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.     

Lifetime measurements of the high spin yrast states in128Ce

Lifetime measurements of the high spin states in the yrast band of¹²⁸Ce were performed using the Doppler shift attenuation method in connection with the reaction¹⁰⁰Ru(³²S, 2p2n)¹²⁸Ce at incident energy of 141 MeV. In the vicinity of the band crossing, the previously reported anomalously highB(E2) value was not observed. The gross behavior of the normalized transition strength is approximate to symmetric rotor. It is confirmed that the trend of increase in collectivity with decreasing neutron number, which was indicated in the previous studies on^130,132,134Ce, continues in¹²⁸Ce. The value of quadrupole deformation parameterβ ₂ deduced from the measured lifetimes is in good agreement with the theoretical calculation using a cranking model based on a non-axially deformed Woods-Saxon potential.     

Lifetime measurements of the high spin yrast states in 128Ce

Lifetime measurements of the high spin states in the yrast band of ¹²⁸Ce were performed using the Doppler shift attenuation method in connection with the reaction ¹⁰⁰Ru(³²S, 2p2n) ¹²⁸Ce at incident energy of 141 MeV. In the vicinity of the band crossing, the previously reported anomalously high B(E2) value was not observed. The gross behavior of the normalized transition strength is approximate to symmetric rotor. It is confirmed that the trend of increase in collectivity with decreasing neutron number, which was indicated in the previous studies on ^{130, 132, 134}Ce, continues in ¹²⁸Ce. The value of quadrupole deformation parameter β₂ deduced from the measured lifetimes is in good agreement with the theoretical calculation using a cranking model based on a non-axially deformed Woods-Saxon potential.     

High-spin yrast and yrare structures in 112In

Up to now, no experimental cross-section data exist for the ⁶⁷Zn (n,a \alpha) ⁶⁴Ni reaction in the MeV neutron energy region. In the present work, the cross-section of the ⁶⁷Zn (n,a \alpha) ⁶⁴Ni reaction was measured at E _n = 6.0 MeV. Experiments were performed at the Van de Graaff accelerator of Peking University, China. Fast neutrons were produced through the D (d, n) ³He reaction using a deuterium gas target. Absolute neutron flux was determined by a small ²³⁸U fission chamber and a BF₃ long counter was used as a neutron flux monitor. A twin gridded ionization chamber was employed as the a \alpha -particle detector and two back-to-back ⁶⁷Zn samples were used for a \alpha events measurement. Background was measured and subtracted from foreground. The measured cross-section of the ⁶⁷Zn (n,a \alpha) ⁶⁴Ni reaction was 7.3 (1±15%) mb at 6.0MeV. The present result was compared with existing evaluations and TALYS code calculations.     

High-spin yrast isomer in theN=83151Er nucleus

An highspin yrast isomer (T_1/2 ? 420ns, E>10.286 MeV, 67/2≤ I≤ 71/2) is observed in the¹⁵¹Er nucleus excited in the¹¹⁶ Sn+⁴⁰ Ca reaction, using the recoil shadow method.     

High-spin yrast levels of 38Ar

High-spin states of ³⁸Ar have been studied with the ³⁵Cl(α, pγ)³⁸Ar reaction at E_α = 18 MeV and with the ²⁴Mg(¹⁶O, 2pγ)³⁸Ar reaction at $\text{E(}{}^{16}\text{O}\text{) = 38}\text{and}\text{45}\text{MeV}$. The ³⁸Ar level scheme is obtained with the former reaction from a proton-γ coincidence measurement. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization experiments have been performed with a Ge(Li)-Na(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{= 7}{}^{\mathrm{?}}\text{, 7}{}^{\mathrm{+}}\text{, 8}{}^{\mathrm{+}}\text{, 7}{}^{\mathrm{?}}\text{, 9}{}^{\mathrm{?}}\text{and}\text{11}{}^{\mathrm{?}}$to the ³⁸Ar levels at E_x = 7.51, 8.08, 8.57, 8.97, 10.17 and 11.61 MeV, respectively, are obtained. The 8.57 MeV, 8⁺ level has a mean life below 0.8 ps. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The experimental results are compared with shell-model calculations.     

High-spin states in123Te

The¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of⁸He. In addition to the known excited state of⁸He at E _x =3.6MeV, withJ ^π=2⁺, three additional states were found at excitation energies of 4.54(25)MeV, 6.03(10)MeV and 7.16(4)MeV.     

High-spin states in148Tb

High spin states of¹¹⁷Xe have been investigated by means of in-beam γ-ray spectroscopy using the reaction⁹²Mo(²⁸Si, 2pn) at beam energies of 100 to 120 MeV. The previously known νh_11/2 bands are confirmed and the νg_7/2 favored-signature band is extended up to 47/2⁺, in which two band crossings are observed at ?ω=0.33 and 0.44 MeV, respectively. Two new positive-parity bands have been established, one of which is most likely the νg_7/2 unfavored-signature band. A new transition cascade with irregular level spacings is also observed.     

High-spin states in121Te

The baryon density calculated at the collision center in relativistic heavy ion collisions is not representative for the density really probed by baryons in the high density collision phase. A decomposition into nucleon- and-resonance densities yields average values of 1.25N/o and 0.25/ ₀ at the time of maximum compression.work supported by GSI and BMFT     

High-spin states in165Hf

High-spin states in¹⁶⁵Hf, populated in the¹³⁰Te(⁴⁰Ca, 5n) reaction, were investigated using the Berkeley HERA -ray spectrometer array. The previously known level scheme of¹⁶⁵Hf is appreciably extended. Intrinsic configurations, band crossing frequencies and aligned angular momenta are interpreted within the frame-work of the cranked shell model. It is suggested that the alignments of the second neutron pair and of the first proton pair in¹⁶⁵Hf occur at 0.44 MeV and 0.48 MeV, respectively. The systematic trend of these alignment frequencies for the Hf isotopes and for theN=93 isotones is discussed.One of us (EMB) acknowledges a fellowship from the Hanns-Seidel Foundation. This work was supported by the Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U.S. Department of Energy (Contract DE-AC03-76SF00098) and by the Bundesminister für Forschung und Technologie BRD (Contract 06 BN 181).     

High-spin states in 208Pb

High-spin states in ²⁰⁸Pb have been studied by γ-ray-spectroscopy methods in deep inelastic reactions induced by beams of ²⁰⁸Pb, ¹³⁶Xe and ⁷⁶Ge beams on a thick ²⁰⁸Pb target. The 11⁺ ₂ state and new γ-transitions between the one-particle one-hole states of highest spin have been found and electromagnetic matrix elements verified. High-spin states of two-particle two-hole structure have been detected for the first time. The results are compared to shell model calculations with realistic interactions in the complete Kuo-Herling space. Received: 31 October 2000 / Accepted: 26 March 2001     

High-spin states in97Tc

The level scheme of⁹⁷Tc was studied by gamma ray spectroscopy using the⁹⁴Zr(⁶Li, 3nγ)⁹⁷Tc reaction. New levels and spins and parities were established.⁹⁷Tc is compared with the neighbouring even-even nucleus and with the results of an IBFM calculation.     

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.     

High-spin states in 61Cu

The study of high spin states in ¹⁰⁰Pd has indicated the presence of both single particle and collective states. More than twenty new transitions have been observed. A substantial modification and extension of the existing level scheme is proposed. The negative parity states can be understood in terms of collective excitations of the core coupled to the 9^? and 5^? bandheads, which are probably based upon two quasineutron ν(h_11/2,g_7/2) and two quasiproton π(g_9/2,p_1/2) configurations respectively.     

High-spin states in68Ga

The⁶⁸Ga nucleus has been studied via the reactions⁶⁵Cu(α, nγ)⁶⁸Ga atE _α=12–21 MeV and⁶⁶Zn(α, p nγ)⁶⁸Ga atE _α=25–40 MeV. The level scheme has been established by means of relative yield functions, electronic timing measurements, prompt and delayedγ-γ coincidences, angular distributions and directional orientation coÏncidences. Spins up to 11⁺ were assigned to levels up to 4 MeV excitation and the higher ones were interpreted by coupling a⁶⁷Ga core with a (v 1 g_9/2) neutron.     

High-spin states in107Sn

High-spin states in¹⁰⁷Sn were studied using the reaction⁵⁴Fe(⁵⁶Fe, 2pn)¹⁰⁷Sn. An odd-parity band was identified as based on thevh _11/2 orbit by measuring theγ-ray linear polarization. Also were confirmed the excited states based on thevd _5/2 andvg _7/2 orbits. The halflives of the 17/2⁺ and 11/2^? states were measured to be 0.25(4) ns and 28(11) ps, respectively. The experimental level structure and its interpretation were in good agreement with a shell model calculation.     

High-spin states in48Ti

The⁴⁵Sc(α, p γ) reaction has been investigated atE ^α=11, 12 and 13MeV. Theγ-decay of 198 levels in⁴⁸Ti up to 8,323 keV excitation energy has been observed. High-spin states were investigated by proton-γ ray angular correlation measurements atE=11 and 13MeV and by DSAM lifetime measurements atE=11 MeV. From the combined evidence spin (-parity) assignments were obtained for the levels atE _x =8,323 keV (J= 10,8,6), 8,091(12, 10, 8, 6), 7,668(10, 8), 7,427(9, 7), 7,374(11, 9, 7), 6,906(10, 8, 6), 6,172(8⁺,6⁺), 6,102(10⁺,8⁺), 6,039(6), 6,034(9⁺, 7⁺), 5,630(7), 5,197(8⁺), 5,169(7⁺), 5,155(5), 4,404(5), 4,398(6⁺) and 4,046keV (5). Most of the ambiguous spin assignments become unique if the 8,091 keV level hasJ=12, an assumption which is favoured by its excitation function. The level spectrum thus obtained is well reproduced by shell model calculations in the pure (f _7/2)⁸ configuration space. Discrepancies exist in the reproduction ofγ-decay modes. The reason is found in low-lying high-spin intruder states which include the 7,427 and 8,323 keV levels. The spectrum of negative-parity states is understood qualitatively by a comparison with⁴⁶Ti and⁴²Ca.     

High-spin states in110Cd

A comparison of the experimental and theoretical K/L conversion-intensity ratios of E0 transitions in the lead region is presented. No major differences were found, the overall agreement being better than 7%. However, with the present data, a systematic 5% deficiency of the measured values, as compared with the calculated ones, can not be ruled out.     

High-spin states in 128I

The high-spin states in 128I have been studied by using in-beam γ-ray spectroscopy with the 124Sn(7Li,3n)128I reaction at beam energies of 25, 28 and 42 MeV. A new level scheme including 20 new levels and 27 new γ-transitions for 128I has been established preliminarily.