Coulomb excitation and lifetime measurements of the 21+ states in 76, 82, 84Kr

A mean lifetime of τ = 35 ± 3 ps of the 2⁺₁ state in ⁷⁶Kr has been measured with the recoil distance method via the reaction ⁶³Cu(¹⁹F, α2n)⁷⁶Kr. The B(E2; 0⁺₁ → 2⁺₁) values and lifetimes of the 2⁺₁ states in ^{82, 84}Kr have been measured via Coulomb excitation using the 1.4 MeV/A UNILAC krypton beams. The intensities of the γ-rays from the Coulomb excited levels of ^{82, 84}Kr were interrelated with those of the target nuclei ²⁷Al, ^{64, 66}Zn and ^{70, 72, 74, 76}Ge and yielded the values $\text{B(}\text{E}\text{2; 0}{}^{\mathrm{+}}{}_1\text{→ 2}{}^{\mathrm{+}}{}_1\text{= 0.255±0.009}\text{and}\text{0.122 ± 0.005}\text{e}\text{2 ·}\text{b}\text{2}\text{for}{}^{\mathrm{82,\; 84}}\text{Kr}$, respectively. In turn, these B(E2) values and the (E2; 0⁺₁ → 2⁺₁ values of the even Ge and Zn isotopes from the literature were used in a Doppler-shift attenuation analysis to obtain experimentally lacking electronic stopping power for Kr ions slowing down in Al, Zn and Ge. for Ge ions in Ge and for Zn ions in Zn.     

Nuclear structure studies of high-spin states in 79Rb and 79Kr

Fluorine and carbon induced fusion-evaporation reactions were used to excite high-spin states in ⁷⁹Rb and ⁷⁹Kr. The level scheme of ⁷⁹Rb was established on the basis of neutron multiplicity measurements, γγ coincidence data and excitation functions. From recoil distance and Doppler shift attenuation lifetime measurements, E2 strengths of the positive-parity yrast states in ${}^{79}\text{Kr}\text{(}\text{up to}\text{I}{}^{\mathrm{\pi }}\text{=}\text{21}\text{2}{}^{\mathrm{+}}$) and the favored and unfavored states in ${}^{79}\text{Rb}\text{(}\text{up to}\text{I}{}^{\mathrm{\pi }}\text{=}\text{25}\text{2}{}^{\mathrm{+}}$) were derived. An interpretation of these data in terms of the asymmetric rotor-plus-particle model and the interacting boson fermion model (with or without separate proton and neutron bosons) is proposed. Energies and lifetimes of a second stretched band in ⁷⁹Rb (probably with negative parity) were also measured.     

The 65Cu(p,t)63Cu reaction and the structure of 63Cu

The ⁶⁵Cu(p, t)⁶³Cu reaction has been studied with 18.0 and 19.5 MeV protons. The states in ⁶³Cu at 1.547 and 2.498 MeV are each assigned $\text{J}{}^{\mathrm{\pi }}\text{=}\text{3}\text{2}{}^{\mathrm{?}}$ on the basis of angular distributions indicating mixed L = 0 and L = 2 transfer. Relative cross sections for L = 2 transfer to the low-lying states are compared with predictions of the shell model and particle-core model.     

The h112 and g72 band structures in 131Ce and 129Ce

High-spin levels in ^{129, 131}Ce have been produced by the reactions ^{116, 118}Sn(¹⁶O, 3n) ^{129, 131}Ce and studied by in-beam γ-ray spectroscopic techniques. Two strongly populated band structures are observed. The odd-parity levels based on a $\text{9}\text{2}{}^{\mathrm{?}}$ state constitute a system explained in the triaxial-rotor-plus-particle model as the result of the coupling of an $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ neutron-hole to a prolate-type triaxial core. The even-parity band built on a $\text{7}\text{2}{}^{\mathrm{+}}$ state corresponds to collective excitations associated with a neutron-hole in the $\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ shell. Backbending effect observed in the yrast cascade is discussed.     

Investigation of i132 excitations in 197Hg and 191Pt

The level schemes of the odd-neutron nuclei ¹⁹⁷Hg and ¹⁹¹Pt have been studied using in-beam spectroscopic methods. Energies, intensities, angular distributions and coincidences of the γ-rays following (α, 2n) reactions were measured. Also conversion electrons and delayed γ-ray spectra were recorded. Most of the levels in both nuclei are de-populated via the $\text{13}\text{2}{}^{\mathrm{+}}$ isomers. Besides the yrast states, several additional states with spin values between $\text{13}\text{2}$ and $\text{21}\text{2}$ were identified. The negative parity of a side band in ¹⁹⁷Hg starting with an $\text{f =}\text{21}\text{2}$ state was proved by the conversion electron measurement. The families of positive-parity states were compared with model calculations where the core was described as rigid triaxial rotor or anharmonic vibrator. For ¹⁹⁷Hg both models give similarly good results for the energy spectrum and the branching ratios of electromagnetic transitions. Several negative-parity states found in ¹⁹⁷Hg are compared with the predictions of a pairing-plus-quadrupole model.     

Lifetimes of the low-lying 72− states in 113, 115Cd

The half-lives of the $\text{7}\text{2}{}^{\mathrm{?}}$ states at 522.6 and 393.9 keV in ¹¹³Cd and ¹¹⁵Cd have been determined to be 0.322±0.012 and 0.75± 0.03 ns, respectively. Values of the $\text{B(}\text{E}\text{2,}\text{7}\text{2}{}^{\mathrm{?}}\text{→}\text{11}\text{2}{}^{\mathrm{?}}$) and the energy difference in odd Cd (A = 113–119) are compared with those in neighbouring even Cd. The level properties are interpreted in the framework of the triaxial rotor model.     

Level structure and lifetimes of low-excitation states in 63Cu

The lifetimes of 9 states in ⁶³Cu up to an excitation energy of 2092 keV have been determined by means of the Doppler-shift attenuation method using the ${}^{60}\text{Ni}\text{(α,}\text{p}\text{γ)}$ reaction. A search was made for a suitable set of M1 and E2 single-particle matrix elements for use with shell-model eigenstates throughout the Ni, Cu and Zn isotopes. The theoretical predictions for the level spectroscopy and electromagnetic transitions and static moments in ⁶³Cu are in satisfactory agreement with the experimental findings.     

Ground-state rotational band in 181Ta

The ground-state rotational band in ¹⁸¹Ta has been observed up to a spin of $\text{21}\text{2}{}^{\mathrm{+}}$ using Coulomb excitation with ⁸⁴Kr ions. The nuclear lifetimes of the band members have been determined from the Doppler-broadened lineshapes of the de-excitation γ-rays, and the angular distributions of the γ-rays have been measured. It is found that the E2 transition rates from higher spin states $\text{(≧}\text{17}\text{2}{}^{\mathrm{+}}\text{)}$ are retarded relative to the rotational model predictions. A suggestion is made that this retardation may be due to the Coriolis antipairing effect.     

Medium-spin levels and the character of the 20.4 ns 132+ isomer in 145Gd

Levels of the N = 81 nucleus ¹⁴⁵Gd have been investigated by in-beam γ-ray and conversion electron spectroscopy with the ¹⁴⁴Sm(³He, 2n) reaction. Fourteen new low- and medium-spin states between 1.0 and 2.4 MeV excitation, the known yrast levels up to spin $\text{21}\text{2}{}^{\mathrm{+}}$, five other high-spin non-yrast states and a new 20.4 ns $\text{13}\text{2}$ isomer at 2200.2 keV in ¹⁴⁵Gd have been observed. The isomer decays via a fast 927.3 keV E3 transition with B(E3) = 48 ± 7 W.u. Another weaker decay branch is a mixed, strongly hindered E1 + M2 + E3 transition to the $\text{v}\text{h}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ state. We propose an octupole $\text{v}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{j}{}^{\mathrm{?2}}\text{× 3}{}^{\mathrm{?}}$ main configuration for the isomer, analogous to the 997 keV $\text{13}\text{2}{}^{\mathrm{+}}$ isomer in ¹⁴⁷Gd. The levels of ¹⁴⁵Gd are discussed on the basis of the spherical shell model.     

High-spin structure in 169W and 170W

High-spin states in ^{169, 170}W have been populated in ${}^{154}\text{Gd}\text{(}{}^{20}\text{Ne}\text{, x}\text{n}\text{)}$ reactions. In-beam γ-ray spectroscopic techniques with multi-detector set-ups, multiplicity filters and an anti-Compton shield have been used. Levels up to about spin 30 (tentatively up to 36) in ¹⁷⁰W and up to $\text{57}\text{2}$ (tentatively up to $\text{61}\text{2}$) in ¹⁶⁹W have been identified. The data are interpreted within the framework of a pairing-selfconsistent cranking model. The nuclear shape evolution with increasing spin is studied theoretically within a configuration-controlled shell correction approach and also pairing effects are studied. The behaviour of the yrast states around 28⁺ in ¹⁷⁰W can be related in a model-dependent way to a reduction of the neutron-pairing correlations.     

Photoemission of Xe and Kr adsorbed on the W(110) plane

The UPS and XPS spectra of Xe adsorbed on clean, O, CO, and Xe covered W(110) surfaces and the UPS spectrum for Kr on clean and O covered W(110) surfaces have been investigated. On clean W, Xe and Kr show a splitting of the $\text{5p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{4p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ hole states respectively. For Xe the coverage dependence of this splitting was investigated in detail; neither the positions nor the intensity ratio of the substates are coverage dependent for θ ? 0.04, suggesting that splitting is due to differences in the image interaction of the $\text{m}{}_{\mathrm{j}}\text{= ±}\text{3}\text{2}$ and $\text{m}{}_{\mathrm{j}}\text{= ±}\text{1}\text{2}$ components. For Xe equal shifts, relative to vacuum, of ~1.0 eV were observed for 5p, 4d, and 3d levels, suggesting that initial state effects are small. Image interaction for Xe and Kr on clean W could best be fitted by assuming an increase, rather than a decrease in the effective hole-image separation from the nominal value, suggesting that the image plane is moved back into the metal by a screening length. For Xe adsorbed on $\text{Xe}\text{W}$(110), or on virgin-$\text{CO}\text{W}\text{(110)}$ polarization of the intermediate layers was found to contribute significantly to relaxation. Coadsorbed oxygen broadened Xe 5p and Kr 4p peaks. There was an almost linear relation between O 2p UPS intensity at the energies of the various peaks and the amounts of broadening, suggesting that the latter results from resonance neutralization by electrons from the O 2p states.     

g-Factors of high-spin isomers in 194Hg and 196Hg

The g-factors of the 10⁺ isomeric states in ¹⁹⁴Hg and ¹⁹⁶Hg have been measured using the in beam IPAD method. The results $\text{g(}{}^{194}\text{Hg}\text{) = ?0.24(4)}$ and $\text{g(}{}^{196}\text{Hg}\text{) = ?0.18(9)}$ are in agreement with the value expected for an ($\text{i}{}_1\text{3}\text{2}$^?2) neutron satructure and clearly contradict the previous assignment as ($\text{h}{}_{\mathrm{<mtext>1</mtext><mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{?2}}$) proton configurations. Cranking model calculations show that the neutron excitation energies in the rotating frame agree satisfactorily with the experimental energies and that the proton excitations are expected ≈2 MeV above the experimental yrast line     

High spin states in 57Co

High spin states of ⁵⁷Co have been studied via prompt γ-ray spectroscopy in the reactions ⁴⁸Ti(¹²C, p2n) and ⁵⁴Fe(α, p) at 26–48 MeV and 12–24 MeV, respectively. The energies and decay modes of these levels were determined from the analysis of γ-ray singles and γ-γ coincidence spectra, excitation functions, angular distributions and correlations. The relevant lifetimes were measured by the Doppler-shift attenuation method. The new levels established in this work are at 4037, 4814 and 5918 keV with the most probable J^π assignment of $\text{15}\text{2}{}^{\mathrm{?}}$, if $\text{17}\text{2}{}^{\mathrm{?}}$ and $\text{19}\text{2}{}^{\mathrm{?}}$, respectively. The previously known level at 2524 keV was assigned to have $\text{J}{}^{\mathrm{\pi }}\text{=}\text{13}\text{2}{}^{\mathrm{?}}$. These together with the known $\text{9}\text{2}{}^{\mathrm{?}}$(1224 keV) and $\text{11}\text{2}{}^{\mathrm{?}}$(1690 keV) levels constitute the yrast states of ⁵⁷Co. The measured lifetimes of the above six levels are (in order of increasing energies) 0.085±0.030, 0.32±0.10, 0.16±0.06, 0.10_?0.07^+0.06, 1.5_?0.5⁴ and 0.17_?0.07^+0.08 ps, respectively. Comparisons with some theoretical calculations are presented.     

Neutron and proton alignment at high spin in 168W

Excited states in the neutron-deficient nucleus ¹⁶⁸W, populated in the ¹⁴⁸Sm(²⁴Mg, 4n)¹⁶⁸W reaction, have been studied using γ-ray spectroscopy. The yrast band, which is identified up to about spin 28, shows a very strong backbend at low frequency, $\text{h}\text{?}\text{ω}{}_{\mathrm{c}}\text{= 0.235}\text{MeV}$, attributed to the $\text{(i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{)}{}^2$ neutron alignment. Evidence for a second backbend is also observed. A strongly populated odd-spin (probably negative-parity) sideband is also identified to the spin, and shows several band-crossing anomalies. The characterisation of the anomalies is made by comparison with CSM calculations. Proton and neutron alignments are probably present in the sideband, and the second backbend in the yrast sequence may be due to alignment of $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ protons.     

Étude par spectroscopie “en ligne” des états d'énergie de 187Au: Interprétation en termes de déformations nucléaires triaxiales

The decay of ¹⁸⁷Hg is studied using “on-line” mass-separated sources. A decay scheme is proposed. The negative parity states are analysed within the “quasi-particle + triaxial rotor” model of Meyer-ter-Vehn: it is found that the $\text{11}\text{2}{}^{\mathrm{?}}$ state at 224 keV corresponds to a nuclear deformation β = 0.14 and γ = 35 and the $\text{9}\text{2}{}^{\mathrm{?}}$ state at 120.6 keV to a deformation β = 0.2 and γ = 21°. A systematic analysis of the heavier odd-mass gold isotopes is given in the framework of this model.     

Decays of 185m + gHg: Low-spin levels of 185Au as a test of nuclear models

The decay of ^{185m + g}Hg has been studied on-line with mass-separated sources from the ISOCELE facility. Precise conversion-electron measurements were performed with a 180° spectrograph. The $\text{13}\text{2}{}^{\mathrm{+}}$ isomeric state of ¹⁸⁵Hg ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 28 ± 5 s}$) was located with respect to the $\text{1}\text{2}$^? ground state ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 55 ± 10 s}$). A level scheme of ¹⁸⁵Au has been established. Two abnormally converted M1 transitions de-excite a state local at 330.2 keV. Excited states of ¹⁸⁵Au have been discussed in the framework of a “quasi-particle + axial rotor” approach, quasi-particle states being issued from Hartree-Fock plus BCS calculations using the SIII Skyrme force. Most of the low-spin negative-parity levels have been identified as h_{$\text{9}\text{2}$} + f _{$\text{5}\text{2}$} or p_{$\text{3}\text{2}$} + f_{$\text{7}\text{2}$} mixed states. The h_{$\text{11}\text{2}$} system has also been discussed using a model of asingle-j quasi-particle coupled to a triaxial rotor.     

High-spin states in 24Mg and upper limits for particle spectroscopy of high spins by heavy-ion compound reactions

High-spin states in ²⁴Mg have been investigated by the reaction ¹⁰B(¹⁶O, d)²⁴Mg up to $\text{E}{}^1\text{≈ 24}\text{MeV}$. High-spin states with $\text{I ≧ 9}$ have been identified at $\text{E}{}^1\text{= 19.20, 20.26, 20.8, 21.6, 23.1,}\text{and}\text{23.5}\text{MeV}$. The 10⁺ yrast state in ²⁴Mg is probably located at 20.26 MeV. The upper limits with respect to spin and excitation energy of the applicability of heavy-ion compound reactions for particle spectroscopy of high-spin states are discussed. The main limitations result from the increasing continuum and from a decrease of the high-spin selectivity when the final spins approach the critical angular momentum for compound-nucleus formation. It will be shown that the difficulty in the analysis of the experiments arising from the decreasing probability of finding isolated yrast states at high excitation energies, i.e. from the increasing level density, can be overcome in such experiments. The decrease in the high-spin selectivity of the total cross section is compensated for spins up to J_max by the fact that the shape of the angular distributions depends on the final spin for states with I ～ J_max. This is caused by the decreasing alignment of the final nucleus with decreasing values of |I ? J_max| and can be used for high-spin spectroscopy.