-
Z. Kohley,
E. Lunderberg,
P. A. DeYoung,
A. Volya,
T. Baumann,
D. Bazin,
G. Christian,
N. L. Cooper,
N. Frank, A. Gade,
C. Hall,
J. Hinnefeld,
B. Luther,
S. Mosby,
W. A. Peters,
J. K. Smith,
J. Snyder,
A. Spyrou,
M. Thoennessen
[show abstract]
[hide abstract]
ABSTRACT: The ground state of neutron-rich unbound $^{13}$Li was observed for the first
time in a one-proton removal reaction from $^{14}$Be at a beam energy of 53.6
MeV/u. The $^{13}$Li ground state was reconstructed from $^{11}$Li and two
neutrons giving a resonance energy of 120$^{+60}_{-80}$ keV. All events
involving single and double neutron interactions in the Modular Neutron Array
(MoNA) were analyzed, simulated, and fitted self-consistently. The three-body
($^{11}$Li+$n+n$) correlations within Jacobi coordinates showed strong
dineutron characteristics. The decay energy spectrum of the intermediate
$^{12}$Li system ($^{11}$Li+$n$) was described with an s-wave scattering length
of greater than -4 fm, which is a smaller absolute value than reported in a
previous measurement.
01/2013;
-
M Matov s,
A Estradé,
H Schatz,
D Bazin,
M Famiano, A Gade,
S George,
W ~G Lynch,
Z Meisel,
M Portillo,
A Rogers,
D Shapira,
A Stolz,
M Wallace,
J Yurkon
Nuclear Instruments and Methods in Physics Research A. 12/2012; 696:171-179.
-
K. Wimmer,
D. Bazin, A. Gade,
J. A. Tostevin,
T. Baugher,
Z. Chajecki,
D. Coupland,
M. A. Famiano,
T. K. Ghosh,
G. F. Grinyer, [......],
P. Quarterman,
A. Ratkiewicz,
A. Sanetullaev,
E. C. Simpson,
S. R. Stroberg,
M. B. Tsang,
D. Weisshaar,
J. Winkelbauer,
R. Winkler,
M. Youngs
[show abstract]
[hide abstract]
ABSTRACT: We report final-state-exclusive measurements of the light charged fragments in coincidence with ^{26}Ne residual nuclei following the direct two-proton removal from a neutron-rich ^{28}Mg secondary beam. A Dalitz-plot analysis and comparisons with simulations show that a majority of the triple-coincidence events with two protons display phase-space correlations consistent with the (two-body) kinematics of a spatially correlated pair-removal mechanism. The fraction of such correlated events, 56(12)%, is consistent with the fraction of the calculated cross section, 64%, arising from spin S=0 two-proton configurations in the entrance-channel (shell-model) ^{28}Mg ground state wave function. This result promises access to an additional and more specific probe of the spin and spatial correlations of valence nucleon pairs in exotic nuclei produced as fast secondary beams.
Physical Review Letters 11/2012; 109:202505. · 7.37 Impact Factor
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O. B. Tarasov,
D. J. Morrissey,
A. M. Amthor,
L. Bandura,
T. Baumann,
D. Bazin,
J. S. Berryman,
G. Chubarian,
N. Fukuda, A. Gade, [......],
M. Hausmann,
N. Inabe,
T. Kubo,
J. Pereira,
M. Portillo,
B. M. Sherrill,
A. Stolz,
C. Sumithrarachchi,
M. Thoennessen,
D. Weisshaar
[show abstract]
[hide abstract]
ABSTRACT: Production cross sections for neutron-rich nuclei from the fragmentation of a
82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions
of 122 neutron-rich isotopes of elements $11 \le Z \le 32$ were determined by
varying the target thickness. Production cross sections with beryllium and
tungsten targets were determined for a large number of nuclei including several
isotopes first observed in this work. These are the most neutron-rich nuclides
of the elements $22 \le Z \le 25$ (64Ti, 67V, 69Cr, 72Mn). One event was
registered consistent with 70Cr, and another one with 75Fe. A one-body Qg
systematics is used to describe the production cross sections based on thermal
evaporation from excited prefragments. The current results confirm those of our
previous experiment with a 76Ge beam: enhanced production cross sections for
neutron-rich fragments near Z=20.
09/2012;
-
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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G. Lorusso,
A. Becerril,
A. Amthor,
T. Baumann,
D. Bazin,
J. S. Berryman,
B. A. Brown,
R. H. Cyburt,
H. L. Crawford,
A. Estrade, [......],
K. Minamisono,
F. Montes,
G. Perdikakis,
J. Pereira,
M. Portillo,
H. Schatz,
K. Smith,
J. Stoker,
A. Stolz,
R. G. T. Zegers
[show abstract]
[hide abstract]
ABSTRACT: Beta-delayed proton emission from nuclides in the neighborhood of 100Sn was
studied at the National Superconducting Cyclotron Laboratory. The nuclei were
produced by fragmentation of a 120 MeV/nucleon 112Sn primary beam on a Be
target. Beam purification was provided by the A1900 Fragment Separator and the
Radio Frequency Fragment Separator. The fragments of interest were identified
and their decay was studied with the NSCL Beta Counting System (BCS) in
conjunction with the Segmented Germanium Array (SeGA). The nuclei 96Cd, 98Ing,
98Inm and 99In were identified as beta-delayed proton emitters, with branching
ratios bp = 5.5(40)%, 5.5+3 -2%, 19(2)% and 0.9(4)%, respectively. The bp for
89Ru, 91,92Rh, 93Pd and 95Ag were deduced for the first time with bp = 3+1.9
-1.7%, 1.3(5)%, 1.9(1)%, 7.5(5)% and 2.5(3)%, respectively. The bp = 22(1)% for
101Sn was deduced with higher precision than previously reported. The impact of
the newly measured bp values on the composition of the type-I X-ray burst ashes
was studied.
05/2012;
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K Wimmer,
D Bazin, A Gade,
J A Tostevin,
T Baugher,
Z Chajecki,
D Coupland,
M A Famiano,
T K Ghosh,
G F Grinyer, [......],
K Meierbachtol,
P Quarterman,
A Ratkiewicz,
A Sanetullaev,
S R Stroberg,
M B Tsang,
D Weisshaar,
J Winkelbauer,
R Winkler,
M Youngs
[show abstract]
[hide abstract]
ABSTRACT: The two-proton removal reaction from 28 Mg projectiles has been studied at 93 MeV/u. First coincidence measurements of the heavy 26 Ne projectile residues, the removed protons, and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations based on the use of eikonal dynamics and sd-shell-model structure amplitudes.
Physical Review C 05/2012; 85:051603(R). · 3.31 Impact Factor
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K. Wimmer,
D. Bazin, A. Gade,
J. A. Tostevin,
T. Baugher,
Z. Chajecki,
D. Coupland,
M. A. Famiano,
T. K. Ghosh,
G. F. Grinyer, [......],
B. Manning,
K. Meierbachtol,
P. Quarterman,
A. Ratkiewicz,
A. Sanetullaev,
S. R. Stroberg,
M. B. Tsang,
D. Weisshaar,
J. Winkelbauer,
R. Winkler M. Youngs
[show abstract]
[hide abstract]
ABSTRACT: The two-proton removal reaction from 28Mg projectiles has been studied at 93
MeV/u at the NSCL. First coincidence measurements of the heavy 26Ne projectile
residues, the removed protons and other light charged particles enabled the
relative cross sections from each of the three possible elastic and inelastic
proton removal mechanisms to be determined. These more final-state-exclusive
measurements are key for further interrogation of these reaction mechanisms and
use of the reaction channel for quantitative spectroscopy of very neutron-rich
nuclei. The relative and absolute yields of the three contributing mechanisms
are compared to reaction model expectations - based on the use of eikonal
dynamics and sd-shell-model structure amplitudes.
05/2012;
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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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J. Chen,
A. A. Chen,
M. Amthor,
D. Bazin,
A. D. Becerril, A. Gade,
D. Galaviz,
T. Glasmacher,
D. Kahl,
G. Lorusso,
M. Matos,
C. V. Ouellet,
J. Pereira,
H. Schatz,
K. Smith,
B. Wales,
D. Weisshaar,
and R. G .T. Zegers
[show abstract]
[hide abstract]
ABSTRACT: A study of 26Si states by neutron removal from a fast radioactive beam of 27Si has been performed. A beam of 27Si of energy 84.3 MeV/nucleon impinged on a polypropylene foil (C3H6) of 180 mg/cm2 thickness. Deexcitation γ rays were detected with a highly segmented germanium detector array, in coincidence with the 26Si recoils, and the corresponding 26Si level energies were determined. In comparing our results to two previous γ-ray spectroscopic studies of 26Si level structures, we find good agreement with a recent measurement of the 12C(16O,2nγ)26Si reaction. Our results support the use of excitation energies from that study in helping determine the important resonance energies for the thermonuclear 25Al(p,γ)26Si reaction rate. We do not observe a bound state at 4093 keV reported in an earlier study of the 24Mg(3He,nγ)26Si reaction.
Physical Review C 04/2012; 85:045809. · 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 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;
-
J Chen,
A A Chen,
A M Amthor,
D Bazin,
A D Becerril, A Gade,
D Galaviz,
T Glasmacher,
D Kahl,
G Lorusso,
M Matos,
C V Ouellet,
J Pereira,
H Schatz,
K Smith,
B Wales,
D Weisshaar,
R G T Zegers
Phys. Rev. C. 04/2012; 85(4):045809.
-
J Chen,
A A Chen,
A M Amthor,
D Bazin,
A D Becerril, A Gade,
D Galaviz,
T Glasmacher,
D Kahl,
G Lorusso,
M Matos,
C V Ouellet,
J Pereira,
H Schatz,
K Smith,
B Wales,
D Weisshaar,
R G T Zegers
Physical Review C. 04/2012; 85(4):045809.
-
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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G. Christian,
N. Frank,
S. Ash,
T. Baumann,
P. A. DeYoung,
J. E. Finck, A. Gade,
G. F. Grinyer,
B. Luther,
M. Mosby,
S. Mosby,
J. K. Smith,
J. Snyder,
A. Spyrou,
M. J. Strongman,
M. Thoennessen,
M. Warren,
D. Weisshaar,
A. Wersal
[show abstract]
[hide abstract]
ABSTRACT: The ground state of $^{28}$F has been observed as an unbound resonance
$2\underline{2}0$ keV above the ground state of $^{27}$F. Comparison of this
result with USDA/USDB shell model predictions leads to the conclusion that the
$^{28}$F ground state is primarily dominated by $sd$-shell configurations. Here
we present a detailed report on the experiment in which the ground state
resonance of $^{28}$F was first observed. Additionally, we report the first
observation of a neutron-unbound excited state in $^{27}$F at an excitation
energy of $25\underline{0}0 (2\underline{2}0)$ keV.
03/2012;
-
G. Christian,
N. Frank,
S. Ash,
T. Baumann,
D. Bazin,
J Brown,
P. A. DeYoung,
J. E. Finck, A Gade,
G. F. Grinyer, [......],
G. F. Peaslee,
W. F. Rogers,
J. K. Smith,
J. Snyder,
A. Spyrou,
M. J. Strongman,
M. Thoennessen,
M. Warren,
D. Weisshaar,
A. Wersal
[show abstract]
[hide abstract]
ABSTRACT: The technique of invariant mass spectroscopy has been used to measure, for
the first time, the ground state energy of neutron-unbound $^{28}\textrm{F},$
determined to be a resonance in the $^{27}\textrm{F} + n$ continuum at
$2\underline{2}0 (\underline{5}0)$ keV. States in $^{28}\textrm{F}$ were
populated by the reactions of a 62 MeV/u $^{29}\textrm{Ne}$ beam impinging on a
288 $\textrm{mg/cm}^2$ beryllium target. The measured $^{28}\textrm{F}$ ground
state energy is in good agreement with USDA/USDB shell model predictions,
indicating that $pf$ shell intruder configurations play only a small role in
the ground state structure of $^{28}\textrm{F}$ and establishing a low-$Z$
boundary of the island of inversion for N=19 isotones.
Physical Review Letters 01/2012; 108(3). · 7.37 Impact Factor
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Christian,
N Frank,
S Ash,
T Baumann,
P A DeYoung,
J E Finck, A Gade,
G F Grinyer,
B Luther,
M Mosby,
S Mosby,
J K Smith,
J Snyder,
A Spyrou,
M J Strongman,
M Thoennessen,
M Warren,
D Weisshaar,
A Wersal
Phys. Rev. C. 01/2012; 85(3):034327.
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A Estradé,
M Matoš,
H Schatz,
A M Amthor,
D Bazin,
M Beard,
A Becerril,
E F Brown,
R Cyburt,
T Elliot, [......],
G Lorusso,
P Möller,
J Pereira,
M Portillo,
A M Rogers,
D Shapira,
E Smith,
A Stolz,
M Wallace,
M Wiescher
[show abstract]
[hide abstract]
ABSTRACT: We present results from time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory that are relevant for neutron star crust models. The masses of 16 neutron-rich nuclei in the scandium-nickel range were determined simultaneously, with the masses of (61)V, (63)Cr, (66)Mn, and (74)Ni measured for the first time with mass excesses of -30.510(890) MeV, -35.280(650) MeV, -36.900(790) MeV, and -49.210(990) MeV, respectively. With these results the locations of the dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit super bursts are now experimentally constrained. We find the experimental Q value for the (66)Fe→(66)Mn electron capture to be 2.1 MeV (2.6σ) smaller than predicted, resulting in the transition occurring significantly closer to the neutron star surface.
Physical Review Letters 10/2011; 107(17):172503. · 7.37 Impact Factor
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A M Rogers,
W G Lynch,
M A Famiano,
M S Wallace,
F Amorini,
D Bazin,
R J Charity,
F Delaunay,
R T de Souza,
J Elson, [......],
S Hudan,
J Lee,
S Lobostov,
S Lukyanov,
M Matoš,
M Mocko,
M B Tsang,
D Shapira,
L G Sobotka,
G Verde
[show abstract]
[hide abstract]
ABSTRACT: The first direct measurement of the proton separation energy, Sp, for the proton-unbound nucleus 69Br is reported. Of interest is the exponential dependence of the 2p-capture rate on Sp which can bypass the 68Se waiting-point in the astrophysical rp process. An analysis of the observed proton decay spectrum is given in terms of the 69Se mirror nucleus and the influence of Sp is explored within the context of a single-zone X-ray burst model.
Journal of Physics Conference Series 09/2011; 312(4):042020.
