-
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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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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A. Lépine-Szily,
G. F. Lima,
A. C. C. Villari,
W. Mittig,
R. Lichtenthäler,
M. Chartier,
N. A. Orr,
J. C. Angélique,
G. Audi, J. M. Casandjian, [......],
S. Lukyanov,
M. MacCormick,
D. J. Morrissey,
A. N. Ostrowski,
B. M. Sherrill,
C. Stephan,
T. Suomijärvi,
L. Tassan-Got,
D. J. Vieira,
J. M. Wouters
[show abstract]
[hide abstract]
ABSTRACT: Proton-rich isotopes of Ga, Ge, As, Se and Br had their total reaction cross-sections (σR) measured. Root-mean-squared matter radii were determined from Glauber model calculations, which reproduced the experimental σR values. For all isotopic series a decrease of the rrms with increasing neutron number and a correlation with deformation was observed.
European Physical Journal A 01/2005; 25:227-230. · 2.19 Impact Factor
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R Raabe,
J L Sida,
J L Charvet,
N Alamanos,
C Angulo, J M Casandjian,
S Courtin,
A Drouart,
D J C Durand,
P Figuera, [......],
S Heinrich,
C Jouanne,
V Lapoux,
A Lepine-Szily,
A Musumarra,
L Nalpas,
D Pierroutsakou,
M Romoli,
K Rusek,
M Trotta
[show abstract]
[hide abstract]
ABSTRACT: Quantum tunnelling through a potential barrier (such as occurs in nuclear fusion) is very sensitive to the detailed structure of the system and its intrinsic degrees of freedom. A strong increase of the fusion probability has been observed for heavy deformed nuclei. In light exotic nuclei such as 6He, 11Li and 11Be (termed 'halo' nuclei), the neutron matter extends much further than the usual nuclear interaction scale. However, understanding the effect of the neutron halo on fusion has been controversial--it could induce a large enhancement of fusion, but alternatively the weak binding energy of the nuclei could inhibit the process. Other reaction channels known as direct processes (usually negligible for ordinary nuclei) are also important: for example, a fragment of the halo nucleus could transfer to the target nucleus through a diminished potential barrier. Here we study the reactions of the halo nucleus 6He with a 238U target, at energies near the fusion barrier. Most of these reactions lead to fission of the system, which we use as an experimental signature to identify the contribution of the fusion and transfer channels to the total cross-section. At energies below the fusion barrier, we find no evidence for a substantial enhancement of fusion. Rather, the (large) fission yield is due to a two-neutron transfer reaction, with other direct processes possibly also involved.
Nature 11/2004; 431(7010):823-6. · 36.28 Impact Factor
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M. Chartier,
G. F. Lima,
A. Lépine‐Szily,
G. Audi,
W. Mittig,
N. Orr,
R. Lichtenthaler,
J.‐C. Angélique, J.‐M. Casandjian,
A. Cunsolo, [......],
M. Mac Cormick,
D. J. Morrissey,
A. N. Ostrowski,
B. M. Sherrill,
C. Stephan,
T. Suomijärvi,
L. Tassan‐Got,
D. J. Vieira,
A. C. C. Villari,
J. M. Wouters
[show abstract]
[hide abstract]
ABSTRACT: The masses of very neutron‐deficient 66As, 68,70,71Se and 71Br were measured for the first time and those of 64,65Ge and 67As remeasured, with total uncertainties ranging from 200 to 1000 keV, including systematic, extrapolation and statistical errors, using the SPEG direct time‐of‐flight method at GANIL. These new results are discussed and compared to other recent experimental data and mass predictions. © 2003 American Institute of Physics
AIP Conference Proceedings. 03/2003; 656(1):275-282.
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G. F. Lima,
A. Lépine-Szily,
G. Audi,
W. Mittig,
M. Chartier,
N. A. Orr,
R. Lichtenthaler,
J. C. Angelique, J. M. Casandjian,
A. Cunsolo, [......],
M. MacCormick,
D. J. Morrissey,
A. N. Ostrowski,
B. M. Sherrill,
C. Stephan,
T. Suomijarvi,
L. Tassan-Got,
D. J. Vieira,
A. C. C. Villari,
J. M. Wouters
[show abstract]
[hide abstract]
ABSTRACT: The masses of neutron-deficient nuclei close to the proton drip line are an important input for the rapid proton-capture process modeling above 56Ni. The measurement of the masses of proton-rich nuclei with 32<~Z<~35 has been made using a direct time-of-flight technique. The masses of the nuclides 66As,68Se, and 71Br are reported for the first time, with mass excesses of -51500(680), -53620(1000), and -57060(570) keV being found. The masses agree well in most cases with the Audi-Wapstra systematics.
Phys. Rev. C. 04/2002; 65(4).
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[show abstract]
[hide abstract]
ABSTRACT: The elastic scattering of strongly bound nuclei at energies of 10 to 70 MeV per nucleon shows the phenomenon of “rainbow scattering.”
A nuclear rainbow appears because of deflection to negative angles. This process involves a strong overlap of nuclear densities,
with values of up to twice the saturation density of nuclear matter. The 16O+16O system is studied with a high precision over a wide energy range from 7 to 70 MeV per nucleon in several laboratories. Primary
Airy maxima and higher order Airy structures are observed. At all energies, excellent fits are obtained with deep potentials
as deduced from the double-folding model involving a nucleon-nucleon interaction weakly dependent on the density. It is shown
that Pauli blocking expected at low energies is strongly reduced if the local momenta are calculated self-consistently. Systematics
confirms a refractive origin of large-angle scattering, at low energies inclusive. Thus, nuclear-rainbow scattering yields
unique information about the properties of cold nuclear matter at higher densities.
Physics of Atomic Nuclei 03/2002; 65(4):678-682. · 0.57 Impact Factor
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W Mittig,
H Savajols,
D Baiborodin, J M Casandjian,
C E Demonchy,
P Roussel-Chomaz,
F Sarazin,
Z Dlouh,
J Mrazek,
A V Belozyorov,
S M Lukyanov,
Y E Penionzhkevich,
N Alamanos,
A Drouart,
A Gillibert,
C Jouanne,
V Lapoux,
E Pollacco,
A Korichi,
J A Scarpaci
[show abstract]
[hide abstract]
ABSTRACT: Following mass measurements in the region N = 20 and N = 28, we have studied inelastic nuclear scattering for the nuclei 34 Si, 33 Al and 32 Mg. No evidence for a low-lying shape isomeric 0 + state was found in 34 Si, and an upper limit for the population cross-section could be established, rendering its existence very unlikely. A new transition was found in 33 Al, that is a good candidate for a 2p-2h state and therefore a determination of the 2p-2h gap at N = 20. Inelastic nuclear scattering strongly excites 3 − states, as seen in 34 Si. A strong transition was found in 32 Mg that should correspond to the first 3 − in this nucleus, lying very low as compared to theory and systematics in this region.
European Physical Journal A 01/2002; 15:157-160. · 2.19 Impact Factor
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M. Chartier,
W. Mittig,
G. Auger,
B. Blank, J. M. Casandjian,
M. Chabert,
J. Fermщ,
L. K. Fifield,
A. Gillibert,
A. S. Lalleman, [......],
M. H. Moscatello,
F. de Oliveira,
N. A. Orr,
G. Politi,
F. Sarazin,
H. Savajols,
C. Spitaels,
P. Van Isacker,
A. C. C. Villari,
M. Wiescher
[show abstract]
[hide abstract]
ABSTRACT: The mass-measurement programme at GANIL aims to measure the masses of heavy nuclei close to the N=Z line which is the ideal region to study neutron-proton pairing. An original direct time-of-flight mass-measurement method
was developed at GANIL which uses the CSS2 cyclotron as a high-resolution spectrometer. The masses of ions of A=68,76,80 and 100 have been measured with a precision of a few 10−6. Mass measurements will be performed with the new CIME cyclotron of SPIRAL using a similar method based on the measurement
of the phase of the accelerated ions for different radio-frequencies. A recently approved experiment will help develop this
new technique and aims to measure the mass of 31Ar radioactive nuclei with a precision of 10−6.
Hyperfine Interactions 12/2000; 132(1):273-279. · 0.21 Impact Factor
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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 $^{255}$Lr and its daughter $^{251}$Md and grand-daughter $^{247}Es were studied in two experiments performed at GANIL and the University of Jyväskylä. The $^{255}$Lr nuclei were produced using the cold fusion-evaporation reaction $^{209}$Bi($^{48}$Ca,2n)$^{255}$Lr at a bombarding energy of 217 MeV. The single-particle structure and decay properties were investigated using $\alpha$, $\gamma$ and electron spectroscopy. The groundstate spin and parity could be assigned for $^{255}$Lr ($1/2^−$) and $^{251}$Md ($7/2^−$). 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.
-
E. Clément,
A. Görgen,
W. Korten,
E. Bouchez,
A. Chatillon,
J.-P. Delaroche,
M. Girod,
H. Goutte,
A. Hürstel,
Y. Le Coz, [......],
T. Czosnyka,
G. De France,
J. Gerl,
R-D Herzberg,
J. Iwanicki,
D.G. Jenkins,
G D Jones,
P.J. Napiokowski,
G. Sletten,
C. Timis
[show abstract]
[hide abstract]
ABSTRACT: Shape coexistence in the light krypton isotopes was studied in two low-energy Coulomb excitation experiments using radioactive $^{74}$Kr and $^{76}$Kr beams from the SPIRAL facility at GANIL. The ground-state bands in both isotopes were populated up to the $8^+$ state via multi-step Coulomb excitation, and several non-yrast states were observed. Large sets of matrix elements were extracted for both nuclei from the observed $\\gamma$-ray yields. Diagonal matrix elements were determined by utilizing the reorientation effect. In both isotopes the spectroscopic quadrupole moments for the ground-state bands and the bands based on excited $0_2^+$ states are found to have opposite signs. The experimental data are interpreted within a phenomenological two-band mixing model and model-independent quadrupole invariants are deduced for the relevant $0^+$ states using the complete sets of matrix elements and the formalism of quadrupole sum rules. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and are compared both with the experimental results and with recent calculations using the Skyrme SLy6 effective interaction and the full generator-coordinate method restricted to axial shapes.
-
V. Lapoux,
N. Alamanos,
F. Auger,
V. Fekou-Youmbi,
A. Gillibert,
F Marie,
S. Ottini-Hustache,
J.-L. Sida,
D.T. Khoa,
Y. Blumenfeld, [......],
M. Chartier,
M.D. Cortina-Gil,
M. Mac Cormick,
W. Mittig,
F. De Oliveira Santos,
A. N. Ostrowski,
P. Roussel-Chomaz,
K. W. Kemper,
N. Orr,
J.S. Winfield
[show abstract]
[hide abstract]
ABSTRACT: To study the effect of the weak binding energy on the interaction potential between a light exotic nucleus and a target, elastic scattering of 6He at 38.3 MeV/nucleon on a 12C target was measured at Grand Accélérateur National d'Ions Lourds (GANIL). The 6He beam was produced by fragmentation. The detection of the scattered particles was performed by the GANIL spectrometer. The energy resolution was good enough to separate elastic from inelastic scattering contributions. The measured elastic data have been analyzed within the optical model, with the real part of the optical potential calculated in the double-folding model using a realistic density-dependent nucleon-nucleon interaction and the imaginary part taken in the conventional Woods-Saxon (WS) form. A failure of the "bare" real folded potential to reproduce the measured angular distribution over the whole angular range suggests quite a strong coupling of the higher-order breakup channels to the elastic channel. To estimate the strength of the breakup effects, a complex surface potential with a repulsive real part (designed to simulate the polarization effects caused by the projectile breakup) was added to the real folded and imaginary WS potentials. A realistic estimate of the polarization potential caused by the breakup of the weakly bound 6He was made based on a parallel study of 6He+12C and 6Li+12C optical potentials at about the same energies.
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A. Chatillon,
Ch. Theissen,
E. Bouchez,
E. Clément,
R. Dayras,
A. Drouart,
A. Görgen,
A. Hürstel,
W. Korten,
Y. Le Coz, [......],
A Korichi,
A. Lopez-Martens,
F.P. Hessberger,
S.M. Lukyanov,
Yu. E. Penionzhkevich,
Yu. G. Sobolev,
O. Dorvaux,
B.J.P. Gall,
F. Khalfallah,
M. Rousseau
-
M.D. Cortina-Gil,
A. Pakou,
N. Alamanos,
W. Mittig,
P. Roussel-Chomaz,
F. Auger,
J. Barrette,
Y. Blumenfeld, J.M. Casandjian,
M. Chartier, [......],
B. Fernandez,
N. Frascaria,
A. Gillibert,
H. Laurent,
A. Lepine-Szily,
N. Orr,
V. Pascalon,
J.A. Scarpaci,
J.-L. Sida,
T. Suomijarvi
-
A. Navin,
V. Tripathi,
Y. Blumenfeld,
V. Nanal,
C. Simenel, J.M. Casandjian,
G. De France,
R. Raabe,
D. Bazin,
A Chatterjee, [......],
S. Kailas,
R. C. Lemmon,
K. Mahata,
R.G. Pillay,
E.C. Pollacco,
K. Ramachandran,
M. Rejmund,
A. Shrivastava,
J.-L. Sida,
E. Tryggestad
[show abstract]
[hide abstract]
ABSTRACT: Partial residue cross sections for fusion and transfer have been measured from the intensities of characteristic gamma-rays for the $^{4,6}$ He + $^{63,65}$Cu systems at energies near the Coulomb barrier (Vb).
-
V. Lapoux,
N. Alamanos,
F. Auger,
V. Fekou-Youmbi,
A. Gillibert,
F Marie,
S. Ottini-Hustache,
J.-L. Sida,
D.T. Khoa, J.M. Casandjian, [......],
W. Mittig,
F.de Oliveira,
P. Roussel-Chomaz,
N. Orr,
J. Winfield,
Y. Blumenfeld,
J. Kelley,
F. Marechal,
J.A. Scarpaci,
T. Suomijarvi
-
E. Clément,
A. Görgen,
E. Bouchez,
A. Chatillon,
W. Korten,
Y. Le Coz,
C. Theisen,
C. Andreoiu,
F. Becker,
B. Blank, [......],
D. Pantelica,
J.A. Pinston,
P Rahkila,
M. Rejmund,
G. Sletten,
M. Stanoiu,
C. Timis,
R Wadsworth,
J.N. Wilson,
M. Zielinska
[show abstract]
[hide abstract]
ABSTRACT: Shape coexistence in the light krypton isotopes was studied in a series of experiments at GANIL using various experimental techniques. A new low-lying $0^+$ state, a so-called shape isomer, was found in delayed conversion-electron spectroscopy after fragmentation reactions. The systematics of such low-lying $0+^$ states suggests that the ground states of the isotopes $^{78}$Kr and $^{76}$Kr have prolate deformation, while states with prolate and oblate shape are practically degenerate and strongly mixed in $^{74}$Kr, and that the oblate configuration becomes the ground state in $^{72}$Kr. This scenario was tested in experiments performing low-energy Coulomb excitation of radioactive $^{76}$Kr and $^{74}$Kr beams from the SPIRAL facility. Both transitional and diagonal electromagnetic matrix elements were extracted from the observed $\gamma$-ray yields. The results find the prolate shape for the ground-state bands in $^{76}$Kr and $^{74}$Kr and an oblate deformation for the excited $2^{+}_{2}$ state in $^{74}$Kr, confirming the proposed scenario of shape coexistence
-
A. Görgen,
E. Clément,
E. Bouchez,
A. Chatillon,
W. Korten,
Y. Le Coz,
Ch. Theisen,
C. Andreoiu,
F. Becker,
B. Blank, [......],
D.G. Jenkins,
F. Johnston-Theasby,
P. Joshi,
I. Matea,
P. Napiorkowski,
F. De Oliveira Santos,
G. Sletten,
C. Timis,
R Wadsworth,
M. Zielinska
[show abstract]
[hide abstract]
ABSTRACT: The light Krypton isotopes were studied in a series of Coulomb excitation experiments using radioactive beams at GANIL. The static quadrupole moments found in these experiments give firm experimental evidence for the shape coexistence scenario that is based on theoretical calculations and on the systematics of low-lying excited 0+ states.
-
V. Lapoux,
N. Alamanos,
F. Auger,
Y. Blumenfeld, J.M. Casandjian,
M. Chartier,
M.D. Cortina-Gil,
V. Fékou-Youmbi,
A. Gillibert,
M. Mac Cormic, [......],
W. Mittig,
F. De Oliveira Santos,
N. A. Orr,
A. N. Ostrowski,
S. Ottini-Hustache,
P. Roussel-Chomaz,
J.A. Scarpaci,
J.-L. Sida,
T. Suomijärvi,
J.S. Winfield
[show abstract]
[hide abstract]
ABSTRACT: The 10;11Be(p,p) and (12C, 12C) reactions were analyzed to determine the in uence of the weak binding energies of exotic nuclei on their interaction potential. The elastic cross sections were measured at GANIL in inverse kinematics using radioactive 10;11Be beams produced at energies of 39:1 A and 38:4A MeV. The elastic proton scattering data were analyzed within the framework of the microscopic Jeukenne-Lejeune-Mahaux (JLM) nucleon-nucleus potential. The angular distributions are found to be best reproduced by reducing the real part of the microscopic optical potential, as a consequence of the coupling to the continuum. These effects modify deeply the elastic potential. Including the Virtual Coupling Potential (VCP), we show the ability of the general optical potentials to reproduce the data for scattering of unstable nuclei, using realistic densities. Finally, the concepts needed to develop a more general and microscopic approach of the VCP are discussed.
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E. Clément,
A. Görgen,
W. Korten,
E. Bouchez,
A. Chatillon,
J.-P. Delaroche,
M. Girod,
H. Goutte,
A. Hürstel,
Y. Le Coz, [......],
T. Czosnyka,
G. De France,
J. Gerl,
R-D Herzberg,
J. Iwanicki,
D.G. Jenkins,
G D Jones,
P. J. Napiorkowski,
G. Sletten,
C. N. Timis
Nuclear Physics Group.
