Multi-quasiparticle excitations in ~(145)Tb

Nuclei with N and Z near magic number can be well described by the nuclear shell model. The 145Tb nucleus has a valence proton and a pair of neutron holes with respect to the doubly closed 146Gd nucleus. Therefore, it is expected that the excitations in 145Tb be dominated by single-particle configurations. A detailed measurement of the excitation scheme in 145Tb would give us an opportunity to examine the behavior of multi-particle excitations involving high angular momentum orbits and provi…     

High spin states in145Gd

The data from two experiments with heavy ion induced reactions at the OSIRIS Compton suppressed Ge detector array has been analyzed to study high spin states in¹⁴⁵Gd. The level scheme of¹⁴⁵Gd has been extended up to an excitation energy of 12 MeV and an estimated spin of 25 ?. No evidence for high spin isomers was found.     

New investigation of83Zr and85Zr beta decay

The decay of on-line mass separated⁸³Zr and⁸⁵Zr sources has been studied by singles and coincident X-ray and-ray and conversion electron measurements. The previous level scheme of⁸³Y is confirmed and 5 new levels have been added up to 2.74 MeV excitation. A decay scheme of^85gZr with 40 levels up to 2.66 MeV in⁸⁵Y is deduced. The experimental observation below 2 MeV excitation in⁸⁵Y agrees qualitatively with the predictions of the interacting boson-fermion model.     

Low-spin states in151Gd

The level structure of the 87-neutron nucleus¹⁵¹Gd has been investigated by studying the EC- andβ ⁺-decay of¹⁵¹Tb. Gamma-ray and conversion electron spectra as well as gamma-gamma coincidence spectra were measured by using semiconductor spectrometers and a high-capacity two-parameter recording system. The proposed decay scheme contains several new energy levels in¹⁵¹Gd, among them a 5^?/2 state at 427 keV. To explain the low-energy level structure, a small stable deformation is assumed for¹⁵¹Gd. Using a single-particle-plus-rotor model based on a generalized Woods-Saxon potential, complete mixing of the shells 1h _9/2, 2f _7/2 and separately 1i _13/2 is observed. By these mixings the correct level order and approximately correct excitation energies up to 1 MeV are reproduced.     

In-beam study of 145Tb

The high-spin states of ¹⁴⁵Tb have been studied in the ¹¹⁸Sn(³²S, 1p4n) reaction at ³²S energies from 161 to 175 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions and γ-γ-t coincidences were performed with 12 BGO(AC)HPGe detectors. Based on the measured results of γ-γ coincidences, γ-ray anisotropies and DCO ratios, a level scheme for ¹⁴⁵Tb was established for the first time. The observed excited states show typical irregular pattern in a spherical nucleus, and the low-lying levels have been interpreted qualitatively with a particle-core coupling. Received: 21 September 2001 / Accepted: 9 November 2001     

High spin states in148Tb

The level scheme of¹⁴⁸Tb has been extended to an excitation energyE _x =14.0 MeV and a spinI≈ 38? in two experiments with the OSIRIS Comptom suppressed detector array at the HMI Berlin using the reactions¹²²Sn(³¹P,5n)¹⁴⁸Tb at 160 MeV and¹²⁰Sn(³¹P,3n)¹⁴⁸Tb at 152 MeV.     

Isobaric analogue resonances in71As through proton elastic scattering on70Ge

The analogues of the low-lying levels in⁷¹Ge have been observed as resonances in the compound nucleus⁷¹As through proton elastic scattering on⁷⁰Ge in the energy rangeE _p=3.5 to 5.3 MeV. The excitation functions cover the analogue resonances corresponding to states upto 2.3 MeV excitation in⁷¹Ge. The sub-structures in the 5.06 MeV resonance, first observed by Temmer and co-workers have been confirmed in the present experiment. The present investigation reveals similar sub-structures in the 4.13 MeV resonance lending further support to the existence of intermediate structure near an isobaric analogue resonance. The resonance parameters and the spectroscopic factors (for the corresponding parent states) have been extracted. The results are compared with the information available from the⁷⁰Ge(d, p)⁷¹Ge reaction.     

The level structure of92Ru up to high spin values

The level structure of⁹²Ru has been studied by means of γ-ray spectroscopy. The nucleus was produced by the⁵⁸Ni(⁴⁰Ca, α2p)⁹²Ru reaction at beam energies of 147 and 187 MeV. The NORDBALL detector system including particle selection was used. A large number of new levels with excitation energies up to 11.3 MeV and spin values up to 22 or 23 units of angular momentum have been established. The level scheme is compared with recent shell model calculations using¹⁰⁰Sn as a core. Some systematics of the g ₉ ^2/?2 configuration is discussed and a strong correlation between the levels in⁹⁰Mo and⁹²Ru is found.     

First observation of high spin states in90Tc

High spin states in⁹⁰Tc have been studied via the⁵⁸Ni (³⁵Cl, 2pn) ⁹⁰Tc reaction at beam energy of 124 MeV. Twenty-six newγ-rays were observed, a new level scheme was established and spins were assigned. Two band-like structures were established up to about 20? with an excitation energy of 6–7 MeV. The band (B) shows collective characteristic at high spin. We suggest it to be of a quasi-particle configurationπg_9/2?vf _5/2.     

Level Scheme of High-Spin States in 145Tb

High-spin states of ¹⁴³Tb have been studied via the ¹¹⁸Sn(³²S,1p4n)¹⁴⁵Tb reaction by means of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions and γ-γ-t coincidences were performed with 12 BGO(AC)HPGe detectors. A level scheme for ¹⁴⁵Tb including 41 γ-rays which come from the deexcitations of the 24 levels, has been established for the first time based on an analysis of the γ-ray excitation functions, γ-γ coincidence relationships, intensity balances and cross-over transitions. The spins for most of the levels in the scheme are assigned according to the results of the measured γ-ray anisotropies. Considering the structure similarity between ¹⁴³Eu and ¹⁴⁵Tb, the low-lying levels in 145Tb are interpreted by coupling a h_9/2 proton to the excited states in ¹⁴⁴Gd core.     

Gammaübergänge und Energieniveaus im49V aus der Reaktion48Ti(p, γ)49V

Deexcitation gamma rays of⁴⁹V from the⁴⁸Ti (p, γ)⁴⁹V reaction have been investigated at the resonancesE _p=1007, 1209, 1362 and 1374 keV corresponding to excited states in⁴⁹V at 7742, 7940, 8090, 8102 keV. A 4 cm²× 0.35 cm lithium-drifted germanium detector was used. The target was TiO₂ enriched in⁴⁸Ti to 99.4%. 71 gamma transitions have been observed. A level scheme of⁴⁹V is proposed involving 8 new levels in the energy range from 0 to 5.2 MeV excitation energy.     

The structure of25Mg

Gamma-decay modes and spin(-parity) assignments of levels in²⁵Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the²⁴Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the²²Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2O d _5/2 — 1s _1/2-O d _3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of²⁵Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of²⁵Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of²⁵Mg in great detail. The prospectiveI ^π=9/2^?, 13/2^?, and 15/2^? members of the established negative-parity,K=1/2 band are found in levels atE _x=7801, 9410, and 8896 keV.     

Level structures of 95,97Mo — A comparative study

High-spin states of ^95,97Mo (Z=42, N=53,55) nuclei have been investigated through ⁸²Se(¹⁸O, xn) reaction at Eb=60 MeV. The level scheme in ⁹⁵Mo has been observed upto ≏ 10 MeV in the present experiment. The level structure shows mainly single particle character. In ⁹⁷Mo, the ground state level sequence has been extended to ≏ 4.5 MeV while the previous information had been up to 2.4 MeV. A negative parity band built on 1437 keV (11/2⁻) excited state has been extended to 5.5 MeV. The structure seems to show a coexistence of single particle and collective modes of excitation. Properties of both the nuclei have been compared with shell model calculations using OXBASH.     

Nuclear resonance fluorescence in238U and a new approach to Doppler-shift-attenuation using high speed rotation

Using⁵⁶Co sources, a 3.254 MeV level in²³⁸U was photoexcited by aγ-line emitted in the decay of the 4.100 MeV level in⁵⁶Fe. 10γ-transitions deexciting this 3.254 MeV level were identified. Spin and parity were determined to be 1⁻. By moving the⁵⁶Co source in a high speed centrifuge the profile of the 3.254 MeV emission line was investigated. By applying a new variety of Doppler shift analysis a lifetime ofτ _Fe=55±25fs was obtained for the 4.100 MeV level in⁵⁶Fe. The cross section for nuclear resonance fluorescence yields a lifetime ofτ _U =0.33±0.12 ps for the 3.254 MeV level in²³⁸U.

     

High-spin structures observed in the 101Tc fission fragment

High-spin states have been studied in ¹⁰¹Tc produced as a fission fragment in the reaction ¹⁷⁶Yb +²⁸Si at 145 MeV. Gamma rays were detected with the EUROGAM2 array. The level scheme of ¹⁰¹Tc has been extended up to 4.2 MeV excitation energy and several band structures are observed. Configurations are assigned to two new bands on the basis of their behaviour and of cranked Hartree-Fock-Bogolyubov calculations. Received: 4 January 1999     

Beyond the N = 50 shell closure: High-spin excitations of 87Kr and ground-state spin of 87Br

The ⁸⁷Kr nucleus has been produced as fission fragment in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. High-spin states of this neutron-rich isotope have been identified for the first time. Its level scheme has been obtained up to 6.3MeV excitation energy and spin I ∼ 23/2ℏ. Its structure is interpreted by analogy with those of the heavier isotones. The proposed configurations involve both proton and neutron excitations from several sub-shells located close to the Fermi levels, particularly νd_5/2, πp_3/2f_5/2 and πg_9/2. Moreover, a revised spin value of 5/2^- for the ⁸⁷Br ground state is proposed.     

High-spin levels in 63 145 Eu82

The level scheme of the N=82 nucleus ¹⁴⁵Eu has been extended to I=(55/2) and E_x=11.2 MeV in an experiment with the Tessa Compton-suppressed Ge detector array using the ¹²⁷I(²²Ne,4n) reaction. Most of the complicated and irregular level scheme of ¹⁴⁵Eu can be interpreted as proton multi-quasiparticle states in comparison to the ₆₄ ¹⁴⁶ Gd₈₂ core nucleus but also excitations across the neutron N=82 core have been observed.     

A study of the 144Sm(d,p) reaction at 19 MeV

The ¹⁴⁴Sm(d, p) reaction has been studied at an incident deuteron energy of 19 MeV using the injector-tandem accelerator and the multichannel magnetic speetrograph of the University of Oxford. Angular distributions have been measured for transitions to levels of ¹⁴⁵Sm up to an excitation energy of 3.2 MeV. Theoretical (d, p) distributions have been calculated using the program DWUCK. and orbital angular momentum transfers and spectroscopic factors have been deduced by comparing these calculations with the experimental data. The spectroscopic information derived from this study is more complete than that previously reported and many new assignments have been made. The level scheme of ¹⁴⁵Sm has been found to resemble closely the level schemes of the other N = 83 nuclei.     

High spin states in the transitional nucleus88Mo

The reaction⁵⁸Ni(³⁶Ar,α qρ)⁸⁸Mo has been studied at 145 MeV beam energy. A detector array consisting of the OSIRIS spectrometer, four charged-particleΔE detectors and seven NE213 neutron detectors has been used to meaure the gamma radiation inγγ- and particle-γγ-coincidence mode. The level scheme of⁸⁸Mo has been extended up to 11.6 MeV excitation energy and probable spin 23?; some 70 transitions and 40 levels have been identified. Spin assignments have been proposed on the basis of measured DCO ratios. Hartree Fock cranking calculations of the Total Routhians and shell model calculations of the high spin states are presented which imply near-sphericity of the yrast line up to the highest spins found. A classification of the high spin states according to their leading seniority is proposed.     

Level structure of 99Rh at high spins

High spins states in ⁹⁹Rh were populated via the ⁶⁶Zn(³⁷Cl, 2p2n)⁹⁹Rh reaction at an incident beam energy of 130 MeV. Seventeen new transitions have been observed in the present study and the level scheme has now been extended up to a spin of J∼ 25ħ and an excitation energy of about E _x∼ 10 MeV. The observation of a positive parity E2 cascade based on the 9/2⁺ isomeric level is suggestive of collective behaviour in this nucleus up to high spins. Spherical shell model (within restricted model space) and Cranked shell model calculations were performed to obtain an insight into the observed level structure. The new collective band observed up to a spin of J∼ 25ħ is suggested to be based on (πg _9/2 ³) ⊗ (νg _7/2 ²) quasi-particle excitations. Received: 12 July 1999 / Revised version: 14 September 1999