K. Helariutta

Gamma‐ray Spectroscopy Of Very Neutron‐Deficient Bi Isotopes

Prompt and delayed γ rays from in 191,193Bi have been identified using the recoil‐decay tagging (RDT), isomer tagging, and recoil gating techniques, resulting in extensive level schemes for both nuclei. Excitation energies of the isomeric 13/2+ states have been established and rotational bands based on them have been observed. The nearly spherical 9/2− ground‐state bands appear to be crossed by more deformed low‐lying structures. TRS calculations have been performed and B(M1)/B(E2) ratios have been extracted for the observed strongly‐coupled bands. In 193Bi, a 3 μs isomer has been interpreted as a h9/2 proton coupled to the 12+ state of the 192Pb core.

Recoil-isomer tagging techniques at RITU

Techniques have been developed to study isomeric states in nuclei with the use of RITU (gas filled separator) at the University of Jyvaskyla. The first was the recoil-isomer tagging technique initially, utilised by D.M. Cullen to study the K π = 8− isomeric state in 138Gd [1]. The juro-sphere array was employed in conjunction with ritu and a focal plane array which consisted of several Compton-suppressed Germanium detectors, placed in close geometry around a multi wire proportional counter (mwpc) and a silicon strip detector used for the implantation of recoiling nuclei. This technique correlates prompt and delayed γ-ray transitions across isomeric states and identifies the lifetime of the isomer. The main constraint of this technique is the timing electronics. Only isomers with a half-life greater than the flight time through RITU(~ 300ns) and less than the collection time of the tdc’s (32 μs) can be identified. This time range and hence technique is ideal for the region of mass A = 140 near proton drip line nuclei which have small production cross-sections in comparison to their more neutron rich neighbours and lack charged particle emission suitable for recoil-decay-tagging. Subsequent experiments to ref.