The Beta-Ray Spectra ofMg27,Cu62and the Nuclear Isomers ofRh104

The beta-ray spectra of several radioactive elements have been investigated by means of a cloud chamber in a uniform magnetic field. The spectrum of ${\mathrm{Mg}}^{27}$ gave an upper limit of 1.8 Mev on the basis of 586 tracks. The spectrum of ${\mathrm{Cu}}^{62}$ gave an upper limit of 2.6 Mev on the basis of 803 tracks. The spectra of the two nuclear isomers of ${\mathrm{Rh}}^{104}$ were found to have the same upper limit and the same shape within experimental error. Their upper limits are 2.3 Mev on the basis of 524 and 529 tracks. The similarity in shape of the two spectra indicates that a direct beta-transition from the 4.37-minute level does not occur to any appreciable extent and that as far as can be determined by this work the disintegration of the 4.37-minute isomer proceeds entirely by a gamma-ray transition to the ground state of ${\mathrm{Rh}}^{104}$ followed by a beta-transition to the ground state of ${\mathrm{Pd}}^{104}$.