0000000000626306
AUTHOR
P. Greenlees
Backbending in the pear-shaped 223(90)Th nucleus: Evidence of a high-spin octupole to quadrupole shape transition in the actinides
International audience; Relatively neutron-rich thorium isotopes lie at the heart of a nuclear region of nuclei exhibiting octupole correlation effects. The detailed level structure of Th223 has been investigated in measurements of γ radiation following the fusion-evaporation channel of the Pb208(O18,3n)Th223 reaction at 85 MeV beam energy. The level structure has been extended up to spin 49/2, and 33 new γ rays have been added using triple-γ coincidence data. The spins and parities of the newly observed states have been confirmed by angular distribution ratios. In addition to the two known yrast bands based on a K=5/2 configuration, a non-yrast band has been established up to spin 35/2. We…
Spectroscopy of 70Kr and isospin symmetry in the T = 1 f pg shell nuclei
International audience; The recoil-β tagging technique has been used in conjunction with the 40 Ca(32 S ,2n) reaction at a beam energy of 88 MeV to identify transitions associated with the decay of the 2 + and, tentatively, 4 + states in the nucleus 70 Kr. These data are used, along with previously published data, to examine the triplet energy differences (TED) for the mass 70 isobars. The experimental TED values are compared with shell model calculations, performed with the JUN45 interaction in the fpg model space, that include a J = 0 isospin nonconserving (INC) interaction with an isotensor strength of 100 keV. The agreement is found to be very good up to spin 4 and supports the expectat…
Chirality of 135 Nd reexamined : Evidence for multiple chiral doublet bands
One new pair of positive-parity chiral doublet bands have been identified in the odd-A nucleus 135Nd which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (MχD) bands in the A ≈ 130 mass region. The properties of the MχD bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed MχD bands in 135Nd represents an important milestone in supporting the existence of MχD in nuclei. peerReviewed
Coulomb excitation of $^{78}$Kr
Expérience à JYFL cyclotron (Jyväskylä, Finlande); The Kr isotopes are considered to be among the best cases for shape coexistence studies in the mass A$\sim$70 region. Our campaign to investigate in detail the development of the shape coexistence in the neutron deficient Kr isotopes was started with the stable nucleus $^{78}$Kr. To obtain the information about the intrinsic shape, Coulomb excitation experiments were performed. A total of 26 matrix elements were determined for $^{78)$Kr. Simple geometrical and algebraic models do not reproduce all details of the electromagnetic structure. A good interpretation of the complex structure of the nucleus with competing oblate and prolate shapes …
Octupole states in Tl207 studied through β decay
The β decay of 207Hg into the single-proton-hole nucleus 207Tl has been studied through γ-ray spectroscopy at the ISOLDE Decay Station (IDS) with the aim of identifying states resulting from coupling of the πs−11/2, πd−13/2, and πh−111/2 shell model orbitals to the collective octupole vibration. Twenty-two states were observed lying between 2.6 and 4.0 MeV, eleven of which were observed for the first time, and 78 new transitions were placed. Two octupole states (s1/2-coupled) are identified and three more states (d3/2-coupled) are tentatively assigned using spin-parity inferences, while further h11/2-coupled states may also have been observed for the first time. Comparisons are made with st…
Signatures of enhanced octupole correlations at high spin in 136Nd
Experimental signatures of moderately enhanced octupole correlations at high spin in 136Nd are indicated for the first time. The extracted dipole moments of two negative-parity bands are only two times smaller than those of the lanthanide nuclei with N≈90 which present well-established octupole correlations. Calculations using the cranked quasiparticle random phase approximation and a model of quadrupole-octupole rotations with octupole vibrations reveal the structure of the bands and the enhanced octupole correlations at high spin in 136Nd. peerReviewed
In-beam γ-ray spectroscopy of 94Ag
A recoil-beta-tagging experiment has been per formed to study the excited T = 0 and T = 1 states in the odd–odd N = Z nucleus 94Ag, populated via the 40Ca(58Ni,1p3n)94Ag reaction. The experiment was con ducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt γ rays emitted at the reaction target, a number of transitions between excited states in 94Ag have been identified. The timing characteris tics of these transitions confirm that they fall within decay sequences that feed the short-lived T = 1 ground state of 94Ag. The transitions are propo…
Competition between allowed and first-forbidden β decays of At208 and expansion of the Po208 level scheme
The structure of 208Po populated through the EC/β+ decay of 208At is investigated using γ-ray spectroscopy at the ISOLDE Decay Station. The presented level scheme contains 27 new excited states and 43 new transitions, as well as a further 50 previously observed γ rays which have been (re)assigned a position. The level scheme is compared to shell model calculations. Through this analysis approximately half of the β-decay strength of 208At is found to proceed via allowed decay and half via first-forbidden decay. The first-forbidden transitions predominantly populate core excited states at high excitation energies, which is qualitatively understood using shell model considerations. This mass r…
Refined description of the positive-parity bands and the extent of octupole correlations in 120Ba
Three new negative-parity bands have been identified in 120Ba, two of them forming a strongly coupled band. The previously known negative-parity band is significantly extended to high spin, while the lower part of the yrare positive-parity band has been modified. From the analysis of the band properties and comparison with the neighboring nuclei a coherent description of all bands is achieved. In particular, a simple explanation of the evolution of the positive-parity bands at high spin is proposed, including the possible occupation of the νf7/2[541]1/2− intruder orbital. Cranked Nilsson-Strutinsky calculations reveal similar quadrupole deformations but different triaxiality of the bands, w…
Characteristics of segmented super clover detector in close geometry decay measurements
Characteristics of the segmented Super Clover germanium detector response in close geometries have been studied. Results obtained with localising hit pattern recognition are compared with results from add-back and individual crystal analysis. The detector has been used at the focal plane of a gas filled recoil separator to detect isomeric gamma-rays from the nuclei produced in the 150Sm(42Ca,4n)188Pb reaction. Coincidence data from the detector was analysed and the level scheme below the 1.2 μ s isomeric state in 188Pb could be deduced. peerReviewed
New gas-filled mode of the large-acceptance spectrometer VAMOS
A new gas-filled operation mode of the large-acceptance spectrometer VAMOS at GANIL is reported. A beam rejection factor greater than 10(10) is obtained for the Ca-40+Sm-150 system at 196 MeV. The unprecedented transmission efficiency for the evaporation residues produced in this reaction is estimated to be around 80% for alpha x n channels and above 95% for x ny p channels. A detailed study of the performance of the gas-filled VAMOS and future developments are discussed. This new operation mode opens avenues to explore the potential of fusion reactions in various kinematics. (C) 2010 Elsevier B.V. All rights reserved.
Spectroscopy of Kr 70 and isospin symmetry in the T=1 fpg shell nuclei SPECTROSCOPY of Kr 70 and ISOSPIN SYMMETRY ... D. M. DEBENHAM et al.
The recoil-β tagging technique has been used in conjunction with the Ca40(S32,2n) reaction at a beam energy of 88 MeV to identify transitions associated with the decay of the 2+ and, tentatively, 4+ states in the nucleus Kr70. These data are used, along with previously published data, to examine the triplet energy differences (TED) for the mass 70 isobars. The experimental TED values are compared with shell model calculations, performed with the JUN45 interaction in the fpg model space, that include a J=0 isospin nonconserving (INC) interaction with an isotensor strength of 100 keV. The agreement is found to be very good up to spin 4 and supports the expectation for analog states that all t…
Tilted precession bands in $^{135}$Nd
International audience; Two new excited bands built on the πh11/2 configuration have been identified in Nd135 in addition to the known πh11/2 band. The energy spectra of the excited bands and the available electromagnetic transition probabilities are in good agreement with theoretical results obtained using quasiparticle-plus-triaxial-rotor model calculations. The properties of the bands identify them as tilted precession bands instead of wobbling bands. Our results give a new insight into the interpretation of the low-lying bands in odd-A mass nuclei, and can stimulate future studies to address the nuclear triaxiality.
High-spin intruder band in $^{107}$In
High-spin states in the neutron deficient nucleus $^{107}$In were studied via the $^{58}$Ni($^{52}$Cr, 3p) reaction. In-beam $\gamma$ rays were measured using the JUROGAM detector array. A rotational cascade consisting of ten $\gamma$-ray transitions which decays to the 19/2$^{+}$ level at 2.002 MeV was observed. The band exhibits the features typical for smooth terminating bands which also appear in rotational bands of heavier nuclei in the A$\sim$100 region. The results are compared with Total Routhian Surface and Cranked Nilsson-Strutinsky calculations.