Reaction dependence and gross structure of the γ-decay of highly excited states in the rare earth nucleus 162Dy

The γ-decay from states with low spin and high excitation energy has been studied using the ¹⁶³Dy(τ, α)¹⁶²Dy and ¹⁶²Dy(τ, τ′)¹⁶²Dy reactions. For excitation energies above 4.5 MeV the γ-ray spectra obtained in the two reactions are almost identical, revealing no reaction dependence.     

High spin structures in194Hg

High spin states in the isotope¹⁹⁴Hg were populated using the¹⁵⁰Nd (⁴⁸Ca,4n) reaction at a beam energy of 213 MeV. The analysis ofγ-γ coincidences has revealed two new structures at excitation energies above 6 MeV and at moderate spin. The two structures are a manifestation of the deviation of nucleus from the collective rotation which dominates its lower excitation behaviour. A comparison with similar structures in the neighbouring Hg isotopes is also attempted.     

High-spin states in108Sn

High spin states in¹⁰⁸Sn have been investigated using the⁹²Mo(¹⁹F,p2nγ)¹⁰⁸Sn reaction. In-beam measurements ofγ-γ-coincidences,γ-ray excitation functions andγ-ray angular distributions were performed with Ge(Li)-detectors, one of which had a Nal Compton suppression shield. A level scheme for¹⁰⁸Sn has been constructed up to anI ^π=(14^?) state.     

High spin states in105Ag

Levels in¹⁰⁵Ag were populated by the¹⁰³Rh(α, 2nγ) reaction,γ-singles spectra,γγ-coincidences, excitation functions, angular distributions and polarisation measurements were taken. These measurements were used to construct a level-scheme and give various spin and parity assignments. Nuclear Reactions:¹⁰³Rh(α, 2nγ)¹⁰⁵Ag; measuredEγ, Iγ, γγ-coincidences, excitation functions, angular distributions, polarisation.     

Statistical properties of fusion reactions involving deformed nuclei

The statistical properties of the ¹⁶⁵Ho(α,2nγ) ¹⁶⁷Tm reaction were investigated. It was found that both the slopes of the excitation functions and the side-feeding intensities are independent of the K quantum number. Regular behaviour of these quantities as a function of the spin I and of the excitation energies of the observed levels provide a means for spin assignments, just as for spherical nuclei. The analysis, in the present case, however, is much more involved.     

A 150 ms 10+ Isomer in146Dy

In the course of systematic studies of very proton rich nuclei in theN≈82 region with Ni induced compound reactions, an unusually long-lived high spin isomer has been found. After in-and off-beamγ and conversion electron measurements, asγ excitation functions,γ andeγ coincidences, pulsed beam techniques and multi spectrum analyses of the residual activities, this isomer has been tentatively assigned to be a 10⁺ state in¹⁴⁶Dy, which decays into two 7^? states byE3 transitions. The half-life of the isomer has been measured to be 150±20ms. The isomer has been found to follow the β decay of the previously unknown 3.9 s isotope¹⁴⁶Ho. The mechanism of the appearance of such an isomer is discussed.     

High-spin states in38Ar

Theγ-decay of 93³⁸Ar levels between 6.84 and 10 MeV excitation energy has been measured using the³⁵Cl(α,pγ) reaction atE _α=14 MeV. A previous measurement of the same reaction could be exploited in the light of the present results, yielding spin(-parity) assignmentsJ ^π(7,070)=5^-, J(7,507)=7,5,J ^π(8,077)=7⁺, J(8,129)=5,6 and J(8,488)=7,5. Theγ-decay modes of yrast levels, which have been previously observed in heavy ion induced reactions, are revised leading to major changes in their spin-parity assignments. New candidates for theJ ^π=8^- and 9⁺ levels were found in the levels at 9,644 and 9,928 keV excitation energy, respectively. A comparison of yrast levels with shell-model calculations is satisfying.     

Analysis of inelastic scattering of3He on14C at 37.9 MeV

The analogue of the 0⁺ ground state in¹¹⁸Sn has been observed in the compound nucleus¹¹⁸Sb through¹¹⁷Sn(p,nγ)¹¹⁷Sb reaction. The neutron decays of this analogue resonance have been studied from the deexcitingγ-rays of the residual nucleus¹¹⁷Sb. From off resonance excitation functions, spin assignments have been made to states in¹¹⁷Sb, on the basis of Hauser-Feshbach formalism. The resonance parameters of the isobaric analogue resonance have been determined, including the total, proton and neutron decay widths.     

Shell model study of high spin states in theN=50 nucleus93Tc

High spin states in theN=50 nucleus⁹³Tc were reinvestigated by using the reaction⁶⁴Zn (³⁵Cl,4p 2n) at a beam energy of 140 MeV. This was done particularly with a view to observe anyγ rays upto 2.7 MeV which may have been missed in our earlier study where the experimental conditions were set to observeγ rays upto 2 MeV. We found four newγ rays of energy: 2484, 2164, 2130 and 69 keV. We have placed theseγ rays in the level scheme and it now gets extended to 49/2^?. Though there is no substantial change in the level scheme, placing theγ rays in the level scheme has resulted into two important conclusions: (1) We have performed shell model calculations for⁹³Tc nucleus within a model space which encompasses an enlarged proton configuration and allows for the excitation of the neutron across theN=50 core. The excitation of a single neutron across theN=50 core satisfactorily explains the new level scheme. (2) The energy of the 17/2^? isomeric state is now unambiguously placed at 2185 keV.     

Shape coexistence and other aspects of nuclear structure in40Ar

Theγ-decay of⁴⁰Ar has been studied by particle-γ-ray coincidence measurements in the³⁷Cl(α, pγ) reaction at 12 and 13 MeV bombarding energy. Particle-γ-ray angular correlations and linear polarizations ofγ-rays were measured at 12 MeV. A lifetime measurement using the Doppler-shift attenuation method was performed at 11 MeV. The coexistence of spherical and deformed states in⁴⁰Ar could be concluded from the observation of aK ^π=0⁺ rotational band which has itsI ^π=0⁺ through 6⁺ members at 2,121, 2,524, 3,515 and 4,959 KeV excitation energy. The intrinsic quadrupole moment derived fromB(E2) values is ∥Q ₀∥=1,320 _?120 ⁺⁶⁰ mb. Negative-parity states with high spin were observed at 4,858(5^?), 4,494(5^?), 4,226(4^?) and 4,991 KeV(4^?) excitation energy. A complete account of all levels below 5 MeV excitation energy is obtained by a model in which twod _3/2 proton holes couple weakly to the⁴²Ca levels below 4.75 MeV excitation energy.     

High spin states in103Rh

High spin states in¹⁰³Rh have been studied using the¹⁰⁰Mo(⁷Li, 4n) reaction. Standard in-beam measurements involving singlesγ-ray,γ-γ-t coincidences, angular distribution and linear polarization measurements have been performed. A perturbed band based on a 9/2⁺ state is interpreted as ag _9/2 coupled band. A sequence built on a 1/2^? state is related to thep _1/2 state. At higher excitation energy, in the range 2.2–3.7 MeV, the strongΔI=1 cascade observed, connecting negative parity levels, probably arises from states including three quasi-particle configurations.     

High-spin states in154Er

High-spin states in¹⁵⁴Er have been populated by bombarding¹⁴⁷Sm and¹⁴⁸Sm with¹²C particles. Excitation functions, lifetimes, angular distributions andγ-γ coincidences were measured. AT _1/2=35ns isomeric state atE _x～3 MeV has been found and is interpreted as a two-quasi-particle state with aligned angular momenta. A cascade of intense individual lines from states with spin up to at least 26 (excitation energy up to 8.543 MeV) was found to feed the isomeric state. The level sequence above this yrast trap exhibits an irregular pattern which cannot be easily interpreted in terms of collective modes.     

High spin states in75Se populated by the72Ge(α,n) and73Ge(α, 2n) reaction

The⁷²Ge(α, n)⁷⁵Se and⁷³Ge(α, 2n)⁷⁵Se reactions have been studied at bombarding energies of 15 MeV and 22.5 MeV respectively using Ge(Li)-detectors.γ-singles spectra,γ-γ-coincidences,γ-angular distributions and excitation functions have been taken. A level scheme has been constructed, which contains a stretched spin and a normal rotational band. Nuclear reactions⁷²Ge(α, n)⁷⁵Se,⁷³Ge(α, 2n)⁷⁵Se; measuredE _γ ,I _γ ,γ-γ-coincidences,γ-angular distribution,γ-excitation function.⁷⁵Se deduced levels,J, π, γ-multipolarity. Enriched target, Ge(Li).     

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.     

First identification of high spin states in160Lu

High spin states of¹²⁸La have been investigated by means ofγ ray spectroscopy. Although two level schemes were reported prior to the present study, those schemes were different at excitation energies near the band head. A new level scheme has been obtained for the detailed discussion of signature dependence.     

Gamma-spectroscopy within the island of high-spin isomers nearN=82

A NaI sum-spectrometer combined with Ge-counters has been used to characterize the members of the island of high spin isomers nearN=82. On the basis of half lives, totalγ-decay energies and discreteγ-lines, assignments of 22 isomers are given or confirmed. The isomers are localized to the region 82≦N≦86 andZ≦68, and the excitation energies vary from 3 MeV to 12.2 MeV. An empirical relation between spin and excitation energy is presented and on this basis isomeric spin values up to (33±2)? are deduced. The isomers are thought to be due to strong alignment of 2 to 8 shell-model particles in a spherical or possibly weakly oblate potential.     

The decay of the 560 ns Isomer at 8.6 MeV in 64 147 Gd83

In (α,xn) and (¹²C, 5n) in-beamγ-ray experiments with pulsed beams the decay of the 560 ns high-spin isomer in¹⁴⁷Gd has been investigated. Extensive coincidence measurements identified in the isomeric decay more than eightyγ-rays which almost all were placed in the level scheme. Of crucial importance for establishing the highly complex decay was the comparison of data from the different reactions and the identification of transitions which bypass the 27 ns isomer at 3.58 MeV. Our data determine the excitation of the 560 ns isomer as 8.588 MeV and suggest 47/2 as its most probable spin.     

Spectroscopy of highly excited states in29Si

Particleγ-ray coincidences have been measured in the²⁸Si (d,pγ) reaction at 6.5 and 7 MeV bombarding energy, in the²⁶Mg (α,nγ) reaction at 12, 14 and 15 MeV, and in the²⁷A1 (τ,pγ) reaction at 9 MeV. Theγ-decay has been observed for all bound states of²⁹Si and for 56 unbound states up to 12,960 KeV excitation energy. Particleγ-ray angular correlations were measured in the²⁸Si (d,pγ) reaction at 6.5 MeV and in the²⁶Mg (α,nγ) reaction at 12 MeV. Spin (-parity) assignments or restrictions were obtained for nearly all bound states and some high-spin states above the binding energy. The assignment of mirror levels in²⁹Si and²⁹P has been extended to 8.2 MeV excitation energy. The excitation energies of 41 positive-parity states are reproduced by shell model calculations. The possible existence of aK ^π=5/2⁺ band with prolate deformation is discussed.     

Band structures in73Se

Excited states of⁷³Se have been investigated up to spin, 21/2 using techniques of in-beamγ-ray spectroscopy in connection with the⁷⁰Ge(α, n) reaction. Mean lifetimes of 12 levels have been determined applying Doppler-shift andγ-RF-methods. Five different bands have been identified that reflect a variety of different excitation modes. The decoupled 9/2⁺ band is likely to correspond to an oblate deformation while the 5/2⁺ band is interpreted as a strongly coupled prolate band built on the Nilsson configuration [422] 5/2⁺. The 3/2^? band is a strongly coupled band built on the [301] 3/2^} configuration.Nuclear reactions:⁷⁰Ge(α,n),E=14, 16, 18, 19, 20MeV; measuredE _γ,I _γ,σ(E _γ,θ),γγ-coin, linear polarization, DSA,γ(t).⁷⁵Se deduced levels,I, π, τ, δ(E2/M1), B(σλ). Enriched targets, Ge detectors.     

Level properties of the light even Sb nuclei 112, 114, 116Sb

The level properties of ^{112, 114, 116}Sb have been investigated with the reactions ^112,114,116Sn(p, nγ)^112,114,116Sb and ¹¹⁵In(³He, xnγ)^112,114Sb (x = 6, 4). Singles γ and electron spectra, neutron-γ coincidences, γ-γ coincidences, excitation functions and half-lives were measured. Hauser-Feshbach calculations were performed for spin assignments. A number of new levels were found, including two 8^? isomeric states. The results are compared with recently performed 2qp calculations.