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W. N. Catford
[show abstract]
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ABSTRACT: The clustering of nucleons in nuclei is a widespread but elusive phenomenon
for study. Here, we wish to highlight the variety of theoretical approaches,
and demonstrate how they are mutually supportive and complementary. On the
experimental side, we describe recent advances in the study of the classic
cluster nucleus 24Mg. Also, recent studies of clustering in nuclei approaching
the neutron drip line are described. In the region near N/Z=2, both theory and
experiment now suggest that multi-centre cluster structure is important, in
particular for the very neutron rich beryllium isotopes.
02/2013;
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C. Beck,
P. Papka,
A. Sanchez i Zafra,
S. Thummerer,
F Azaiez,
P. Bednarczyk,
S. Courtin,
D. Curien,
O. Dorvaux,
A. Goasduff, [......],
D. Kamanin,
G De Angelis,
A. Gadea,
S. Lenzi,
D. R. Napoli,
S. Szilner,
M. Milin, W. N. Catford,
D.G. Jenkins,
G. Royer
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C. Beck,
P. Papka,
A. Sanchez i Zafra,
S. Thummerer,
F Azaiez,
P. Bednarczyk,
S. Courtin,
D. Curien,
O. Dorvaux,
A. Goasduff, [......],
D. Kamanin,
G De Angelis,
A. Gadea,
S. Lenzi,
D. R. Napoli,
S. Szilner,
M. Milin, W. N. Catford,
D.G. Jenkins,
G. Royer
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A. Banu,
F. Carstoiu,
N. L. Achouri, W. N. Catford,
M. Chartier,
B. Fernández-Domínguez,
M. Horoi,
B. Laurent,
N. A. Orr,
S. Paschalis,
N. Patterson,
B. Pietras,
B. T. Roeder,
P. Roussel-Chomaz,
J. S. Thomas,
L. Trache,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: Background: To understand explosive hydrogen burning in stars and to explore various explosive scenarios such as type I x-ray bursts (XRBs), reliable reaction rates are needed. The cross sections for radiative proton capture on near-dripline nuclei are necessary for the determination of the reaction rates, but cannot be measured directly.Purpose: To determine the reaction rate for the radiative proton capture reaction 23Al(p,γ)24Si using indirect methods and, as a consequence, evaluate if sequential 2p capture on 22Mg seed nuclei is significant at high temperatures.Method: Nonresonant radiative proton capture on 23Al is investigated using the one-proton breakup of 24Si at 61 MeV/nucleon and the asymptotic normalization coefficient (ANC) for 24Sigs→23Al+p is deduced.Results: From the ANC, the nonresonant component of the astrophysical S-factor for the 23Al(p,γ)24Si reaction is determined and, using other new experimental data the resonant component is re-evaluated.Conclusions: The 23Al(p,γ)24Si reaction is of interest for type I XRB nucleosynthesis and its reaction rate can affect both the 22Na abundance and the total energy output. New determinations of the rates for the 22Mg(p,γ)23Al(p,γ)24Si reaction chain are provided here and we point to the need that they be included in XRB scenarios.
Phys. Rev. C. 07/2012; 86(1).
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Zs. Podolyák,
S. J. Steer,
S. Pietri,
M. Górska,
P. H. Regan,
D. Rudolph,
A. B. Garnsworthy,
R. Hoischen,
J. Gerl,
H. J. Wollersheim, [......],
R. Krücken,
S. Lalkovski,
Z. Liu,
A. Maj,
S. Myalski,
S. Schwertel,
T. Shizuma,
P. M. Walker,
E. Werner-Malento,
O. Wieland
[show abstract]
[hide abstract]
ABSTRACT: Heavy neutron-rich nuclei have been populated through the relativistic fragmentation of a 20882Pb\ensuremath ^{208}_{\ 82}{\rm Pb} beam at E/A = 1\ensuremath E/A = 1 GeV on a 2.5 g/cm2\ensuremath 2.5 {\rm g/cm^2} thick Be target. The synthesised nuclei were selected and identified in-flight using the fragment separator at GSI. Approximately
300 ns after production, the selected nuclei were implanted in an ~ 8\ensuremath \sim 8 mm thick perspex stopper, positioned at the centre of the RISING g\ensuremath \gamma -ray detector spectrometer array. A previously unreported isomer with a half-life T1/2 = 163(5)\ensuremath T_{1/2} = 163(5) ns has been observed in the N = 126 closed-shell nucleus 20579Au\ensuremath ^{205}_{\ 79}{\rm Au} . Through g \gamma -ray singles and g \gamma -g \gamma coincidence analysis a level scheme was established. The comparison with a shell model calculation tentatively identifies
the spin-parity of the excited states, including the isomer itself, which is found to be Ip = (19/2+)\ensuremath I^{\pi} = (19/2^+) .
European Physical Journal A 04/2012; 42(3):489-493. · 2.19 Impact Factor
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M. Assié,
J. A. Scarpaci,
D. Lacroix,
J. C. Angélique,
D. Bazin,
D. Beaumel,
Y. Blumenfeld, W. N. Catford,
M. Chabot,
A. Chatterjee,
M. Fallot,
H. Iwasaki,
F. Maréchal,
D. Mengoni,
C. Monrozeau,
J. Nyberg,
C. Petrache,
F. Skaza,
T. Tuna
[show abstract]
[hide abstract]
ABSTRACT: The nuclear break-up of 6He on a 208Pb target was studied at 20A MeV using a secondary beam of 6He produced by the SPIRAL facility at GANIL. a \alpha -particles were detected in coincidence with two neutrons with a large angular coverage and the reaction mechanism was identified.
From the distribution of the relative angles between the two neutrons the correlation function was extracted. It shows a strong
correlation at small relative angles attributed to the contribution of the di-neutron configuration of 6He .
European Physical Journal A 04/2012; 42(3):441-446. · 2.19 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present the results of an experimental work that studied the direct component of the radiative proton capture reaction 23Al(p,γ)24Si for its relevance in X-ray burst nucleosynthesis. The experiment was performed at GANIL using one-proton nuclear breakup reaction at intermediate energies to determine the Asymptotic Normalization Coefficient (ANC) of the system 24Si→23Al + p. Using the ANC, we evaluated the corresponding astrophysical S factor and reaction rate.
Journal of Physics Conference Series 02/2012; 337(1):012059.
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M. Freer,
N. L. Achouri,
C. Angulo,
N. I. Ashwood,
D. W. Bardayan,
S. Brown, W. N. Catford,
K. A. Chipps,
N. Curtis,
P. Demaret, [......],
T. Munoz-Britton,
N. A. Orr,
S. D. Pain,
D. Price,
R. Raabe,
N. Soić,
J. S. Thomas,
C. Wheldon,
G. Wilson,
V. A. Ziman
[show abstract]
[hide abstract]
ABSTRACT: Measurements of the 4He(7Be,α)7Be and 4He(7Be,p)10B reactions were performed using 7Be beam energies of 7.1 and 23 MeV and a helium-4 target, employing the thick target technique. Resonances were observed between Ex(11C)=8.6 to 13.8 MeV. An R-matrix analysis was performed to characterize the spins and partial widths. This analysis showed that the observed sequence of states was consistent with that found for 7Li + α resonant scattering populating resonances in 11B. A comparison of the proposed partial widths for decay with the Wigner limit indicates that several of the states are associated with cluster-like structures.
Phys. Rev. C. 01/2012; 85(1).
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M Freer,
N L Achouri,
C Angulo,
N I Ashwood,
D W Bardayan,
S Brown, W N Catford,
K A Chipps,
N Curtis,
P Demaret, [......],
T Munoz-Britton,
N A Orr,
S D Pain,
D Price,
R Raabe,
N Soiifmmode acutecelse 'cfi,
J S Thomas,
C Wheldon,
G Wilson,
V A Ziman
Phys. Rev. C. 01/2012; 85(1):014304.
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M Freer,
N L Achouri,
C Angulo,
N I Ashwood,
D W Bardayan,
S Brown, W N Catford,
K A Chipps,
N Curtis,
P Demaret, [......],
T Munoz-Britton,
N A Orr,
S D Pain,
D Price,
R Raabe,
N Soiifmmode acutecelse 'cfi,
J S Thomas,
C Wheldon,
G Wilson,
V A Ziman
Physical Review C. 01/2012; 85(1):014304.
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A. Banu,
L. Trache,
F. Carstoiu,
N. L. Achouri,
A. Bonaccorso, W. N. Catford,
M. Chartier,
M. Dimmock,
B. Fernández-Domínguez,
M. Freer, [......],
N. Patterson,
E. S. Paul,
M. Petri,
B. Pietras,
B. T. Roeder,
F. Rotaru,
P. Roussel-Chomaz,
E. Simmons,
J. S. Thomas,
R. E. Tribble
[show abstract]
[hide abstract]
ABSTRACT: The ground state of the proton-rich nucleus 23 Al has been studied by one-proton removal on a carbon target at about 50 MeV/nucleon using the EXOGAM + SPEG experimental setup at GANIL. Longitudinal momentum distributions of the 22Mg breakup fragments, inclusive and in coincidence with γ rays de-exciting the residues, were measured. The ground-state structure of 23 Al is found to be a configuration mixing of a d-orbital valence proton coupled to four core states—0gs+, 21+, 41+, 42+. We confirm the ground state spin and parity of 23 Al as Jπ=5/2+. The measured exclusive momentum distributions are compared with extended Glauber model calculations to extract spectroscopic factors and asymptotic normalization coefficients (ANCs). The spectroscopic factors are presented in comparison with those obtained from large-scale shell model calculations. We determined the asymptotic normalization coefficient of the nuclear system 23 Algs → 22Mg(0+) + p to be Cd5/22(23Algs)=(3.90±0.44)×103 fm−1, and used it to infer the stellar reaction rate of the direct radiative proton capture 22Mg(p,γ)23 Al. Astrophysical implications related to 22Na nucleosynthesis in ONe novae and the use of one-nucleon breakup at intermediate energies as an indirect method in nuclear astrophysics are discussed.
Phys. Rev. C. 07/2011; 84(1).
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S J Steer,
Zs. Podolyak,
S Pietri,
M Gorska,
H Grawe,
K H Maier,
P H Regan,
D Rudolph,
A B Garnsworthy,
R Hoischen, [......],
R Krucken,
S Lalkovski,
Z Liu,
A Maj,
S Myalski,
S Schwertel,
T Shizuma,
P M Walker,
E Werner-Malento,
O Wieland
[show abstract]
[hide abstract]
ABSTRACT: Heavy neutron-rich nuclei were populated via the fragmentation of a E/A=1 GeV 208 82Pb beam. Secondary fragments were separated and identified and subsequently implanted in a passive stopper. By the detection of delayed γ rays, isomeric decays associated with these nuclei have been identified. A total of 49 isomers were detected, with the majority of them observed for the first time. The newly discovered isomers are in 204,205 80Hg, 201,202,204,205 79Au, 197,203,204 78Pt, 195,199−203 77Ir, 193,197−199 76Os, 196 75Re, 190,191 74W, and 189 73Ta. Possible level schemes are constructed and the structure of the nuclei discussed. To aid the interpretation, shell-model as well as BCS calculations were performed.
Physical Review C 05/2011; 84:044313. · 3.31 Impact Factor
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B. Fernandez-Dominguez,
J. S. Thomas, W. N. Catford,
F. Delaunay,
S. M. Brown,
N. A. Orr,
M. Rejmund,
M. Labiche,
M. Chartier,
N. L. Achouri, [......],
N. Patterson,
B. Pietras,
E. C. Pollacco,
A. Leprince,
A. Ramus,
J. A. Scarpaci,
N. de Sereville,
I. Stephan,
O. Sorlin,
G. L. Wilson
Physical Review C 01/2011; · 3.31 Impact Factor
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B. Fernandez-Dominguez,
J S Thomas, W. N. Catford,
F. Delaunay,
S. M. Brown,
N. A. Orr,
M. Rejmund,
N. L. Achouri,
H. Al Falou,
N. A. Ashwood, [......],
N. Patterson,
B. Pietras,
E.C. Pollacco,
A. Leprince,
A. Ramus,
J.A. Scarpaci,
N. De Séréville,
I. Stefan,
O. Sorlin,
G Wilson
[show abstract]
[hide abstract]
ABSTRACT: The spectroscopy of 21O has been investigated using a radioactive 20O beam
and the (d,p) reaction in inverse kinematics. The ground and first excited
states have been determined to be Jpi=5/2+ and Jpi=1/2+ respectively. Two
neutron unbound states were observed at excitation energies of 4.76 +- 0.10 and
6.16 +- 0.11. The spectroscopic factor deduced for the lower of these
interpreted as a 3/2+ level, reveals a rather pure 0d3/2 single-particle
configuration. The large energy difference between the 3/2+ and 1/2+ states is
indicative of the emergence of the N=16 magic number. For the higher lying
resonance, which has a character consistent with a spin-parity assignment of
3/2+ or 7/2-, a 71% branching ratio to the first 2+ state in 20O has been
observed. The results are compared with new shell model calculations.
12/2010;
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C. Beck,
P. Papka,
A. Sanchez i Zafra,
S. Thummerer,
F Azaiez,
P. Bednarczyk,
S. Courtin,
D. Curien,
O. Dorvaux,
A. Goasduff, [......],
D. Kamanin,
G De Angelis,
A. Gadea,
S. Lenzi,
D. R. Napoli,
S. Szilner,
M. Milin, W. N. Catford,
D.G. Jenkins,
G. Royer
[show abstract]
[hide abstract]
ABSTRACT: A great deal of research work has been undertaken in the alpha-clustering
study since the pioneering discovery, half a century ago, of 12C+12C molecular
resonances. Our knowledge of the field of the physics of nuclear molecules has
increased considerably and nuclear clustering remains one of the most fruitful
domains of nuclear physics, facing some of the greatest challenges and
opportunities in the years ahead. In this work, the occurence of "exotic"
shapes in light N=Z alpha-like nuclei is investigated. Various approaches of
superdeformed and hyperdeformed bands associated with quasimolecular resonant
structures are presented. Results on clustering aspects are also discussed for
light neutron-rich Oxygen isotopes.
11/2010;
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T Muñoz-Britton,
M Freer,
N I Ashwood,
T A D Brown, W N Catford,
N Curtis,
S P Fox,
B R Fulton,
C W Harlin,
A M Laird,
P Mumby-Croft,
A St J Murphy,
P Papka,
D L Price,
K Vaughan,
D L Watson,
D C Weisser
[show abstract]
[hide abstract]
ABSTRACT: A search for the 2+ excitation of the Hoyle state in 12C has been performed using the 12C(12C,3α)12C reaction at a beam energy of 101.5 MeV. An angular correlation analysis was used to suppress known contributions to the excitation energy spectrum, enhancing the experimental sensitivity. No strong evidence was found for new states in 12C between 9 and 11 MeV; rather upper limits for their excitation in the 12C+12C inelastic scattering reaction are determined.
Journal of Physics G Nuclear and Particle Physics 07/2010; 37(10):105104. · 4.18 Impact Factor
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W N Catford,
C N Timis,
R C Lemmon,
M Labiche,
N A Orr,
B Fernández-Domínguez,
R Chapman,
M Freer,
M Chartier,
H Savajols, [......],
G de France,
W Gelletly,
X Liang,
S D Pain,
V P E Pucknell,
B Rubio,
O Sorlin,
K Spohr,
Ch Theisen,
D D Warner
[show abstract]
[hide abstract]
ABSTRACT: The transfer of neutrons onto 24Ne has been measured using a reaccelerated radioactive beam of 24Ne to study the (d,p) reaction in inverse kinematics. The unusual raising of the first 3/2+ level in 25Ne and its significance in terms of the migration of the neutron magic number from N=20 to N=16 is put on a firm footing by confirmation of this state's identity. The raised 3/2+ level is observed simultaneously with the intruder negative parity 7/2- and 3/2- levels, providing evidence for the reduction in the N=20 gap. The coincident gamma-ray decays allowed the assignment of spins as well as the transferred orbital angular momentum. The excitation energy of the 3/2+ state shows that the established USD shell model breaks down well within the sd model space and requires a revised treatment of the proton-neutron monopole interaction.
Physical Review Letters 05/2010; 104(19):192501. · 7.37 Impact Factor
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W. N. Catford,
C. N. Timis,
R. C. Lemmon,
M. Labiche,
N. A. Orr,
B. Fernandez-Dominguez,
R Chapman,
M. Freer,
M. Chartier,
H. Savajols, [......],
G. De France,
W Gelletly,
X Liang,
S. D. Pain,
V. P. E. Pucknell,
B Rubio,
O. Sorlin,
K Spohr,
Ch. Theisen,
D D Warner
[show abstract]
[hide abstract]
ABSTRACT: The transfer of neutrons onto 24Ne has been measured using a reaccelerated radioactive beam of 24Ne to study the (d,p) reaction in inverse kinematics. The unusual raising of the first 3/2+ level in 25Ne and its significance in terms of the migration of the neutron magic number from N=20 to N=16 is put on a firm footing by confirmation of this state's identity. The raised 3/2+ level is observed simultaneously with the intruder negative parity 7/2- and 3/2- levels, providing evidence for the reduction in the N=20 gap. The coincident gamma-ray decays allowed the assignment of spins as well as the transferred orbital angular momentum. The excitation energy of the 3/2+ state shows that the established USD shell model breaks down well within the sd model space and requires a revised treatment of the proton-neutron monopole interaction. Comment: Phys. Rev. Lett. in press (4 pages, 3 figures)
04/2010;
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W. N. Catford,
C. N. Timis,
R. C. Lemmon,
M. Labiche,
N. A. Orr,
L. Caballero,
R Chapman,
M. Chartier,
M. Rejmund,
H. Savajols,
for the TIARA Collaboration
[show abstract]
[hide abstract]
ABSTRACT: A general experimental technique for high resolution studies of nucleon transfer reactions using radioactive beams is briefly described, together with the first new physics results that have been obtained with the new TIARA array. These first results from TIARA are for the reaction 24Ne(d,p)25Ne, studied in inverse kinematics with a pure radioactive beam of 100,000 pps from the SPIRAL facility at GANIL. The reaction probes the energies of neutron orbitals relevant to very neutron rich nuclei in this mass region and the results highlight the emergence of the N=16 magic number for neutrons and the associated disappearance of the N=20 neutron magic number for the very neutron rich neon isotopes. Comment: Proceedings of the Carpathian Summer School of Physics, Mamaia-Constanta, Romania, 13-24 June 2005
12/2009;
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A. B. Garnsworthy,
P. H. Regan,
S. Pietri,
Y. Sun,
F. R. Xu,
D. Rudolph,
M. Górska,
L. Cáceres,
Zs. Podolyák,
S. J. Steer, [......],
S. Lalkovski,
Z. Liu,
A. Maj,
S. Myalski,
M. Pfützner,
S. Schwertel,
T. Shizuma,
A. J. Simons,
P. M. Walker,
O. Wieland
[show abstract]
[hide abstract]
ABSTRACT: The relativistic projectile fragmentation of a 750 MeV per nucleon beam of 107Ag was used to populate isomeric states in neutron-deficient nuclei around A=80–90. Reaction products were separated and unambiguously identified using the GSI FRagment Separator (FRS) and its ancillary detectors. At the final focal plane, the fragments were slowed from relativistic energies by means of an aluminium degrader and implanted in a passive stopper in the center of the high-efficiency, high-granularity Stopped Rare Isotope Spectroscopic INvestigation at GSI (RISING) germanium array. This allowed the identification of excited states in the N=Z nuclei 4386Tc and, for the first time, 4182Nb. Isomeric states have also been identified for the first time in 87,88Tc, and a previously unreported isomer was observed in 84Nb. Experimental results are presented along with a discussion on the structure of these nuclei based on interpretations provided by several theoretical models.
Physical Review C 12/2009; 80(6):064303. · 3.31 Impact Factor
