Radiative electron capture in Mn54 and Cr51

The continuous spectrum of photons accompanying the allowed electron-capture transition from Mn54 to the first excited state in Cr54, as well as that from Cr51 to the first excited state in V51 have been measured in coincidence with the nuclear γ rays from the deexcitation of these states. The end-point energy of the spectrum from Mn54 was determined to be 518 ± 8 keV, which is somewhat at variance with the value 537 ± 4 keV calculated from accepted mass differences. The probability of radiative capture relative to ordinary nonradiative capture was determined to be (15.4 ± 0.8) × 10-5 for Mn54 in the energy range 82-515 keV. This is considerably larger than the value 10.9 × 10-5 predicted by the relativistic theory of Martin and Glauber. The shape of the photon spectrum is nevertheless in excellent agreement with the theoretical prediction. For Cr51 the end point was determined to be 424 ± 16 keV in excellent agreement with accepted mass differences. The relative rate of radiative capture with a photon energy greater than 130 keV was determined to be (7.2 ± 0.4) × 10-5, in disagreement with the theoretical value of 5.5 × 10-5, while the spectrum shape agrees excellently with the theory. A survey of the experimental verification of the Martin and Glauber theory is presented.