Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 38: Spectroscopy 104 ≤ A < 140

HK 38.7: Group Report

Tuesday, March 17, 1998, 18:30–19:00, D

Precision lifetime measurements for transitional nuclei in the
A=130 mass region — •A. Dewald¹, T. Klemme¹, O. Stuch¹, R. Peusquens¹, H. Tiesler¹, S. Kasemann¹, R. K"uhn¹, T. Klug¹, R. Kr"ucken¹, I. Wiedenh"over¹, K.O. Zell¹, P. von Brentano¹, D. Bazzacco², C. Rossi-Alvarez², S. Lunardi², C. Petrache², G. de Angelis³, M. de Poli³, C. Ender⁴, T. H"artlein⁴, F. K"ock⁴, O. Koschorrek⁴, P. Reiter⁴, and D. Schwalm⁴ — ¹Institut f"ur Kernphysik, Universit"at zu K"oln, 50937 K"oln — ²Dipartimento di Fisica and INFN, Sezione di Padova, Padova, Italy — ³INFN,Laboratori Nationale, Legnaro, Italy — ⁴Max-Planck-Institut f"ur Kernphysik, Heidelberg, 69029 Heidelberg

Transition probabilities are crucial quantities for testing nuclear models and can be directly related to the nuclear deformation. Thus it is an important progress that it is possible now to measure lifetimes with high precision. This has become feasible by using e.g. advanced experimental techniques like recoil distance coincidence measurements with the new multi-detector γ-ray spectrometers as well as elaborate analyzing techniques like the differential decay curve method.
We will report on two coincidence plunger experiments performed with the GASP spectrometer in its configuration two (5,8% efficiency) at Legnaro and with the 3x3 Cluster setup at Heidelberg. Lifetimes of positive and negative parity states in ^134,135Nd and ^130,129Ba were determined using the ¹¹⁰Pd(²⁸Si,xn) reaction at E_Si=135 MeV (GASP) and the ¹¹⁶Cd(¹⁸O,xn) reaction at E_O=76 MeV (Cluster setup), respectively. The achieved accuracy for some lifetimes is better than 2%. The experimental data are used for stringent tests of collective nuclear models. In addition deformation driving effects caused by the occupation of different Nilsson orbitals are investigated. In ¹³⁴Nd a large Q_t-value of about 6 eb was measured after the ν(h_11/2)² band crossing thus giving evidence for an extreme shape change above the band crossing.
In ¹³⁰Ba and ¹³⁴Nd the mixing of S-band states (π(h_11/2)² or ν(h_11/2)²) with members of the ground band or quasi γ-band was found to occur already at spin 8ℏ.
Supported by the BMBF under Contract No. 06 OK 668.