A new half-life measurement of the long-lived fission product Sn-126

The half-life of the long-lived fission product Sn-126 has been determined through a specific activity measurement to be (2.07 +/- 0.21) x 10(5) a. The measurement was performed with Sn-126 material extracted from spent fuel rods of a nuclear power reactor. The activity concentration in this material was measured to be 4.97 +/- 0.15 Bq Sn-126/mg Sn. The half-life was determined by combining this activity concentration with the isotopic abundance of Sn-126/Sn = (9.23 +/- 0.87) x 10(-6) [P. Gartenmann et al., this issue, preceeding paper]. The latter was measured by accelerator mass spectrometry (AMS) and is reported in an adjacent paper. This is the first direct measurement of the half-life of Sn-126, which previously had been estimated to be similar to 10(5) years.