D. Tonev

On the line-shape and lifetime determination in recoil distance Doppler-shift measurements

Abstract A method for the calculation of the γ-ray line-shapes observed in recoil distance Doppler-shift measurements of nuclear lifetimes is presented emphasising the case where a gate is set on a transition which feeds directly the level of interest. A description of such coincidence spectra is proposed for the first time. It is shown that a successful reproduction of the data requires to take into account the emission of γ-rays during the slowing-down of the ions in the stopper if the investigated lifetime is shorter than or comparable to the slowing-down time. The corresponding formalism for lifetime determination in the framework of the differential decay-curve method is developed. The new approach is illustrated by an application to experimental data obtained in the 110 Pd ( 28 Si , 4 n ) 134 Nd reaction at a beam energy of 125 MeV.

Test of the critical point symmetry X(5) in the mass A = 180 region

Based on the energy spectra and relative transition probabilities 176,178,180 Os turned out to be very promising candidates for testing the features of the critical point symmetry X(5). In order to also test absolute transition probabilities predicted in the framework of the X(5) symmetry lifetime measurements were performed at the Cologne FN tandem accelerator. The lifetimes of the first 2 + states in 176,178,180 Os were measured using electronic timing and in the case of 178 Os with the recoil distance Doppler shift (RDDS) technique using an 16 O-induced fusion evaporation reaction. In addition, a coincidence RDDS measurement was performed at the Laboratori Nazionali di Legnaro with the GASP spectrometer using the 154 Sm( 29 Si,5n) 178 Os reaction. The deduced transition quadrupole moments agree well with the X(5) predictions, thus further supporting an X(5) structure for 178 Os. The experimental data for 178 Os are compared to calculations in the framework of the interaction boson model (IBM) and of the general collective model (GCM).

On the two-quasineutron rotational band in 128Ba

Abstract The lifetimes of five levels of the two-quasineutron band in 128 Ba populated via the 116 Cd( 16 O ,4 n) reaction were measured for the first time by means of the recoil-distance Doppler-shift method. For the data-analysis, a new version of the differential decay-curve method in singles-like mode was developed which takes into account the velocity distribution of the recoils and the effect of the Doppler-shift attenuation in the stopper. The high values of 〈K 2 〉 and K eff characterising the band are confirmed by the determined B (E2 ,I→I−2 ) and B (M1 ,I→I−1 ) transition strengths. At the same time, the rigid-rotor model is not able to describe the behaviour of the experimental B (E2 ,I→I−1 ) and B (M1 ,I→I−1 ) values. A new theoretical effort seems to be needed for a consistent explanation of the intraband transition strengths within two-quasiparticle bands in γ -soft nuclei.

Lifetime analysis using the Doppler-shift attenuation method with a gate on depopulating transition

A method for lifetime determination via the description of the γ-ray line shapes observed in coincidence measurements using the Doppler-shift attenuation method is proposed for the case where the gate is set on a transition which depopulates the level of interest. The method presented takes precisely into account the time-velocity correlations inherent to coincidence measurements. The new procedure is illustrated and checked by an application to simulated data.

Transition rates and nuclear structure changes in mirror nuclei 47 Cr and 47 V

Lifetime measurements in the mirror nuclei

High-spin structure in K-40

{}^{47}\mathrm{Cr}

Transfer and neutron capture reactions to 194Ir as a test of Uν(6/12)⊗Uπ(6/4) supersymmetry

and

Lifetime determination in delayed-coincidence experiments using the differential decay-curve approach

{}^{47}\mathrm{V}

Lifetime measurements in mirror nuclei 31S and 31P: A test for isospin mixing

were performed by means of the Doppler-shift attenuation method using the multidetector array EUROBALL, in conjunction with the ancillary detectors ISIS and the Neutron Wall. The determined transition strengths in the yrast cascades are well described by full

Test of the critical point symmetry X(5) in neutron deficient osmium isotopes at A≈180

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