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G. F. Grinyer,
D. Bazin,
A. Gade,
J. A. Tostevin,
P. Adrich,
M. D. Bowen,
B. A. Brown,
C. M. Campbell,
J. M. Cook,
T. Glasmacher, S. McDaniel,
A. Obertelli,
K. Siwek,
J. R. Terry,
D. Weisshaar,
R. B. Wiringa
[show abstract]
[hide abstract]
ABSTRACT: A systematic investigation of the inclusive cross sections for single-nucleon knockout reactions from p-shell nuclei has been performed. A total of seven reactions were studied for projectiles with masses between A=7 and 10, having a wide range of nucleon separation energies. Results were obtained for a range of incident beam energies and targets. These differences were found to have a minimal impact on the deduced cross sections. Experimental results were compared to theoretical predictions based on variational Monte Carlo (VMC) nuclear structure calculations, whose radial overlap functions and neutron and proton densities were included in the reaction description. These results are compared with the conventional model, developed for heavier nuclei, that uses shell-model and Hartree-Fock structure inputs. The VMC-based calculations agreed with the experimental data for several reactions where deeply bound nucleons are removed but does not describe some of the more weakly bound nucleon removal cases with comparable accuracy.
Phys. Rev. C. 08/2012; 86(2).
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R Winkler,
A Gade,
T Baugher,
D Bazin,
B A Brown,
T Glasmacher,
G F Grinyer,
R Meharchand, S McDaniel,
A Ratkiewicz,
D Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei (47,48)Ar using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced B(E2) transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N=28 remains a challenge.
Physical Review Letters 05/2012; 108(18):182501. · 7.37 Impact Factor
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A Lemasson,
H Iwasaki,
C Morse,
D Bazin,
T Baugher,
J S Berryman,
A Dewald,
C Fransen,
A Gade, S Mcdaniel,
A Nichols,
A Ratkiewicz,
S Stroberg,
P Voss,
R Wadsworth,
D Weisshaar,
K Wimmer,
R Winkler
[show abstract]
[hide abstract]
ABSTRACT: The lifetimes of the first 2+ states in the neutron-deficient 76,78 Sr isotopes were measured using a unique combination of the γ -ray line-shape method and two-step nucleon exchange reactions at intermediate energies. The transition rates for the 2 + states were determined to be B(E2; 2 + → 0 +) = 2220(270) e2fm4 for 76 Sr and 1800(250) e2fm4 for 78 Sr, corresponding to large deformation of β 2 = 0.45(3) for 76 Sr and 0.40(3) for 78 Sr. The present data provide experimental evidence for mutually enhanced collectivity that occurs at N = Z = 38. The systematic behavior of the excitation energies and B(E2) values indicates a signature of shape coexistence in 76 Sr, characterizing 76 Sr as one of most deformed nuclei with an unusually reduced E(4 +)/E(2 +) ratio.
Physical Review C 04/2012; 85:041303. · 3.31 Impact Factor
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A. Lemasson,
H. Iwasaki,
C. Morse,
D. Bazin,
T. Baugher,
J. S. Berryman,
A. Dewald,
C. Fransen,
A. Gade, S. McDaniel,
A. Nichols,
A. Ratkiewicz,
S. Stroberg,
P. Voss,
R. Wadsworth,
D. Weisshaar,
K. Wimmer,
R. Winkler
[show abstract]
[hide abstract]
ABSTRACT: The lifetimes of the first 2$^{+}$ states in the neutron-deficient
$^{76,78}$Sr isotopes were measured using a unique combination of the
$\gamma$-ray line-shape method and two-step nucleon exchange reactions at
intermediate energies. The transition rates for the 2$^{+}$ states were
determined to be $B$(E2;2$^{+}$$\to 0^{+}$) = 2220(270) e$^{2}$fm$^{4}$ for
$^{76}$Sr and 1800(250) e$^{2}$fm$^{4}$ for $^{78}$Sr, corresponding to large
deformation of $\beta_2$ = 0.45(3) for $^{76}$Sr and 0.40(3) for $^{78}$Sr. The
present data provide experimental evidence for mutually enhanced collectivity
that occurs at $N$ = $Z$ = 38. The systematic behavior of the excitation
energies and $B$(E2) values indicates a signature of shape coexistence in
$^{76}$Sr, characterizing $^{76}$Sr as one of most deformed nuclei with an
unusually reduced $E$(4$^{+}$)/$E$(2$^{+}$) ratio.
04/2012;
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R Meharchand,
R G T Zegers,
B A Brown,
Sam M Austin,
T Baugher,
D Bazin,
J Deaven,
A Gade,
G F Grinyer,
C J Guess, [......],
J Pereira,
A M Prinke,
A Ratkiewicz,
A Signoracci,
S Stroberg,
L Valdez,
P Voss,
K A Walsh,
D Weisshaar,
R Winkler
[show abstract]
[hide abstract]
ABSTRACT: We present a novel technique for studying the quenching of shell gaps in exotic isotopes. The method is based on extracting Gamow-Teller (ΔL=0, ΔS=1) transition strengths [B(GT)] to low-lying states from charge-exchange reactions at intermediate beam energies. These Gamow-Teller strengths are very sensitive to configuration mixing between cross-shell orbitals, and this technique thus provides an important complement to other tools currently used to study cross-shell mixing. This work focuses on the N=8 shell gap. We populated the ground and 2.24 MeV 0+ states in 12Be using the 12B(1+) (7Li, 7Be) reaction at 80 MeV/u in inverse kinematics. Using the ground-state B(GT) value from β-decay measurements (0.184±0.007) as a calibration, the B(GT) for the transition to the second 0+ state was determined to be 0.214±0.051. Comparing the extracted Gamow-Teller strengths with shell-model calculations, it was determined that the wave functions of the first and second 0+ states in 12Be are composed of 25±5% and 60±5% (0s)4(0p)8 configurations, respectively.
Physical Review Letters 03/2012; 108(12):122501. · 7.37 Impact Factor
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S. McDaniel,
A. Gade,
J. A. Tostevin,
T. Baugher,
D. Bazin,
B. A. Brown,
J. M. Cook,
T. Glasmacher,
G. F. Grinyer,
A. Ratkiewicz,
D. Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: Background: Thick-target-induced nucleon-adding transfer reactions onto
energetic rare-isotope beams are an emerging spectroscopic tool. Their
sensitivity to single-particle structure complements one-nucleon removal
reaction capabilities in the quest to reveal the evolution of nuclear shell
structure in very exotic nuclei. Purpose: To add intermediate-energy,
carbon-target-induced one-proton pickup reactions to the arsenal of
$\gamma$-ray tagged direct reactions applicable in the regime of low beam
intensities and to apply these for the first time to $fp$-shell nuclei.
Methods: Inclusive and partial cross sections were measured for the
$\nuc{12}{C}(\nuc{48}{Cr},\nuc{49}{Mn}+\gamma)$X and
$\nuc{12}{C}(\nuc{50}{Fe},\nuc{51}{Co}+\gamma)$X proton pickup reactions at
56.7 and 61.2 MeV/nucleon, respectively, using coincident particle-$\gamma$
spectroscopy at the NSCL. The results are compared to reaction theory
calculations using $fp$-shell-model nuclear structure input. For comparison
with our previous work, the same reactions were measured on \nuc{9}{Be}
targets. Results: The measured partial cross sections confirm the specific
population pattern predicted by theory, with pickup into high-$\ell$ orbitals
being strongly favored; driven by linear and angular momentum matching.
Conclusion: Carbon target-induced pickup reactions are well-suited, in the
regime of modest beam intensity, to study the evolution of nuclear structure,
with specific sensitivities that are well described by theory.
01/2012;
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C Fransen,
W Rother,
H Iwasaki,
A Dewald,
T Baugher,
D Bazin,
B A Brown,
H L Crawford,
A Gade,
T N Ginter, [......],
D Miller,
P Petkov,
T Pissulla,
A Ratkiewicz,
K Starosta,
C A Ur,
P Voss,
K A Walsh,
D Weisshaar,
K O Zell
[show abstract]
[hide abstract]
ABSTRACT: The properties of exotic neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 are of particular interest for the understanding of the shell structure for large neutron excess. Effects related to the energy gap between the neutron fp and 1g9/2 shells lead to a strong variation of collectivity for nuclei around N = 40. Whereas 68Ni was found to have doubly magic properties, this was not observed in neighbouring nuclei. Recent shell model calculations for the neutron rich iron isotopes clearly reveal the difficulty to describe nuclei in this mass region and resulted in large deviations of the predicted collectivity depending on the valence space. However, no experimental data on the transition strength existed for the very exotic nucleus 66Fe at N = 40. Here we present the newest results on absolute transition strengths of the lowest excited states in 62,64,66Fe measured model independently using the recoil distance Doppler-shift (RDDS) method. The experiments were performed at NSCL at Michigan State University with the Cologne/NSCL plunger device using Coulomb excitation in inverse kinematics at energies of 80 MeV/u. Our results yield a much higher collectivity for 64,66Fe than expected and allow tests of new calculations.
Journal of Physics Conference Series 09/2011; 312(9):092025.
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M Petri,
P Fallon,
A O Macchiavelli,
S Paschalis,
K Starosta,
T Baugher,
D Bazin,
L Cartegni,
R M Clark,
H L Crawford, [......], S McDaniel,
D Miller,
M M Rajabali,
A Ratkiewicz,
W Rother,
P Voss,
K A Walsh,
D Weisshaar,
M Wiedeking,
B A Brown
[show abstract]
[hide abstract]
ABSTRACT: Establishing how and when large N/Z values require modified or new theoretical tools is a major quest in nuclear physics. Here we report the first measurement of the lifetime of the 2(1)+ state in the near-dripline nucleus 20C. The deduced value of τ(2(1)+)=9.8±2.8(stat)(-1.1)(+0.5)(syst) ps gives a reduced transition probability of B(E2; 2(1)+→0(g.s.)+)=7.5(-1.7)(+3.0)(stat)(-0.4)(+1.0)(syst) e2 fm4 in good agreement with a shell model calculation using isospin-dependent effective charges.
Physical Review Letters 09/2011; 107(10):102501. · 7.37 Impact Factor
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G F Grinyer,
D Bazin,
A Gade,
J A Tostevin,
P Adrich,
M D Bowen,
B A Brown,
C M Campbell,
J M Cook,
T Glasmacher, S McDaniel,
P Navrátil,
A Obertelli,
S Quaglioni,
K Siwek,
J R Terry,
D Weisshaar,
R B Wiringa
[show abstract]
[hide abstract]
ABSTRACT: Absolute cross sections have been determined following single neutron knockout reactions from 10Be and 10C at intermediate energy. Nucleon density distributions and bound-state wave function overlaps obtained from both variational Monte Carlo (VMC) and no core shell model (NCSM) ab initio calculations have been incorporated into the theoretical description of knockout reactions. Comparison to experimental cross sections demonstrates that the VMC approach, with the inclusion of 3-body forces, provides the best overall agreement while the NCSM and conventional shell-model calculations both overpredict the cross sections by 20% to 30% for 10Be and by 40% to 50% for 10C, respectively. This study gains new insight into the importance of 3-body forces and continuum effects in light nuclei and provides a sensitive technique to assess the accuracy of ab initio calculations for describing these effects.
Physical Review Letters 04/2011; 106(16):162502. · 7.37 Impact Factor
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A. Gade,
D. Bazin,
B. A. Brown,
C. M. Campbell,
J. M. Cook,
S. Ettenauer,
T. Glasmacher,
K. W. Kemper, S. McDaniel,
A. Obertelli,
T. Otsuka,
A. Ratkiewicz,
J. R. Terry,
Y. Utsuno,
D. Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: Excited states in the very neutron-rich nuclei 35Mg and 33Na were populated in the fragmentation of a 38Si projectile beam on a Be target at 83 MeV/u beam energy. We report on the first observation of γ-ray transitions in 35Mg, the odd-N neighbor of 34Mg and 36Mg, which are known to be part of the ‘island of inversion” around N=20. The results are discussed in the framework of large-scale shell-model calculations. For the A=3Z nucleus 33Na, a new γ-ray transition was observed that is suggested to complete the γ-ray cascade 7/2+→5/2+→3/2gs+ connecting three neutron two-particle–two-hole intruder states that are predicted to form a close-to-ideal K=3/2 rotational band in the strong-coupling limit.
Phys. Rev. C. 04/2011; 83(4).
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A Gade,
J A Tostevin,
T. Baugher,
D. Bazin,
B A Brown,
C M Campbell,
T. Glasmacher,
G. F. Grinyer, S McDaniel,
K. Meierbachtol,
A Ratkiewicz,
S. R. Stroberg,
K. A. Walsh,
D. Weisshaar,
R. Winkler
[show abstract]
[hide abstract]
ABSTRACT: New measurements and reaction model calculations are reported for single
neutron pickup reactions onto a fast \nuc{22}{Mg} secondary beam at 84 MeV per
nucleon. Measurements were made on both carbon and beryllium targets, having
very different structures, allowing a first investigation of the likely nature
of the pickup reaction mechanism. The measurements involve thick reaction
targets and $\gamma$-ray spectroscopy of the projectile-like reaction residue
for final-state resolution, that permit experiments with low incident beam
rates compared to traditional low-energy transfer reactions. From measured
longitudinal momentum distributions we show that the $\nuc{12}{C}
(\nuc{22}{Mg},\nuc{23}{Mg}+\gamma)X$ reaction largely proceeds as a direct
two-body reaction, the neutron transfer producing bound \nuc{11}{C} target
residues. The corresponding reaction on the \nuc{9}{Be} target seems to largely
leave the \nuc{8}{Be} residual nucleus unbound at excitation energies high in
the continuum. We discuss the possible use of such fast-beam one-neutron pickup
reactions to track single-particle strength in exotic nuclei, and also their
expected sensitivity to neutron high-$\ell$ (intruder) states which are often
direct indicators of shell evolution and the disappearance of magic numbers in
the exotic regime.
03/2011;
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A Gade,
D. Bazin,
B A Brown,
C M Campbell,
J M Cook,
S Ettenauer,
T. Glasmacher,
K. W. Kemper, S McDaniel,
A. Obertelli,
T Otsuka,
A Ratkiewicz,
J R Terry,
Y Utsuno,
D. Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: Excited states in the very neutron-rich nuclei 35Mg and 33Na were populated
in the fragmentation of a 38Si projectile beam on a Be target at 83 MeV/u beam
energy. We report on the first observation of gamma-ray transitions in 35Mg,
the odd-N neighbor of 34Mg and 36Mg, which are known to be part of the "Island
of Inversion" around N = 20. The results are discussed in the framework of
large- scale shell-model calculations. For the A = 3Z nucleus 33Na, a new
gamma-ray transition was observed that is suggested to complete the gamma-ray
cascade 7/2+ --> 5/2+ --> 3/2+ gs connecting three neutron 2p-2h intruder
states that are predicted to form a close-to-ideal K = 3/2 rotational band in
the strong-coupling limit.
03/2011;
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W Rother,
A Dewald,
H Iwasaki,
S M Lenzi,
K Starosta,
D Bazin,
T Baugher,
B A Brown,
H L Crawford,
C Fransen, [......], S McDaniel,
D Miller,
P Petkov,
Th Pissulla,
A Ratkiewicz,
C A Ur,
P Voss,
K A Walsh,
D Weisshaar,
K-O Zell
[show abstract]
[hide abstract]
ABSTRACT: The transition rates for the 2(1)+ states in (62,64,66)Fe were studied using the recoil distance Doppler-shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N = 40. The results are interpreted using the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N = 40 as governed by the number of valence protons with respect to Z ≈ 30. The trend of collectivity suggested by the experimental data is described by state-of-the-art shell-model calculations with a new effective interaction developed for the fpgd valence space.
Physical Review Letters 01/2011; 106(2):022502. · 7.37 Impact Factor
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A. Gade,
T. Baugher,
D. Bazin,
B. A. Brown,
C. M. Campbell,
T. Glasmacher,
G. F. Grinyer,
M. Honma, S. McDaniel,
R. Meharchand,
T. Otsuka,
A. Ratkiewicz,
J. A. Tostevin,
K. A. Walsh,
D. Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: The neutron-rich N=50 isotones 82Ge and 84Se were investigated using intermediate-energy Coulomb excitation on a 197Au target and inelastic scattering on 9Be. As typical for intermediate-energy Coulomb excitation with projectile energies exceeding 70 MeV/nucleon, only the first 2+ states were excited in 82Ge and 84Se. However, in the inelastic scattering on a 9Be target, a strong population of the first 4+ state was observed for 84Se, while there is no indication of a similarly strong excitation of the corresponding state in the neighboring even-even isotone 82Ge. The results are discussed in the framework of systematics and shell-model calculations using three different effective interactions.
Phys. Rev. C. 06/2010; 81(6).
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W. Rother,
A. Dewald,
H Iwasaki,
S. M. Lenzi,
K. Starosta,
D. Bazin,
T. Baugher,
B A Brown,
H. L. Crawford,
C. Fransen, [......], S McDaniel,
D Miller,
P Petkov,
Th. Pissulla,
A Ratkiewicz,
C. A. Ur,
P Voss,
K. A. Walsh,
D. Weisshaar,
K O Zell
[show abstract]
[hide abstract]
ABSTRACT: The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied
using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb
excitation reactions. The deduced E2 strengths illustrate the enhanced
collectivity of the neutron-rich Fe isotopes up to N=40. The results are
interpreted by the generalized concept of valence proton symmetry which
describes the evolution of nuclear structure around N=40 as governed by the
number of valence protons with respect to Z~30. The deformation suggested by
the experimental data is reproduced by state-of-the-art shell calculations with
a new effective interaction developed for the fpgd valence space.
06/2010;
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A Gade,
T. Baugher,
D. Bazin,
B A Brown,
C M Campbell,
T. Glasmacher,
G. F. Grinyer,
M. Honma, S McDaniel,
R. Meharchand,
T Otsuka,
A Ratkiewicz,
J A Tostevin,
K. A. Walsh,
D. Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: The neutron-rich N=50 isotones 82Ge and 84Se were investigated using intermediate-energy Coulomb excitation on a 197Au target and inelastic scattering on 9Be. As typical for intermediate-energy Coulomb excitation with projectile energies exceeding 70 MeV/nucleon, only the first 2^+ states were excited in 82Ge and 84Se. However, in the inelastic scattering on a 9Be target, a strong population of the first 4^+ state was observed for 84Se, while there is no indication of a similarly strong excitation of the corresponding state in the neighboring even-even isotone 82Ge. The results are discussed in the framework of systematics and shell-model calculations using three different effective interactions. Comment: Accepted for publication in Phys. Rev. C
06/2010;
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S. McDaniel,
A. Gade,
R. V. F. Janssens,
D. Bazin,
B. A. Brown,
C. M. Campbell,
M. P. Carpenter,
J. M. Cook,
A. N. Deacon,
D. -C. Dinca,
S. J. Freeman,
T. Glasmacher,
P. G. Hansen,
B. P. Kay,
P. F. Mantica,
W. F. Mueller,
J. R. Terry,
J. A. Tostevin,
S. Zhu
[show abstract]
[hide abstract]
ABSTRACT: The one-proton knockout reaction 9Be(54Ti,53Sc+γ)X at 72 MeV/nucleon has been measured. The location of the first 3/2- state at 2110(3) keV was confirmed, and new γ-ray transitions were observed at 1111(2), 1273(2), 1539(4), and 2495(5) keV. Large spectroscopic strength to excited states in 53Sc was found and attributed to the knockout of sd-shell protons.
Phys. Rev. C. 02/2010; 81(2).
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D Bazin,
R J Charity,
R T de Souza,
M A Famiano,
A Gade,
V Henzl,
D Henzlova,
S Hudan,
J Lee,
S Lukyanov,
W G Lynch, S McDaniel,
M Mocko,
A Obertelli,
A M Rogers,
L G Sobotka,
J R Terry,
J A Tostevin,
M B Tsang,
M S Wallace
[show abstract]
[hide abstract]
ABSTRACT: We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions 9Be(9C,8B+X)Y and 9Be(8B,7Be+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.
Physical Review Letters 07/2009; 102(23):232501. · 7.37 Impact Factor
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A Gade,
P Adrich,
D Bazin,
B A Brown,
J M Cook,
C Aa Diget,
T Glasmacher, S McDaniel,
A Ratkiewicz,
K Siwek,
D Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: We report on the first in-beam gamma-ray spectroscopy study of the very neutron-rich nucleus 46S. The N=30 isotones 46S and 48Ar were produced in a novel way in two steps that both necessarily involve nucleon exchange and neutron pickup reactions 9Be(48Ca,48K)X followed by 9Be(48K,48Ar+gamma)X at 85.7 MeV/u midtarget energy and 9Be(48Ca,46Cl)X followed by 9Be(46Cl,46S+gamma)X at 87.0 MeV/u midtarget energy, respectively. The results are compared to large-scale shell-model calculations in the sd-pf shell using the SDPF-NR effective interaction and Z-dependent modifications.
Physical Review Letters 06/2009; 102(18):182502. · 7.37 Impact Factor
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A Gade,
P Adrich,
D. Bazin,
M D Bowen,
B A Brown,
C M Campbell,
J M Cook,
T. Glasmacher,
K Hosier, S McDaniel,
D McGlinchery,
A. Obertelli,
L A Riley,
K Siwek,
J A Tostevin,
D. Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: We report on the first in-beam $\gamma$-ray spectroscopy of \nuc{23}{Al} using two different reactions at intermediate beam energies: inelastic scattering off \nuc{9}{Be} and heavy-ion induced one-proton pickup, \nuc{9}{Be}(\nuc{22}{Mg},\nuc{23}{Al}$+\gamma$)X, at 75.1 MeV/nucleon. A $\gamma$-ray transition at 1616(8) keV -- exceeding the proton separation energy by 1494 keV -- was observed in both reactions. From shell model and proton decay calculations we argue that this $\gamma$-ray decay proceeds from the core-excited $7/2^+$ state to the $5/2^+$ ground state of \nuc{23}{Al}. The proposed nature of this state, $[\nuc{22}{Mg}(2^+_1) \otimes \pi d_{5/2}]_{7/2+}$, is consistent with the presence of a gamma-branch and with the population of this state in the two reactions. Comment: Physics Letters B, accepted
07/2008;
