The decay of ${\mathrm{K}}^{43}$ has been reinvestigated in an attempt to clarify the discrepancies existing in the ordering of the energy levels of ${\mathrm{Ca}}^{43}$. The external conversion spectrum showed lines corresponding to the following gamma-ray energies: 0.220±0.002, 0.371±0.002, 0.388±0.002, 0.394±0.002, 0.591±0.003, 0.614±0.004 Mev. In addition a $\gamma$ ray of 1.005 Mev was observed in the scintillation spectrum. $\beta -\gamma$ coincidence measurements establish that the gamma transitions to the ground state are the 0.371-Mev and the 0.591-Mev gamma rays and not the 0.614-Mev gamma as believed previously. These results and the $\gamma -\gamma$ coincidence measurements indicate only one possible level scheme in ${\mathrm{Ca}}^{43}$: 0, 0.371, 0.591, 0.985, 1.373 Mev. These energy levels as well as their proposed spin and parity assignments are in good agreement with the results from the Massachusetts Institute of Technology nuclear reaction data. A two-cycle baffle for the solenoid $\beta$ spectrometer is described. This baffle reduces significantly the background due to scattered gamma radiation from very strong external conversion sources.

• Received 2 February 1959

DOI:https://doi.org/10.1103/PhysRev.115.108