Thomas K. Keenan

Electronic Spectra of Cesium Fluoride Complexes of Pentavalent Neptunium

The absorption spectra of magenta‐colored CsNpF6 both as a mull of the crystalline solid and as a solution in CsF·2HF were obtained under various conditions. The room‐temperature spectra were unique to the electronic energy levels of the seven Russell–Saunders states for the 5f2 configuration, split by spin–orbit coupling into 13 free‐ion levels; this confirms the chemical evidence for the presence of pentavalent neptunium. At liquid‐nitrogen temperatures the spectra of CsNpF6 mulls were interpreted in terms of the free‐ion f–f transitions of Np5+ split by an Oh crystal field. Term assignments to the following experimental energy levels obtained at room temperature were made on the basis of the observed Stark splitting in the low‐temperature spectra, and agreement with calculated energy levels (in cm−1): 3F2 = 4337, 3H5 = 8425, 3F3 = 8797, 3F4 = 9701, 3H6 = 13 738, 3P0 = 16 129, 1D2 = 16 736, 1G4 = 18 265, 3P1 = 19 531, 1I6 = 20 619, 3P2 = 26 667. All levels above the 3H4 ground state were observed except...

A New Determination of the Half‐Life of Am242m; the Problem of Counting Short‐Lived Activities

The half‐life of Am242m has been redetermined to yield a value of 16.01±0.02 hours (99 percent confidence level). A simple relationship is developed between experimentally measured average counts/minute and true dN/dt; a convenient rule of thumb states that there is <0.1 percent error between average disintegration rate (finite counting interval) and dN/dt (at the mid‐point of the counting interval) when the counting interval does not exceed 20 percent of the half‐life.