Decay energies of the low-spin states of147Tb and148Tb

Using¹¹²Cd(⁴⁰Ar,pxn) reactions andγ-ray spectroscopy, the EC/β ⁺ and EC(K)/β ⁺ probability ratios were determined for individualβ-transitions in the¹⁴⁷Tb(1.6 h)→¹⁴⁷Gd and¹⁴⁸Tb(60 min)→¹⁴⁸Gd decays. Under assumption of applicability of theoretical ratios for allowedβ-decays on the first-forbidden nonunique transitions studied here, the experimental ratios were converted into information on decay energies. Combining the results with the known masses of^147,148Gd andQ _α values of neutron-deficient holmium-to-lutetium isotopes, mass excesses could be determined for¹⁴⁷Tb,¹⁴⁸Tb, low-spin¹⁵¹Ho, low-spin¹⁵²Ho,¹⁵⁵Tm,¹⁵⁶Tm and¹⁵⁹Lu.     

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 in147Tb

The level scheme of¹⁴⁷Tb has been extended to 116 levels and 198 transitions in two experiments with the OSIRIS Compton suppressed detector array at the HMI Berlin with the reactions¹²²Sn(³¹P, 6n)¹⁴⁷Tb at 160 MeV and¹²⁰Sn(³¹P, 4n)¹⁴⁷Tb at 152 MeV. Evidence for a new high spin isomer atE=7664.1 keV with a life-time of the order of 2 ns has been found.     

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.     

Continuous gamma radiation feeding high-spin isomers in 148, 149, 151, 152Dy and 147Gd

The energy, multipolarity and multiplicity spectra of the continuum gamma radiation feeding high-spin isomers in ^{148, 149, 151, 152}Dy and ¹⁴⁷Gd have been measured at several bombarding energies. The final nuclei were selected via a delayed coincidence technique while the use of a NaI(Tl) Compton shielded crystal allowed the primary gamma-ray spectra to be generated reliably from the observed spectra.It was found that: (i) the energy of both the gamma-ray statistical cascade and the neutron cascade increases with increasing excitation energy, the latter much more rapidly than expected; (ii) the multiplicity of gamma-ray cascades, in which a statistical transition was detected, is generally lower than that of the average cascade; (iii) stretched E2 spin-correlated transitions occur above $\text{J? 39}\text{h}\text{?}\text{in}{}^{152}\text{Dy}$ and above $\text{～ 50.5}\text{h}\text{?}\text{in}{}^{147}\text{Gd}$, indicating the onset of collectivity at these spins — in addition, a region of predominantly dipole emitting states is located below $\text{T? 44}\text{h}\text{?}\text{in}{}^{147}\text{Gd}$; (iv) effective moments of inertia derived from the bump edge are 50–100% larger than those deduced from the density of stretched E2 transitions in the bump; (v) in ^149,151Dy the bump edge is very sharp but no multiplicity features are observed; (vi) although the four Dy isotopes were populated at approximately the same excitation energy, they display considerable differences in their continuum properties.Probable interpretations of these observations are discussed, in particular we have suggested that several of the observed effects are consistent with the possible presence of high-K collective bands above the yrast line.     

Yrast isomers and very high spin states in 148, 149, 151, 152Dy and 147Gd

We have studied level schemes for the feeding and decay of high-spin isomers in the nuclei ^{148, 149, 151, 152}Dy and ¹⁴⁷ Gd. A variety of techniques involving γ-ray spectroscopy with pulsed heavy-ion beams have been applied including linear polarization, γ-γ correlations and recoil distance measurements.The general aspect of these level schemes is in accordance with the idea that the states near and along the yrast line can be described by a spheroidal shell model in which the nucleus is axially symmetric with respect to the total spin. In these cases the spin is generated not by collective rotation, but by alignment of many single-particle orbits around a common axis.     

Seniority-three yrast states in theN=82 nucleus147Tb

Firm spin-parity assignments for the high-spin states up to 3.5 MeV in the one-proton nucleus¹⁴⁷Tb were obtained from¹⁴⁴Sm(⁶Li, 3n) in-beamγ-ray and conversion electron measurements. The energies of these two-particle one-hole excitations were calculated from the shell model with empirical nucleon-nucleon interaction energies. The calculated energy splittings agree well with experiment, whereas the theoretical excitation energies disagree by ?1 MeV if recently measured ground state masses are used.     

Magnetic moments,E3 transitions and the structure of high-spin core excited states in 211Rn

The results of g-factor measurements of high-spin states in ²¹¹Rn are: $\text{E}{}_{\mathrm{<mtext>x</mtext>}}\text{= 8856 + Δ′}\text{keV}\text{(J}{}^{\mathrm{\pi }}\text{=}\text{63}\text{2}{}^{\mathrm{?}}\text{)}$, g = 0.626(7); $\text{6101 + Δ′}\text{KeV}\text{(}\text{49}\text{2}{}^{\mathrm{+}}\text{), 0.766(8)}$; $\text{5347 + Δ′}\text{KeV}\text{(}\text{43}\text{2}{}^{\mathrm{?}}\text{), 0.74(2)}$; $\text{3927 + Δ}\text{KeV}\text{(}\text{35}\text{2}{}^{\mathrm{+}}\text{), 1.017(12)}$; $\text{1578 + Δ}\text{KeV}\text{(}\text{17}\text{2}{}^{\mathrm{?}}\text{), 0.912(9)}$. These results together with measured E3 transition strengths and shell model calculations are used to assign configurations to the core excited states in ²¹¹Rn. Mixed configurations are required to explain the g-factors and enhanced E3 strengths simultaneously.     

Decays of millisecond isomers in odd-oddN=81 nuclei146Tb,148Ho and150Tm

Following reactions induced by 245 MeV⁶⁰Ni ions, isomers have been identified in the odd-oddN=81 isotones¹⁴⁶Tb,¹⁴⁸Ho and¹⁵⁰Tm with half-lives of 1.18(2), 2.35(4) and 5.2(3) ms, respectively. Their decays have been characterized byγ-ray spectroscopy. The isomers are interpreted as (πh _11/2 νh ₁ ^2/?1 ) 10⁺ states decaying to members ofπh _11/2 νd ₃ ^2/?1 andπh ₁₁ ^2/?1 multiplets. The observed level spectra and M1 branching ratios are found to be in good agreement with shell model predictions based on empirical and Schiffer-Trueπν ^?1 residual interactions.     

Excitation of high-spin particle-hole states in A = 28 nuclei by 27Al(α, t) and (α, 3He) reactions

The ²⁷Al(α, t) and (α, ³He) reactions have been measured at E_α = 64.5 MeV. The experimental angular distributions were analyzed by the exact finite-range DWBA calculations assuming a nucleon stripping mechanism. The distributions of spectroscopic strengths for the single-particle transitions with transferred angular momenta l = 0, 1, 2, 3 and 4 have been obtained. The strengths for the transitions to the stretched 6^? states in ²⁸Si and ²⁸Al are compared to those obtained from inelastic scattering on ²⁸Si. The present results show no distinctive differences in the structures for 6^?T = 0 and 1 states in ²⁸Si such as are observed in proton and pion inelastic scattering on ²⁸Si.     

Yrast and high-spin states in 22Ne

High-spin states in ²²Ne have been investigated by the reactions ¹¹B(¹³C, d)²²Ne and ¹³(¹¹B, d)²²Ne up to $\text{E}{}^1\text{～- 19}\text{MeV}$. Yrast states were observed at 11.02 MeV (8⁺) and 15.46 MeV (10⁺) excitation energy. A backbending in ²²Ne is observed around spin 8⁺. The location of high-spin states I ≦ 10 is discussed in terms of the rotational band structure, Strutinsky-type calculations, and pure shell-model predictions.     

Isomers and high-spin states in 205At

The properties of high-spin states in ²⁰⁵At have been investigated to $\text{J ?}\text{37}\text{2}$ and an excitation energy of > 4.0 MeV. The properties of the $\text{29}\text{2}$⁺ isomer at 2340 keV have been established and those of the $\text{25}\text{2}$⁺ isomer at 2063 keV have been further investigated. In the present study the mean lives of these isomers have been determined as 11.2±0.2μs and 98±2 ns respectively. The M2 branch of the $\text{13}\text{2}$⁺ state at 970 keV to the $\text{9}\text{2}$⁺ ground state has been measured. This decay is attributed to a proton single-particle $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{→}\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ transition. The trend of excitation energies of a number of proton excitations in the odd-mass nuclei from ²¹¹At to ²⁰¹At has been compared to the corepolarization model and the average $\text{ν}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}\text{π}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ interaction energy has been deduced. Comments are made upon probable configurations for many of the levels.     

New high-spin states of 147Nd and 145Ce: Octupole correlation in the N = 87 isotones

High-spin states of the N = 87 nuclei, ¹⁴⁷Nd and ¹⁴⁵Ce, have been populated in the ¹²C + ²³⁸U and ¹⁸O + ²⁰⁸Pb fusion-fission reactions at 90 MeV and 85 MeV bombarding energy, respectively. The emitted γ-radiation was detected using the Euroball III and IV arrays. High-spin states of the ¹⁴⁷Nd isotope have been identified for the first time. The high-spin yrast and near-to-yrast structures of the ¹⁴⁵Ce nucleus have been considerably extended. The newly observed structures, discussed by analogy with the neighbouring isotones, show the coupling of an h_9/2 neutron to the quadrupole and octupole excitations of the core.     

Systematics of high-spin isomers in N = 83 isotones and a high-spin isomer beam

Isomers in N = 83 isotones of Z = 60-66, were studied systematically. Their spins and parities are 49/2⁺ and 27⁺ for odd and odd-odd nuclei, respectively. Nearly constant excitation energies of these isomers indicated a decrease of a Z = 64 shell gap energy as Z decreases from 64 to 60 within the framework of a deformed independent-particle model (DIPM). Their configurations are [ν(f _7/2 h _9/2 i _13/2),π(h _11/2)²]_49/2+ and [ν(f _7/2 h _9/2 i _13/2),π(h _11/2)²(d _5/2)^-1]₂₇₊ for odd and odd-odd nuclei, respectively. The shape of the yrast states changes suddenly at spin 49/2(odd) and 27(odd-odd) from a near spherical to an oblate shape. Transitions from isomers are highly hindered because of the shape changes. They may be categorized to be shape isomers. The development of a secondary beam produced by using these high-spin isomers is also described. Received: 1 May 2001 / Accepted: 4 December 2001     

Shape coexistence and high-spin states in 28Si

The spectrum of ²⁸Si is investigated within the cranked Nilsson-Strutinsky model with all kinds of many-particle-many-hole excitations accounted for. Calculated excitation energies and quadropole moments are compared with experimental data. The recently observed backbend from 8⁺ to 10⁺ is suggested to be caused by the crossing of the oblate ground band with a prolate or slightly triaxial band having one proton and one neutron excited to the fp shell.     

Yrast traps and high-spin states in 210Rn

Yrast and near-yrast states have been investigated in ²¹⁰Rn to high spin (J > 30) and high energy (E_x > 10 MeV). Three different (HI, xn) reactions were used to populate the states of interest and several different γ-ray spectroscopic techniques were utilized. Three high-spin yrast traps were discovered. Two de-excite by strong E3 transitions while the third decays mainly via an extremely inhibited E2 transition. The E3 decays are interpreted as allowed single-particle transitions between proton or neutron states above the ²⁰⁸Pb shell closure while the inhibited E2 transition is interpreted as indicating a substantial change in structure as the decay proceeds down the yrast line. The interpretation has been given in terms of shell-model calculations.     

Yrast level structure of the neutron-deficient N = 80 isotones 146Dy, 147Ho and 148Er up to high-spin values

High-spin level schemes of the N = 80 isotones ¹⁴⁶Dy, ¹⁴⁷Ho and ¹⁴⁸Er have been investigated by in-beam γ-ray spectroscopic methods using the NORDBALL Compton-suppressed multidetector array including proton and neutron selection. The projectile-target system ⁵⁸Ni + ⁹²Mo at 260 MeV beam energy has been used to produce the neutron-deficient N = 80 isotones. The previously known schemes have been extended to considerably higher spin and exitation energy, up to I = 23?, E _x≈ 8.9 MeV in ¹⁴⁶Dy, I = 53/2?, E _x≈ 8.7 MeV in ¹⁴⁷Ho and I = 23?, E _x≈ 9.6 MeV in ¹⁴⁸Er. The results are discussed in terms of the spherical shell model. Many of the levels can be described within this framework. Received: 12 January 2001 / Accepted: 11 April 2001     

Structure of high-spin states in 143Pm

High-spin states of ¹⁴³Pm have been studied in the reactions ¹⁴¹Pr(α, 2n)¹⁴³Pm and ¹⁴³Nd(d, 2n)¹⁴³Pm by means of in-beam spectroscopy. The level scheme, spin and parity assignments are based on results obtained from singles γ-ray spectra, conversion electron spectra, prompt and delayed γ-γ coincidences, γ-ray angular distribution and linear polarization measurements. Positive- and negative-parity states with energies up to 4580 keV and spins up to $\text{25}\text{2}$ have been established including 22 new levels. For two nanosecond isomeric states the nuclear spin precession in an external magnetic field was observed providing the following g-factors:

$\text{g(}\text{11?}\text{2}\text{, 959.7 keV)=1.14(9), g(}\text{15+}\text{2}\text{, 1898.3 keV)=1.00(7).}$

The experimental results are well understood by calculations which have been performed in the framework of the shell model (for positive-parity states of 11 valence protons above a Z = 50, N = 82 core) and of the cluster-vibration model (for 3 holes in a Z = 64, N = 82 core). In the case of positive-parity states no evidence for particle-core coupling could be found, while the negative-parity states could qualitatively be understood within the particle-core coupling picture.