Measurement of the half-life of ~(79)Se with accelerator mass spectrometry

The accelerator mass spectrometry(AMS) is an effective method for the determination of the half-life of long-lived radionuclides. In this paper, we report a method for measurement of the half-life of79 Se. The number of79 Se atoms was determined from measured79Se/Se absolute ratios with the AMS system at the China Institute of Atomic Energy and the decay rate of79 Se was determined by counting the emitted β-rays with a liquid scintillation spectrometer. The major improvements of our measurements include using the high abundance of an79 Se sample which was cooled for many years to exclude the interference of short-lived nuclides, the extraction of SeO-2molecular ions, that results in a suppression of the79 Br background by as much as about five orders of magnitude. Also, an AMS measurement of the absolute ratio of79Se/Se was developed to avoid systematic errors. The results show that79Se/Se is(2.35±0.12)×10-7in the reference sample and the radioactivity of79 Se is(1.24±0.05) Bq/g, so the half-life of79 Se is(2.78±0.18)×105a.     

Production of projectile and target K-vacancy in near-symmetric collisions of 60-100 MeV Cu9+ ions with thin Zn target

We report studies on both target and projectile K-shell ionization by collisions of Cu⁹⁺ ions on the thin Zn target in the energy range of 60-100 MeV. In this work, the relative ratio for the production of the target to projectile K-vacancy is measured. The result shows that it almost remains stable over this energy range and has good consistency with the predictions by vacancy transfer via the 2pσ-1sσ rotational coupling, which gives experimental evidence for K-vacancy sharing between two partners. Furthermore, the discussion for comparisons between the experimental ionization cross sections and the possible theoretical estimations is presented. These comparisons suggest that the experimental data agree well with those predicted by the Binary-Encounter approximation (BEA) model but are not in good agreement with the modified BEA calculations. It allows us to infer that the direct ionization (and/or excitation) is of importance to initial K-vacancy production before 2pσ-1sσ transitions in the present collision condition.     

New high spin level scheme of 87Sr

High spin states of the odd-A ⁸⁷Sr were populated by the fusion-evaporation reaction ⁸²Se(⁹Be, 4n) ⁸⁷Sr at a beam energy of 46 MeV. Excited levels of ⁸⁷Sr have been extended up to an excitation energy of 7.4 MeV at spin 31/2ħ. The coupling of a g_9/2 neutron hole to the yrast states of the ⁸⁸Sr core can account for the low-lying states in ⁸⁷Sr. The structure of the higher spin states is discussed by analogy with those of the neighboring odd-A N=49 isotones and possible configurations are proposed.