The influence of νh11/2 occupancy on the magnetic moments of collective 21+ states in A∼100 fission fragments

AbstractThe magnetic moments of Iπ=21+ states in even–even A∼100 fission fragments have been measured using the Gammasphere array, using the technique of time-integral perturbed angular correlations. The data are interpreted within the context of the interacting boson model (IBA2) leading to the suggestion of a strong νh11/2 component in the deformed 21+ states of this region

High-spin structures in 155Tb and signature splitting systematics of the πh11/2 bands in odd A≈160 nuclei

The reactions 152Sm(7Li,4n) at 45 MeV and 124Sn(36S,p4n) at 165 MeV were used to study high-spin states of the N590 nucleus 155Tb. Previously known bands have been greatly extended in spin (I'45\) and a new decoupled sequence was identified. Several band crossings or quasiparticle alignments have been observed in each of the structures, and as a result a configuration assignment has been given to the new band. B(M1)/B(E2) transition strength ratios have been extracted from the data and comparisons were made with theoretical predictions. A comprehensive analysis of the signature splitting in the energy levels and B(M1)/B(E2) ratios for the ph11/2 bands of the A'160 region has been performed. Possible interpretations for the observed trends in the signature splitting of these structures are discussed

Second proton and neutron alignments in the doubly-odd nuclei 154,156Tb

High-spin states in the doubly-odd nuclei 154,156Tb have been populated in two separate experiments using the 36S1124Sn reaction at different beam energies ~160 and 175 MeV!. The yrast structures of both nuclei were extended to much higher spin (I<48\) than previously known and several quasiparticle alignments have been identified. These include the second neutron alignment and a clear delineation of the second proton crossing in 156Tb. Systematics of these crossings for odd-Z nuclei and comparisons with results of cranked shell model calculations are discussed

Rotational band structures in N=89 153Gd

The reactions 152Sm(α,3n) at 37 MeV and 124Sn(36S,α3n) at 165 MeV were used to produce high-spin states in the transitional rare-earth nucleus 153Gd. Significant extensions in angular momentum and excitation energy with respect to earlier work were achieved and several new rotational sequences were observed. The rotational behavior of 153Gd is described in terms of quasiparticle assignments and the observed alignment properties are analyzed within the framework of the cranked shell model. Detailed comparisons with other N=89 nuclei are presented. These have led to corrections to the 157Er level scheme

Triaxial strongly deformed bands in Tm160,161

High-spin states in Tm160,161 were populated using the Te128(Cl37, 5n and 4n) reactions at a beam energy of 170 MeV. Emitted γ rays were detected in the Gammasphere spectrometer. Two rotational bands with high moments of inertia were discovered, one assigned to Tm160, while the other tentatively assigned to Tm161. These sequences display features similar to bands observed in neighboring Er, Tm, Yb, and Lu nuclei which have been discussed in terms of triaxial strongly deformed structures. Cranked Nilsson Strutinsky calculations have been performed that predict well-deformed triaxial shapes at high spin in Tm160,161

Fast-timing measurements in neutron-rich odd-mass zirconium isotopes using LaBr3:Ce detectors coupled with Gammasphere

A fast-timing experiment was performed at the Argonne National Laboratory to measure the lifetimes of the lowest lying states of nuclei belonging to the deformed regions around mass number A 110 and A 150. These regions were populated via spontaneous fission of 252 Cf and the gamma radiation following the decay of excited states in the fission fragments was measured using 51 Gammasphere detectors coupled with 25 LaBr 3 :Ce detectors. A brief description of the acquisition system and some preliminary results from the fast-timing analysis of the fission fragment 100Zr are presented. The lifetime value of \u3c4 = 840(65) ps was found for the 2 + state in 100 Zr consistent within one standard deviation of the adopted value with 791 +26 -35 ps. This is associated with a quadrupole deformation parameter of 0.36(2) which is within one standard deviation of the literature value of 0.3556 +82 -57

Relative quadrupole moments of exotic shapes at ultrahigh spin in 154Er: Calibrating the TSD/SD puzzle

Transition quadrupole moments, Qt, of two ultrahigh-spin, collective structures in 154Er have been measured for the first time using the Doppler Shift Attenuation Method (DSAM). Data were acquired at the ATLAS accelerator facility of Argonne National Laboratory, using the Gammasphere detector array. A thick, gold-backed 110Pd foil was bombarded by a beam of 48Ti ions at 215 MeV. The Qt for each band was determined from the Doppler shift of gamma rays emitted by the resulting recoil nuclei. The extracted transition quadrupole moments are significantly different in magnitude, suggesting the two structures in 154Er represent distinct exotic nuclear shapes, namely axial superdeformed (SD) with Q t 20 eb, and triaxial strongly deformed (TSD) with Qt ≈ 11 eb. Indeed, the results calibrate the quadrupole moments of TSD bands recently measured in light erbium nuclei, 157,158Er

Quadrupole moments of coexisting collective shapes at high spin in 154Er

Four high-spin collective bands have been populated in 68154Er86 via the 110Pd(48Ti,4nγ)154Er reaction. Average transition quadrupole moments Qt have been measured for three of the bands by using the Doppler-shift attenuation method. The strongest band has a value of Q t=11.0±1.0eb, similar to values found recently for four triaxial strongly deformed (TSD) bands in 157,158Er. The second band has a value of Qt=19.5±3.2eb, consistent with a predicted axially symmetric superdeformed (SD) shape, similar in deformation to the 152Dy isotone, and is used as a calibration point. The third, new band has a value of Qt=9.9±2.2eb. The results confirm the unexpectedly large Qt moments for the favored TSD bands in light erbium isotopes

Fast-timing measurements in the ground-state band of Pd114

Using a hybrid Gammasphere array coupled to 25 LaBr3(Ce) detectors, the lifetimes of the first three levels of the yrast band in Pd-114, populated via Cf-252 decay, have been measured. The measured lifetimes are tau(2+) = 103(10) ps, tau(4+) = 22(13) ps, and tau(6+) &lt;= 10 ps for the 2(1)(+), 4(1)(+), and 6(1)(+) levels, respectively. Palladium-114 was predicted to be the most deformed isotope of its isotopic chain, and spectroscopic studies have suggested it might also be a candidate nucleus for low-spin stable triaxiality. From the lifetimes measured in this work, reduced transition probabilities B(E2; J -&gt; J - 2) are calculated and compared with interacting boson model, projected shell model, and collective model calculations from the literature. The experimental ratio R-B(E2) = B(E2; 4(1)(+) -&gt; 2(1)(+))/B(E2; 2(1)(+) -&gt; 0(1)(+)) = 0.80(42) is measured for the first time in Pd-114 and compared with the known values R-B(E2) in the palladium isotopic chain: the systematics suggest that, for N = 68, a transition from gamma-unstable to a more rigid gamma-deformed nuclear shape occurs

High-spin yrast structure of 159Ho

An investigation of the yrast structure of the odd-Z 159Ho nucleus to high spin has been performed. The 159Ho nucleus was populated by the reaction 116Cd(48Ca,p4nγ) at a beam energy of 215 MeV, and resulting γ decays were detected by the Gammasphere spectrometer. The h11/2 yrast band has been significantly extended up to Iπ=75/2- (tentatively 79/2-). A lower frequency limit for the second (h11/ 2)2 proton alignment was extracted consistent with the systematics of this alignment frequency, indicating an increased deformation with neutron number in the Ho isotopes. The energy-level splitting between the signature partners in the h11/2 structures of the Ho isotopes and the neighboring N=92 isotones is discussed