Microscopic determination of band interaction in 154Gd and 164Er

Microscopic equations describing the direct coupling of the ground state band with the beta-, gamma- and K^π = 1⁺ (responsible for the RAL effect) rotational bands are solved and the interaction strengths are obtained using a Woods-Saxon potential and P + QQ residual forces. The calculated non-adiabatic characteristics are found to be in good agreement with experimental data and are compared to other theories.     

Measurement of lifetimes for high spin states in 152Sm, 154Gd and 156Gd by the Doppler broadened lineshape method

Lifetimes of the ground band levels up to spin 10⁺ in ¹⁵²Sm, ¹⁵⁴Gd and ¹⁵⁶Gd have been measured by the Doppler broadened lineshape (DBLS) analysis of peaks observed following Coulomb excitation of enriched metallic targsts by 132–143 MeV ³⁵Cl beams. The γ-ray lineshapes were measured in time coincidence with backscattered ions and were analyzed with a computer program incorporating tabulated electronic stopping powers. The nuclear stopping power of Lindhard et al and multiple scattering treatment by Blaugrund were assumed. Renormalization of the electronic stopping powers given by Northclifie and Schilling was found necessary to reproduce the accurately known lifetime of the 6⁺ state in ¹⁵²Sm. Stopping powers for Sm in Sm inferred from the tabulated ⁴He stopping power of Ziegler and Chu support this renormalization. The stretching parameter a derived from the lifetimes of the ground band are (2.0 ± 0.6) × 10^?3, (1.85 ± 0.40) × 10^?3 and (0.0 ± 0.45) × 10^?3, in ¹⁵²Sm, ¹⁵⁴Gd and ¹⁵⁶Gd, respectively.     

Magnetic moments of high-spin states above the rotational band of 168Hf and 172Hf

The transient magnetic field IMPAC technique was used to measure the magnetic moments of high-spin states above the rotational band of ¹⁶⁸Hf and ¹⁷²Hf, populated in the reactions ^{156, 160}Gd(¹⁶O, 4n). The average g-factors of these prerotational feeding states were deduced to be 0.07 ± 0.04 and 0.14 ± 0.04 for ¹⁶⁸Hf and ¹⁷²Hf, respectively. These results are in agreement with a reduction of the collective g-factors due to a neutron phase transition.     

Lifetimes of high-spin yrast states in 154Er

Lifetimes for high-spin levels (between about 10 and 30 ?) in ¹⁵⁴Er have been measured by the recoil-distance method. Non-collective, moderately collective and collective E2 transitions from states with lifetimes between at most 10 and 400 ps have been found. All available data on this nucleus are discussed within the framework of the oblate coupling scheme with the addition of collective degrees of freedom.     

Continuous gamma radiation feeding high-spin isomers in 148, 149, 151, 152Dy and 147Gd

The energy, multipolarity and multiplicity spectra of the continuum gamma radiation feeding high-spin isomers in ^{148, 149, 151, 152}Dy and ¹⁴⁷Gd have been measured at several bombarding energies. The final nuclei were selected via a delayed coincidence technique while the use of a NaI(Tl) Compton shielded crystal allowed the primary gamma-ray spectra to be generated reliably from the observed spectra.It was found that: (i) the energy of both the gamma-ray statistical cascade and the neutron cascade increases with increasing excitation energy, the latter much more rapidly than expected; (ii) the multiplicity of gamma-ray cascades, in which a statistical transition was detected, is generally lower than that of the average cascade; (iii) stretched E2 spin-correlated transitions occur above $\text{J? 39}\text{h}\text{?}\text{in}{}^{152}\text{Dy}$ and above $\text{～ 50.5}\text{h}\text{?}\text{in}{}^{147}\text{Gd}$, indicating the onset of collectivity at these spins — in addition, a region of predominantly dipole emitting states is located below $\text{T? 44}\text{h}\text{?}\text{in}{}^{147}\text{Gd}$; (iv) effective moments of inertia derived from the bump edge are 50–100% larger than those deduced from the density of stretched E2 transitions in the bump; (v) in ^149,151Dy the bump edge is very sharp but no multiplicity features are observed; (vi) although the four Dy isotopes were populated at approximately the same excitation energy, they display considerable differences in their continuum properties.Probable interpretations of these observations are discussed, in particular we have suggested that several of the observed effects are consistent with the possible presence of high-K collective bands above the yrast line.     

In-beam study of 144Gd

A level scheme of ¹⁴⁴Gd has been established using the ¹⁴⁴Sm(α, 4nγ) reaction and in-beam spectroscopy methods. Excitation functions, γ-ray angular distributions, γ-γ coincidence spectra, γ-spectra time related to the cyclotron beam bursts and conversion coefficients for the delayed transitions have been measured.The level scheme comprises 11 levels with spins up to I = 12. Two isomers, a 13 ± 2 ns, 7^? state at 2471.4 keV and a 145 ± 30 ns, 10⁺ state at 3433.0 keV have been observed. The former has similar excitation energy as the 7^? isomers in ¹⁴²Sm, ¹⁴⁰Nd and ¹³⁸Ce and it may arise from the $\text{{ν}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{× ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{}}$ configuration although its lifetime seems to indicate some degree of collectivity. The 10⁺ state has a similar excitation energy as the 10⁺ isomer found in ¹³⁸Ce and it may arise from the dominant $\text{ν}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}{}^{\mathrm{?2}}$ configuration. Below the 10⁺ isomer in ¹⁴⁴Gd only two excited states have positive parity; the hitherto known first 2⁺ and 4⁺ states. The 11⁺ and 12⁺ states must include four-particle configurations or they have to be of collective nature. The latter possibility is supported by the considerable E2/M1 mixture (≈ 20 %) observed for the 11⁺ to 10⁺ transition. An analysis of the systematics of ground band levels in the N = 80 isotones shows the same gradual behavior between the two VMI solutions previously found for the Te isotopes.     

Excitation energy of the lowest 2+ and 3− levels in 32Mg and 146Gd

The excitation energy of the lowest 2⁺ and 3^? levels is calculated for neutron rich Mg-isotopes as well as for N=82 isotones. The calculations are made by assuming quadrupole-quadrupole and octupole-octupole forces. The quasiparticle energies and occupation numbers are taken from the energy density method.     

Collective and two-quasiparticle states in 158Gd observed through study of radiative neutron capture in 157Gd

The level structure of ¹⁵⁸Gd has been studied using the prompt γ-rays and conversion electrons emitted following neutron capture in ¹⁵⁷Gd. The γ-ray energy and intensity measurements were made using both Ge(Li) detectors and a curved-crystal spectrometer. Conversion-electron energy and intensity measurements were made using two separate magnetic spectrometers: one to measure the primary electron spectrum and the other to measure the lower energy secondary electron spectrum. Some γ-γ coincidence measurements were also made among the secondary γ-rays. From these data, a neutron separation energy of 7937.1 ± 0.5 keV has been determined for ¹⁵⁸Gd. A level scheme containing 59 excited states with energies < 2.25 MeV, for which de-excitation modes have been identified, is proposed for ¹⁵⁸Gd. Many of these states have been grouped into rotational bands. A total of thirteen excited rotational bands with band-head energies below 2.0 MeV are contained in the level scheme. Features of the proposed level scheme include: the K^π = 0^?, 1^? and 2^? octupole-vibrational bands with band-head energies of 1263, 977 and 1793 keV, respectively; the γ-vibrational band at 1187 keV; three excited K^π = 0⁺ bands with band-head energies of 1196, 1452 and 1743 keV; several two-quasiparticle bands with band-head energies in keV (and K^π assignments) of 1380 (4⁺), 1636 (4^?), 1847 (1⁺), 1856 (1^?), 1920 (4⁺) and 1930 (1⁺). An analysis of (d, p) reaction data is presented which permits definite two-quasiparticle configuration assignments to be made to most of these latter bands. Evidence is presented which suggests strong mixing of some two-neutron and two-proton bands. A phenomenological four-band mixing analysis is made of the energy and E2 transition-probability data for the ground-state band and the three lowest-lying excited collective positive-parity bands. Good agreement with experiment is obtained. A Coriolis-mixing analysis of the octupole bands has been carried out and good agreement with the data on level energies and E1 transition probabilities to the ground-state band has been achieved. Values of Z, the ratio of the E1 transition matrix element with ΔK = 1 to that with ΔK = 0, involving the octupole bands and the first four 0⁺ bands are derived. For three of these 0⁺ bands, absolute values of these matrix elements are deduced. An interesting alternation in the sign of Z is observed for these four 0⁺ bands.     

Monopole effects and high-spin levels in neutron-rich 132Te

The neutron-rich nuclei near doubly magic ¹³²Sn have attracted considerable interest in both nuclear physics and nuclear astrophysics. For the particle-hole nuclei in this region, the low-lying and high core excitations have been well described by shell model calculations using the extended pairing plus multipole-multipole force model. However, there is a significant difference between experiment and theory in the high-spin level 17⁺ of ¹³²Te. We intend to illust...     

A high-spin isomer in 204Bi

By making use of heavy-ion and α-particle induced reactions an isomeric state has been found in ²⁰⁴Bi, with a half-life of $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 1.07 ± 0.03}\text{ms}$ and the quantum characteristics I^π = 16⁺. The four-quasiparticle configuration $\text{ν(}\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?2}}\text{ν(}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}{}^1\text{π(}\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^1$ has been ascribed to this state.     

Large transient magnetic fields for rare-earth ions recoiling in gadolinium and g-factors of high-spin states in 156, 158, 160Gd

We have determined the transient magnetic field for Coulomb-excited rare-earth nuclei recoiling with velocities in the range between 0.7ν₀ and 6ν₀ into ferromagnetic gadolinium cooled to a temperature T = 80 K. Measured and calculated g-factors in ¹⁶⁹Tm have been used as calibration standards. The transient field is found at first to increase with increasing recoil velocity, and then to level off, approaching a nearly constant value of 5.5 kT at ν = 6ν₀. At the higher velocities (3ν₀ < ν < 6ν₀) the transient fields for ¹⁶⁹Tm recoils in gadolinium are a factor of 1.42 ± 0.12 larger than those in iron, whereas the densities of polarized electrons are the same in both ferromagnets. This result demonstrates that an explanation of the transient field must take into account the atomic structure of the host (and probably also that of the recoil). The transient field is too large to be described only in a statistical picture in which inner-shell (ns) vancancies are filled by capture of polarized (4f) electrons. Possible mechanisms may involve either polarization transfer from the outer shells by spin-flip interactions, or direct vacancy polarization by diabatic molecular orbitals.The transient field calibration has been corroborated making use of known g-factors of low-spin states in ^{156, 158, 160}Gd populated by Coulomb excitation of thick Gd single crystals. For the high-spin states in these nuclei, the g-factors are found to decrease slightly, with the ratio $\text{g(10}{}^{\mathrm{+}}\text{)}\text{g(2}{}^{\mathrm{+}}$) reduced to 0.89±0.12, 0.83±0.11, and 0.93±0.13, respectively. Similar decreases have been observed previously for other N = 90?96 nuclei.     

The photoneutron cross section of 151Eu, 153Eu and 156Gd in the giant resonance region

The ¹⁵¹Eu, ¹⁵³Eu and ¹⁵⁶Gd photoneutron cross sections in the giant dipole resonance region have been measured using bremsstrahlung from the University of Melbourne betatron. Absolute cross-section values, lorentzian parameters, intrinsic quadrupole moments, deformation parameters and integrated cross-section values are derived. For ¹⁵¹Eu and ¹⁵³Eu the measured cross sections are in good agreement with the predictions of the extended dynamic collective model.     

High resolution Raman spectroscopy of the fundamental vibrational band of 16O2

The vibrational Raman spectrum of ¹⁶O₂ has been recorded with high resolution (0.05 cm^?1 for the Q branch). The expansion of the Hamiltonian as a sum of irreducible tensors of the O(3) group allowed us to obtain easily the expressions for the energy levels, taking into account the off-diagonal matrix elements. From the analysis of the spectrum the excited state constants have been calculated; in particular the rotational constants obtained are: B₁ = 1.421884 ± 0.000013 cm^?1 and D₁ = (?4.864 ± 0.014)10^?6 cm^?1.     

Magnetic moments,E3 transitions and the structure of high-spin core excited states in 211Rn

The results of g-factor measurements of high-spin states in ²¹¹Rn are: $\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{= 8856 + Δ′}\text{keV}\text{(J}{}^{\mathrm{\pi }}\text{=}\text{63}\text{2}{}^{\mathrm{?}}\text{)}$, g = 0.626(7); $\text{6101 + Δ′}\text{KeV}\text{(}\text{49}\text{2}{}^{\mathrm{+}}\text{), 0.766(8)}$; $\text{5347 + Δ′}\text{KeV}\text{(}\text{43}\text{2}{}^{\mathrm{?}}\text{), 0.74(2)}$; $\text{3927 + Δ}\text{KeV}\text{(}\text{35}\text{2}{}^{\mathrm{+}}\text{), 1.017(12)}$; $\text{1578 + Δ}\text{KeV}\text{(}\text{17}\text{2}{}^{\mathrm{?}}\text{), 0.912(9)}$. These results together with measured E3 transition strengths and shell model calculations are used to assign configurations to the core excited states in ²¹¹Rn. Mixed configurations are required to explain the g-factors and enhanced E3 strengths simultaneously.     

Structure of high-spin states in 143Pm

High-spin states of ¹⁴³Pm have been studied in the reactions ¹⁴¹Pr(α, 2n)¹⁴³Pm and ¹⁴³Nd(d, 2n)¹⁴³Pm by means of in-beam spectroscopy. The level scheme, spin and parity assignments are based on results obtained from singles γ-ray spectra, conversion electron spectra, prompt and delayed γ-γ coincidences, γ-ray angular distribution and linear polarization measurements. Positive- and negative-parity states with energies up to 4580 keV and spins up to $\text{25}\text{2}$ have been established including 22 new levels. For two nanosecond isomeric states the nuclear spin precession in an external magnetic field was observed providing the following g-factors:

$\text{g(}\text{11?}\text{2}\text{, 959.7 keV)=1.14(9), g(}\text{15+}\text{2}\text{, 1898.3 keV)=1.00(7).}$

The experimental results are well understood by calculations which have been performed in the framework of the shell model (for positive-parity states of 11 valence protons above a Z = 50, N = 82 core) and of the cluster-vibration model (for 3 holes in a Z = 64, N = 82 core). In the case of positive-parity states no evidence for particle-core coupling could be found, while the negative-parity states could qualitatively be understood within the particle-core coupling picture.     

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     

Average g-factors for high-spin states in 78Kr

Inverse reactions of ^{63, 65}Cu beams on ^{18, 16}O targets have been used to populate states of ⁷⁸Kr by fusion-evaporation reactions. The excited nuclei recoiled at high velocity v/c ≈ 7 % through a polarized iron (⁵⁴Fe) layer and were stopped in a copper layer. During the period in iron, 0.05–0.65 ps, the nuclei were subjected to the intense transient magnetic field (initially ～ 3500 T). The resulting precession of the high-spin nuclear states populated during this time was determined by measuring the time integral rotation angle of the discrete γ-ray transitions at low spin.The average g-factor at low spin 2 ≦ J ≦ 8 compared to that at higher spin 8 ≦ J ≦ 12 in ⁷⁸Kr was found to be identical within the experimental uncertainties of ～ 15 %. This result implies that either there are no rotational alignment effects at the backbend in ⁷⁸Kr or more plausibly, proton (g ≈ 1) and neutron (g ≈ 0) aligned bands are equally competitive and both populated in the reaction. It is then likely that the resulting g-factor represents an average over many populated proton and neutron aligned bands.     

Yrast and high-spin states in 22Ne

High-spin states in ²²Ne have been investigated by the reactions ¹¹B(¹³C, d)²²Ne and ¹³(¹¹B, d)²²Ne up to $\text{E}{}^1\text{～- 19}\text{MeV}$. Yrast states were observed at 11.02 MeV (8⁺) and 15.46 MeV (10⁺) excitation energy. A backbending in ²²Ne is observed around spin 8⁺. The location of high-spin states I ≦ 10 is discussed in terms of the rotational band structure, Strutinsky-type calculations, and pure shell-model predictions.     

Isomers and high-spin states in 205At

The properties of high-spin states in ²⁰⁵At have been investigated to $\text{J ?}\text{37}\text{2}$ and an excitation energy of > 4.0 MeV. The properties of the $\text{29}\text{2}$⁺ isomer at 2340 keV have been established and those of the $\text{25}\text{2}$⁺ isomer at 2063 keV have been further investigated. In the present study the mean lives of these isomers have been determined as 11.2±0.2μs and 98±2 ns respectively. The M2 branch of the $\text{13}\text{2}$⁺ state at 970 keV to the $\text{9}\text{2}$⁺ ground state has been measured. This decay is attributed to a proton single-particle $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{→}\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ transition. The trend of excitation energies of a number of proton excitations in the odd-mass nuclei from ²¹¹At to ²⁰¹At has been compared to the corepolarization model and the average $\text{ν}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{π}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ interaction energy has been deduced. Comments are made upon probable configurations for many of the levels.