Protonh 2 11/2 and octupole excitations in148 66Dy82 and149 66Dy83

The yrast states of¹⁴⁸Dy and¹⁴⁹Dy have been studied by γ-ray and conversion electron measurements in (α, xn) and (¹⁶O,xn) reactions on enriched¹⁵²Gd and¹³⁵Ce targets. Level schemes to above 4 MeV for the two nuclei are reported. The πh ² _11/2 spectrum identified in¹⁴⁸Dy and the πh _11/2 effective chargee _eff=1.52±0.05e, derived from the measuredE2 transition rate between the (πh ² _11/2) 10⁺ and 8⁺ states, are discussed and compared with results for other two-particle nuclei. The yrast cascades in¹⁴⁸Dy and¹⁴⁹Dy continue above the (πh ² _11/2) 10⁺ and πh ² _11/2 vf _7/2) 27/2^? states by ～ 1 MeVE1 transitions de-exciting the lowest members of octupole multiplets built on these states. The energy shifts for the observed members of the πh ² _11/2 × 3^? multiplet are analyzed in terms of twoparticle-phonon exchange coupling using an empirical coupling strength extracted from the one valence particle nucleus¹⁴⁷Tb. The dominantvf _7/2×3^? character of low-lying 13/2⁺ isomers in¹⁴⁹Dy and otherN=83 nuclei is emphasized.     

TheN=83 nucleus149Dy from Gamow-Teller decay of its 11/2− and 1/2+ 149Ho parents

A high-sensitivityγ-spectroscopic study of the¹⁴⁹Hoπh _11/2 andπs _1/2 β-decays using mass separated sources has located dominant 0⁺ → 1⁺ GT decay strength associated with decay of pairedh _11/2 protons, leading to 3п-states in the¹⁴⁹Dy daughter nucleus. In theirγ-decay low-lying¹⁴⁹Dy levels characteristic of anN=83 nucleus are excited. They include theνf _7/2,νp _3/2,νh _9/2 andνp _1/2 single particle- and theνs ₁ ^2/?1 andνd ₃ ^2/?1 two-particle one-hole states, as well as the νf _7/2 × 3^? andνf _7/2 × 2⁺ particle-phonon multiplets. A synopsis is given of these excitations in theN=83 isotones from¹⁴⁹Nd to¹⁵³Yb. The¹⁴⁹Dy GT decay strength is discussed in terms of the¹⁴⁷Tb₈₂ and¹⁴⁸Dy₈₂ decays. The strength function results are also compared with independent¹⁴⁹Ho 11/2^? decay data from the literature based on totalγ-ray absorption measurements.     

Properties of the 69 150 Tm81 6− β-decaying isomer

Decay experiments for¹⁴⁸Ho 6^? and¹⁵⁰Tm 6^? were carried out at the GSI On-line mass separator using 5 MeV/A⁵⁸Ni-beams on⁹⁴Mo and⁹⁶Ru targets. Gammaγ-andγX-coincidences established the¹⁵⁰Tm 6^? decay scheme, and e^? gave firm I ^π assignments for¹⁴⁸Dy and¹⁵⁰Er levels fed in the decays. It was found that the previously unknown 6 ₁ ^? state in¹⁵⁰Er receives significantβ-strength, which strongly suggestsπh _11/2 νs ₁ ^2/?1 character for the¹⁵⁰Tm 6^? isomer. The results are discussed in terms of the expected GT strength function. Shell model calculations for theπh ₁₁ ^2/4 yrast states are presented.     

In-beamγ-ray spectroscopy of the neutron deficient100Ag

The neutron deficient nucleus¹⁰⁰Ag, three proton holes below and three neutron particles above the N=Z=50 shell closure at¹⁰⁰Sn, has been identified and studied by in-beam spectroscopy. The reactions⁴⁶Ti(⁵⁸Ni,3pn) at 231 MeV and⁶⁴Zn(⁴⁰Ca,3pn) at 167 MeV of the respective⁵⁸Ni and⁴⁰Ca beams were used, and states up to 8.7 MeV excitation energy and spin I?20 were found in two mainγ-ray cascades forming band-like structures of even and odd parity. Large scale shell model calculations suggest predominantπg ₉ ^2/?3 ν(d_5/2,g_7/2)³ andπg ₉ ^2/?3 ν(d_5/2,g_7/2)²h_11/2 structures with maximum spins I ^π = 19⁺ and I ^π =22^?, respectively, for the two level sequences. The influence ofπp_1/2 vs.νh_11/2 excitations is discussed for low lying odd-parity levels.     

Gamow-teller strength and particle-phonon states in149Dy from decay of its 11/2− and l/2+ 149Ho parents

Studies of the¹⁴⁹Ho 11/2^? and 1/2⁺ GT-decays using on-line mass separation have established in the N=83¹⁴⁹Dy nucleus the single neutron excitations below 1.8 MeV and members of the νf_7/2×3^? and νf_7/2×2⁺ particle-phonon multiplets. Quantitative analysis of the GT-decay strength to¹⁴⁹Dy 1qp- and 3qp-states is made in terms of the strength values measured in¹⁴⁹Dy₀ and¹⁴⁷Tb_11/2? decay.     

Yrast band spectroscopy of155Gd and157Dy

The yrast bands of¹⁵⁵Gd and¹⁵⁷Dy have been observed to high spins (I～25–40). The systematic properties of the N=91 isotones with particular reference to the second i_13/2 neutron and first h_11/2 proton alignments are discussed.     

Two proton high-spin excitations and dipole bands in192Hg

The¹⁹²Hg nucleus was populated in the¹⁶⁰Gd(³⁶S, 4n) reaction at a beam energy of E=159 MeV. Emittedγ-rays were detected with the EUROGAM array comprising 43 Compton-suppressed large volume Ge detectors. The level scheme of¹⁹²Hg has been extended up to an excitation energy of E=10.4 MeV and spin I=34 ?. Two new structures, made of competing ΔI=1 and ΔI=2 transitions have been observed and their connexions with the low-lying levels established. Their lowest levels are located at 6.304 MeV and 6.879 MeV excitation energy. The experimental results are compared with mean-field HF+BCS calculations. It is proposed that the new structures originate from deformation-aligned quasi-proton excitations π(i_13/2 * h_9/2)_K=11 andπ (h_9/2) _K=8 ² , coupled to rotation-aligned quasi-neutron ν(i_13/2)ⁿ and quasi-proton π(h_11/2)² excitations.     

High spin levels in151Ho

We report here on the first study of the level structure of¹⁵¹Ho. High spin levels in¹⁵¹Ho have been populated in the¹⁴¹Pr+¹⁶O and¹⁴⁴Sm+¹²C reactions. The level structure has been established up to 6.6 MeV energy and the spins and parities determined up to 49/2^?. Most of the proposed level configurations can be explained by the coupling ofh _11/2 protons tof _7/2 and/orh _9/2 neutrons. An isomer with 14±3 ns half-life and a delayed gamma multiplicity equal to 17±2 has been found. Its spin is larger than 57/2? units.     

Neutronh 11/2 alignments in the triaxial nucleus133La

High spin states have been studied in¹³³La via the¹²²Sn (¹⁵N, 4ny) fusion evaporation reaction. Bands build on low lying h_11/2,g_7/2 and d_5/2 proton states have been identified. At higher spin a h_11/2 neutron alignment is observed. The softness with respect to the triaxial deformation makes the nuclear shape sensitive to the quasiparticle configurations and coexistence between states withy ≈ + 30°,y ≈ ? 30° andy ≦ ? 60° was found. The results have been interpreted using total routhian surface (TRS) model calculations.     

First observation of a superdeformed nucleus produced in an α xn reaction channel

Excited states in the neutron deficient ¹⁴⁵ Dy nucleus have been identified by means of the reaction ¹¹²Sn(³⁵ Cl,pn) at 159 MeV. The level scheme above the 11/2 ^? state and up to spin I～37/2 was obtained using γ-ray spectroscopy methods. The level structure is discussed in terms of the coupling of a h _11/2 neutron hole with the N=80 core excitations.     

A 0.5 μs 10+ isomer in148Dy82 and the πh11/2 effectiveE 2 charge

In¹⁵²Gd(α,8n) and¹³⁶Ce(¹⁶O,4n) reaction studies a 48O ns 10⁺ isomer in¹⁴⁸Dy has teen identified, and its decay has been characterized. All members of the πh ₁₁ ^2/2 level spectrum have been located, and the 10⁺ → 8⁺ B(E2) value gives the πh ₁₁ ^2/2 effective charge as 1.53 e. The 2⁺ and 3^? level energies in¹⁴⁸Dy₈₂ provide supporting evidence for a shell closure at Z=64.     

High-spin levels in138Ce and140Nd Observed in the (α, 4n γ) reactions

Levels of¹³⁸Ce and¹⁴⁰Nd have been studied using the¹³⁸Ba(α,4nγ)¹³⁸Ce and¹⁴⁰Ce(α, 4nγ)¹⁴⁰Nd reactions. Singleγ-ray spectra,γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured. A number of higher excited states with excitation energies up to about 5 MeV and with spin value up to 12 are populated in both nuclei. The lower states with spins and parities 7^?, 5^?, 6^? and 10⁺ can be explained by two-quasiparticle neutron configurations of the types (h _11/2 ^?1 ,d _3/2 ^?1 ) 7^? , (h _11/2 ^?1 ,S _1/2 ^?1 ) 5^?, 6^? and (h _11/2 ^?2 ) 10⁺. Several high-spin states observed in¹³⁸Ce and¹⁴⁰Nd can be explained qualitatively as four-quasiparticle states with two-proton-two-neutron configurations. The 3^? state at an energy of 2,137.4 keV is observed in¹³⁸Ce. The evidence for the existence of the low-lying 3^? states in¹⁴⁰Nd at 2,124.0 keV is discussed. Beside the known 9.6 ms (7^?) isomeric state in¹³⁸Ce another state at 3,538.5keV (10⁺) with a half life of about 200 ns has been observed. The observed levels in the¹³⁸Ce and¹⁴⁰Nd nuclei are compared with theoretical predictions using delta force interaction.     

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.     

Atomic masses of147m, 148m, 149m Tb,148Dy,150m, 152m Ho derived from decay properties

Using nuclear fusion reactions of⁴⁰Ar ions with¹¹²Cd,¹¹⁴Sn and¹¹⁶Sn and subsequentγ-ray spectroscopy, the probability ratios of positron emission and electron capture,β ⁺/EC _k andβ ⁺/(EC+β ⁺), are determined for individualβ-transitions in the decay of^147m ,^148m ,^149m Tb,¹⁴⁸Dy and^150m ,^152m Ho. From comparison with theoretical ratios the followingQ _EC values, given in keV, are derived:^147m Tb, 4.620(60);^148m Tb, 5.730(30);^149m Tb, 3.610(50);¹⁴⁸Dy, 2.680(30);^150m Ho, 6.625(120) and^152m Ho, 6.470(80). The present decay-energy data are compared with earlier measurements and the new information obtained for the mass surface around¹⁴⁶Gd is discussed.     

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.     

g-factors of the ground state rotational band of158Dy

Theg-factors of the four lowest states of the ground state rotational band of¹⁵⁸Dy have been determined asg(2 ₁ ⁺ )=+0.362(23),g(4 ₁ ^su+ )=+0.340(20),g(6 ₁ ^su+ )=+0.207(36) andg(8 ₁ ^su+ )=+0.21(11). Theg-factors of the 2⁺ and 4⁺ states were measured by the IPAC method with radioactive samples of 2.4 h¹⁵⁸Er in external magnetic fields. To investigate the higher states, for the first time an on-line γ—γ IPAC experiment was performed with the reaction¹⁵⁶Gd(α, 2n)¹⁵⁸Dy by use of the static hyperfine field of DyGd.     

Shell model yrast states in theN=79 nuclei141Sm and143Gd

In (α,5n) in-beam γ- and electron measurements we have established high-spin states in the 3-neutronhole nuclei¹⁴¹Sm and¹⁴³Gd. Observed energy levels below 4 MeV are interpreted in terms of shell model configurations where the odd h_11/2 neutron hole couples to the N=80 core excitations containing one h_11/2 proton particle or one h_11/2 neutron hole. Higher-lying yrast states are built on a 23/2? level at Rd 3.2 MeV probably involving the πh ₁ ^2/2 guh ₁₁ ^2/?1 configUTa-tion.     

Transition probabilities and energy levels in heavy odd-mass isotopes of Sn (A=119–125)

The de-excitation of levels in^119–125Sn populated in the decay of In isotopes has been studied using on-line isotope separators. Level half-lives have been measured in^119–123Sn. a near cancellation of the matrix element for B(E2; g_7/2→ d_3/2) is observed to occur in¹²¹Sn and is probably due to pairing effects. Very low lying 9/2^? levels have been observed in^121–125Sn and are suggested in^{127, 129}Sn. These levels have been interpreted as three quasi-particle states based on the unique parity h_11/2 level. A possible mixing of theg _7/2 level with a close lying 7/2⁺ three quasi-particle state in¹²³Sn is discussed. Radioactivity.^119–125In from²³⁵U(n, f) and²³⁸U(α, f), isotope separated sources; measuredE _γ ,I _γ , E_ce, I_ce,γγ-coin,Βγ-delay, deduced multipolarities.^119–123Sn deduced levels,I, π, B(λ). Ge(Li), Si(Li), NaI(Tl) and plastic detectors, Ge(Li)-Ge(Li) coin, plastic detector — NaI(Tl) delay.     

Two-nucleon excitations in 66 148 Dy82 from Gamow-Teller decay of the 67 148 Ho81 6− isomer

Two-particle excitations in the two-proton nucleus¹⁴⁸Dy populated inβ-decay of 10-s ¹⁴⁸Ho(6^?) were investigated throughγ-ray measurements following on-line mass separation. Theπh _11/2s_1/2 two-proton doublet and the (vh _9/2 s ₁ ^2/?1 )5^? neutron particle hole configuration are firmly identified, and theπh _11/2 d ₅ ^2/?1 and πh_11/2D_3/2 multiplets are also observed. The results suggest dominantπh _11/2vs ₁ ^2/?1 character for the¹⁴⁸Ho 6^?-isomer.     

High-spin bands in117,119I and118Xe

Excited states in¹¹⁷I,¹¹⁸Xe and¹¹⁹I were populated in the reactions¹⁰⁶Pd+¹⁶O and^{108, 110}Cd+¹²C. The groundstate band in¹¹⁸Xe was observed to its (18⁺) member and the 11/2^? bands in¹¹⁷I and¹¹⁹I to their (35/2^?) and (43/2^?) members, respectively. The structure of the bands in the I isotopes is interpreted as aπ h _11/2 proton coupled to an even-even band structure in Xe, and the band crossings observed in¹¹⁸Xe and¹¹⁹I are interpreted in the Cranked Shell Model framework asAB _n ofv h _11/2.