J.P. Vorlet

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 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.

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.

Study of 113Cd by the 110Pd(α,nγ) reaction

Abstract The nuclear structure of 113 Cd was studied using in-beam γ-ray spectroscopy. A level scheme, consisting of 65 levels and more than 100 transitions, was constructed on the basis of γγ coincidences using five compton-suppressed Ge detectors. Spins were assigned by means of excitation function slopes and angular distribution analysis. The resulting level scheme was interpreted in the framework of the interacting boson-fermion model.

Long-lived isomers in 190Ir

Abstract Long-lived isomeric states in 190 Ir have been investigated with the 192 Os(p,3n) 190 Ir and 192 Os(d,4n) 190 Ir reactions using beams of 18–31 MeV protons and 27.8 MeV deuterons, respectively. A series of measurements, including excitation functions, half lives, e − γ coincidences and e − e − coincidences, was performed. Five new transitions were observed, and the results of e − γ and e − e − coincidences indicate that these transitions are fed by the 148.7 keV M4 transition that depopulates the 11 − isomer. The previous decay scheme is shown to be incorrect, and the results allow the ground state parity and mass excess to be determined.

Study of the 171Tm nuclear structure by a massive transfer reaction

Abstract Levels in 171Tm were excited by the 170Er(7Li, α2nγ) reaction. Seven rotational bands were observed, including those built on the 1 2 + [411] and 7 2 − [523] intrinsic states up to spin 19 2 . Resul on g-factors are presented and specific properties of the reaction are discussed.

Nuclear levels in 190Ir studied with the 192Os(p,3nγ) and 192Os(d,4ne−) reactions

Abstract Nuclear levels in 190 Ir have been investigated with the 192 Os(p,3n γ ) and 192 Os(d,4n e − ) reactions using beams of 18–31 MeV protons and 27.8 MeV deuterons. A series of measurements, including excitation functions, γγ and e − e − coincidences, and life time measurements, was performed. From the singles measurements, a total of 140 γ rays were assigned as belonging to the 192 Os(p,3n) 190 Ir channel. The results of the coincidence measurements show that many of these lines are multiplets. Using information from a previous isomer study and single-nucleon transfer reactions, a level scheme is proposed comprising of 112 γ rays placed between 76 levels. It is shown that most of the γ intensity arises from bands having K π ≥4 + . Several negative-parity bands are also proposed. Calculations performed using values of ϵ and γ characteristic of the region reproduce qualitatively some aspects of the level scheme.