Dipole excitations in the semi-magic nucleus 51V studied with the (γ,γ′) reaction

We report on a nuclear resonance fluorescence experiment on the semi-magic odd-mass fp-shell nucleus ⁵¹V. The detected dipole strength distribution is discussed on the basis of modern shell-model calculations employing a model space allowing for excitations of protons and neutrons from the 1f_7/2 to the (2p_1/2,2p_3/2,1f_5/2) shells. The calculations indicate that the main body of transitions is of magnetic dipole type, and they are capable of reproducing the observed distribution well. Possible electric dipole and quadrupole contributions are also discussed.     

Effects of configuration mixing on predominantlyf 7 2/n states inA=52–55 nuclei

Extensive shell-model calculations are performed onf _7/2 nuclei withA=52–55. The model space includes the excitation of onef _7/2 nucleon to thep _3/2,f _5/2 orp _1/2 orbit. Spectra, electromagnetic properties (M1,E2,E4) andβ-decay are studied. It is found that almost all observables calculated in the enlarged space are in much better agreement with experiment than those of the simplef ₇ ^2/n space.     

Structure of odd Ge isotopes with 40 < N < 50

We have interpreted recentlymeasured experimental data of ⁷⁷Ge, and also for ^73,75,79,81Ge isotopes in terms of state-of-the-art shell-model calculations. Excitation energies, B(2) values, quadrupole moments and magnetic moments are compared with experimental data when available. The calculations have been performed with the recently derived interactions, namely with JUN45 and jj44b for f _5/2pg9/2 space. We have also performed calculation for fpg _9/2 valence space using an fpg effective interaction with ⁴⁸Ca core and imposing a truncation to study the importance of the proton excitations across the Z = 28 shell in this region. The predicted results of jj44b interaction are in good agreement with experimental data.     

Core polarisation effect on the 3p 1/2, 3p 3/2, 2f 5/2, 2f 7/2 and 1i 13/2 proton states of209Bi

The weak fragments of the 3p_1/2, 3p_3/2, 2f_5/2, 2f_7/2 and 1i_13/2 proton states of²⁰⁹Bi as seen in the²⁰⁸Pb (³He,d) reaction can be explained with the coupling of the renormalised proton states and the vibrational states of²⁰⁸Pb. The energies of the zerothorder proton shell-model states as well as the collective admixtures of the weak fragmented proton states of²⁰⁹Bi have been deduced from the core-particle coupling model.     

A study of high spin states in the transitional nucleus90Mo

The reaction⁵⁸Ni(³⁶Ar, 4p)⁹⁰Mo has been studied at a beam energy of 149 MeV. A detector array consisting of the OSIRIS spectrometer (12 Compton-suppressed Ge detectors), four charged-particleδE detectors and seven NE-213 neutron detectors at the VICKSI accelerator in Berlin has been used to measure the gamma radiation inγγ- and particle-γγ-coincidence mode. An additional Ge detector was placed at 162? to the beam direction to provide information on DCO ratios. The level scheme of⁹⁰Mo has been extended up to an excitation energy of about 12 MeV and probable spin 23?. Some 70 transitions and 40 levels have been newly identified. Spin assignments have been proposed on the basis of measured DCO ratios. Shell model calculations in a model space consisting of the proton 1f _5/2, 2p _3/2, 2p _1/2, and 1g _9/2 orbits and the neutron 2p _1/2, 1g _9/2, 1g _7/2, 2d _5/2, 2d _3/2, and 3s _1/2 orbits with some truncation were made for states above 9? and the predicted structure of these states is discussed.     

High spin states of 62,64Zn

In-beam γ-ray spectroscopy studies of high-spin states of ^62,64 Zn have been performed via the fusion-evaporation reaction ⁴⁰Ca + ²⁸Si and a charged-particle filter. Levels up to an excitation energy of about 14 MeV have been observed. The results are compared with a shell-model calculation in the k ≤ 3 model space with (0 f _5/21p _3/21p _1/2) ^{A - 56 - k} (0g _9/2) ^k . The parity changes in yrast sequences can be well understood in terms of crossing of level sequences with different k configurations.     

Shell-model calculations on Ni and Cu isotopes

Binding energies, excitation energies and spectroscopic factors have been calculated for^57–67Ni and^58–68Cu in an unrestricted (2p_3/2, lf _5/2,2p_1/2) shell-model space. The effective two-body matrix elements are obtained from the modified surface delta interaction (MSDI) and from a least-squares fit to experimental binding and excitation energies (ASDI). The average deviation between about 100 experimental and calculated energies is 0.14MeV for MSDI and 0.08 MeV for ASDI. Excitation energies of high-spin states are given also. Spectroscopic factors have been calculated for all single-nucleon transfer reactions on stable Ni or Cu targets leading to Ni or Cu isotopes. For spectroscopic factors larger than 0.4 the average deviation between theory and experiment is about 30%. The experimentally observed and calculated spectroscopic strengths are compared by using sum rules and are found to be consistent. An extensive compilation has been made of experimental data on energies,J ^π assignments and spectroscopic factors.     

Quasiparticle-phonon model calculations on doubly even Zn and Ge nuclei

The doubly even isotopes of Zn and Ge have been investigated in a model in which two quasiparticle excitations, constructed in a (0f _7/2), 1p _3/2, 0f _5/2, 1P _1/2, 0g _9/2 configuration space, are coupled with quadrupole vibrations of the core, viz.⁴⁰Ca or⁵⁶Ni. The 0f _7/2 orbit is excluded in case of a⁵⁶Ni core. The spectra, except for low-lying excited 0⁺ states, could be reproduced reasonably well. The calculatedE2 strengths and quadrupole moments are in fair agreement with experiment.     

Calculations of the energy spectra of Zn,Ga, and Ge isotopes by the shell model

The effective Hamiltonian which was determined empirically by Koops and Glaudemans is tested in shell model calculations for the^65–68Zn,^67–69Ga, and^68–70Ge nuclei in the full (1p _3/2,0f _5/2,1p _1/2) ⁿ space. The resulting energy spectra are compared with the experimental spectra and results of previous calculations. The overall agreement with experiment is as satisfactory for these nuclei as for the Ni and Cu isotopes, by which the Hamiltonian was determined. It is noticed that the spectra of⁶⁷Zn and^67,69Ga calculated in this work are similar to those provided by the Alaga model.     

The shell model and collective structures in54,55,56Fe

Extensive shell-model calculations have been performed on^54,55,56Fe. The results obtained in a model space with two and with up to threef _7/2 holes in the,⁵⁶Ni core are compared with experiment. The Surface Delta Interaction (SDI) and the Kuo Brown interaction (KB) have been used to calculate energy levels, spectroscopic factors and electromagnetic properties resulting especially for⁵⁶Fe in a remarkably good agreement with experiment. Admixtures of three-hole components in the wave functions are significant and increase with mass number. Properties of high-spin states withJ≦15 are discussed. Pronounced collective features derived microscopically are expected in⁵⁶Fe. Finally some suggestions for interesting experiments are given.     

X-ray M4,5 resonant Raman scattering from Gd with final 4p hole: calculations with 4p–4d–4f configuration interaction in the final state and comparison with the experiment

We present calculations of resonant Raman scattering (RRS) at the M_4,5 thresholds of Gd in the scattering channel 3d¹⁰4f⁷→3d⁹4f⁸→[4p⁵4f⁸↔4d⁸4f⁹]. We have included in the final state the interaction between the two configurations within the brackets, having one 4p and two 4d holes, respectively. The influence of the configuration interaction on the scattering spectra is shown to be important. The calculations are made within a purely ionic model including only the spectral features dispersing with the incident photon energy and do not account for the M₄ to M₅ Coster-Kronig conversion. The calculations are compared with recent experimental results on Gd metal. The agreement is excellent when choosing the excitation energy in the M₅ region. In the M₄ region the calculations agree with the measurements by assuming that the Coster-Kronig contribution is approximated in shape by the RRS spectrum measured with direct M₅ excitation. The implications of the results are discussed.     

A shell-model study ofA=48–52 nuclei and magnetic strength distributions in50Ti

An extensive shell-model calculation has been performed on fivefp-shell nuclei in the mass regionA = 48–52. The model space, which includes 1p-1h excitations, reproduces the experimental spectra very well except for the 0 ₂ ⁺ state in⁵⁰Ti. It is demonstrated that the 0 ₂ ⁺ state can be reproduced by a model space which also includes 2p-2h excitations. Strong neutronp-h components in the wave functions of states in ₂₂ ⁵⁰ Ti₂₈ are found despite the closure of the neutron f_7/2 orbit. Magnetic transitions in⁵⁰Ti are discussed, and in contrast to the 1p-1h results a sufficiently large quenching ofB(M1) strengths in the 2p-2h model space is found. Effects of 2p-2h admixtures onM 5 transition strengths are discussed as well.     

Dipole bands and multi-quasiparticle excitations in 193Pb

The nucleus ¹⁹³Pb was populated via the ¹⁶⁸Er(³⁰Si,5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipole Δ I = 1 cascades have been found. These structures have been connected to the level scheme which has been considerably extended up to a spin of ? and an excitation energy of about 8 MeV. Angular distribution coefficients, a₂, have been measured and confirm the dipole character of the in-band transitions. B(M1)/B(E2) ratios have been extracted for the two most intense cascades. The ¹⁹³Pb dipole bands are discussed in comparison with those known in odd lead isotopic series and the structure of the band heads is analyzed in terms of microscopic HF+BCS calculations. The proposed configurations are based on a high-K two quasiproton excitation, π ([505]9/2^t? ? [606]13/2⁺)_K=11^t -, coupled to one or three rotation aligned quasineutrons involving the i_13/2, p _3/2, f_5/2 and/or h{9/2} subshells. The main difference, compared with the heavier lead isotopes, is the presence of large Ω orbitals from the ν (i_13/2) shell near the Fermi surface which are responsible for the increasing band-head spin as A decreases.     

The calculation of logft values and spectroscopic factors for nuclei in the mass range 10–15

Wave functions obtained in previous shell-model calculations [1, 2] for states of nuclei with massesA=10–15 are used to calculate logft values and spectroscopic factors. These wave functions, which were based on a modified surface delta two-body interaction, comprise the following active shell-model spaces: the 1p _3/2 and 1p _1/2 orbitals for mass 10–14 nuclei and restricted combinations of the 1p _1/2, 2s _1/2, 1d _5/2 and 1d _3/2 orbitals for mass 15 nuclei, leading to four different calculations in the latter case. The calculated results support evidence that the modified surface delta interaction is a valid approximation to the effective interaction in light nuclei.     

Shell-model results in <Emphasis Type="Italic">fp</Emphasis> and <Emphasis Type="Italic">fpg</Emphasis><Subscript>9/2</Subscript> spaces for <Superscript>61,63,65</Superscript>Co isotopes

Low-lying spectra and several high-spin states of odd-even ^61,63,65Co isotopes are calculated in two different shell-model spaces. First set of calculations have been carried out in fp-shell valence space (full fp space for ^63,65Co and a truncated one for ⁶¹Co) using two recently derived fp-shell interactions, namely GXPF1A and KB3G, with ⁴⁰Ca as core. Similarly, the second set of calculations have been performed in fpg _9/2 valence space using an fpg effective interaction due to Sorlin et al., with ⁴⁸Ca as core and imposing a truncation. It is seen that the results of GXPF1A and KB3G are reasonable for ^61,63Co. For ⁶⁵Co, shell-model results show that the fpg interaction adopted in the study is inadequate and also points out that it is necessary to include orbitals higher than 1g _9/2 for neutron-rich Co isotopes.     

Investigations of europium isotopes with neutron numbers between 84 and 93 by collinear laser ion-beam spectroscopy

Hyperfine structures and isotope shifts of the transition Eu II 4f⁷(⁸S ₇ ^2/O )6p_3/2 (7/2,3/2)₄ — 4f⁷ (⁸S ₇ ^2/O )5d⁹D ₄ ^O ,λ=6O4.95 nm, of the radioactive isotopes^{147, 149, 155, 156}Eu have been studied by collinear laser-ion beam spectroscopy (CLIBS). The nuclear moments and the differences of the mean square nuclear charge radii as well as the deformation parameters have been deduced. The experimental data for the odd-A nuclei are in a good agreement with simple Nilsson model calculations.     

Dipole bands and multi-quasiparticle excitations in193Pb

The nucleus¹⁹³Pb was populated via the¹⁶⁸Er(³⁰Si,5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipoleΔI=1 cascades have been found. These structures have been connected to the level scheme which has been considerably extended up to a spin of 61/2? and an excitation energy of about 8 MeV. Angular distribution coefficients,α ₂, have been measured and confirm the dipole character of the in-band transitions. B(M1)/B(E2) ratios have been extracted for the two most intense cascades. The¹⁹³Pb dipole bands are discussed in comparison with those known in odd lead isotopic series and the structure of the band heads is analyzed in terms of microscopic HF-BCS calculations. The proposed configurations are based on a high-K two quasiproton excitation,π([505]9/2^??[606]13/2⁺) _K =11^?, coupled to one or three rotation aligned quasineutrons involving thei _13/2,p _3/2,f _5/2 and/orh _9/2 subshells. The main difference, compared with the heavier lead isotopes, is the presence of largeΩ orbitals from theν (i _13/2) shell near the Fermi surface which are responsible for the increasing band-head spin as A decreases.     

Structures and decay of deep-hole states in light nuclei populated by the (p, 2p 2p) reactions

Decay particles from the s-hole states in ¹¹B and ¹⁵N have been measured in coincidence with the quasifree ¹²C(p, 2p) and ¹⁶O(p, 2p) reactions at E _p =392 MeV. Triton decay is found to be dominant for the ¹¹B(s-hole) state and also found to be larger than α decay for the ¹⁵N(s-hole) state despite its smaller Q value compared to α decay. Measured decay branching ratios are discussed in comparison with the results of statistical-model, SU(3)-model, and shell-model calculations. The energy spectra around the s-hole states in both ¹¹B and ¹⁵N exhibit some bumplike structures, which can be qualitatively explained by recent shell-model calculations for both nuclei.     

Fragmentation of the high spin discrete neutron and proton states of209Pb and209Bi

The distribution of the discrete 1h _9/2, 2f _7/2, 1i _13/2 and 2f _5/2 proton states of²⁰⁹Bi and 2g _9/2, 1i _11/2, 1j _15/2 and 2g_7/2 neutron states of²⁰⁹Pb have been obtained within the particle-vibration coupling model calculation and compared with the experimental datas baising on the most recent high resolution stripping reaction on²⁰⁸Pb using 480 MeV¹²C projectile. The optimised shell model energies arising from the core-polarisation effect have profound influence for both the study of the structures of the high spin continuum shell model states of²⁰⁸Pb and stability of superheavy nuclei.