Jc Bacelar

Rotational bands in 181Pt

Abstract The 144 Nd( 40 Ar, 3n) 181 Pt reaction has been used to study rotational bands by means of an extensive set of gamma spectroscopic measurements. The bands 1 2 − [521], 5 2 − [512], 7 2 − [514] a 9 2 + [624] are identified up to maximum spin of ( 53 2 ). A sharp bandcrossing is observed at a rotational energy of h ω = 0.28 MeV in the 7 2 − [514] bands. The crossings are discussed in terms of possible v i 13 2 and πh 9 2 alignments. Exceptionally strong M1 transitions are observed above the crossing.

High-spin state spectroscopy in 165, 166Yb

Abstract Level schemes of 165Yb and 166Yb are studied up to high spins. Triple γ-ray coincidence spectra are analyzed for the first time. The observed bands in both nuclei are interpreted in terms of the cranked-shell model. In particular, the continuation of the lowest i 13 2 single quasineutron aligned band beyond the first observed backbend is seen in an odd-N nucleus and the interaction strength between this band and the three-quasiparticle band is evaluated. Constancy of the moment of inertia in 166Yb is observed at high spins and interpreted.

SATURATION OF THE WIDTH OF THE GIANT-DIPOLE RESONANCE AT HIGH-EXCITATION ENERGIES

Abstract Gamma-ray energy spectra have been measured for the 16 O + 118 Sn reaction at incident beam energies of 200 and 280 MeV. Comparing the experimentally obtained spectra with statistical-model calculations shows that the width of the isovector giant dipole resonance saturates beyond excitation energies of 165 MeV in the compound nucleus.

Superdeformed bands in Nd nuclei

Abstract Superdeformed bands were found in 134, 136 Nd. Their dynamic moments of inertia are about as large as those of the known superdeformed bands in 135 Nd and 132 Ce, corresponding to β ≈ 0.5. A high probability for staying in band is measured for the discrete superdeformed bands in 134, 136 Nd, in contrast to the unresolved superdeformed ridges.

Loss of collectivity along the yrast line in 158Er

Abstract Lifetimes of yrast states from spin 14 through 40 have been measured in 158Er. The Doppler-shift recoil-distance method was used in conjunction with the multi-Ge detector array HERA, and γγ coincidences were analyzed. The collectivity of the nucleus drops from 200 W.u. to 110 W.u. in the region of the second backbend. By spin 38 it has decreased further to 25 W.u., consistent with a band termination.

GDR DISSIPATION AND NUCLEAR SHAPE IN HOT FAST-ROTATING DY NUCLEI

Abstract The statistical γ-ray decay of the GDR built on excited states in Dy nuclei has been investigated for selected domains of angular momentum up to about 70ħ and temperatures in the range 1–2 MeV. The GDR strength distribution extracted from the data indicate large average nuclear deformations ( β ∼ 0.35) at high angular momentum and average temperatures T ⩾ 1.5 MeV. The experimental observation is supported by results from calculations in which thermal shape fluctuations are taken into account around an oblate equilibrium deformation β eq . Although this equilibrium deformation increases with angular momentum, the calculations show rather large and constant average deformations 〈 β ∼0.35.

New structures at high spin in 159Er

Abstract The nucleus 159 Er was studied with the HERA γ-ray spectrometer. Three rotational bands were extended to higher spins, and three new bands were found. It is shown that specific orbitals rather strongly influence the high-spin behavior, some states remaining collective (somewhat triaxial), others evolving towards a non-collective oblate structure. One of the new bands is a higher- K band, similar to those found in heavier nuclei.

DEVELOPMENT OF A SPECIAL ANTI-COMPTON SPECTROMETER

This paper describes the investigation of the possibility to build a compact anti-Compton spectrometer consisting of a Ge detector and a cooled BGO suppressor. Monte Carlo calculations were carried out to obtain information about the performance of two different detector configurations. Light output and timing properties of a BGO-photodiode detector have been measured as a function of temperature and will be compared with computer simulations of light output.

Particle-hole states at high spin in 150Dy

Abstract The level scheme of the nucleus 150 Dy up to spin around 40 was obtained using the reaction 114 Cd( 40 Ar, 4n). Above spins 20 to 22 — the highest obtainable from the valence nucleons — the breaking of the 146 Gd pproton and neutron cores occurs in separate parallel cascades.

POSITRON-ELECTRON DECAY OF SI-28, AT AN EXCITATION-ENERGY OF 50-MEV

Abstract The electron-position pair decay of 28Si at 50 MeV excitation produced by the isospin T =0 (α + 24 Mg ) and the mixed isospin T =0,1 ( 3 He + 25 Mg ) reactions has been studied using a special designed Positron-Electron pair spectrometer PEPSI.