Confirmation of the superdeformed band in192Pb

High-spin states in¹⁹²Pb were populated via the reaction¹⁷³Yb(²⁴Mg,5n) at a beam energy of 140 MeV, and the resulting-rays were deteced using GAMMASPHERE. A previously observed superdeformed band in¹⁹²Pb has been confirmed.     

Rotational damping motion in nuclei

The recently proposed model to explain the mechanism of the rotational motion damping in nuclei is exactly solved. When compared with the earlier approximative solution, we find significative differences in the low excitation energy limit (i.e. ). For the strength functions we find distributions going from the Wigner semicircle through gaussians to Breit-Wigner shapes.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday. Work supported in part by the DFG and Cicyt, project PB88-0177     

Study ofγ radiation from100Pd decay

This paper presents a study of the rays from the electron capture decay of 3.63d ¹⁰⁰Pd. Singles and coincidence measurements provided an accurate determination of-ray intensities and an improved knowledge of the¹⁰⁰Rh level scheme. Experimental evidence supports excitation of levels in¹⁰⁰Rh at 86-, 136- and 154 keV, not previously reported from the decay of¹⁰⁰Pd.On leave from Departamento de Fisica, Comision Nacional de Energia Atomica, Buenos Aires, Argentina     

Identification of near-spherical multiparticle-hole states in89Tc

he so far unknown nucleus¹⁴⁷Er has been identified by means of - recoil and — coincidences through the reaction⁹²Mo(⁵⁸Ni,2pn) at a bombarding energy of 260 MeV. The level scheme has been obtained up to 5.0 MeV of excitation energy and shows collective excitations built on the h_11/2 intruder orbital.     

γ-decay of the particle-hole states with the highest spins in208Pb

²⁰⁸Pb has been excited with inelastic heavy ion scattering of 350 MeV⁶⁴Ni and 420 MeV⁸²Se on a thick²⁰⁸Pb target. With - coincidence measurements 2 new decays of the 10⁺ isomer, namely a 34.5 keVE2-transition to 8 ₂ ⁺ and a 857.7 keVE3 transition to 7^– have been found and the wavefunctions of the participating levels deduced. An observed gamma cascade of 295.3, 348.0, 865.4 and 340.2 keV on top of the 10⁺ isomer is assigned to the particle-hole states with the highest spins 14^– 6744.1 keV13^– 6448.9 keV12⁺ 6100.9 keV11⁺ 5235.6 keV10⁺ 4895.4 keV.This work has been supported in part through the agreement on scientific cooperation between Poland and Germany.     

Spin and parity of isomeric and ground states of the doubly-odd nucleus184Au

Low-spin states in doubly-odd¹⁸⁴Au have been populated in the ⁺/EC decay of¹⁸⁴Hg produced by bombarding¹⁸⁴Sm targets with an 185 MeV⁴⁰Ar beam. Radioactive Hg nuclei were transported by a He jet system. A new level scheme has been established from --t and X--t coincidence measurements. Spin and parity values I=5⁺, I =2⁺ and I=3^– were assigned to the ground state and the two isomeric states of¹⁸⁴Au, respectively. The structure of these states is discussed using B(E1) values.     

Fine structure of the strength function for β<Superscript>+</Superscript>/<Emphasis Type="Italic">EC</Emphasis> decay of <Superscript>160<Emphasis Type="Italic">g</Emphasis></Superscript>Ho (25.6 min)

A strength function for the β⁺/EC decay of the deformed ^160g Ho (25.6 min) nucleus has been obtained from experimental data. The fine structure of the strength function S _β(E) is analyzed. It is found to have a pronounced resonant structure for Gamow-Teller transitions. In S _β(E) with μ_τ = +1 the Gamow-Teller resonance has been observed to split into two components. This splitting is associated with anisotropy of isovector density oscillation in deformed nuclei. The β⁺/EC strength function for first-forbidden transitions is obtained in the Coulomb (ξ) approximation. It is shown that S _β(E) for first-forbidden transitions does not have a pronounced resonant structure. The text was submitted by the authors in English.     

Nuclear structure study of the neutron deficient cadmium isotopes100, 101, 102Cd

The neutron-deficient nuclei^100,101Cd were identified for the first time in — beam following the reactions⁵⁸Ni +^46,48Ti and⁵⁸Ni +⁵⁰Cr at 230 MeV and 245 MeV bombarding energy of the⁵⁸Ni beams. The-decay of the isotopes^100,101,102Cd was studied inp, pp,n, nn, andn prompt and delayed coincidence spectra. Isomers were found with spin and half life {ie1-01}=8⁺, T_1/2=52(5) ns in¹⁰⁰Cd, {ie1-02}=(19/2⁺), T_1/2=4.6(4) ns in¹⁰¹Cd and {ie1-03}=8⁺, T_1/2=56(4) ns in¹⁰²Cd. In a PAD experiment theg-factor of the {ie1-04}=8⁺ isomer in¹⁰⁰Cd was measured to be g=1.24(6). Using the reaction³⁶Ar +⁷⁰Ge at 135 MeV energy of the³⁶Ar beam, theg-factor and the quadrupole moment of the {ie1-05}=8⁺ isomer in¹⁰²Cd were measured to be g=1.29(3) and Q=87(10) fm², respectively. The spectroscopic results are discussed within a shell model approach using a¹⁰⁰Sn core, which accounts well for the electromagnetic properties of the proton aligned isomers. The structure of the spherical neutron states, dominated by the close lying vd_5/2, g_7/2 orbitals, and the gradually developing quadrupole collectivity are reproduced by the shell model calculations.The authors gratefully acknowledge fruitful discussions with K. Heyde and are indebted to him for communicating unpublished theoretical results. The help of N.A.F.M. Poppelier and A.G.M. van Hees in running the RITSSCHIL code is very much appreciated.     

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).     

Experimental beta-decay energies of very neutron-rich isobars with mass numbers A=101 and A=102

TheQ -values of¹⁰¹Rb,^101,102Sr and^101,102Y have been measured for the first time at the mass separator ISOLDE by means of-coincidence techniques with a plastic scintillation detector telescope and a large Ge(HP)-detector. For some of these nuclei, also new details of their decay schemes could be derived from the measured-decay properties. The experimental results are discussed, as far as the systematics of two-neutron separation energies derived from them is concerned. In addition, the nuclear masses deduced from theseQ -values are compared with the predictions of recent mass calculations.Dedicated to Prof. Dr. Peter Armbruster on the occasion of his 60th birthday     

Coulomb excitation of154Sm

The deformed nucleus¹⁵⁴Sm was studied by Coulomb excitation with NORDBALL by using a⁵⁸Ni beam. The ground-state band, the beta band, the gamma band and the octupole band (K=0-) were excited up to the 16+ state, the 6+ state, the 6+ state and the 13-state, respectively. A new band was established from 6+ to 14+ on the basis of the gamma-gamma coincidence spectra. The excitation probability of the new band is larger than that of the beta band.We would like to thank Dr. G. Sletten, Mr. J. Westergaard and the members of TAL, Niels Bohr Institute for their kind support. A part of this research is supported by Monbusho International Scientific Research Program (Joint Research No.01044037).     

Study of theβ +/EC decay of the neutron deficient nuclei76,78Sr and79Y

The +/EC decay of the neutron deficient nuclei^76,78Sr and⁷⁹Y was studied employing mass separated molecular beams of SrF⁺ and YF₂ ⁺ from the ISOLDE mass separator. The halflives of^76,78Sr and⁷⁹Y were measured as t_1/2=8.9(3)s, 159(8)s and 14.4(15)s, respectively, and decay schemes were established for⁷⁶Sr and⁷⁹Y. In the⁷⁸Sr decay 10 new -ray transitions were identified.     

Electromagnetic decay of the 6+ isomer of102Rh

Conversion electrons, and X rays from¹⁰²Rh^m (6⁺,T _1/2=1057 d) have been studied. An electromagnetic branch (2.3±0.3) ·10^–3 feeding the¹⁰²Rh first excited state has been observed in the 6⁺ isomeric decay. The excitation energy of the 6⁺ isomer turns out to be 140.7 keV above the 2^– ground state.We wish to thank P. Del Carmine, M. Ottanelli, and A. Pecchioli for their skillful collaboration during the measurements and the Technical Staffs of LNS and LNL for operation of the Tandem Accelerators.     

M1-transitions and the mutual orientation of the unpaired nucleons in odd-odd nuclei

Experimental lifetimes and branching ratiosB(M1)/B(E2) are used to determine reduced M1-transition probabilities between collective-band levels withI=1 in^{102, 104, 106}Ag and in the odd-odd isotopes of La, Pr, Pm and Tl. The extractedB(M1) values are compared with calculations in the framework of the quasiclassical approximation and the model axial rotor+two quasiparticles. The reduced M1-transition probabilities along with the magnetic moments were found to depend on the mutual orientation of the angular momenta of the unpaired nucleons in the odd-odd nuclei.The authors would like to thank the staffs of Cyclotron Laboratory of P.T.I. in St. Petersburg and the Nuclear Moments Laboratory of I.N.R. in Kiev for assistance in the experiments. One of us (A.I.L.) wishes to thank the Sektion Physik of the Ludwig Maximilians Universität München for its hospitality and financial support.     

Can strong electric dipole transitions in deformed rare earth nuclei be explained by the macroscopic behavior of the octupole phonon?

StrongE1 transitions of greater than 10^–3 Weisskopf units occur in many octupole states in the deformed rare earth region. It is shown using the droplet model that the electric dipole moment resulting from the macroscopic behaviour of the octupole phonon cannot by itself account for the observedE1 strengths, and it is observed that this result is consistent with the proposal of Donner and Greiner and of Zilges von Brentano and Richter that admixtures of the giant dipole resonance into the low energy octupole states are responsible for the fastE1 transitions. It is also suggested that calculations similar to those performed by Egido and Robledo forN 92 nuclei may be able to reproduceE1 transitions inN=94–104 nuclei.Supported by the National Science Foundation and the State of Florida     

Gamow-Teller beta decay of the very neutron-deficientN=50 nuclide98Cd

For the first time, detailed decay-spectroscopic investigations were performed for the very neutron-deficientN=50 nuclide⁹⁸Cd. The⁹⁸Cd activity was produced in spallation reactions between 600 MeV protons and a natural tin target, yielding a⁹⁸Cd beam intensity of 10 to 60 atoms/s at the collector of the ISOLDE massseparator. By means of-ray and conversion-electron spectroscopy, 19 transitions were found to follow the ⁺/EC decay⁹⁸Cd⁹⁸Ag. The transitions at 61 and 107 keV were shown to beM1(+E2) andE2, respectively, and the⁹⁸Cd half-life was measured as 9.2±0.3 s. TheQ _EC value of⁹⁸Cd is determined semiempirically and is compared to model predictions together with the measuredQ _EC values of the neighbouring cadmium isotopes^100,102Cd and theN=50 isotones⁹²Mo,⁹⁴Ru, and⁹⁶Pd, taken from the literature. The newly established decay scheme of⁹⁸Cd includes 9 excited states of⁹⁸Ag. Four states at 1691, 1861, 2164, and 2544 keV are directly fed by 0⁺ 1⁺ Gamow-Teller beta transitions with a summed strength of 3.5 _–0.7 ^+0.8 . This value corresponds to 25±5% of the strength predicted for the GT transformation of a g_9/2 proton (in⁹⁸Cd) into a g_7/2 neutron (in⁹⁸Ag) by the extreme single-particle shell model. The GT-strength splitting and quenching, observed for⁹⁸Cd, are compared with the corresponding data for lighter even-even N=50 isotones, and are discussed with reference to the predictions of more sophisticated nuclear models. We find that only in some cases it is possible to explain qualitatively the observed GT strength distribution and its total magnitude without renormalizing the free-neutron value of the axial-vector coupling constant.Dedicated to Prof. P. Armbruster on the occasion of his 60th birthday     

The structure of28Si above 10 MeV excitation energy II: Assignments of quantum numbers

New assignments of quantum numbers have been obtained for more than 50 levels in²⁸Si between 8953 and 15915 keV excitation energy. They are based on the measurement of -ray angular distributions or anisotropies on 29 resonances of the²⁷Al(p, ) reaction and on the²⁴Mg(a, ) resonance atE =3355 keV. A total of 15 high-spin states withI=5–7 has been obtained and the spectrum ofT=1 states has been identified up to 15915 keV excitation energy and a maximum spinI=6.     

High-spin states of odd-odd156Ho

High spin states in the nucleus¹⁵⁶Ho have been studied via the fusion-evaporation reaction¹⁴⁰Ce(¹⁹F,3n)¹⁵⁶Ho at the beam energy of 82 MeV.- coincidences, E, I and excitation functions have been measured. With two rotationally-aligned bands identified as [h_11/2] [i_13/2], we found two new bands with a signature splitting, whose structure is believed to arise from either [h_9/2] or [f_7/2] coupled to [h_11/2]. Our placement of rays belonging to these new bands suggests that the previously known level scheme should be corrected. We also found many new low-energy rays in the low excitation energy. As compared to¹⁵⁴Ho, the present nucleus with two more neutrons becomes more collective, and shows well-observed rotationally-aligned bands with a clear signature splitting.Communicated by B. Herskind     

The (EC+β+) decay of153Er

¹⁵³Er has been produced by irradiation of¹⁴²Nd with¹⁶O,and studied using a He-jet recoil tape transport system.A decay scheme is proposed for the first time,based on X- and - coincidence measurements, which takes account of 12 observed -rays.This work was supported by Academia Sinica     

On the newly proposed levels in152Gd and152Sm

It is shown that there is no evidence for the existence of levels at 1312.41, 1485.67 and 1698.34 keV in¹⁵²Gd and at 1436.65 and 1681.56 keV in¹⁵²Sm, which were recently claimed to be observed in the decay of¹⁵²Eu(3^–, 15 y).Work supported in part by the Natural Science Fund of China and in part by the Department of Science and Technology of China Nuclear Energy Industry Corporation