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M. Freer,
M.P. Nicoli,
S.M. Singer,
C.A. Bremner, S.P.G. Chappell,
W.D.M. Rae,
I. Boztosun,
B.R. Fulton,
D.L. Watson,
B.J. Greenhalgh,
G.K. Dillon,
R.L. Cowin,
D.C. Weisser,
Nuclear and Astrophysics Laboratory, University of Oxford, Keble Road, Oxford,
Department of Physics, University of York, Heslington, York,
Department of Nuclear Physics, Australian National University, Canberra ACT
[show abstract]
[hide abstract]
ABSTRACT: The {sup 12}C({sup 12}C,{sup 8}Be+{sup 8}Be){sup 8}Be reaction has been studied with 18 beam energies from 82 to 120 MeV. The detection of four of the six final-state {alpha}-particles in an array of eight 16-element strip detectors permitted the full reconstruction of the reaction kinematics. {sup 16}O excitation energy spectra spanning 19-40 MeV were measured, which provided evidence for {sup 16}O excited states up to 35.1 MeV. Angular correlation analysis indicates the dominant spins are 6 and 8 ({Dirac_h}/2{pi}), possibly extending to 10 ({Dirac_h}/2{pi}) at the highest excitation energies. The resulting energy-spin systematics are compared with the predictions of the {alpha} cluster model and cranked Nilsson-Strutinsky calculations.
Physical Review. C, Nuclear Physics. 11/2004; 70(6).
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B. J. Greenhalgh,
G. K. Dillon,
B. R. Fulton,
D. L. Watson,
R. L. Cowin,
M. Freer,
S. M. Singer, S. P. G. Chappell,
C. A. Bremner,
W. D. M. Rae,
D. C. Weisser
[show abstract]
[hide abstract]
ABSTRACT: An excitation function measurement has been performed over the laboratory range 52–94 MeV investigating resonance phenomena in the single excitation 16O (16O,16O*→12Cg.s.+α)16Og.s. breakup reaction. A number of enhancements are observed in these excitation functions for excitation to the 41+, 10.35 MeV and 42+, 11.09 MeV excited states in 16O. The overlap between these and previously measured enhancements is discussed. Excitation functions for the 22+, 9.84 MeV and 23+, 11.52 MeV excited states are also presented.
Phys. Rev. C. 05/2004; 69(5).
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F. M. Marqués,
M. Labiche,
N. A. Orr,
J. C. Angélique,
L. Axelsson,
B. Benoit,
U. C. Bergmann,
M. J. G. Borge,
W. N. Catford, S. P. G. Chappell, [......],
T. Nilsson,
A. Ninane,
G. Nyman,
I. Piqueras,
K. Riisager,
M. G. Saint Laurent,
F. Sarazin,
S. M. Singer,
O. Sorlin,
L. Stuttgé
[show abstract]
[hide abstract]
ABSTRACT: A new approach to the production and detection of bound neutron clusters is presented. The technique is based on the breakup of beams of very neutron-rich nuclei and the subsequent detection of the recoiling proton in a liquid scintillator. The method has been tested in the breakup of intermediate energy (30–50 MeV/nucleon) 11Li, 14Be, and 15B beams. Some six events were observed that exhibit the characteristics of a multineutron cluster liberated in the breakup of 14Be, most probably in the channel 10Be+4n. The various backgrounds that may mimic such a signal are discussed in detail.
Phys. Rev. C. 03/2002; 65(4).
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C. A. Bremner, S. P. G. Chappell,
I. Boztosun,
B. Fulton,
D. L. Watson,
B. J. Greenhalgh,
G. K. Dillon,
R. L. Cowin,
M. Freer,
M. P. Nicoli,
S. M. Singer
[show abstract]
[hide abstract]
ABSTRACT: New experimental data for the 12C+12C reaction have been measured in the centre-of-mass energy range E_{c.m.}= 40 to 60 MeV. Excitation functions for a number of single and mutual $^{12}$C inelastic channels have been measured which include the 0_{gs}, 2_{1}^+, 0_{2}^+, 3_{1}^-, and 4$_1^+$ 12C states. All of the reactions display largely unstructured excitation functions over this energy range. The absence of further resonances in this energy region for the 12C(12C,2C[3_1^-])12C[3_1^-$] reaction confirms theoretical predictions of the termination of the band of resonances found at lower centre-of-mass energies in this channel.
11/2001;
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P J Leask,
L Achouri,
J C Angélique,
B Benoit,
C Bremner,
W N Catford,
R Chapman, S P G Chappell,
N M Clarke,
E de Góes Brennard, [......],
X Liang,
F M Marqués,
M P Nicoli,
A Ninane,
N A Orr,
M Shawcross,
S M Singer,
M Smith,
K Spohr,
L Stuttgé
[show abstract]
[hide abstract]
ABSTRACT: In order to search for a proposed α:2n:α:2n:α molecular structure in 16C its break-up into 10Be + 6He, 12Be + α, 8He + 2α and 6He + 6He + α has been studied using a 560 MeV 16C beam inelastically excited on a 12C target. States in 16C appear to be only weakly populated in this reaction.
Journal of Physics G Nuclear and Particle Physics 07/2001; 27(8):B9. · 4.18 Impact Factor
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F M Marqués,
M Labiche,
N A Orr,
J C Angélique,
L Axelsson,
B Benoit,
U C Bergmann,
M J G Borge,
W N Catford, S P G Chappell, [......],
T Nilsson,
A Ninane,
G Nyman,
I Piqueras,
K Riisager,
M G Saint Laurent,
F Sarazin,
S M Singer,
O Sorlin,
L Stuttgé
[show abstract]
[hide abstract]
ABSTRACT: Three-body correlations in the dissociation of two-neutron halo nuclei are explored using a technique based on intensity interferometry and Dalitz plots. This provides for the com-bined treatment of both the n-n and core-n interactions in the exit channel. As an example, the breakup of 14 Be into 12 Be+n+n by Pb and C targets has been analysed and the halo n-n separation extracted. A finite delay between the emission of the neutrons in the reaction on the C target was observed and is attributed to 13 Be resonances populated in sequential breakup.
04/2001;
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[show abstract]
[hide abstract]
ABSTRACT: An angular correlation analysis of the breakup fragments from the 12C(24Mg,12C16O)8Be and 12C(24Mg,12C12C)12C reactions is presented. For the 12C+16O breakup of 28Si, spins of 13-, 8+(10+), and (12,14)+ are assigned to states at excitation energies of 28.0, 33.4, and 34.5 MeV, respectively. The results are compared to the resonances observed in 12C+16O scattering studies and to the predictions of nuclear models. For the 12C+12C breakup of 24Mg, previous spin assignments are verified and new assignments of (2+), 6+(8+), (6+), and 8+ are proposed for states at 20.5, 23.8, 25.1, and 26.4 MeV, respectively.
Phys. Rev. C. 02/2001; 63(3).
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M Freer,
J C Angelique,
L Axelsson,
B Benoit,
U Bergmann,
W N Catford, S P G Chappell,
N M Clarke,
N Curtis,
A D'Arrigo, [......],
J T Murgatroyd,
T Nilsson,
A Ninane,
N A Orr,
I Piqueras,
Saint M G Laurent,
S M Singer,
O Sorlin,
L Stuttge,
D L Watson
Phys. Rev. C. 01/2001; 63:034301.
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M Labiche,
N A Orr,
F M Marqués,
J C Angélique,
L Axelsson,
B Benoit,
U C Bergmann,
M J G Borge,
W N Catford, S P G Chappell, [......],
A Ninane,
G Nyman,
F.de Oliveira,
I Piqueras,
K Riisager,
Saint M G Laurent,
F Sarazin,
S M Singer,
O Sorlin,
L Stuttgé
Phys. Rev. Lett. 01/2001; 86:600-603.
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J.S. Winfield,
S. Fortier,
W. N. Catford,
S. Pita,
N. A. Orr,
J. Van de Wiele,
Y. Blumenfeld,
R Chapman, S. P. G. Chappell,
N. M. Clarke, [......],
S. Gales,
H. Langevin-Joliot,
H. Laurent,
I. Lhenry,
J. M. Maison,
P. Roussel-Chomaz,
M. Shawcross,
K Spohr,
T. Suomijarvi,
A. de Vismes
[show abstract]
[hide abstract]
ABSTRACT: The 11Be(p,d)10Be reaction has been performed in inverse kinematics with a radioactive 11Be beam of E/A = 35.3 MeV. Angular distributions for the 0+ ground state, the 2+, 3.37 MeV state and the multiplet of states around 6 MeV in 10Be were measured at angles up to 16 deg CM by detecting the 10Be in a dispersion-matched spectrometer and the coincident deuterons in a silicon array. Distorted wave and coupled-channels calculations have been performed to investigate the amount of 2+ core excitation in 11Be gs. The use of "realistic" 11Be wave functions is emphasised and bound state form factors have been obtained by solving the particle-vibration coupling equations. This calculation gives a dominant 2s component in the 11Be gs wave function with a 16% [2+ x 1d] core excitation admixture. Cross sections calculated with these form factors are in good agreement with the present data. The Separation Energy prescription for the bound state wave function also gives satisfactory fits to the data, but leads to a significantly larger [2 x 1d] component in 11Be gs. Comment: 39 pages, 12 figures. Accepted for publication in Nuclear Physics A. Added minor corrections made in proof to pages 26 and 34
09/2000;
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[show abstract]
[hide abstract]
ABSTRACT: A measurement of the 12C+16O breakup of 28Si following 24Mg scattering from targets of carbon, lithium oxide, and beryllium has been performed. A study of the relative energy of the correlated 12C and 16O fragments has allowed the excitation energy of states in 28Si to be determined. A comparison of the excitation energy spectra in 28Si obtained from the three targets indicates that the same states are populated in the 12C(24Mg,12C16O)8Be, 7Li(24Mg,12C16O)t, and 9Be(24Mg,12C16O)5He reactions. The data support the hypothesis that the reaction mechanism populating the 12C+16O breakup states observed in these channels is α transfer, and rule out an alternative involving resonant, or “doorway,” states in the 12C+24Mg compound system.
Phys. Rev. C. 07/2000; 62(3).
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M. Labiche,
N. A. Orr,
F. M. Marques,
J.C. Angelique,
L. Axelsson,
B. Benoit,
U. C. Bergmann,
M. J. G. Borge,
W. N. Catford, S. P. G. Chappell, [......],
A. Ninane,
G. Nyman,
F. De Oliveira,
I. Piqueras,
K. Riisager,
M G Saint-Laurent,
F. Sarazin,
S. M. Singer,
O. Sorlin,
L. Stuttge
[show abstract]
[hide abstract]
ABSTRACT: The two-neutron halo nucleus 14Be has been investigated in a kinematically complete measurement of the fragments (12Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross-sections, neutron angular distributions and invariant mass spectra characteristic of a halo were observed and the electromagnetic (EMD) contributions deduced. Comparison with three-body model predictions indicate that the halo wavefunction contains a large 2s1/2^2 admixture. The EMD invariant mass spectrum exhibited a relatively narrow structure near threshold (Edecay=1.8+/-0.1 MeV, Gamma = 0.8+/-0.4 MeV) consistent with a soft-dipole excitation.
07/2000;
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M Freer,
J C Angélique,
L Axelsson,
B Benoit,
U Bergmann,
W N Catford, S P G Chappell,
N M Clarke,
N Curtis,
A D'Arrigo, [......],
J T Murgatroyd,
T Nilsson,
A Ninane,
N A Orr,
I Piqueras,
Saint M G Laurent,
S M Singer,
O Sorlin,
L Stuttgé,
D L Watson
Phys. Rev. Lett. 01/1999; 82:1383.
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J S Winfield,
S Fortier,
W N Catford,
S Pita,
N A Orr,
Y Blumenfeld,
R Chapman, S P G Chappell,
N M Clarke,
N Curtis, [......],
H Langevin-Joliot,
H Laurent,
I Lhenry,
J-M Maison,
P Roussel-Chomaz,
M Shawcross,
M Smith,
K Spohr,
T Suomijärvi,
A de Vismes
[show abstract]
[hide abstract]
ABSTRACT: We have performed the Be reaction in inverse kinematics. The were detected in the SPEG spectrometer and the deuterons detected in a silicon array in coincidence. The yield to the first excited state of is greater than that to the ground state, and increases with angle. Strong population of the two-alpha plus two-neutron states near 6 MeV (in the two-centre shell-model description) is observed. The ultimate goal is to study the microscopic structure of from the extracted spectroscopic factors.
Journal of Physics G Nuclear and Particle Physics 12/1998; 25(4):755. · 4.18 Impact Factor
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M. Freer,
N. A. Orr,
M. Labiche,
F. M. Marqués,
J. C. Angélique,
L. Axelsson,
B. Benoit,
U. Bergmann,
M. J. G. Borge,
W. N. Catford, [......],
A. Ninane,
G. Nyman,
I. Piqueras,
K. Riisager,
M. G. Saint Laurent,
F. Sarazin,
S. Singer,
O. Sorlin,
L. Stuttgé,
D. L. Watson
[show abstract]
[hide abstract]
ABSTRACT: The two nuclei 12Be and 14Be have been studied using breakup reactions on p, 12C and 208Pb targets. The decay of 12Be into two helium clusters (6He+6He and 4He+8He) was observed from a series of excited states between 10 and 25 MeV, with spins in the range 4+ to 8+. The single neutron angular distributions for 14Be exhibit the narrow forward peak characteristic of a halo. The widths of these distributions in coincidence with 12Be fragments are ΓL = 78±6 and 80±1 MeV/c for breakup on carbon and lead. © 1998 American Institute of Physics.
AIP Conference Proceedings. 12/1998; 455(1):314-318.
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S. Fortier,
J. S. Winfield,
S. Pita,
W. N. Catford,
N. A. Orr,
Y. Blumenfeld,
R. Chapman, S. P. G. Chappell,
N. M. Clarke,
N. Curtis, [......],
H. Langevin-Joliot,
H. Laurent,
I. Lhenry,
J. M. Maison,
P. Roussel-Chomaz,
M. Shawcross,
M. Smith,
K. Spohr,
T. Suomijarvi,
A. de Vismes
[show abstract]
[hide abstract]
ABSTRACT: The reaction 11Be(p,d)10Be has been studied for
the first time, using a secondary 11Be beam of 35.3
MeV/nucleon. Angular distributions up to about
15cmo were measured by detecting 10Be
in a spectrometer and coincident deuterons in a position sensitive
silicon detector array. Preliminary analysis provides evidence for a
large core excitation component in the structure of
11BeGS.
11/1998; 455:239-244.
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[show abstract]
[hide abstract]
ABSTRACT: Resonances in12C+12C scattering have fuelled one of the longest debates in nuclear physics and there is no sign of any abatement as new experimental
results yield yet more resonances and raise new questions. These new data come from recent experiments at Argonne by Wuosmaa
and Betts, the Australian National University (ANU) by the Charissa collaboration and at several other laboratories throughout
the world. Many of the new results come from the study of the breakup of the two12C nuclei into six alpha particles. This renewed interest in12C+12C scattering has also resulted in new theoretical work on the nature of these resonant phenomena. In particular, resonances
involving the breakup of the12C+12C system into 6 alpha particles, suggest that alpha clustering may play an important role. In this paper we will review these
new experimental data and present some new theoretical calculations.
Il Nuovo Cimento A 04/1997; 110(9):1001-1006.
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M. Labiche,
N. A. Orr,
F. M. Marqués,
J. C. Angélique,
L. Axelsson,
B. Benoit,
U. C. Bergmann,
María José García Borge,
W. N. Catford, S. P. G. Chappell, [......],
A. Ninane,
G. Nyman,
F. De Oliveira,
Inmaculada Piqueras,
K. Riisager,
M G Saint-Laurent,
F. Sarazin,
S. M. Singer,
O. Sorlin,
L. Stuttgé
[show abstract]
[hide abstract]
ABSTRACT: 4 pages, 3 figures.-- PACS nrs.: 27.20.+n, 24.30.Gd, 25.60.Dz, 25.60.Gc. The two-neutron halo nucleus Be-14 has been investigated in a kinematically complete measurement of the fragments (Be-12 and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation. The authors are grateful to the support provided by the technical and operations staff of LPC and GANIL. Discussions with Ian Thompson and Pierre Descouvemont are also acknowledged. Peer reviewed
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F. M. Marqués,
M. Labiche,
N. A. Orr,
J. C. Angélique,
L. Axelsson,
B. Benoit,
U. C. Bergmann,
María José García Borge,
W. N. Catford, S. P. G. Chappell, [......],
T Nilsson,
A. Ninane,
G. Nyman,
I. Piqueras,
K. Riisager,
M G Saint-Laurent,
F. Sarazin,
S. M. Singer,
O. Sorlin,
L. Stuttgé
[show abstract]
[hide abstract]
ABSTRACT: 7 pages, 5 figures.-- PACS nrs.: 25.75.Gz; 21.10.Gv; 27.20.+n. The technique of intensity interferometry is proposed as a probe of the spatial configuration of two-neutron haloes. After exploring the sensitivity of interferometry to the n-n configuration, it is demonstrated that the application of the standard method for constructing the correlation function is not valid for halo neutrons. A new iterative method is presented and applied to measurements of the dissociation of He-6, Li-11 and Be-14. The correlation functions for these systems have thus been extracted for the first time and the corresponding root-mean-square n-n separations estimated. The results are in agreement with the predictions of available three-body models. This work was funded under the auspices of the IN2P3-CNRS (France) and EPSERC (United Kingdom). Additional support from the ALLIANCE programme (Ministère des Affaires Etrangères and British Council) and the Human Capital and Mobility Programme of the European Community (contract n8 CHGE-CT94-0056) is also acknowledged. Peer reviewed
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M. Freer,
I. Boztosun,
C. A. Bremner, S. P. G. Chappell,
R. L. Cowin,
G. K. Dillon,
B. R. Fulton,
B. J. Greenhalgh,
T. Munoz-Britton,
M. P. Nicoli,
W. D. M. Rae,
S. M. Singer,
N. Sparks,
D. L. Watson,
D. C. Weisser
[show abstract]
[hide abstract]
ABSTRACT: An analysis of the 12C(12C,3α)12C reaction was made at beam energies between 82 and 106 MeV. Decays to both the ground state and the excited states of 8Be were isolated, allowing states of different characters to be identified. In particular, evidence was found for a previously observed state at 11.16 MeV. An analysis of the angular distributions of the unnatural parity states at 11.83 and 13.35 MeV, previously assigned Jπ=2-, calls into question the validity of these assignments, suggesting that at least one of the states may correspond to Jπ=4-. Evidence is also found for 1- and 3- strengths associated with broad states between 11 and 14 MeV.
Phys. Rev. C. 76(3).
