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[show abstract]
[hide abstract]
ABSTRACT: Recent data show that both the 2+ and 4+ levels in the even neutron-rich Cr and Fe isotopes decrease in excitation energy toward N = 40. This observation, along with Coulomb excitation and lifetime data, strongly indicates an increase in collectivity near N = 40 in contradiction with expectations based on first principles. A straightforward two-band mixing model is used to investigate the structure of these neutron-rich Cr and Fe nuclei. The approach takes advantage of the extensive data available for 60 Fe to provide the parameter values with which to reproduce the experimental observations in the 58−64 Cr and 60−68 Fe isotopic chains. Comparisons between the model and the data suggest marked structural differences for the ground-state configurations of N = 40 Cr and Fe.
Physical Review C 04/2013; 87:041315. · 3.31 Impact Factor
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A D Ayangeakaa,
U Garg,
M D Anthony,
S Frauendorf,
J T Matta,
B K Nayak,
D Patel,
Q B Chen,
S Q Zhang,
P W Zhao, [......],
J Meng, R V F Janssens,
M P Carpenter,
C J Chiara,
F G Kondev,
T Lauritsen,
D Seweryniak,
S Zhu,
S S Ghugre,
R Palit
[show abstract]
[hide abstract]
ABSTRACT: Two distinct sets of chiral-partner bands have been identified in the nucleus 133Ce. They constitute a multiple chiral doublet, a phenomenon predicted by relativistic mean field (RMF) calculations and observed experimentally here for the first time. The properties of these chiral bands are in good agreement with results of calculations based on a combination of the constrained triaxial RMF theory and the particle-rotor model.
Physical Review Letters 04/2013; 110(17):172504. · 7.37 Impact Factor
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A D Ayangeakaa,
U Garg,
M A Caprio,
M P Carpenter,
S S Ghugre, R V F Janssens,
F G Kondev,
J T Matta,
S Mukhopadhyay,
D Patel,
D Seweryniak,
J Sun,
S Zhu,
S Frauendorf
[show abstract]
[hide abstract]
ABSTRACT: Low-lying collective excitations in even-even vibrational and transitional nuclei may be described semiclassically as quadrupole running waves on the surface of the nucleus ("tidal waves"), and the observed vibrational-rotational behavior can be thought of as resulting from a rotating condensate of interacting d bosons. These concepts have been investigated by measuring lifetimes of the levels in the yrast band of the ^{102}Pd nucleus with the Doppler shift attenuation method. The extracted B(E2) reduced transition probabilities for the yrast band display a monotonic increase with spin, in agreement with the interpretation based on rotation-induced condensation of aligned d bosons.
Physical Review Letters 03/2013; 110(10):102501. · 7.37 Impact Factor
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A. D. Ayangeakaa,
U. Garg,
M. D. Anthony,
S. Frauendorf,
J. T. Matta,
B. K. Nayak,
D. Patel,
Q. B. Chen,
S. Q. Zhang,
P. W. Zhao, [......],
J. Meng, R. V. F. Janssens,
M. P. Carpenter,
C. J. Chiara,
F. G. Kondev,
T. Lauritsen,
D. Seweryniak,
S. Zhu,
S. S. Ghugre,
R. Palit
[show abstract]
[hide abstract]
ABSTRACT: Two distinct sets of chiral-partner bands have been identified in the nucleus
$^{133}$Ce. They constitute a multiple chiral doublet (M$\chi$D), a phenomenon
predicted by relativistic mean field (RMF) calculations and observed
experimentally here for the first time. The properties of these chiral bands
are in good agreement with results of calculations based on a combination of
the constrained triaxial RMF theory and the particle-rotor model.
02/2013;
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D. G. Jenkins,
C. J. Lister,
M. P. Carpenter,
P. Chowdury,
N. J. Hammond, R. V. F. Janssens,
T. L. Khoo,
T. Lauritsen,
D. Seweryniak,
T. Davinson,
P. J. Woods,
A. Jokinen,
H. Penttila,
F. Haas,
S. Courtin
[show abstract]
[hide abstract]
ABSTRACT: Recent antisymmetrized molecular dynamics (AMD) calculations for 28Si suggest the presence of a superdeformed (SD) band with a dominant 24Mg+α clustering for its configuration, with firm predictions for its location and associated moment of inertia. This motivates a review of the experimental results reported in the literature with a particular focus on 24Mg(α,γ) studies, as well as on α-like heavy-ion transfer reactions such as 12C(20Ne,α)28Si. Combining this information for the first time leads to a set of candidate SD states whose properties point to their α-cluster structure and strong associated deformation. Analysis of data from Gammasphere allows the electromagnetic decay of these candidate states to be probed and reveals further supporting evidence for such a structure. This paper appraises this body of information and finds the evidence for an SD band is strong.
Phys. Rev. C. 12/2012; 86(6).
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F G Kondev,
M A Riley, R V F Janssens,
J Simpson,
A V Afanasjev,
I Ragnarsson,
I Ahmad,
D J Blumenthal,
T B Brown,
M P Carpenter, [......],
S M Fischer,
G Hackman,
D J Hartley,
C A Kalfas,
T L Khoo,
T Lauritsen,
W C Ma,
D Nisius,
J F Sharpey-Schafer,
P G Varmette
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J. F. Smith,
L. J. Angus,
E. S. Paul,
C. J. Chiara,
M. P. Carpenter,
H. J. Chantler,
P. T. W. Choy,
C. N. Davids,
M. Devlin,
D. B. Fossan,
S. J. Freeman, R. V. F. Janssens,
N. S. Kelsall,
T. Koike,
D. R. LaFosse,
D. G. Sarantites,
D. Seweryniak,
K. Starosta,
R. Wadsworth,
A. N. Wilson
[show abstract]
[hide abstract]
ABSTRACT: Excited states have been identified in the very neutron-deficient Z=58 nucleus 123Ce. This is the most neutron-deficient odd-A cerium isotope in which excited states have been identified. The states have been unambiguously assigned to 123Ce by detecting de-excitation γ rays in coincidence with evaporated charged particles and neutrons. Three rotational bands, each consisting of at least eight E2 transitions, have been observed. The bands have tentatively been assigned to be based on neutrons in g7/2 and h11/2 orbitals. Two of the bands have been assigned to be signature partners, although no interband transitions have been observed. The aligned angular momenta of the bands have been studied in comparison with neighboring nuclei and with the results of Woods-Saxon cranking calculations. Observation of the deformation-dependent π(h11/2)2 quasiparticle alignment at 0.36 MeV/ℏ in each of the bands suggests a quadrupole deformation of β2≃0.3, in good agreement with theoretical predictions for the suggested possible configuration assignments.
Physical Review C 09/2012; 86(3):034303. · 3.31 Impact Factor
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T Möller,
N Pietralla,
G Rainovski,
T Ahn,
C Bauer,
M P Carpenter,
L Coquard, R V F Janssens,
J Leske,
C J Lister,
E A McCutchan,
O Möller,
D Seweryniak,
S Zhu
Physical Review C 09/2012; 86(3):031305. · 3.31 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The evolution of the one-quadrupole phonon mixed-symmetry state is important for understanding the role of the quadrupole proton-neutron interaction in the valence shell. To study the evolution of the 21,ms+ mixed-symmetry state in the N=78 isotones above Z=50, a Coulomb excitation measurement was performed to identify the 21,ms+ state in 136Ce by measuring absolute transition strengths. The 21,ms+ state was found to be predominantly concentrated in the 24+ state of this nucleus. The simple picture of shell stabilization given to account for the fragmentation of the strength observed in 138Ce does not seem to apply to 136Ce.
Phys. Rev. C. 07/2012; 86(1).
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H. Watanabe,
G. J. Lane,
G. D. Dracoulis,
A. P. Byrne,
P. Nieminen,
F. G. Kondev,
K. Ogawa,
M. P. Carpenter, R. V. F. Janssens,
T. Lauritsen,
D. Seweryniak,
S. Zhu,
P. Chowdhury
[show abstract]
[hide abstract]
ABSTRACT: The nucleus 127Sb\ensuremath {\rm ^{127}Sb} , which is on the neutron-rich periphery of the b\ensuremath \beta -stability region, has been populated in complex nuclear reactions involving deep-inelastic and fusion-fission processes
with 136Xe\ensuremath {\rm {}^{136}Xe} beams incident on thick targets. The previously known isomer at 2325 keV in 127Sb\ensuremath {\rm {}^{127}Sb} has been assigned spin and parity 23/2+\ensuremath 23/2^+ , based on the measured g\ensuremath \gamma - g\ensuremath \gamma angular correlations and total internal conversion coefficients. The half-life has been determined to be 234(12) ns, somewhat
longer than the value reported previously. The 2194 keV state has been assigned Jp = 19/2+\ensuremath J^{\pi} = 19/2^+ and identified as an isomer with T1/2 = 14(1) ns\ensuremath T_{1/2} = 14(1) {\rm ns} , decaying by two E2\ensuremath E2 branches. The observed level energies and transition strengths are compared with the predictions of a shell model calculation.
Two 15/2+\ensuremath 15/2^+ states have been identified close in energy, and their properties are discussed in terms of mixing between vibrational and
three-quasiparticle configurations.
European Physical Journal A 04/2012; 42(2):163-169. · 2.19 Impact Factor
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D. Steppenbeck, R. V. F. Janssens,
S. J. Freeman,
M. P. Carpenter,
P. Chowdhury,
A. N. Deacon,
M. Honma,
H. Jin,
T. Lauritsen,
C. J. Lister, [......],
J. Peng,
D. Seweryniak,
J. F. Smith,
Y. Sun,
S. L. Tabor,
B. J. Varley,
Y.-C. Yang,
S. Q. Zhang,
P. W. Zhao,
S. Zhu
[show abstract]
[hide abstract]
ABSTRACT: The structure of 58Fe was investigated at Gammasphere using 48Ca(13,14C,xn) fusion-evaporation reactions at a beam energy of 130 MeV. The level scheme has been revised and extended to J∼17ℏ and an excitation energy of 16.6 MeV. Regular band structures consisting of low-energy ΔJ=1ℏ transitions have been observed at moderate spin (J∼8ℏ–15ℏ) and are candidates for magnetic rotational bands. Self-consistent tilted-axis-cranking calculations within a relativistic mean-field theory were applied to investigate these bands and were found to reproduce the experimental results well. In other parts of the level scheme, quasirotational bands composed of stretched-E2 transitions have been extended to high spin, and other new bands have been identified. Positive-parity experimental states were compared to predictions of the spherical shell model using the GXPF1A, KB3G, and FPD6 effective interactions in the fp model space. The projected shell model, with a deformed quasiparticle basis including the neutron νg9/2 orbital, was applied to interpret regular ΔJ=2ℏ band structures that extend beyond the maximum spin available for π[(f7/2)−2] ⊗ ν[(p3/2f5/2p1/2)4] configurations and exhibit features characteristic of rotational alignment. It is clear that the νg9/2 intruder orbital plays a crucial role in describing the quasirotational structures in this nucleus, even starting as low as J∼5ℏ.
Physical Review C 04/2012; 85(4). · 3.31 Impact Factor
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P. T. Wady,
J. F. Smith,
E. S. Paul,
B. Hadinia,
C. J. Chiara,
M. P. Carpenter,
C. N. Davids,
A. N. Deacon,
S. J. Freeman,
A. N. Grint, R. V. F. Janssens,
B. P. Kay,
T. Lauritsen,
C. J. Lister,
B. M. McGuirk,
M. Petri,
A. P. Robinson,
D. Seweryniak,
D. Steppenbeck,
S. Zhu
[show abstract]
[hide abstract]
ABSTRACT: Gamma-ray transitions have been observed in the proton-emitting N=Z+2 (Tz=1) isotope 112Cs. The transitions have been unambiguously assigned to 112Cs by correlation with the characteristic proton decay, using the method of recoil-decay tagging with mass selection. The measured proton-decay energy and half-life are Ep=810(5) keV and T1/2=470(50) μs, respectively, which are consistent with previous measurements. Five γ-ray transitions have been observed which appear to form a rotational sequence. The energy differences between excited states in the sequence are consistent with an assignment as the favored signature of the ν(h11/2)⊗π(h11/2) structure. Tentative evidence for fine structure in the 112Cs proton decay is also observed.
Phys. Rev. C. 03/2012; 85(3).
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S. Zhu, R. V. F. Janssens,
M. P. Carpenter,
C. J. Chiara,
R. Broda,
B. Fornal,
N. Hoteling,
W. Krolas,
T. Lauritsen,
T. Pawlat,
D. Seweryniak,
I. Stefanescu,
J. R. Stone,
W. B. Walters,
X. Wang,
J. Wrzesinski
[show abstract]
[hide abstract]
ABSTRACT: Excited states in Ni-67 were populated in deep-inelastic reactions of a Ni-64
beam at 430 MeV on a thick U-238 target. A level scheme built on the previously
known 13 micro-s isomer has been delineated up to an excitation energy of ~5.3
MeV and a tentative spin and parity of (21/2-). Shell model calculations have
been carried out using two effective interactions in the f5/2pg9/2 model space
with a Ni-56 core. Satisfactory agreement between experiment and theory is
achieved for the measured transition energies and branching ratios. The
calculations indicate that the yrast states are associated with rather complex
configurations, herewith demonstrating the relative weakness of the N=40
subshell gap and the importance of multi particle-hole excitations involving
the g9/2 neutron orbital.
03/2012;
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[show abstract]
[hide abstract]
ABSTRACT: γ-Ray emission probabilities from the decay of the long-lived (T(1/2)=160.44d) isomeric state in (177m)Lu were measured with planar (LEPS) and coaxial Ge detectors. The isomer γ-ray and β(-)-decay branching intensities were also determined. Measurements were carried out at low absolute efficiencies in order to minimize coincidence summing losses. The results are compared with the previous measurements.
Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 02/2012; 70(9):1867-70. · 1.09 Impact Factor
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C. J. Chiara,
I. Stefanescu,
W. B. Walters,
S. Zhu, R. V. F. Janssens,
M. P. Carpenter,
R. Broda,
B. Fornal,
A. A. Hecht,
N. Hoteling,
E. G. Jackson,
B. P. Kay,
W. Królas,
T. Lauritsen,
E. A. McCutchan,
T. Pawłat,
D. Seweryniak,
X. Wang,
A. Wöhr,
J. Wrzesiński
[show abstract]
[hide abstract]
ABSTRACT: The nuclei 65,67Cu were studied in reactions between a 430-MeV 64Ni beam and a thick 238U target with the Gammasphere array. Decay schemes for both nuclei have been extended, with spin and parity assignments of observed states constrained by measured γ-ray angular distributions and correlations. Positive-parity level structures, based on p3/2 protons coupled to negative-parity states in the Ni cores, have been identified above the known 9/2+ states. In 67Cu, a negative-parity dipole band built upon a πf7/2−1 state has been observed, as were two shorter negative-parity sequences. A qualitative description of the level structures has been obtained through comparison with systematics of the odd-A57–71Cu isotopes and with states in the neighboring even-even Ni and Zn cores. Shell-model calculations using JUN45 and jj44b effective interactions were performed for 65,67Cu, with jj44b providing overall better agreement with the data. Both are limited, however, by the restriction that the f7/2 and g9/2 orbitals are not available simultaneously in the basis. Proton f7/2 and neutron g9/2 orbitals are required for the full negative-parity spectrum of states, while g9/2 protons and neutrons are both important for positive-parity levels. The latter states are found to be better described in terms of weak coupling of a proton to the Ni core.
Phys. Rev. C. 02/2012; 85(2).
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E. A. McCutchan,
C. J. Lister,
Steven C. Pieper,
R. B. Wiringa,
D. Seweryniak,
J. P. Greene,
P. F. Bertone,
M. P. Carpenter,
C. J. Chiara,
G. G?urdal,
C. R. Hoffman, R. V. F. Janssens,
T. L. Khoo,
T. Lauritsen,
S. Zhu
[show abstract]
[hide abstract]
ABSTRACT: The lifetime of the J=2+ state in 10C was measured using the Doppler Shift
Attenuation Method following the inverse kinematics p(10B,n)10C reaction at 95
MeV. The 2+ state, at 3354 keV, has tau = 219\pm(7)stat \pm(10)sys fs
corresponding to a B(E2) # of 8.8(3) e2fm4. This measurement,combined with that
recently determined for 10Be (9.2(3) e2fm4), provides a unique challenge to
abinitio calculations, testing the structure of these states, including the
isospin symmetry of the wave functions. Quantum Monte Carlo calculations using
realistic two- and three-nucleon Hamiltonians that reproduce the 10Be B(E2)
value generally predict a larger 10C B(E2) probability but with considerable
sensitivity to the admixture of different spatial symmetry components in the
wave functions, and to the three-nucleon potential used.
01/2012;
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Somnath Nag,
A. K. Singh,
A. N. Wilson,
J. Rogers,
H. Hübel,
A. Bürger,
S. Chmel,
I. Ragnarsson,
G. Sletten,
B. Herskind, [......],
F. G. Kondev,
T. Lauritsen,
S. Zhu,
A. Korichi,
Hoa Ha,
P. Fallon,
A. O. Macchiavelli,
B. M. Nyakó,
J. Timár,
K. Juhász
[show abstract]
[hide abstract]
ABSTRACT: High-spin states in 120Te were populated in the reaction 80Se(48Ca, α4n)120Te at a beam energy of 207 MeV and γ-ray coincidences were measured using the Gammasphere spectrometer. The previously known level scheme is extended to higher spin and new interband transitions and side-feeding branches are established. Five highly deformed rotational bands, extending up to almost I=50, are observed for the first time. The bands are compared with similar structures found recently in neighboring nuclei. The experimental results are interpreted within the framework of the cranked Nilsson-Strutinsky model. Configuration assignments to several terminating states and to the high-spin bands are discussed.
Phys. Rev. C. 01/2012; 85(1).
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R O Hughes,
G J Lane,
G D Dracoulis,
A P Byrne,
P H Nieminen,
H Watanabe,
M P Carpenter,
P Chowdhury, R V F Janssens,
F G Kondev,
T Lauritsen,
D Seweryniak,
S Zhu
[show abstract]
[hide abstract]
ABSTRACT: High-spin states in the odd-proton thulium isotopes Tm-173 and Tm-175 have been studied using deep-inelastic reactions and gamma-ray spectroscopy. In Tm-173, the low-lying structure has been confirmed and numerous new states have been identified, including a three-quasiparticle K-pi = 19/2(-) isomer with a lifetime of tau = 360(100) ns at 1906 keV and a five-quasiparticle K-pi = 35/2(-) isomer with a lifetime of tau = 175(40) ns at 4048 keV. The K-pi = 35/2(-) state is interpreted as a t-band configuration that shows anomalously fast decays. In Tm-175, the low-lying structure has been reevaluated, a candidate state for the 9/2(-) [514] orbital has been identified at 1175 keV, and the 7/2(-)[523] bandhead has been measured to have a lifetime of tau = 460(50) ns. Newly identified high-K structures in Tm-175 include a K-pi = 15/2(-) isomer with a lifetime of tau = 64(3) ns at 947 keV and a K-pi = 23/2(+) isomer with a lifetime of tau = 30(20) mu s at 1518 keV. The K-pi = 15/2(-) isomer shows relatively enhanced decays to the 7/2(-) [523] band that can be explained by chance mixing with the 15/2(-) member of the 7/2(-) band. Multiquasiparticle calculations have been performed for Tm-173 and Tm-175, the results of which compare well with the experimentally observed high-spin states.
Physical Review C 01/2012; 86(5). · 3.31 Impact Factor
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G D Dracoulis,
G J Lane,
A P Byrne,
H Watanabe,
P O Hughes,
N Palalani,
F G Kondev,
M P Carpenter,
D Seweryniak,
S Zhu, R V F Janssens,
C J Lister,
T Lauritsen,
P Chowdhury,
Y Shi,
F R Xu
[show abstract]
[hide abstract]
ABSTRACT: Deep-Inelastic reactions have been used to populate high-spin states in the even-even osmium isotopes and in the iridium neighbors. New isomers have been identified in Os-190, Os-192, Os-194, Ir-191 and Ir-193. These include a 2 ns 12(+) state at 2865 keV and a 295 ns, 20+ state at 4580 keV in Os-192. Although a number of multi-quasiparticle states arising from prolate and triaxial deformations are expected in these nuclei, the main structures in Os-192 can be interpreted as a two-stage alignment of i(13/2) neutrons at oblate deformation, in close analogy with similar structures in the isotones Pt-194 and Hg-196. The isomers are attributed to low-energy E2 transitions at the point of the alignment gains. The isomer observed in Ir-191 is long-lived (tau(m) similar to 8 s) and probably arises from coupling of the h(11/2) proton to the 10(-) nu 9/2(-)[505]11/2(+) [615] prolate configuration that gives rise to long-lived isomers in Os-190 and Os-192, although potential-energy-surface calculations indicate that the resultant three-quasiparticle state will be triaxial.
RUTHERFORD CENTENNIAL CONFERENCE ON NUCLEAR PHYSICS; 01/2012
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M. J. Taylor,
M. A. Bentley,
J. R. Brown,
P. E. Kent,
R. Wadsworth,
C. J. Lister,
D. Seweryniak,
M. P. Carpenter, R. V. F. Janssens,
S. Zhu,
T. Lauritsen,
L.-L. Andersson,
E. K. Johansson,
P. E. Garrett,
K. L. Green,
G. A. Demand,
S. M. Lenzi
[show abstract]
[hide abstract]
ABSTRACT: Excited states in the N=Z−2 nucleus 44V have been observed for the first time. The states have been identified through particle-γ-γ coincidence relationships and comparison with analog states in the mirror nucleus 44Sc. Mirror energy differences have been extracted and compared to state-of-the-art shell-model calculations which include charge-symmetry-breaking forces. Observed decay pattern asymmetries between the mirror pair are discussed in terms of core excitations, electromagnetic spin-orbit effects and isospin mixing.
Phys. Rev. C. 12/2011; 84(6).
