Energy Correlations of γ-Rays from Superdeformed States in Z=66 and 68 Isotopes; Multipolarities in ¹⁵²Dy

Abstract

The search has been carried out at LBL by the first two authors and the coauthors at Berkeley using the High Energy Resolution Array (HERA), which consists of 21 BGO Compton-suppressed Ge detectors for the measurement of E _γ(1)–E _γ(2) correlations. Thin targets of enriched ^114,116Cd and ^118,120Sn were bombarded with 180 MeV ⁴⁰Ar beams. The recoils were stopped in a lead catcher, positioned at a distance of 20 cm behind the target which corresponds to a flight time of ~28ns in the case of ^151,152Dy, and at a distance of 13 cm in the other cases. The cylindrical BGO detector at 0°, surrounding the beam pipe with the catcher foil, provided a signal on delayed γ-ray emission from the recoils. All recorded energy signals of the Ge detectors were corrected for the Doppler shifts as to be gain matched on-line. In addition, the time spectrum obtained from the 0° BGO crystal with respect to the OR-signal (first time signal of all detectors) of the Ge detectors has been recorded for each event. Only triple coincidences and higher folds were written on magnetic tape. Typical event rates amounted to 2000 s^-1, with a beam current of 15 nA. Two days of running time did yield ~200 million triple and higher-fold events resulting in more than 600 million double coincidences in the case of ¹⁵²Dy and about 1/3 of that in the other searches.