METASTABILITY OF THE MUONIC BORON 2S STATE

The cascade of muonic boron and the two-photon decay 2S --> IS have be en investigated. The x-ray measurement with Ge and Si(Li) detectors wa s performed at low target gas pressures of pure B2H6 and admixtures-wi th He. The 2S population of mu B is found to be epsilon(2S) = 3.1(2)%. Cascade calculations indicate that more than half of the 2S states ar e populated with an empty electron shell. Two-photon decays have been observed in mixtures of B2H6 in He at partial diborane pressures of 67 Pa and below. The measured fraction of metastable 2S states per mu B atom is 0.58(16)% in an admixture of 1% B2H6 in He at 6.7 kPa and is i nterpreted in terms of pressure dependent quenching.