The half-lives of nine isomeric states in the rare earth region were measured using magnetic beta-ray spectrometers and an associated fast-slow coincidence system utilizing a time-to-pulse-height converter. The half-lives of the 8. 40-, 118- and 139-keV levels in Tm1 69 were determined to be (4. 13 ± 0. 12) nsec, (63 ± 7) psec and (289 ± 24) psec, respectively. The half-life of the 8. 40-keV level was determined using both Erl69 and Ybl69 decay. Several different methods were used to measure the 8. 40-keV level lifetime including applying various accelerating voltages to the radioactive sources. Comparisons are made with theory for the K = 1/2 rotational band in Tm169. The half-life obtained for the 8. 40-keV level in Tm169 corresponds to an energy level width of (1. 10 ± 0. 03) x l0-7 eV. If there were no broadening of the individual line profiles in the Mossbauer effect pattern, the width at half-maximum of the resolved Mossbauer lines would be (2. 20 ± 0. 06) x 10-7 eV compared to the narrowest experimental Mossbauer gross line width of 5. 04 x 10-7 eV. The half-lives of the 87- and 105-keV levels in Gd155 were also determined and were found to be (6. 27 ± 0. 35) nsec and (1. 20 ± 0. 04) nsec, respectively. Comparisons were made with the theoretical predictions of Nilsson for these two levels. The theoretical-experimental comparison would assign a spin of 5/2 to the 1 05-keV level and a spin of 3/2 to the 87-keV level if the comparison could be taken at face value. The half-lives of the 122-keV level in Sml52, 89-keV level in Gdl56, 396-keV level in Lu175 and 80-keV level in Prl44 were also determined. The half-lives of these four levels were found to be (1. 36 ± 0. 06) nsec, (2. 22 ± 0. 08) nsec, (3. 31 ± 0. 10) nsec and (143 ± 11) psec, respectively. These four half-life values agree well with values obtained by other investigators.
McAdams, Robert E. and Hatch, Eastman N., "Some lifetime measurements of isomeric states in the rare earth region with magnetic coincidence beta-ray spectrometers" (1964). Ames Laboratory Technical Reports. 98.