Conversion electron spectrum from Ce 144 decay

Abstract

The internal conversion electron spectrum following the β decay of Ce 144 has been studied in the Chalk River iron-free π√2 β spectrometer at a momentum resolution of ≈ 0.1%. The 33 conversion lines observed are identified with 7 transitions of energies (in keV) and multipolarities 33.57±0.03, M1; 40.93±0.03, M1; 53.41±0.03, M1; 59.03±0.03, M3; 80.12±0.03, Ml; 99.95±0.03, E2; and 133.53±0.03, M1. The multipolarity assignment for each transition was obtained by comparing the observed conversion line intensity ratios with the theoretical line intensity ratios of Sliv. The intensity of the K conversion line of the 133.53 keV transition has been measured relative to the total intensity of the Pr 144 β spectrum; I K 133/ I Pr β sp. = 0.053±0.002. The momentum ratio of the Ce 144 K 133.53 and Cs 137 K 661.6 lines, corrected for electron energy loss in the Ce course, is B ρK 133/ B ρK 661 = 0.31495±0.00003. Intensity limits are placed on all previously reported Ce 114 conversion lines not presently observed. Relative quantum intensities and total transition intensities are deduced from the conversion line data. A decay scheme for Ce 144 is given which satisfactorily accounts for all the results of this investigation and is compatible with the results of earlier workers when some line reassignments are made. Interpretations of the Pr 144 levels, established in this work, are discussed in terms of both the shell model and the unified model. With δ ≈ +0.07, the unified model accounts for the experimental evidence in a simple but convincing fashion.