-
J. M. Daugas,
I. Matea,
J.-P. Delaroche,
M. Pfützner,
M. Sawicka,
F. Becker,
G. Bélier,
C. R. Bingham,
R. Borcea, E. Bouchez, [......],
K. Rykaczewski,
M. G. Saint-Laurent,
J. E. Sauvestre,
O. Sorlin,
M. Stanoiu,
I. Stefan,
Ch. Stodel,
Ch. Theisen,
D. Verney,
J. Żylicz
[show abstract]
[hide abstract]
ABSTRACT: A decay spectroscopic study of the neutron-rich isotopes has been performed using fragmentation of a 86Kr primary beam. Fragments from this reaction have been selected by the LISE2000 spectrometer at the Grand Accélérateur National d’Ions Lourds (GANIL). Half-lives of 29 isotopes, including the first ones identified for 61Ti (15±4 ms), 64V (19±8 ms), and 71Fe (28±5 ms), have been determined and compared with model predictions. 67,68Mn β-delayed γ rays were observed for the first time. The branching for the β-delayed neutron emission was measured to be greater than 10(5)% in the 67Mn decay. The 67Fe isomeric level is firmly determined at higher energy than assigned in previous works. The excitation energies of the first (2+) and (4+) states of 68Fe are suggested to lie at 522(1) and 1389(1) keV, respectively, thus bringing confirmation of assignments based on in-beam γ-ray spectroscopy. Beyond-mean-field calculations with the Gogny D1S force have been performed for even-mass nuclei through the Fe isotopic chain. Not only 68Fe but most of the neutron-rich Fe isotopes with neutron numbers below N=50 are interpreted as soft rotors. The calculated mean occupancy of the neutron g9/2 and d5/2 orbitals in correlated ground states is steadily growing with increasing neutron number throughout the isotopic chain. Interpretation of 67Fe data is based upon the present calculations for the 66Fe and 68Fe even cores.
Physical Review C 05/2011; 83(5). · 3.31 Impact Factor
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B. Jurado,
G. Kessedjian,
M. Petit,
M. Aïche,
G. Barreau,
A. Bidaud,
S. Boyer,
N. Carjan,
S. Czajkowski,
D. Dassie, [......],
Y Lecoz,
R. Lucas,
Ch. Theisen,
O. Sérot,
E. Bauge,
A. Billebaud,
L. Perrot,
I Ahmad,
J P Greene,
R. V. F. Janssens
[show abstract]
[hide abstract]
ABSTRACT: We present a review of the fission cross section measurements made by the CENBG collaboration over the last years using the surrogate reaction method. For example the neutron-induced fission cross sections of 233Pa(T1/2 = 27 d), 242Cm(T1/2 d) and 243Cm(T1/2 y) have been obtained by our group with this technique. The advantages and the difficulties of the surrogate method are discussed. Special attention is paid to the comparison between cross sections measured with the surrogate method and those obtained directly with neutrons at low energies. This comparison provides information on possible differences between the spin-parity distributions achieved in the two methods.
EPJ Web of Conferences. 01/2010;
-
D. Mücher,
J. Iwanicki,
J. Jolie,
I. Stefanescu,
J. Van de Walle,
F. Becker,
U. Bergmann,
A. Blazhev, E. Bouchez,
P. Butler, [......],
D. Schwalm,
T. Sieber,
Ch. Theisen,
P. Van Duppen,
N. Warr,
D. Weisshaar,
F. Wenander,
B. Wolf,
P. Woods,
M. Zielinska
[show abstract]
[hide abstract]
ABSTRACT: B(E2;21+→01+) values have been measured for the unstable nuclei 88Kr (N = 52) and 92Kr (N = 56) using projectile Coulomb excitation at ISOLDE, CERN. With this experiment the local maximum in E(21+) in 92Kr and the role of the N = 56 subshell closure can be studied.
AIP Conference Proceedings. 01/2009; 1090(1):587-588.
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S. Ketelhut,
P. T. Greenlees,
A. Chatillon, E. Bouchez,
P. A. Butler,
E. Clément,
O. Dorvaux,
S. Eeckhaudt,
B. J. P. Gall,
A. Görgen, [......],
J. Perkowski,
P. Rahkila,
M. Rousseau,
J. Sarén,
C. Scholey,
Ch. Theisen,
J. Uusitalo,
J. N. Wilson,
P. Bonche,
P.-H. Heenen
[show abstract]
[hide abstract]
ABSTRACT: Two rotational bands have been found in the transfermium nuclei
251Md and 255Lr, the latter being the heaviest
nucleus so far studied in-beam. Both are assigned to a
[521]1/2- Nilsson state by comparison to theory. The
experiments have been carried out in the Accelerator Laboratory of the
University of Jyväskylä (JYFL), where the array of germanium
detectors JUROGAM was used in conjunction with the recoil-seperator RITU
and the focal-plane setup GREAT for gamma-spectroscopic studies.
04/2008; 1012:368-370.
-
A Chatillon,
Ch Theisen, E Bouchez,
P A Butler,
E Clément,
O Dorvaux,
S Eeckhaudt,
B J P Gall,
A Görgen,
T Grahn, [......],
P Nieminen,
J Pakarinen,
J Perkowski,
P Rahkila,
M Rousseau,
C Scholey,
J Uusitalo,
J N Wilson,
P Bonche,
P-H Heenen
[show abstract]
[hide abstract]
ABSTRACT: A rotational band has been unambiguously observed in an odd-proton transfermium nucleus for the first time. An in-beam gamma-ray spectroscopic study of 101/251Md has been performed using the gamma-ray array JUROGAM combined with the gas-filled separator RITU and the focal plane device GREAT. The experimental results, compared to Hartree-Fock-Bogolyubov calculations, lead to the interpretation that the rotational band is built on the [521]1/2(-) Nilsson state.
Physical Review Letters 04/2007; 98(13):132503. · 7.37 Impact Factor
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A. Görgen,
E. Clément,
W. Korten, E. Bouchez,
A. Chatillon,
A. Hürstel,
Y. Le Coz,
Ch. Theisen,
J. N. Wilson,
M. Zielinska, [......],
T. Czosnyka,
G. de France,
J. Gerl,
R.-D. Herzberg,
J. Iwanicki,
D. G. Jenkins,
G. D. Jones,
P. J. Napiorkowski,
G. Sletten,
C. Timis
[show abstract]
[hide abstract]
ABSTRACT: The coexistence of prolate and oblate shapes in the light krypton
isotopes was investigated by Coulomb excitation of radioactive
74Kr and 76Kr beams at sub-barrier energies from the SPIRAL
facility at GANIL. States up to the 8+ in the ground-state band
and several non-yrast states were populated in both cases via
multi-step Coulomb excitation. A large set of both transitional and
diagonal matrix elements was extracted from the measured differential
Coulomb excitation cross sections. A complementary lifetime measurement
using the recoil-distance Doppler shift method gave important
constraints for the determination of the matrix elements. The
signs of the quadrupole moments of the yrast and excited bands
represent direct evidence for the coexistence of prolate and oblate
shapes in both isotopes under study. The results are compared to
recent configuration mixing calculations based on the generator
coordinate method and Skyrme Hartree-Fock-Bogolyiubov mean-field
states.
The European Physical Journal Special Topics 01/2007; 150(1):117-120. · 1.56 Impact Factor
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O Perru,
O Sorlin,
S Franchoo,
F Azaiez, E Bouchez,
C Bourgeois,
A Chatillon,
J M Daugas,
Z Dlouhy,
Zs Dombrádi, [......],
F Nowacki,
Yu-E Penionzhkevich,
F de Oliveira Santos,
F Pougheon,
M G Saint-Laurent,
G Sletten,
M Stanoiu,
C Stodel,
Ch Theisen,
D Verney
[show abstract]
[hide abstract]
ABSTRACT: The reduced transition probabilities B(E2;0(+) --> 2(+)(1)) of the neutron-rich (74)Zn and (70)Ni nuclei have been measured by Coulomb excitation in a (208)Pb target at intermediate energy. These nuclei have been produced at Grand Accélérateur National d'Ions Lourds via interactions of a 60A MeV (76)Ge beam with a Be target. The B(E2) value for (70)Ni(42) is unexpectedly large, which indicates that neutrons added above N=40 strongly polarize the Z=28 proton core. In the Zn isotopic chain, the steep rise of B(E2) values beyond N=40 continues up to (74)Zn(44). The enhanced proton core polarization in (70)Ni is attributed to the monopole interaction between the neutron in the g(9/2) and protons in the f(7/2) and f(5/2) spin-orbit partner orbitals. This interaction could result in a weakening of magicity in (78)Ni(50).
Physical Review Letters 07/2006; 96(23):232501. · 7.37 Impact Factor
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J. M. Daugas,
M. Sawicka,
M. Pfützner,
I. Matea,
H. Grawe,
R. Grzywacz,
N. L. Achouri,
J. C. Angélique,
D. Baiborodin,
F. Becker, [......],
M. G. Saint‐Laurent,
J. E. Sauvestre,
G. Sletten,
O. Sorlin,
M. Stanoiu,
I. Stefan,
C. Stodel,
C. Theisen,
D. Verney,
J. Zylicz
[show abstract]
[hide abstract]
ABSTRACT: An island of isomers have recently been observed on both sides of the N=40 shell below the Ni isotopes. Isomeric states in the 65Fe and 67Fe allow the knowledge of the single particle structure around the νg9/2 shell. Moreover, the excitation energy of the first 2+ and 4+ states in the 68Fe have been established by β‐γ correlation. The evolution of the structure of the Fe isotopes going far away from the valley of stability is, for the first time, given for N>40. © 2006 American Institute of Physics
AIP Conference Proceedings. 04/2006; 831(1):427-429.
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J. E. Bastin,
R.-D. Herzberg,
P. A. Butler,
G. D. Jones,
R. D. Page,
D. G. Jenkins,
N. Amzal,
P. M. T. Brew,
N. J. Hammond,
R. D. Humphreys, [......],
W. Meczynski,
J. Styczen,
T. L. Khoo,
C. J. Lister,
A. V. Afanasjev,
H. J. Maier,
P. Reiter,
P. Bednarczyc,
K. Eskola,
K. Hauschild
[show abstract]
[hide abstract]
ABSTRACT: We report on a set of in-beam studies of excited states in 250Fm. We detected prompt γ rays by using the JUROSPHERE IV array and conversion electrons by using the SACRED spectrometer. Both devices were used in conjunction with the RITU gas-filled recoil separator located at the University of Jyväskylä. 250Fm nuclei were produced through the 204Hg(48Ca,2n)250Fm fusion-evaporation reaction. An experimental excitation function gave a maximum reaction cross section of (980 ± 160) nb at an energy of 209 MeV in the center of the target. Tagging techniques were employed, and a number of E2 transitions were observed that connected the ground-state band levels from spin 4+ up to 18+. The highly converted 4+→2+ transition is observed only by use of conversion electron spectroscopy. The observed ground-state band transitions indicate a rotational structure. We deduce a quadrupole deformation parameter of β2=0.28 ± 0.02. A low-energy background of apparent nuclear origin is observed in conversion electrons and postulated to arise from the decay of high-K bands. The half-life of 250Fm is measured to be 30.4 ± 1.5 min.
Phys. Rev. C. 02/2006; 73(2).
-
A. Chatillon,
Ch. Theisen,
P. T. Greenlees,
G. Auger,
J. E. Bastin, E. Bouchez,
B. Bouriquet,
J. M. Casandjian,
R. Cee,
E. Clément, [......],
S. Siem,
M. G. Saint-Laurent,
C. Simenel,
Yu. G. Sobolev,
Ch. Stodel,
J. Uusitalo,
A. Villari,
M. Bender,
P. Bonche,
P. -H. Heenen
[show abstract]
[hide abstract]
ABSTRACT: The odd-Z isotope 255Lr, its daughter 251Md and grand-daughter 247Es were studied in two experiments performed at GANIL and the University of Jyväskylä. The 255Lr nuclei were produced using the cold fusion-evaporation reaction 209Bi(48Ca, 2n)255Lr at a bombarding energy of 217MeV. The single-particle structure and decay properties were investigated using α, γ and electron
spectroscopy. The ground-state spin and parity could be assigned for 255Lr (1/2-) and 251Md (7/2-). States corresponding to the 7/2+[633], 7/2-[514] and 1/2-[521] Nilsson orbitals were observed. Results are compared to experimental data obtained in neighbouring isotopes and to Hartree-Fock-Bogoliubov
calculations using the Skyrme interaction SLy4 and a density-dependent pairing interaction. The position of the 1/2-[521] orbital from the spherical 2f
5/2 shell is discussed.
European Physical Journal A 01/2006; 30(2):397-411. · 2.19 Impact Factor
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S. Eeckhaudt,
N. Amzal,
J. E. Bastin, E. Bouchez,
P. A. Butler,
A. Chatillon,
K. Eskola,
J. Gerl,
T. Grahn,
A. Görgen, [......],
J. Perkowski,
A. Pritchard,
P. Reiter,
P. Rahkila,
C. Scholey,
Ch. Theisen,
J. Uusitalo,
K. Van de Vel,
J. Wilson,
H. J. Wollersheim
[show abstract]
[hide abstract]
ABSTRACT: The recoil-tagging technique has been employed to perform an in-beam gamma-ray spectroscopic study of the transfermium nucleus 254No. The experiment was carried out at the Department of Physics of the University of Jyvskyl and utilised the JUROGAM array of germanium detectors coupled to the gas-filled recoil separator RITU. The ground-state rotational band was extended and evidence for non-yrast states was observed for the first time.
European Physical Journal A 08/2005; 25:605-607. · 2.19 Impact Factor
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S. Eeckhaudt,
P. T. Greenlees,
N. Amzal,
J. E. Bastin, E. Bouchez,
P. A. Butler,
A. Chatillon,
K. Eskola,
J. Gerl,
T. Grahn, [......],
J. Pakarinen,
J. Perkowski,
A. Pritchard,
P. Reiter,
P. Rahkila,
C. Scholey,
Ch. Theisen,
J. Uusitalo,
K. Van de Vel,
J. Wilson
[show abstract]
[hide abstract]
ABSTRACT: Evidence for the decay of non-yrast states in 254No has been observed for the first time in an experiment performed at the University of Jyväskylä. The experiment employed
the JUROGAM array of germanium detectors coupled to the gas-filled recoil separator RITU and the focal-plane spectrometer
GREAT. The ground-state rotational band has been tentatively extended up to a spin of 24ℏ and has a smoothly behaving dynamical
moment of inertia. It is speculated that the observation of high-energy γ-rays is due to the decay of a K = 3 band-head state.
European Physical Journal A 01/2005; 26(2):227-232. · 2.19 Impact Factor
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D C Biswas,
A G Smith,
R M Wall,
D Patel,
G S Simpson,
D M Cullen,
J L Durell,
S J Freeman,
J C Lisle,
J F Smith, [......],
M Petit,
C Theisen, E Bouchez,
M Houry,
R Lucas,
B Cahan,
A Le Coguie,
B J P Gall,
O Dorvaux,
N Schulz
[show abstract]
[hide abstract]
ABSTRACT: Lifetimes of excited states have been measured for the positive-parity rotational bands in neutron-rich Ba-142,Ba-144 as well as the 7(-) and 9(-) states of the negative-parity band in Ba-144 using the differential Doppler shift method. The deduced quadrupole moment, Q(t), of the positive-parity band decreases with angular momentum and overall shows good agreement with earlier measurements. The measured lifetimes of 7(-) and 9(-) states are used to determine the electric dipole moment, D-0=0.17(3) and 0.09(1) e fm, respectively, in the negative-parity octupole band of Ba-144.
Physical Review C. 01/2005; 71(1).
-
P. T. Greenlees,
N. Amzal,
J. E. Bastin, E. Bouchez,
P. A. Butler,
A. Chatillon,
O. Dorvaux,
S. Eeckhaudt,
K. Eskola,
B. Gall, [......],
P. Nieminen,
J. Pakarinen,
P. Rahkila,
P. Reiter,
M. Rousseau,
C. Scholey,
Ch. Theisen,
J. Uusitalo,
J. Wilson,
H. -J. Wollersheim
[show abstract]
[hide abstract]
ABSTRACT: Over the past few years a great deal of new spectroscopic data has been obtained for transfermium nuclei. Recoil separators,
coupled with modern target position and focal-plane spectrometers, allow detailed studies of the structure and decay properties
of transfermium nuclei to be peformed. In-beam studies using the recoil-gating and recoil-decay tagging techniques mainly
provide information on yrast states, whilst complementary focal-plane decay studies give access to non-yrast and isomeric
structures. In-beam studies of nuclei in this region have largely been performed at ANL and JYFL, and decay experiments at
GSI, JYFL, GANIL and ANL. The present contribution is focussed on recent developments and experiments carried out by a number
of collaborating institutes at JYFL.
12/2004: pages 599-604;
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A. Hürstel,
Y. Le Coz, E. Bouchez,
A. Chatillon,
A. Görgen,
P. T. Greenlees,
K. Hauschild,
S. Juutinen,
H. Kettunen,
W. Korten, [......],
R. Julin,
H. Kankaanpää,
A. Keenan,
P. Kuusiniemi,
M. Leino,
A.-P. Leppänen,
M. Muikku,
J. Pakarinen,
P. Rahkila,
J. Uusitalo
[show abstract]
[hide abstract]
ABSTRACT: Prompt and delayed gamma-ray spectroscopy of very neutron-deficient bismuth isotopes 187, 189Bi has been performed using the recoil decay tagging method. A rotational band has been observed in 189Bi and is interpreted as a complete decoupling of a single proton from the deformed lead core. The results for 187Bi suggest a similar structure and coupling scheme. This study gives the first evidence for a prolate band in a light bismuth nucleus and confirms the prolate character of the low-lying rotational band observed in the core nuclei 188Pb and 186Pb.
European Physical Journal A 08/2004; 21(3):365-368. · 2.19 Impact Factor
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M. Sawicka,
I. Matea,
H. Grawe,
R. Grzywacz,
M. Pfützner,
M. Lewitowicz,
J. M. Daugas,
B. A. Brown,
A. Lisetskiy,
F. Becker, [......],
K. Rykaczewski,
M. G. Saint-Laurent,
J. E. Sauvestre,
O. Sorlin,
M. Stanoiu,
I. Stefan,
C. Stodel,
Ch. Theisen,
D. Verney,
J. Żylicz
[show abstract]
[hide abstract]
ABSTRACT: A decay spectroscopy study of the neutron-rich cobalt isotopes has been performed using fragmentation of a 86Kr36+ beam and the new LISE2000 spectrometer at GANIL. For 71Co and 73Co, the -delayed radiation has been observed for the first time, and the half-lives were found to be 79(5) ms and 41(4) ms, respectively. Features of the decay are discussed qualitatively in terms of nuclear models.
European Physical Journal A 01/2004; 22(3):455-459. · 2.19 Impact Factor
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M. Sawicka,
R. Grzywacz,
I. Matea,
H. Grawe,
M. Pfützner,
J. M. Daugas,
M. Lewitowicz,
D. L. Balabanski,
F. Becker,
G. Bélier, [......],
K. P. Rykaczewski,
M. G. Saint-Laurent,
J. E. Sauvestre,
O. Sorlin,
M. Stanoiu,
I. Stefan,
C. Stodel,
Ch. Theisen,
D. Verney,
J. Żylicz
[show abstract]
[hide abstract]
ABSTRACT: The yrast J = 8+ states in neutron-rich 70,72,74,76Ni nuclei are predicted to be isomeric. The present paper
describes two GANIL experiments. In the first of them a search was made for the 8+ isomeric states in 72,74Ni
nuclei via fragmentation of 76Ge using the ion -decay correlation technique. Although these states were not
observed, limits for their lifetimes were determined. In the second experiment the decay spectroscopy of
70,72
Co nuclei was performed using fragmentation of a 86Kr36+ beam and the new LISE2000 spectrometer. The
delayed rays from the decay of 70,72Co to 70,72Ni were observed using the EXOGAM germanium detectors.
The half life of 72Co was measured to be 62(3) ms and the level sequence of the lowest excited states in 72Ni
was suggested, with the 2+ state at 1096 keV. An attempt to reproduce the level scheme in terms of shell-model
calculations was undertaken. The reasons for the disappearance of the 8+ isomer in 72Ni are discussed.
Physical Review C 10/2003; 68:044304. · 3.31 Impact Factor
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A. Lopez-Martens,
T. Døssing,
T.L. Khoo,
B. Herskind,
T. Lauristen,
M. Matsuo,
K. Yoshida,
A. Korichi,
F. Hannachi,
I. Ahmad, [......],
G. Mukherjee,
M. Rejmund,
D. Rossbach,
C. Rossi Alvarez,
C. Schück,
G. Schonwasser,
A.K. Singh,
Ch Theisen,
Ch Vieu,
C. Ur
[show abstract]
[hide abstract]
ABSTRACT: We report on four recent results concerning the population and the decay of superdeformed states, namely the structure of excited superdeformed states in 194Hg, the search for fine structure of the last superdeformed transitions in 194Pb, the primary decay-out strength analysis in 194Hg and, as a consequence of this, the possibility of using the decay-out as a tool to study order-to-chaos properties of normally deformed states.
European Physical Journal A 03/2003; 20(1):49-53. · 2.19 Impact Factor
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M. Sawicka,
M. Pfützner,
R. Grzywacz,
J.M. Daugas,
I. Matea,
M. Lewitowicz,
H. Grawe,
F. Becker,
G. Bélier,
C. Bingham, [......],
O. Perru,
O. Roig,
K.P. Rykaczewski,
M.G. Saint-Laurent,
O. Sorlin,
M. Stanoiu,
I. Stefan,
C. Stodel,
C. Theisen,
D. Verney
[show abstract]
[hide abstract]
ABSTRACT: In the experiment performed at the LISE2000 spectrometer at GANIL neutron-rich nickel isotopes were studied by microsecond isomer spectroscopy. Evidence for an isomer in 76Ni is found, consistently with the shell model prediction of an 8 + state of
n(g9/2)2\nu (g_{9/2})^2
structure.
European Physical Journal A 03/2003; 20(1):109-110. · 2.19 Impact Factor
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P.T. Greenlees,
A.N. Andreyev,
J. Bastin,
F. Becker, E. Bouchez,
P.A. Butler,
J.F.C. Cocks,
Y. Coz,
K. Eskola,
J. Gerl, [......],
J. Pakarinen,
P. Rahkila,
P. Reiter,
Ch Schlegel,
C. Scholey,
Ch Theisen,
J. Uusitalo,
K. Vel,
R. Wadsworth,
H.-J. Wollersheim
[show abstract]
[hide abstract]
ABSTRACT: In recent years (1996-2001) the recoil-decay tagging technique has been employed with great success at the Department of Physics of the University of Jyvskyl. Various arrays of germanium detectors have been coupled to the RITU gas-filled separator in order to study nuclei far from stability. An overview of the physics studied with these arrays, along with discussion of technical development of the RITU separator, is presented. Even with a comparatively modest array of germanium detectors it has been possible to study nuclei produced with cross-sections as low as 200 nb.
European Physical Journal A 03/2003; 20(1):87-92. · 2.19 Impact Factor
