New yrast excited states of the N = 84 nucleus 142Ce observed in deep inelastic reactions

Excited states of ¹⁴²Ce, populated in deep inelastic reactions of ⁸²Se projectiles bombarding ¹³⁹La target, have been studied up to medium spins using in-beam γ spectroscopy techniques. Three new levels have been identified at 2625, 2995, 3834 keV, and assigned as 8⁺, 9^(-) and 11^(-), respectively. These new yrast states follow closely the level systematics of the even mass N = 84 isotones. Their strctures have been discussed with the help of empirical shell model calculations. Received: 2 November 2001 / Accepted: 15 January 2002     

High-spin states and yrast isomerism in 153Er

Energy levels in ¹⁵³Er have been populated in the reaction ¹⁴⁴Sm(¹²C. 3n)¹⁵³Er. Isotopically enriched targets were bombarded with 53–65 MeV ¹²C ions and the emitted γ-ray and conversion electron spectra were investigated. From studies of excitation functions. γ- coincidences, γ-ray multiplicities, delayed γ-radiation and angular distributions, the level scheme of ¹⁵³Er has been constructed. The properties of the energy levels are discussed and compared with the results of calculations with a deformed shell model. The remarkable similarities and some important discrepancies of the level structure, when compared with adjacent, N = 85 nuclides, are emphasized.     

Low-spin states of153Gd observed in the decay of153Tb

Level structure of the 89-neutron nucleus¹⁵³Gd has been investigated by studying theEC-decay of isotope-separated¹⁵³Tb sources with several semiconductor detectors. In addition to singles gamma and electron spectra,γ-γ ande ^?-γ coincidences were investigated by using Ge(Li) and Si(Li) spectrometers and a high-capacity two-parameter recording system. In all, 191γ-rays are assigned to the decay of the 2.4d¹⁵³Tb. The proposed level scheme of¹⁵³Gd containing most of the observed transitions shows a very high density of low-spin states (45 states below 1.5MeV). Spin and/or parity assignments based mainly on coincidence data and measured transition multipolarities are proposed for a majority of these states. Nilsson model classifications of some levels are discussed. On the basis of logf t values the spin and parity of the ground state of¹⁵³Tb are suggested to be 3/2⁺ or 5/2⁺.     

High-spin yrast states in Ce

Yrast states up to spin 18 have been identified in ¹³²Ce. The energies and spins of the levels suggest the existence of two fairly well-behaved collective bands. The results are compared with those obtained in the rare-earth deformed region.     

Three-nucleon yrast states in145Sm

In-beamγ-ray and conversion electron measurements with (α, xn) reactions have established the¹⁴⁵Sm highspin states up toI ^π=25/2⁺ at 3.5 MeV excitation. A shell model analysis using empirical two- and one-body energies from neighbouring nuclei classifies the low-lying odd-parity levels as 3-quasiparticle states formed by the¹⁴⁴Sm two-proton-hole excitations and thef _7/2 valence neutron. The higher-lying positive-parity states involve particle-hole core excitations with one proton inh _11/2.     

Negative parity yrast states in deformed nuclei

The negative parity yrast states in even-even deformed nuclei are studied. For low I values these states are interpreted as octupole states. At high spin values, however, the coupling of participating quasiparticles is change; their angular momenta become parallel and aligned with the rotational axis. The transition between the two regimes occurs at I ≈ 21–25 in light actinide nuclei and as low as I ≈ 9–11 in light rare-earth nuclei.     

Study of the yrast band in the doubly odd156Tm

The yrast band in the doubly odd¹⁵⁶Tm nucleus was studied through¹⁴⁴Sm(¹⁹F,2p5n)¹⁵⁶Tm reaction at beam energy of 105MeV. Several high-spin states of¹⁵⁶Tm were identified and the highest spin of the band with configuration7/2^–[523] v1/2⁺[660] could be built up to spin 25. The level structure shows the onset of a non- or weak collectivity which generally appears at neutron number of 87 in neutron-deficient rare-earth nuclei.This work was supported in part by the Fok Ying Tung Education Foundation and the Natural Science Fund of China.     

High spin yrast states in even platinum isotopes

The high spin yrast states up toJ=20⁺ in^{184, 186}Pt and^{190, 192, 194}Pt are studied in a microscopic approach of variation with number-conserved projected states. The energy spectra, quadrupole moments andB(E2) values are calculated by employing the Hamiltonian with quadrupole plus pairing interactions. The results of the calculations are in fair agreement with the available experimental data.     

Description of negative parity yrast states in156Er

Positive and negative parity yrast states are studied in ₆₈ ¹⁵⁶ Er₈₈ with a particle number projected Hartree-Fock-Bogoliubov method constrained on an average angular momentum. The theory predicts a second anomaly of the positive parity yrast states due to the alignment of ah _11/2 proton pair. The double backbending in the negative yrast band is understood: AtJ ^π=9^? to 11^? it is due to the intersection of the (πg _7/27/2⁺)×(πh _11/27/2^?) and the (πi _13/21/2⁺)×(πh _9/23/2^?) 2q.p. bands. The second backbending found experimentally fromJ ^π=21^? to 23^? is connected with an alignment of ai _13/2 neutron pair of the core in the proton 2q.p. band.     

Isomeric yrast states in 206Tl

We have found isometric states in ²⁰⁶Tl with $\text{J}{}^{\mathrm{\pi }}\text{= 12}{}^{\mathrm{?}}\text{(T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 3.76}\text{min}\text{)}$, 7⁺ (10ns) and 5⁺ (78ns) and have identified their proton-neutron hole structure. New electromagnetic properties of proton hole orbitals have been determined.     

Excited states in 69Ge observed in the 69Ga(p,nγ) reaction

Energy levels of ⁶⁹Ge are populated by the ⁶⁹Ga(p, n) reaction. Angular distributions and DSAM are used to extract information on spins and γ-decay properties of the levels of this nucleus. The observed structure of the negative- and positive-parity states is compared with the predictions of the one- and three-particle-cluster—core coupling model.     

High spin states in153Er

High spin states in¹⁵³Er have been populated in the¹⁴⁴Sm(¹²C, 3n)¹³³Er reaction. Excitation functions, lifetimes, angular distributions,γ-γ coincidences and internal conversion coefficients were measured. Three isomeric states at 2.75 MeV (T _1/2=400 ns), 2.95 MeV (T _1/2～10 ns) and 5.2 MeV (T _1/2=200 ns) have been observed. A fourth isomer seems to be weakly excited above 6.8 MeV. The level scheme proposed is discussed in term of the nuclear shell model.     

Seniority-three yrast states in theN=82 nucleus147Tb

Firm spin-parity assignments for the high-spin states up to 3.5 MeV in the one-proton nucleus¹⁴⁷Tb were obtained from¹⁴⁴Sm(⁶Li, 3n) in-beamγ-ray and conversion electron measurements. The energies of these two-particle one-hole excitations were calculated from the shell model with empirical nucleon-nucleon interaction energies. The calculated energy splittings agree well with experiment, whereas the theoretical excitation energies disagree by ?1 MeV if recently measured ground state masses are used.     

Analytical method for yrast line states in interacting Bose-Eeinstein condensates

We propose a method to investigate the energy eigenvalue problem and corresponding yrast line for harmonically trapped interacting N-boson systems. This method is particularly simple and effective to obtain the explicit analytical expressions of low-L energy eigenstates with L denoting systems' total angular momentum but with an arbitrarily large N. We have derived the explicit analytical results for L = 0,1,....,9 and discussed the yrast line for these low- L energy eigenstates.     

Studies on low spin yrast states in212m Po

High resolution laser spectroscopy has been performed on mass-separated beams of barium ions, in a collinear geometry. Isotope shifts and hyperfine structures of the 5d ² D _3/2→6p ² P _3/2 transition and the 5d ² D _5/2→6p ² P _3/2 transition were measured. The results are interpreted in terms of core polarization effects.     

Identification and structure of yrast levels in theN=89 odd-odd158Tm nucleus

Excited levels have been identified in the odd-odd¹⁵⁸Tm nucleus produced in the¹⁵⁰Sm (¹⁴N,6n) reaction. The observed level structure based on an isomeric state (T_1/216±4 ns) is interpreted as a rotational aligned band.     

Rb晕带signature反转的机理

将角动量投影壳模型应用到84Rb核，对组态为πg9/2νg9/2的正宇称晕带和组态为π(p3/2,f5/2)νg9/2的负宇称晕带理论计算和实验结果进行了比较，特别是对正宇称晕带中的signature反转机理进行了探讨.角动量投影壳模型计算显示正宇称晕带中的signature反转是原子核随自旋增加形状发生变化的信号，其间原子核从低自旋的长椭球通过三轴形变变到高自旋的扁椭球.此外，还确定了此两带的原子核形状.     

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.