays in the same film allowed the determination of the probability per unit time of bound ${\mathrm{B}}^{12}$ formation. Forty-six boron decays were observed yielding (7.6±1.2)×${10}^3$ ${\sec }^{-1\mathrm{}}$ for the rate of bound ${\mathrm{B}}^{12}$ production. Possible interpretation of this result in terms of a universal V-A Fermi interaction is discussed.

• Received 8 September 1959

DOI:https://doi.org/10.1103/PhysRev.118.319