M. Górska

Proton-neutron interaction at N≅Z — First observation of the Tz=1 nucleus 46 94 Pd48 in-beam

The neutron deficient nucleus94Pd was identified and studied for the first time by in-beam spectroscopy. An Iπ=(14+) isomer with t1/2=0.8 (2) μs was observed in a recoil catcher setup inside the multi-detector γ-array OSIRIS. Filter detectors for neutrons and charged particles were used to identify the (2p2n) exit channel of the reaction58Ni+40Ca, populated with only 0.06% of the total evaporation residue cross section. The structure of the isomer is discussed within the frame work of shell model calculations in the (p1/2,g9/2) model space with emphasis on the g92/2 T=0, I=1,9 ”pairing” two-body matrix elements.

High-spin studies of the neutron deficient nuclei In-103, In-105, In-107, and In-109

High-spin states of the isotopes In-103,In-105,In-107,In-109 have been investigated using in-beam gamma-ray spectroscopic methods. Results from three different experiments are presented. Targets of Fe-54, Cr-50, and Mo-92 were bombarded by a 270 and 261 MeV Ni-58 beam and by a 95 MeV F-19 beam, respectively. Reaction channel separation was achieved with a charged-particle detector array and in the first two experiments also with a 1 pi neutron detector system. As a result of these experiments the level schemes of In-103,In-105,In-107,In-109 were significantly extended. Excited states of these odd-A indium isotopes are discussed within the framework of the nuclear shell model and the hole-core coupling scheme. The systematics of excited states of light odd-A indium isotopes is also discussed

Picosecond lifetime measurement of neutron core-excited states in the N = 50 nucleus 95Rh

Abstract Lifetimes of high-spin states in the N = 50 nucleus 95Rh were measured using the recoil-distance Doppler-shift technique. The nuclei were produced via the reaction 58Ni(40Ca,3p) at 145 MeV beam energy and the γ radiation was detected in six EUROBALL cluster detectors. Reduced transition probabilities for seventeen γ transitions and limits for nine further transitions were extracted and compared with the predictions of the spherical shell model based on the extended configuration space, ( 0f 5 2 , 1p 3 2 , 1p 1 2 , 0g 9 2 ) for protons and ( 0g 9 2 , 1d 5 2 ) for neutrons relative to a hypothetical 68Ni core. The results indicate that all observed states with 27 2 ⩽ I ⩽ 39 2 are built from a neutron g 9 2 → d 5 2 excitation across the N = 50 shell closure, coupled to up to five valence protons in different configurations. Evidence of stretched dipole cascades having large M1 strengths was found and explained by spin recoupling within the ν( g 9 2 ) −1 ν( d 5 2 ) neutron part of the wavefunctions.

The decay of theIπ=8+ isomer in100Cd-neutron particle and proton hole states

The γ-decay and half life of the t1/2=60(3) ns Iπ=8+ isomer in100Cd have been studied with a recoil catcher setup inside the multidetector π-array OSIRIS. Evaporation neutrons and charged particles from the reaction58Ni+46Ti were measured in coincidence with delayed γ-rays. Six new γ-ray transitions with intensities of 1–10% of the main γ-ray cascade were found, two new states established and firm spin-parity assignments were made to all states below the isomer. The new states were identified as the 4+ and 6+ members of the proton πg9/2−2 multiplet.

Present status and future aspects of nuclear structure close to Sn-100 - The OSIRIS, NORDBALL-PEX and EUROBALL collaborations

The present status of experimental approach to 100Sn in the spectroscopy of excited states is landmarked by the Tz=3/2 nuclei between 95Pd and 101In and the Tz=1 nuclei 94Pd and 98Cd. The detection limits with Pre-EUROBALL γ-arrays and ancillary detectors are below the 10−5 level of the total fusion- evaporation residue cross section. A large scale shell model analysis of the existing data reveals the shell structure at 100Sn, which shows a remarkable similarity to 56Ni. Evidence for an increasing proton-neutron interaction in approaching the N=Z line is deduced from high spin isomers and spherical yrast lines. The effective E2 operator for protons and neutrons and implications for a low lying particle-hole (ph) E2 excitation in 100Sn are discussed.

Nuclear structure in the region of 100Sn at N≃Z

With the recent development of efficient γ-arrays with highly selective ancillary detectors, studies of shell structure and residual interaction in exotic nuclei like 100Sn have become feasible. The shell structure at N=Z=50 (100Sn) shows a remarkable similarity to N=Z=28 (56Ni), albeit recent experiments on the 100Sn neighbors 102,104Sn and 98Cd indicate substantial and puzzling deviations in the E2 and E3 polarizability of the magic core 1–3. New experimental results and their shell model interpretation are discussed.

Nuclear structure near the doubly-magic 100Sn

The single particle (hole) energies in 100Sn, as extrapolated by a shell model analysis of the neighboring nuclei, show a remarkable similarity to those in 56Ni, one major shell lower. This is borne out in nearly identical Iπ=2+ excitation energies, implying E(2+)≃3u200aMeV in 100Sn, and a large neutron effective E2 charge e⩾1.6e. In contrast a small proton polarization charge δe⩽0.3e is found, pointing to a large isovector charge. Mean field predictions for single particle energies show substantial deviations from the experimental extrapolation. From the experimental two-proton hole spectrum in 98Cd an improved empirical interaction is extracted for the π(p1/2,g9/2) model space yielding a good description of the N=50 isotones 95Rh to 98Cd. In 104Sn, for the first time in this region, strong E3 transitions with B(E3)⩾17u200aW.u. were identified, indicating E(3−)≃3u200aMeV in 100Sn. New experimental devices, as the Ge-cluster cube and total absorption spectrometers, applied in a pioneering experiment to the β+/EC deca...