Coincidence measurements on the decay of Tm (87 d)

The decay of ¹⁶⁸Tm(87 d) has been studied with Ge(Li) detectors in singles and in coincidence with a NaI detector. The energies and intensities of the following previously established transitions were obtained: 79.8, 99.3, 173.8, 184.4, 198.3, 273.0, 348.5, 4.22.2, 447.6, 546.8, 557.0, 631.7, 645.75, 673.7, 720.4, 730.7, 741.4, 748.25, 816.0, 821.1, 829.9, 914.8, 928.9, 1014.2, 1167.3, 1277.3, 1323.7, 1351.4 and 1461.5 keV. Additional γ-ray transitions at 284.5, 853.2, 1262.6 and 1489.7 keV were observed. These data were combined with the available internal conversion electron data to obtain internal conversion coefficients. Branching ratios for E2 transitions de-exciting levels in the gamma band and E1 transitions de-exciting the negative-parity states were calculated and compared with theoretical estimates. Prompt and delayed coincidence measurements were carried out using a 2 mm Ge(Li) detector and a 7.6 cm × 7.6 cm NaI detector. Gates were set at 79.8, 99.3, 184.4, 198.3 and 447.6 keV and on transitions in the region from 700 to 850 keV. The delayed coincidence measurements were made to investigate the population and decay of the 0.12 μsec state at 1094.1 keV and support the placement of the 348.5 keV transition in the decay scheme. A revised decay scheme is presented.