S. Drissi

The 112Cd nucleus: A laboratory for the study of collective excitations

Abstract The level structure of the even-even 112 Cd nucleus was investigated by means of the 110 Pd(α, 2nγ) reaction spectroscopy. On the basis of the γγ-coincidences measured using three Compton-suppression spectrometers, 151 transitions (out of 190 lines assigned to 112 Cd) were placed in the decay scheme. Most of the 80 observed excited states were grouped into 6 well-developed collective bands. The level scheme was extended by 43 new levels. The systematic use of the excitation function slopes and of the side-feeding intensities, together with the results gained from the angular distribution allowed us to assign the spins and the parities to nearly all observed levels. The collective states, including in particular those of the ground-state, intruder, quasi-γ and octupole bands, and their electromagnetic properties were investigated in the framework of the spdf 1BA-1 model with configuration mixing of normal and intruder states.

Study of 110Cd by the 108Pd(α, 2nγ) reaction

Abstract The gamma-ray transitions following the 108Pd(α, 2n) reaction have been observed using different semiconductor detector systems, including a Compton suppression spectrometer. Approximately 200 transitions assigned to 110Cd were identified in the energy range 120 to 1600 keV. About 2.5 × 107 γγ-coincidence events were recorded and the angular distributions of most transitions were analyzed. The 110Cd level scheme was extended by 28 new levels. With the angular distribution results and a systematic use of the excitation slopes and of the side-feeding intensities (ESSI-method), the spins and parities of nearly all observed levels were determined. The results regarding the ground-state, intruder and octupole bands are interpreted in the framework of the s-p-d-f interacting boson model in which intruder mixing is explicitly included. The predictions of strong configuration mixing are also examined in detail in the neutron-proton interacting boson model framework. We shortly discuss possible non-collective, broken-pair excitations in a qualitative way.

Systematic study of the yrast band in the doubly-odd 158,160,162,164,166Tm nuclei☆

Abstract High-spin rotational states of 158,160,162,164Tm were investigated by in-beam γ-spectroscopy using the (14N, 4n) and (14N, 6n) reactions. The strongly-aligned band π[ h 11 2 ]ν[ i 13 2 ] has been observed in all these nuclei. Our experimental results, together with the data obtained by another group on 166Tm, are interpreted in the frame of a cranking-model analysis. The behaviour of the moment of inertia versus rotational frequency and the existence of a triaxial shape is discussed.

Study of 124Te by the 122Sn(α,2nγ) reaction and by the decay of 124I

Abstract In-beam γ-ray spectroscopy and the decay of 124 I were used to study the nuclear structure of 124 Te. On the basis of γγ-coincidences, a level scheme was constructed with over 100 levels and 170 transitions. The use of excitation functions and angular distributions for the (α, 2n) reaction, and the log( ft ) values for the decay, allowed spin assignments for a large number of the levels to be made. The resulting level scheme was interpreted in the framework of the interacting boson model and the particle-core coupling model.

Electromagnetic properties of high-K rotational bands in the odd-odd 160Ho nucleus☆

The electromagnetic properties of levels up to spin 19ħ in the yrast band and 9ħ in the ground-state band of the odd-odd nucleus 160Ho have been measured with standard in-beam γ-ray spectroscopy using the 159Tb(α, 3n) reaction. For the yrast band, the experimental B(M1, I → I − 1)/ B(E2, I → I − 2) ratios increase sharply for rotational frequencies larger than 0.25 MeV, while observed energies do not show any sudden change. This effect suggests a change in the nature of the wave functions. The results are interpreted in terms of the particle-rotor model, cranking shell model and compared to the available data on the neighbouring odd-A nuclei.

Nuclear structure of 166Tm from (α,3n) γ-ray and conversion electron measurements

Abstract Excited levels of the strongly-deformed odd-odd nucleus 166 Tm, populated by the 165 Ho(α,3nγ) reaction, were investigated using standard in-beam γ-ray spectroscopy, including measurements of a few conversion electron lines, and by high-resolution curved-crystal spectroscopy. A level scheme consisting of 178 transitions among 6 well-developed and 4 partial rotational bands is proposed. Level spins and parities were determined and the results were interpreted in the framework of the Nilsson model by comparison with predictions. The Gallagher-Moszkowski splitting for the { π 1 2 + [411] ± ν 5 2 + [642] } configuration was determined to be 245(20) keV. An anomalous signature splitting was observed for the {π 7 2 + [404] + ν 5 2 + [642]}K π = 6 + configuration.

Signature inversion and electromagnetic properties of aligned bands in 166Tm

Abstract Excited states of 166 Tm were investigated by means of the 165 Ho(α, 3n) reaction. Two rotational bands were identified up to tentative spins of 20 − and 18 + . Their electromagnetic.properties were studied and interpreted in the framework of the cranking shell model (CSM) and of the particle-rotor model (PRM). Both the revised Donau and Frauendorf formula (CSM) and the PRM calculations reproduce the experimental results rather well for spins between 10 and 14, whereas they fail at low and high angular momenta. The two models predict different I -dependences for the B (M1) values in the angular momentum region of I j p + j n . The existence and interpretation of the signature inversion of the yrast band is discussed using three different models. The results show that the occurrence of signature inversion does not necessarily mean the presence of trixial nuclear shape.

Study of the levels in 174Lu by (p, 3nγ) spectroscopy

Abstract The nuclear levels in 174 Lu were investigated by means of 176 Yb(p, 3nγ) reaction spectroscopy. Standard germanium detector techniques as well as an on-line curved crystal spectrometer were used. Six well-developed rotational bands are observed. These results confirm and extend the scheme previously obtained by direct reactions. The presented data document a study on the anomalous g -factors of the 142 d isomeric band.

Rotational bands in odd-odd 174Lu

Abstract Levels of 174 Lu, excited by the 170 Er( 7 Li,3nγ) reaction, were studied using standard in-beam γ-ray spectroscopy techniques. Eleven rotational bands were observed, some members were identified up to spin 15 h . An analysis of the experimental results in the framework of the cranking shell model was performed with particular emphasis on the mixed { p 1 2 − [541]± n 5 2 − [512]}, K π =3 + & 2 + and { p 7 2 + [404]+ n 7 2 + [633]}, K π =7 + bands, where one quasiparticle is coupled to the axis of rotation and the other to the axis of deformation. The law of additivity for the particle alignment and for the routhians appears to be valid in these cases.

Aligned bands and gyromagnetic ratios in 162,164Tm☆

Abstract High-spin states in 162 Tm and 164 Tm have been studied by 152,154 Sm( 14 N, 4n) reactions. Measurements of γ-rays, angular distributions and γγ-coincidences were performed using Ge detectors. In each isotope, two side bands are observed besides the yrast band, which are followed up to high-spin states. An interpretation of the experimental results is proposed in the framework of the cranked shell-model. Results on gyromagnetic ratios in the yrast band of a series of odd- N Tm nuclei are presented. Magnetic properties of the side bands are also discussed.