Magnetic dipole moments of the145–149Eu ground states

Nuclear orientation measurements at low temperatures have been carried out on radioactive isotopes of^145–149Eu in Fe and of^147,149Eu in Gd. The initial-state orientation coefficients determined from the measured gamma-ray anisotropies yield the magnetic dipole moments of the europium nuclei with A=145, 146, 147, 148 and 149 to be 3.2(5), 1.7(3), 3.1(4), 2.1(3) and 2.5(5), Μ_N, respectively. The values obtained for odd-A nuclei follow the systematics of the 5/2⁺ state magnetic moments of the nuclei in this region and are close to the values given by the single-particle model.     

Collective excitations in148Gd populated in thep p′-reaction on a radioactive target

Collective excitations in the two-particle nucleus¹⁴⁸Gd up to 2.9 MeV have been investigated by thepp′-reaction at 25 MeV beam energy, and angular distributions have been analyzed with standard DWBA calculations. It is found that¹⁴⁸Gd has larger octupole- than quadrupole collectivity in the energy range investigated. The 3^? strength distribution is in quantitative agreement with predicted results for the levels formed by the coupling of two valence particles to the¹⁴⁶Gd core octupole phonon.     

The ground state mass of147Gd from single-neutron-transfer reactions and its impact on derived mass values

Using a¹⁴⁸Gd radioactive target and the (p,d), (d,t), and (³He,α) single neutron pick-up reactions we have measured the¹⁴⁷Gd mass excess as — 75,366(4) keV, which differs by 139(24) keV from the adopted value of the 1983 mass table. From this result, and from recently reported first transfer-reaction mass determinations for¹⁴⁵Eu and¹⁴⁶Eu, we have recalculated the masses of nuclei above¹⁴⁶Gd from a previous shell model analysis of high-spin states.     

In-beam γ-ray spectroscopy on56Ni

Yrast levels in the doubly-magic nucleus⁵⁶Ni have been studied by in-beam gg-spectroscopy with the reaction⁵⁴Fe(α, 2n)⁵⁶Ni. A cascade of five γ -transitions is established. A shell model calculation of 2p2h, T=0 states, using empirical matrix elements, suggests the assignments 8⁺ and 10⁺ for the two highest levels.     

Particle plus octupoleM2/E3 isomers and high-spin particle-hole states in147Tb and148Tb

The level structures of theN=82 andN=83 nuclei¹⁴⁷Tb and¹⁴⁸Tb have been studied by means of (α, 8n) and (α,7n) reactions induced by 68 to 110 MeVα particle bombardments of¹⁵¹Eu targets. In-beam conversion electron measurements have established that isomers withT _1/2=4.8(6)ns in¹⁴⁷Tb andT _1/2=22(1)ns in¹⁴⁸Tb decay byM2+E3 transitions to the ground states. The measuredB(E3) values show that the isomeric states arise from the coupling of the valence nucleon(s) to the¹⁴⁶Gd core octupole. Particlephonon coupling in these nuclei and in the one-neutron nucleus¹⁴⁷Gd is discussed and compared with well known cases involving the²⁰⁸Pb core. The higher lying yrast states in the two Tb nuclei are described as shell-model particle-hole excitations using empirical single particle energies and nucleon-nucleon interactions.     

Shell model isomers near Z = 64, N = 82: g-factors of Yrast states in 146Gd and 147Gd

Nuclear g-factors have been measured for the 7^? isomer in ¹⁴⁶Gd and for the $\text{27}\text{2}{}^{\mathrm{?}}$ isometer in ¹⁴⁷Gd. For ¹⁴⁷Gd the results is consistent with the expectation for a pure shell model configuration.     

Shell model and octupole states in148Gd from in-beam experiments

Through (α, 4n) and (τ, 3n) reactions the high-spin states in the two-neutron nucleus¹⁴⁸Gd were populated up toI ^π=21? at 7.2 MeV, including numerous states above the yrast line. The¹⁴⁸Gd energy spectrum is interpreted in terms of the spherical shell model. Identification of the (νf _7/2 i _{1 3/2})_10? state gives the νi _13/2 single particle energy free of octupole admixtures as 2.1(1) MeV. Eight high-spin states between 1.2 and 3.7 MeV were identified as the couplings of the two valence-particles to the¹⁴⁶Gd octupole phonon, and three above-lying levels are assigned as double-octupole excitations including a 12⁺ state which decays by anE3-E3 stretched cascade. All these octupole levels can be quantitatively predicted from the one-particle x phonon spectrum of¹⁴⁷Gd. The high-spin states above 3 MeV are four-quasiparticle excitations ofπ ⁺¹ π ^?1 ν ² andπ ² ν ² type and their energies are in good accord with shell model estimates.     

Particle hole yrast states in146Gd and147Gd and the Z=64 shell closure

The level structures of¹⁴⁶Gd and¹⁴⁷Gd have been investigated by in-beamγ-ray ande ^? spectroscopy with (α, xn) reactions on enriched Sm targets. Detailed level schemes up to ～4 MeV, which differ radically from earlier schemes, are reported. The energy levels are characterized as particle-hole excitations using empirical single particle energies and two nucleon interactions. Analysis of pure 1p 1h proton excitations demonstrates that theZ=64 andN=82 energy gaps are about equally large.     

Revised single-particle energies in N=83 nuclei

Half-life measurements show that the lowest high-j state in ¹⁴¹Ce, ¹⁴³Nd, ¹⁴⁵Sm, and ¹⁴⁷Gd, earlier assigned as an h_9/2 fragment, is an i_13/2 single-neutron excitation which previously was thought to lie above 3 MeV in the N = 83 nuclei.     

Production and identification of100Sn

We report the first observation of the doubly-magic nucleus¹⁰⁰Sn. This isotope was produced by nuclear fragmentation of¹²⁴Xe projectiles at 1095 A·MeV using the heavy-ion synchrotron SIS at GSI, Darmstadt. The projectile fragments were separated in flight with the projectile-fragment separator FRS and identified by measuring event by event the magnetic rigidity, the time of flight and the energy deposition.     

A new neutron-deficient isotope,235Am

The level scheme of theN=82 nucleus¹⁴⁵Eu has been extended toI=(55/2) andE _x =11.2 MeV in an experiment with the Tessa Compton-suppressed Ge detector array using the¹²⁷I(²²Ne,4n) reaction. Most of the complicated and irregular level scheme of¹⁴⁵Eu can be interpreted as proton multi-quasiparticle states in comparison to the ₆₄ ¹⁴⁶ Gd₈₂ core nucleus but also excitations across the neutronN=82 core have been observed.     

Excited states in145Gd from the (3He, 2n) reaction

Medium and high spin states in¹⁴⁵Gd up to 3.5 MeV excitation energy have been studied by in-beam gamma ray and conversion electron spectroscopy bombarding enriched¹⁴⁴Sm target with a³He beam. For a part of the identified levels a configuration is proposed in terms of weak coupling of one neutron hole with the¹⁴⁶Gd core or of one neutron particle with the¹⁴⁴Gd core.     

Magnetic moments of nuclei around146Gd

Nuclear orientation measurements down to 2.5 mK have been performed on implanted sources of¹⁴⁶Eu,¹⁴⁷Gd and¹⁴⁹Gd in iron. Using a two site model interaction frquencies were deduced from the data. From these, ratios of magnetic moments have been derived as ¦(¹⁴⁸Eu)/(¹⁴⁶Eu)¦=1.90±0.20 and ¦(¹⁴⁹Gd)/(¹⁴⁷Gd)¦=0.86±0.05.     

Production of high multiplicity yrast isomers in147Gd and146Gd in a-particle induced reactions

High spin isomers in ¹⁴⁷ Gd and ¹⁴⁶ Gd have been produced in (α, xn)reactions, and their half-lives, excitation energies and maximum spins have been determined. It is proposed that these isomers are identical with those recently observed in bombardments with ⁵⁰ Ti and ⁴⁰ Ar projectiles.     

Medium-spin levels and the character of the 20.4 ns 132+ isomer in 145Gd

Levels of the N = 81 nucleus ¹⁴⁵Gd have been investigated by in-beam γ-ray and conversion electron spectroscopy with the ¹⁴⁴Sm(³He, 2n) reaction. Fourteen new low- and medium-spin states between 1.0 and 2.4 MeV excitation, the known yrast levels up to spin $\text{21}\text{2}{}^{\mathrm{+}}$, five other high-spin non-yrast states and a new 20.4 ns $\text{13}\text{2}$ isomer at 2200.2 keV in ¹⁴⁵Gd have been observed. The isomer decays via a fast 927.3 keV E3 transition with B(E3) = 48 ± 7 W.u. Another weaker decay branch is a mixed, strongly hindered E1 + M2 + E3 transition to the $\text{v}\text{h}{}^{\mathrm{?1}}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ state. We propose an octupole $\text{v}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{j}{}^{\mathrm{?2}}\text{× 3}{}^{\mathrm{?}}$ main configuration for the isomer, analogous to the 997 keV $\text{13}\text{2}{}^{\mathrm{+}}$ isomer in ¹⁴⁷Gd. The levels of ¹⁴⁵Gd are discussed on the basis of the spherical shell model.     

Hyperfine Interactions of Pm in Nd and Gd Hosts

Time differential perturbed angular correlation measurements were carried out using short lived isomeric 5/2⁺ state in ¹⁴⁷Pm to investigate the magnetic and electric hyperfine interactions in Nd and Gd hosts at different temperatures. At 10 K the magnetic hyperfine fields at ¹⁴⁷Pm in Nd and Gd hosts are 361(42) kG and 256(30) kG, respectively, and are very low as compared to the free-ion value while the electric field gradients are of comparable order. The magnetic hyperfine field in Gd is constant with temperature. The results are interpreted in terms of singlet ground state of Pm ion. This revised version was published online in September 2006 with corrections to the Cover Date.     

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.     

Measurement of the147Gd mass excess by the (12C,9Be) reaction

The mass excess of the¹⁴⁷Gd nucleus was measured from the¹⁴⁴Sm(¹²C,⁹Be)¹⁴⁷Gd reaction using the 72 MeV¹²C beam of the Orsay MP Tandem and the “Bacchus” magnetic spectrometer. The measurement is auto-calibrated by the¹⁰Be spectrum from the¹⁴⁴Sm(¹²C,¹⁰Be) reaction. The derived value of the mass excess of¹⁴⁷Gd is ?75.401±0.025 MeV. It is compared with other recent results and with calculated values.     

Lifetimes of rotational levels in170W

Lifetimes of the first 2⁺, 4⁺ and 6⁺ levels in¹⁷⁰W have been measured by the recoil-distance method based on the Doppler effect, using the¹⁵⁵Gd (²⁰Ne, 5n)¹⁷⁰W reaction. The following conclusions can be drawn from the results: if there are any deviations from the predictions of the rotational model for the lifetimes of the 4⁺ and 6⁺ states, they are smaller than 8.5 %; if this model accurately describes the nucleus¹⁷⁰W, the intrinsic quadrupole moment of this nucleus is: Q₀=5.93±0.06 barns, and its deformation is: β=0.240±0.003. The value of Q₀ is compared with the predictions of various calculations for the tungsten isotopes.