Intrinsic states,high-spin rotational bands and rotation alignment in 177Os and 179Os

Low-lying intrinsic states and their associated rotational bands have been identified in ¹⁷⁷Os and ¹⁷⁹Os. They are the mixed i_{$\text{13}\text{2}$} neutron states and the $\text{1}\text{2}$^?[521] states in ¹⁷⁷Os and ¹⁷⁹Os, as well as the $\text{5}\text{2}$^?[512] state in ¹⁷⁷Os and the $\text{7}\text{2}$^?[514] state in ¹⁷⁹Os. The $\text{1}\text{2}$^? sta is assumed to be the ground state, the other intrinsic states giving rise to isomers. The in-band decay properties of the $\text{7}\text{2}$^?[514] band, and the i_{$\text{13}\text{2}$} bands show the effect of mixing. In the rotational bands in ¹⁷⁷Os a low frequency backbending anomaly is observed but no anomaly is observed in the i_{$\text{13}\text{2}$}. band. In ¹⁷⁹Os the i_{$\text{13}\text{2}$} band does backbend but at a higher frequency than in the yrast bands of the even neighbours. The systematics of the backbending frequencies, and the effects of blocking, are discussed. The rotation aligned angular momentum is deduced, and a comparison made between the i_{$\text{13}\text{2}$} bands and the s-bands in the even neighbours. The results broadly support the identification of the s-bands with the aligned (i_{$\text{13}\text{2}$})² configuration.     

The rotational bands 12+[411]and 12−[541]in 175Lu

In a study of the γ-radiation emitted in the reaction ¹⁷⁶Yb(p, 2n) excited states of the nucleus ¹⁷⁵Lu up to spin I = $\text{13}\text{2}$ have been investigated. The main results concern the rotational bands $\text{1}\text{2}$⁺ [411]and $\text{1}\text{2}$^? [541]with the corresponding band heads found at 626.60 and 370.88 keV, respectively. The half-life of the $\text{1}\text{2}$⁺[411] level has been determined to be $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 10.7±0.5}\text{ns}$. Furthermore, the band heads $\text{3}\text{2}$^?[532]and $\text{3}\text{2}{}^{\mathrm{+}}$[411]are proposed at energies of 999.0 and 1150.8 keV, respectively. Experimental E1 transition probabilities between both $\text{K =}\text{1}\text{2}$ bands are compared with calculations including the Coriolis and pairing effects, as well as theoretically deduced quadrupole deformation parameters.     

Study of the 176Lu(n, γ)177Lu reaction using a gamma band-filter spectrometer

The γ-ray spectrum from the ¹⁷⁶Lu(n, γ)¹⁷⁷Lu reaction has been investigated in the energy range 450 to 1420 keV using a newly developed gamma band-filter spectrometer. A total of 153 transitions have been observed. Improvements to the ¹⁷⁷Lu scheme are suggested, and in particular the γ-decay of several levels of the $\text{1}\text{2}$^?[530↑] and $\text{3}\text{2}$^?[532↓] rotational bands is proposed. Special attention has been given to the Coriolis coupling between the two latter bands and the $\text{1}\text{2}$^?[541↓] band. Results on a complementary investigation of the ¹⁷⁵Lu(n, γ)¹⁷⁶Lu reaction are presented.     

Intrinsic and rotational excitations in 175Lu

The γ-ray cascades following the ¹⁷⁶Yb(p, 2n)¹⁷⁵Lu reaction are studied with Ge(Li) detectors and interpreted within the level scheme of ¹⁷⁵Lu. According to this interpretation the $\text{1}\text{2}$⁺[411], $\text{1}\text{2}$^?[541], $\text{5}\text{2}$⁺[402], $\text{7}\text{2}$⁺[404] and $\text{9}\text{2}$^?[514] rotat $\text{15}\text{2}$⁺, $\text{21}\text{2}$^?, $\text{13}\text{2}$⁺, $\text{19}\text{2}$⁺ and $\text{19}\text{2}$^? members, respectively. Fu band head is determined to be 626.6 keV. The data for the rotational bands are discussed within the particle-rotor model and compared with the available information on the corresponding bands in the adjacent Lu isotopes.     

Étude du schéma de niveaux de 225Ac

The ²²⁵Ac level scheme, populated by the α-branching (0.25%) of ²²⁹Pa, was investigated with an α-spectrograph and a two-dimensional α-γ coincidence device. The proposed level scheme was interpreted in terms of rotational bands and we tried to describe it in terms of the Nilsson configurations $\text{3}\text{2}{}^{\mathrm{+}}\text{[651],}\text{5}\text{2}{}^{\mathrm{+}}\text{[642],}\text{3}\text{2}{}^{\mathrm{?}}\text{[532],}\text{and}\text{5}\text{2}{}^{\mathrm{?}}\text{[523]}$. The perturbation bands due to the Coriolis coupling were also discussed.     

A coupled-channels born-approximation analysis of rare-earth (d,t) transitions

A CCBA (coupled-channels Born approximation) analysis has been performed on a very large set of rare-earth (d, t) transitions. Calculations were performed for states in ¹⁵⁹Gd, ^{161, 163}Dy and ^{165, 167}Er which have been identified as members of rotational bands built on the Nilsson single- hole states $\text{11}\text{2}$^?[505], $\text{1}\text{2}$^?[521], $\text{3}\text{2}$^?[521], $\text{5}\text{2}$^?[523], $\text{5}\text{2}$⁺[642], $\text{5}\text{2}$⁺[633] and $\text{7}\text{2}$⁺[404]. In the cases where the DWBA works well, the CCBA gives results similar to those of DWBA. For the anomalous transitions the CCBA calculations tend to fit better than do the DWBA calculations — but the overall agreement is still rather poor.     

Rotational bands in the light odd-mass Tl nuclei

The odd-mass nuclei ^191–197Tl have been formed in a variety of (HI, xn) reactions and studied by in-beam spectroscopic techniques. The decay of the high-spin Pb isomers, also formed in (HI, xn) reactions, leading to ^193–197Tl has also been investigated. Evidence is presented for the existence of levels of the previously proposed $\text{9}\text{2}{}^{\mathrm{?}}\text{[505]}$rotational bands in the nuclei. Tentative evidence is given for the existence of oblate rotational bands, based on the $\text{13}\text{2}{}^{\mathrm{+}}\text{[606]}$ state, in ^191–195Tl.     

Inelastic processes and form factor effects in the 162, 164Dy(3He,d) reactions at 46.5 MeV

The 162, 164Dy(³He, d) reactions at E_3He = 46.5 MeV are analyzed using the coupled channels Born approximation (CCBA) and improved form factors derived from a deformed Woods-Saxon potential. The latter are generated using the coupled channels procedure of Rost. The transitions considered populate the $\text{7}\text{2}$^?[523], $\text{1}\text{2}$⁺[411], $\text{3}\text{2}$⁺[411], $\text{1}\text{2}$^?[541] and $\text{5}\text{2}$⁺ orbitals in ^{163, 165}Ho. Indirect processes induced by inelastic scattering are found to have an influence on the cross sections comparable to that deduced for neutron transfer reactions on rare earth nuclei at lower energies. Considered alone, these can alter the cross sections even of strong transitions by a factor of two and of weaker ones by an order of magnitude. For the weaker transitions equally large changes can result when the improved form factors, rather than conventional spherical Woods-Saxon functions, are used in the calculations. In the examples considered these two effects tend to cancel, often, but not always, resulting in predicted cross sections similar in magnitude to the results of conventional DWBA calculations made with spherical Woods-Saxon form factors. The CCBA angular distributions are generally similar in shape to DWBA predictions, which usually give good fits to the experimental angular distributions over the 0–35° range of the data. Compared with DWBA predictions which use (he same optical parameters, but spherical Woods-Saxon form factors, the CCBA with deformed Woods-Saxon form factors is in better overall agreement with the experimental cross-section magnitudes. However there are a number of cases in which the CCBA, although usually predicting larger cross sections than the DWBA, still underestimates the experimental cross sections by nearly factor of two. These cases all occur in the $\text{71}\text{2}$^?[541] band or in the strongly Coriolis mixed $\text{1}\text{2}$⁺[411] and $\text{3}\text{2}$⁺[411] bands, and include the majority of transitions populating these orbitals. Since both nuclear structure and reaction mechanism effects are interwoven m the calculations, further data would be most useful in probing the origin of the discrepancy.     

Backbending behaviour of rotational bands in 163,165,167Yb

Several rotational bands in ^163,165,167Yb are observed in (HI,xnγe^?) experiments. The $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ and $\text{3}\text{2}{}^{\mathrm{?}}\text{[521]}$ bands do not backbend, whereas the $\text{5}\text{2}{}^{\mathrm{?}}\text{[523]}$ bands do, indicating additional processes besides the rotational alignment of one $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron pair that are responsible for the backbending.     

Single-Proton states of159Ho studied with the (p,α) reaction spectroscopic evidence for the unusual coriolis strengths in159, 161, 163Ho nuclei

The proton-hole character of states in¹⁵⁹Ho has been studied using the^{162, 164}Er(p, α)^{159, 161}Ho reactions with 17 MeV protons. The shapes of angular distributions measured for both nuclei were compared, with good agreement in most cases, to tritoncluster-transfer DWBA calculations. The deviations obtained and the experimental normalization factors deduced for the¹⁶⁴Er(p, α)¹⁶¹Ho reaction by comparisons to (t, α) cross sections indicate a need for a revised treatment of the mechanism of the (p, α) reaction on deformed nuclei. By comparisons to the well-known states in¹⁶¹Ho, nuclear structure factors were obtained for many levels in¹⁵⁹Ho. The Nilsson assignments for the 3/2⁺[411], 5/2^?[532] and 5/2⁺[413] bands were confirmed and the lowest rotational members of these bands were established. The anomalous strengths of the strongly mixed positive parity states in^{159, 161, 163}Ho are discussed in the frame-work of the Nilsson model with the pairing and effective Coriolis strengths included. The Coriolis strengths giving best fits to excitation energies also improve the agreement of theory with the experimental nuclear structure factors. Rotational spacings of the 5/2⁺[413] and especially those of the 5/2^?[532] bands in^{159, 161, 163}Ho show mixmg effects unexplainable by the present calculations.     

Study of the levels in 167Tm by the 165Ho(α, 2nγ)167Tm reaction

Gamma-ray spectra following the ¹⁶⁵Ho(α, 2n)¹⁶⁷Tm reaction have been studied using different semiconductor detector systems including a Compton suppression spectrometer. Approxi- mately 400 transitions have been observed in the energy range 60 to 1250 keV and 4 × 10⁷ γγ coincidence events have been recorded. The angular distributions of the more intense γ-rays have been determined. The level scheme of ¹⁶⁷Tm has been extended in several respects: The four previously known rotational bands based on the Nilsson orbitais $\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}$, $\text{7}\text{2}{}^{\mathrm{+}}\text{[404]}$, $\text{7}\text{2}{}^{\mathrm{?}}\text{[523]}$ an $\text{1}\text{2}{}^{\mathrm{?}}\text{[541]}$ have been extended up to spin values $\text{31}\text{2}$, $\text{31}\text{2}$, $\text{31}\text{2}$, $\text{33}\text{2}$ respective based on the $\text{3}\text{2}{}^{\mathrm{+}}\text{[411]}$ and $\text{5}\text{2}{}^{\mathrm{+}}\text{[402]}$ orbitals have been established for which only few levels were known previously. Finally two hitherto unknown rotational bands have been found for which we propose the assignments $\text{{}\text{7}\text{2}{}^{\mathrm{+}}\text{[404]; K + 2}}$ and $\text{3}\text{2}{}^{\mathrm{?}}\text{[532] + {}\text{1}\text{2}{}^{\mathrm{?}}\text{[541]; K?2}}$. Coriolis coup calculations are presented. The value of $\text{(1?δ}{}_{\mathrm{<mtext>K,\; </mtext><mtext>1</mtext><mtext>2</mtext>}}\text{b}{}_0\text{) (g}{}_{\mathrm{K}}\text{?g}{}_{\mathrm{R}}\text{)/Q}{}_0$ was determined for three bands from branching ratios and from angular distributions.     

Multi-quasiparticle states in 179Ta and structural changes in the yrast line of the odd tantalum isotopes

High-spin states in ¹⁷⁹Ta have been studied by a variety of γ-ray spectroscopic techniques following the ¹⁷⁶Yb(⁷Li,4n) reaction. The new results independently confirm and extend the one-, three- and five- quasiparticle bands proposed previously. The more comprehensive results obtained allow firm spin assignments to be made and also the identification of rotational bands associated with the higher seniority intrinsic states. Configuration assignments follow from analysis of these rotational band properties. To explain changes in the yrast line across the chain of isotopes from ¹⁷³Ta to ¹⁷⁹Ta, multi-quasiparticle calculations have been performed and compared with experiment. The calculations, which treat pairing correlations using the Lipkin-Nogami approach and include blocking, incorporate single-particle energies adjusted to reproduce the observed one-quasiparticle bandheads. Properties specific to ¹⁷⁹Ta include evidence for configuration mixing in the $\text{21}\text{2}{}^{\mathrm{-}}$ isomer configuration. Its decay is one of several anomalously fast K-hindered transitions observed and discussed in terms of configuration changes and other mechanisms.     

One- and three-quasiparticle states in 171Hf and high spin rotational bands

The $\text{1}\text{2}{}^{\mathrm{?}}\text{[521]}\text{and}\text{7}\text{2}{}^{\mathrm{+}}\text{[633]}$ one-quasiparticle bands in the N = 99 nucleus ¹⁷¹Hf have been identified to spins of about $\text{45}\text{2}$ using (heavy ion, xn) reactions. The moments of inertia of these bands are consistent with the absence of backbending in the N = 98 core nucleus. The half-life of the $\text{5}\text{2}{}^{\mathrm{?}}\text{[512]}$ intrinsic state was measured as 63.6 ns. The strength of the $\text{5}\text{2}{}^{\mathrm{?}}\text{[512] →}\text{7}\text{2}{}^{\mathrm{+}}\text{[633]}\text{E}\text{1}$ transition is discussed. Two three-quasiparticle isomers with spins and parities $\text{19}\text{2}{}^{\mathrm{+}}\text{and}\text{23}\text{2}{}^{\mathrm{?}}$ have been identified and their suggested configurations are a $\text{7}\text{2}{}^{\mathrm{+}}\text{[633]}$ neutron added to the 6⁺ and 8^? two-quasiproton states of the core. The moment of inertia of a rotational band based on the $\text{23}\text{2}{}^{\mathrm{?}}$ isomer supports this suggestion, and shows the effect of partial rotation alignment of the $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron.     

The level structure of 187Os

A study of the level structure of ¹⁸⁷Os has been performed by means of (d, p), (d, t) and (d, d$\text{)}\text{?}$ reactions. Based upon the data presented and information available from the 10.5 h decay of ¹⁸⁷Ir, a level scheme including several new states and level assignments is proposed. The low-lying rotational bands built on the $\text{1}\text{2}{}^{\mathrm{?}}$ [510] and the $\text{3}\text{2}{}^{\mathrm{?}}$ [512] single-particle states have been analysed by means of Coriolis-coupling calculations including attenuations of the coupling matrix elements. The calculations involve fits to energies, to neutron transfer cross sections and to ratios of B (E2) values.     

The decay of 159Tm (9.0 min) to 159Er

The decay of ¹⁵⁹Tm ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 9.0±0.4min}$) has been investigated with Ge(Li) andSi(Li) detectors, B-spectrographs and a toroidal spectrometer using isotopically separated samples produced by the YASNAPP facility at Dubna. The singles γ-ray spectrum, the conversion electron spectrum, the positron spectrum, prompt and delayed γ-γ coincidences were measured. Using strong thulium activities, conversion electrons were also measured with high resolution b-spectrographs. In the ¹⁵⁹Tm decay 81 new γ-ray transitions were observed. A decay scheme of ¹⁵⁹Tm is proposed involving 12 excited states in ¹⁵⁹Er. The first members of the rotational bands $\text{3}\text{2}$^?[521], $\text{5}\text{2}$^?[523], $\text{3}\text{2}$⁺[402 + 651], $\text{11}\text{2}$^?505 and $\text{7}\text{2}$^?[514] and the $\text{5}\text{2}$, $\text{7}\text{2}$ and $\text{9}\text{2}$ states of a strongly perturbed positive parity band were identified. The Q-value of ¹⁵⁹Tm was determined to be 3.4±0.3 MeV.     

The decay of 161Gd to 161Tb

The level scheme of ¹⁶¹Tb populated by the β-decay of 3.7 min ¹⁶¹Gd has been studied using Ge(Li) detectors as singles and coincidence γ-ray spectrometers. A total of 130 transitions has been observed. An investigation of the Coriolis coupling between the $\text{5}\text{2}{}^{\mathrm{?}}\text{[532↑]}\text{and}\text{7}\text{2}{}^{\mathrm{?}}\text{[523↑]}$ bands is presented. Rotational bands previously only observed in charged particle transfer work are discussed. Several additional levels are suggested.     

Intrinsic and rotational states in 173Ta

High spin rotational levels in ¹⁷³Ta are populated in the ¹⁶⁵Ho(¹²C, 4n)¹⁷³Ta and ¹⁷⁵Lu(α, 6n)¹⁷³Ta reactions. The de-excitation γ-ray cascades are studied with Ge(Li) detectors. The rotational bands, which are built on the $\text{7}\text{2}$⁺(404), $\text{5}\text{2}$⁺(402), $\text{9}\text{2}$^?(514) and $\text{1}\text{2}$^?(541) intrinsic states, are identified up to high spin values. A state, interpreted as a three quasi-particle state with a probable spin of $\text{21}\text{2}$ is located at 1713 keV. Its half-life is about 100 ns. The behaviour of the moment of inertia of each rotational band versus the rotational frequency is compared with that of the doubly even core.     

Three- and five-quasiparticle isomers,rotational bands and residual interactions in 175Hf

Two 3-quasiparticle isomers with spins, parities and half-lives of $\text{19}\text{2}$⁺, 1.1 μs and $\text{23}\text{2}$^?, 1.2 ns have been identified at 1433 and 1766 keV in ¹⁷⁵Hf. A third isomer, possibly $\text{35}\text{2}$^? with a 1.2 μs half-life, is found at 3015 keV. The first two are characterised as a $\text{7}\text{2}$⁺ [633] neutron coupled to the known 6⁺ and 8^? 2-proton isomers of the core nuclei. Rotational bands based on the 3-qp isomers are highly perturbed, due to Coriolis mixing, and their structure is reproduced in a band mixing calculation. The energy depression of the 3-quasiparticle states relative to the 2-quasiproton core states is attributed mainly to the residual proton-neutron interaction, and possibly also to blocking effects through neutron admixtures.