J. Iwanicki

Information on antiprotonic atoms and the nuclear periphery from the PS209 experiment

A. Trzcińska, J. Jastrzȩbski, T. Czosnyka, T. von Egidy, K. Gulda, F. J. Hartmann, J. Iwanicki, B. Ketzer, M. Kisieliński, B. K los, W. Kurcewicz P. Lubiński, P. J. Napiorkowski, L. Pieńkowski, R. Schmidt, E. Widmann Heavy Ion Laboratory, Warsaw University, PL-02-093 Warsaw, Poland Physik-Department, Technische Universität München, D-85747 Garching, Germany Institute of Experimental Physics, Warsaw University, PL-00-681, Warsaw, Poland Institute of Physics, University of Silesia, PL-40-007 Katowice, Poland CERN, CH-1211 Geneva 23, Switzerland

0(gs)+ -->2(1)+ transition strengths in 106Sn and 108Sn.

The reduced transition probabilities, B(E2; 0(gs)+ -->2(1)+), have been measured in the radioactive isotopes (108,106)Sn using subbarrier Coulomb excitation at the REX-ISOLDE facility at CERN. Deexcitation gamma rays were detected by the highly segmented MINIBALL Ge-detector array. The results, B(E2;0(gs)+ -->2(1)+)=0.222(19)e2b2 for 108Sn and B(E2; 0(gs)+-->2(1)+)=0.195(39)e2b2 for 106Sn were determined relative to a stable 58Ni target. The resulting B(E2) values are approximately 30% larger than shell-model predictions and deviate from the generalized seniority model. This experimental result may point towards a weakening of the N=Z=50 shell closure.

Electromagnetic structure of 98Mo

Abstract The nucleus 98 Mo was multiply Coulomb excited using 20 Ne, 84 Kr and 136 Xe beams. Eighteen E2 and M1 reduced matrix elements connecting 7 low-lying levels have been determined using the least-squares code GOSIA. The results are compared with the predictions of an extended version of the IBM1 model. The quadrupole sum rules approach was used to determine the shape parameters in two 0 + (ground and first excited) states. The rotational invariants 〈Q 2 〉 and 〈 cos 3δ〉 obtained show the shape coexistence in 98 Mo nucleus: the triaxial ground state and the prolate first excited state.

Spectroscopic Quadrupole Moments in {96,98}Sr: Evidence for Shape Coexistence in Neutron-Rich Strontium Isotopes at N=60.

Neutron-rich {96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.

First Use of Post-Accelerated Isomeric Beams for Coulomb Excitations Studies of Odd-Odd Nuclei Around N=40

We report on the first use of post-accelerated radioactive isomeric beams. Long-lived isomeric states in 68Cu and 70Cu have been produced and separated at ISOLDE, CERN. Subsequently they were post-accelerated to 2.86 MeV/u and sent to a target in the center of the MINIBALL spectrometer, used for the detection of the γ-rays of interest. The preliminary results from the Coulomb excitation of the Iπ=6-, 1+ states in 68Cu and the Iπ=6- one in 70Cu, compared to a large-scale shell model calculations, hint the importance of the excitations across the Z=28 gap for the understanding of the nuclear structure in the neutron-rich N=40 region.

SEARCH FOR SHAPE COEXISTENCE IN EVEN – EVEN STABLE MOLYBDENUM ISOTOPES USING COULOMB EXCITATION METHOD

Coulomb excitation experiments were performed with 96Mo, 98Mo and 100Mo isotopes using both beam and target excitation. As a result, quadrupole deformation parameters were deduced for two lowest-lying (ground and excited) 0+ states. Surprising shape changes of these states were observed.

Antiprotonic investigation of the nuclear periphery

Some results inferred from a program devoted to the study of the nuclear periphery using antiprotonic atoms are presented.

Coulomb excitation of 68Ni at “safe” energies

The B(E2;0+2+) value in 68Ni has been measured using Coulomb excitation at safe energies. The 68Ni radioactive beam was postaccelerated at the CERN on-line isotope mass separator (ISOLDE) facility to 2.9 MeV/u and directed to a 108Pd target. The emitted rays were detected by the MINIBALL detector array. Not only directly registered but also indirectly deduced information on the nucleus emitting the ray was used to perform the Doppler correction, leading to a larger center-of-mass angular range to infer the excitation cross section. The obtained value of 2.8×102e2 fm4 is in good agreement with the value measured at intermediate energy Coulomb excitation, confirming the low 0+2+ transition probability.

Coulomb excitation of neutron-rich Cd isotopes at REX-ISOLDE

We report on the “safe” Coulomb excitation of neutron‐rich Cd isotopes in the vicinity of the doubly magic nucleus 132Sn. The radioactive nuclei have been produced by ISOLDE at CERN and postaccelerated by the REX‐ISOLDE facility. The γ‐decay of excited states has been detected by the MINIBALL array. Preliminary results for the B(E2) values of 122,124Cd are consistent with expectations from phenomenological systematics.

In-beam γ-ray spectroscopy of 103Cd

Excited states of Cd-103 were studied in the reaction Ni-58(Cr-50,4pn)Cd-103. The NORDBALL array with neutron and charged particle detectors was employed for the detection of gamma rays and light evaporated particles. The level scheme of Cd-103 was significantly extended. A strong cascade of E2 transitions connecting negative parity states was found, Shell model calculations were performed and positive parity excited states were interpreted in terms of neutron-particle and proton-hole excitations with respect to the doubly magic N = Z = 50 core. The negative parity band was well reproduced by the total routhian surface calculations