R. Broda

Particle hole yrast states in146Gd and147Gd and the Z=64 shell closure

The level structures of146Gd and147Gd have been investigated by in-beamγ-ray ande− spectroscopy with (α, xn) reactions on enriched Sm targets. Detailed level schemes up to ∼4 MeV, which differ radically from earlier schemes, are reported. The energy levels are characterized as particle-hole excitations using empirical single particle energies and two nucleon interactions. Analysis of pure 1p 1h proton excitations demonstrates that theZ=64 andN=82 energy gaps are about equally large.

Structure of 52,54Ti and shell closures in neutron-rich nuclei above 48Ca

Abstract The level structure of 5422Ti32 has been explored for the first time by combining β-decay measurements from fragmentation products with prompt γ-ray spectroscopy following deep inelastic reactions. The latter technique was also instrumental in tracing 52Ti30 to higher spin. The data provide new tests of effective interactions for full pf-shell calculations in neutron-rich nuclei above 48Ca. The data indicate the presence of a significant subshell gap at N=32 and comparisons between theory and experiment suggest an additional shell closure at N=34 in Ca and Ti isotopes.

Spectroscopy of Rn, Ra and Th isotopes using multi-nucleon transfer reactions

Abstract High-spin spectroscopy of Rn, Ra and Th isotopes has been performed. The nuclei have been populated using multi-nucleon transfer reactions involving a 232 Th target and a 136 Xe projectile. This type of reaction offers the only mechanism for populating high-spin states in many of these nuclei. Interleaving bands with opposite parities have been observed to high spin ( ∼28 h ) in 218,220,222 Rn, 222,224,226,228 Ra and 228,230,234 Th. A systematic study of the rotational alignment properties of octupole bands in radon, radium and thorium isotopes reveals information concerning the role of the octupole phonon and the onset of stable octupole deformation with increasing rotational frequency. Measurement of the magnitude of the intrinsic electric dipole moment, D 0 , provides additional information concerning the strength of octupole interactions in these nuclei.

Spectroscopy of neutron-rich Ni isotopes produced in 208Pb + 64Ni collisions

Abstract The neutron-rich Ni isotopes from A = 64 to 67 have been studied by the multidetector γ-γ coincidence technique using quasi- and deep-inelastic reactions of 350 MeV 64Ni with a thick 208Pb target. Cross coincidences between γ-rays of the two nuclei in the exit channel were used for isotopic identification. The information on the level structure of Ni isotopes has been significantly extended particularly on high-spin states and the role of the g 9 2 neutron orbital. The M2 g 9 2 isomers have been identified in 65Ni T 1 2 = 25(5) ns and in 67Ni T 1 2 ⩾ 0.3 μ s as well as the 6− isomeric state in 66Ni T 1 2 = 4.3(3) ns . The experimental levels are compared with shell model calculations performed using two different approaches with 56Ni as core and various sets of residual interactions.

Particle plus octupoleM2/E3 isomers and high-spin particle-hole states in147Tb and148Tb

The level structures of theN=82 andN=83 nuclei147Tb and148Tb have been studied by means of (α, 8n) and (α,7n) reactions induced by 68 to 110 MeVα particle bombardments of151Eu targets. In-beam conversion electron measurements have established that isomers withT1/2=4.8(6)ns in147Tb andT1/2=22(1)ns in148Tb decay byM2+E3 transitions to the ground states. The measuredB(E3) values show that the isomeric states arise from the coupling of the valence nucleon(s) to the146Gd core octupole. Particlephonon coupling in these nuclei and in the one-neutron nucleus147Gd is discussed and compared with well known cases involving the208Pb core. The higher lying yrast states in the two Tb nuclei are described as shell-model particle-hole excitations using empirical single particle energies and nucleon-nucleon interactions.

The decay of the 560 ns Isomer at 8.6 MeV in 64 147 Gd83

In (α,xn) and (12C, 5n) in-beamγ-ray experiments with pulsed beams the decay of the 560 ns high-spin isomer in147Gd has been investigated. Extensive coincidence measurements identified in the isomeric decay more than eightyγ-rays which almost all were placed in the level scheme. Of crucial importance for establishing the highly complex decay was the comparison of data from the different reactions and the identification of transitions which bypass the 27 ns isomer at 3.58 MeV. Our data determine the excitation of the 560 ns isomer as 8.588 MeV and suggest 47/2 as its most probable spin.

Yrast excitations in A = 126–131 Te nuclei from deep inelastic 130Te+64Ni reactions

Abstract Thick target γγ coincidence measurements for the system 130 Te + 275 MeV 64 Ni have been performed using the GASP Ge detector array at Legnaro. For the isotopic assignments of previously unknown γ-ray cascades, prompt γγ coincidences observed between Te and Ni partner products were of vital importance. The results yield much new information about excited states of moderate spins in A = 126–131 tellurium nuclei, especially about yrast excitations of the little studied odd- A isotopes 127 Te, 129 Te, and 131 Te. Level systematics of tellurium nuclei are presented, and both single-particle and collective aspects of the level spectra are discussed.

STRUCTURE OF NEUTRON–RICH NUCLEI FROM DEEP–INELASTIC REACTIONS

Neutron rich nuclei have been populated using the 82Se+192Os deep-inelastic reaction. New experimental results on 188W, 188,190Os target-like nuclei, as well as 74,76,78Ge beam-like nuclei are presented.

Inelastic and transfer reactions in 92Mo+255 MeV 60Ni collisions studied by γγ coincidences

Abstract For the 92 Mo +255 MeV 60 Ni system, inelastic and few-nucleon transfer events populating non-collective states of moderately high spin have been studied by γγ coincidence measurements. Besides the strong inelastic scattering channel, twelve transfer processes were identified, ranging from 1 n to 2α transfer; typically, cross coincidences between the γ-rays from both products were observed. Potential spectroscopic applications are indicated.

Gamma coincidence study of 208Pb+350 MeV 64Ni collisions

Abstract Products of 208 Pb+ 64 Ni collisions at an energy 12% above the Coulomb barrier have been studied in a gamma spectroscopy thick target experiment. The product yield distribution has been established from the γ – γ coincidence analysis supplemented by target radioactivity measurements. Neutron evaporation from excited primary products has been estimated to determine the pre-emission map of fragments. We discuss the transfer of protons and neutrons between the colliding ions in terms of the N / Z ratio equilibration.