-
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;
-
I. Stefanescu,
W. B. Walters,
P. F. Mantica,
B. A. Brown,
A. D. Davies, A. Estrade,
P. T. Hosmer,
N. Hoteling,
S. N. Liddick,
W. D. M. Rae, [......],
W. F. Mueller,
M. Ouellette,
E. Pellegrini,
P. Santi,
D. Seweryniak,
H. Schatz,
J. Shergur,
A. Stolz,
J. R. Stone,
B. E. Tomlin
[show abstract]
[hide abstract]
ABSTRACT: Excited states in the neutron-rich 121, 123, 125Ag were studied via the fragmentation of a 136Xe beam at 120MeV/nucleon in a thick 9Be target. The levels in 121Ag were populated in the b \beta decay of 121Pd while those assigned to 123, 125Ag were identified via isomer spectroscopy. The transitions identified in 121Ag are consistent with the g \gamma -rays reported in 117, 119Ag . The newly observed transitions were placed in the level schemes of 123, 125Ag based on the analysis of g \gamma -g \gamma coincidences and the systematics. We attribute the onset of isomerism in the 123, 125Ag isotopes to the drop in energy of the negative-parity levels similar to the 5- state in the even-even Cd cores. The proposed level scheme for 125Ag is well described by the NuShellX shell model calculations.
European Physical Journal A 04/2012; 42(3):407-413. · 2.19 Impact Factor
-
M Quinn,
A. Aprahamian,
J. Pereira,
R. Surman,
O. Arndt,
T. Baumann,
A. Becerril,
T. Elliot, A. Estrade,
D. Galaviz, [......],
F. Montes,
B. Pfeiffer,
M. Portillo,
H. Schatz,
F. Schertz,
L. Schnorrenberger,
E Smith,
A. Stolz,
W. B. Walters,
A. Wohr
[show abstract]
[hide abstract]
ABSTRACT: Nuclear structure plays a significant role on the rapid neutron capture
process (r-process) since shapes evolve with the emergence of shells and
sub-shells. There was some indication in neighboring nuclei that we might find
examples of a new N=56 sub-shell, which may give rise to a doubly magic Se-90
nucleus. Beta-decay half lives of nuclei around Se-90 have been measured to
determine if this nucleus has in fact a doubly-magic character. The
fragmentation of Xe-136 beam at the National Superconducting Cyclotron
Laboratory at Michigan State University was used to create a cocktail of nuclei
in the A=90 region. We have measured the half lives of twenty-two nuclei near
the r-process path in the A=90 region. The half lives of As-88 and Se-90 have
been measured for the first time. The values were compared with theoretical
predictions in the search for nuclear-deformation signatures of a N=56
sub-shell, and its possible role in the emergence of a potential doubly-magic
Se-90. The impact of such hypothesis on the synthesis of heavy nuclei,
particularly in the production of Sr, Y and Zr elements was investigated with a
weak r-process network. The new half lives agree with results obtained from a
standard global QRPA model used in r-process calculations, indicating that
Se-90 has a quadrupole shape incompatible with a closed N=56 sub-shell in this
region. The impact of the measured Se-90 half-life in comparison with a former
theoretical predication associated with a spherical half-life on the
weak-r-process is shown to be strong.
12/2011;
-
J Pereira,
A Aprahamian,
O Arndt,
A Becerril,
T Elliot, A Estrade,
D Galaviz,
S Hennrich,
P Hosmer,
R Kessler, [......],
B Pfeiffer,
M Quinn,
P Santi,
H Schatz,
F Schertz,
L Schnorrenberger,
E Smith,
A Stolz,
W B Walters,
A Wöhr
[show abstract]
[hide abstract]
ABSTRACT: The present paper reports on several r-process motivated β-decay experiments undertaken at the National Superconducting Cyclotron Laboratory. β-decay half-lives and β-delayed neutron-emission probabilities were measured for nuclei around the r-process A = 70–80 and A = 90 – 110 mass regions. The data are discussed on the basis of quasi-random phase approximation calculations. The emphasis is made on the impact of these data upon calculations of r-process abundances.
Journal of Physics Conference Series 09/2011; 312(4):042019.
-
A. D. Becerril,
G. Lorusso,
A. M. Amthor,
T. Baumann,
D. Bazin,
J. S. Berryman,
B A Brown,
H. L. Crawford, A. Estrade,
A Gade, [......],
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: The isomeric and {\beta} decays of the N = Z +2 nucleus 96Ag were
investigated at NSCL. A cascade of {\gamma}-ray transitions originating from
the de-excitation of a {\mu}s isomer was observed for the first time and was
found in coincidence with two previously-known transitions with energies of 470
and 667 keV. The isomeric half-life was determined as 1.45(7) {\mu}s, more
precise than previously reported. The existence of a second, longer-lived
{\mu}s isomer, associated with a 743-keV transition, is also proposed here.
Shell model results within the (p_{3/2}p_{1/2}f_{5/2}g_{9/2}) model space,
using the jj44b interaction, reproduced level energies and isomeric decay
half-lives reasonably well.
08/2011;
-
P. Hosmer,
H. Schatz,
A. Aprahamian,
O. Arndt,
R. R. C. Clement, A. Estrade,
K. Farouqi,
K. -L. Kratz,
S N Liddick,
A. F. Lisetskiy, [......],
E. Pellegrini,
J. Pereira,
B. Pfeiffer,
P. Reeder,
P. Santi,
M. Steiner,
A. Stolz,
B. E. Tomlin,
W. B. Walters,
A Wöhr
[show abstract]
[hide abstract]
ABSTRACT: The {\beta} decays of very neutron-rich nuclides in the Co-Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL {\beta}-counting station in conjunction with the neutron detector NERO. We measured the branchings for {\beta}-delayed neutron emission (Pn values) for 74Co (18 +/- 15%) and 75-77Ni (10 +/- 2.8%, 14 +/- 3.6%, and 30 +/- 24%, respectively) for the first time, and remeasured the Pn values of 77-79Cu, 79,81Zn, and 82Ga. For 77-79Cu and for 81Zn we obtain significantly larger Pn values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of 75Co (30 +/- 11 ms) and 80Cu (170+110 -50 ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron-capture process (r-process) is explored. We find that with our new data, the classical r-process model is better able to reproduce the A = 78-80 abundance pattern inferred from the solar abundances. The new data also influence r-process models based on the neutrino-driven high-entropy winds in core collapse supernovae. Comment: 13 pages, 13 figures
11/2010;
-
P. Hosmer,
H. Schatz,
A. Aprahamian,
O. Arndt,
R. R. C. Clement, A. Estrade,
K. Farouqi,
K.-L. Kratz,
S. N. Liddick,
A. F. Lisetskiy, [......],
E. Pellegrini,
J. Pereira,
B. Pfeiffer,
P. Reeder,
P. Santi,
M. Steiner,
A. Stolz,
B. E. Tomlin,
W. B. Walters,
A. Wöhr
[show abstract]
[hide abstract]
ABSTRACT: The β decays of very neutron-rich nuclides in the Co–Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL β-counting station in conjunction with the neutron detector NERO. We measured the branchings for β-delayed neutron emission (Pn values) for 74Co (18±15%) and 75-77Ni (10±2.8%, 14±3.6%, and 30±24%, respectively) for the first time, and remeasured the Pn values of 77-79Cu, 79,81Zn, and 82Ga. For 77-79Cu and for 81Zn we obtain significantly larger Pn values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of 75Co (30±11 ms) and 80Cu (170-50+110 ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron-capture process (r-process) is explored. We find that with our new data, the classical r-process model is better able to reproduce the A=78–80 abundance pattern inferred from the solar abundances. The new data also influence r-process models based on the neutrino-driven high-entropy winds in core collapse supernovae.
Phys. Rev. C. 08/2010; 82(2).
-
A. D. Becerril,
A. M. Amthor,
T. Baumann,
D. Bazin,
J. S. Berryman,
H. Crawford, A. Estrade,
A. Gade,
T. Ginter,
C. J. Guess, [......],
R. Meharchand,
K. Minamisono,
F. Montes,
J. Pereira,
G. Perdikakis,
M. Portillo,
H. Schatz,
K. Smith,
J. Stoker,
R. T. G. Zegers
[show abstract]
[hide abstract]
ABSTRACT: The decay properties of rp‐process nuclei in the vicinity of 100Sn have been studied at the National Superconducting Cyclotron Laboratory (NSCL). The measured β‐decay half‐life for 100Sn is 0.55−0.31+0.70 s, in agreement with a previous measurement. In 98In, the β‐decay of the ground state plus that of a long lived isomer were observed with half‐lives of 47(13) ms and 0.66(40) s respectively. The half‐life of 96Cd, measured for the first time, is 1.03−0.21+0.24 s; however, the existence of a predicted isomeric state in this nucleus could not be confirmed. Additionally, a gamma cascade de‐exciting a μ‐isomer in the odd‐odd nucleus 96Ag was observed. The implications of the measured half‐life of 96Cd on the calculated rp‐process final abundances are discussed.
AIP Conference Proceedings. 08/2010; 1265(1):139-143.
-
D Galaviz,
A M Amthor,
D Bazin,
A D Becerril,
B A Brown,
A A Chen,
A Cole,
J M Cook,
T Elliot, A Estrade, [......],
F Schertz,
Y Shimbara,
E Smith,
K Smith,
A Tamii,
A Stolz,
D Weisshaar,
M Wallace,
M Wiescher,
R G T Zegers
[show abstract]
[hide abstract]
ABSTRACT: We report in this study the nuclear properties of proton-rich isotopes located along the rp-process path. The experiments have recently been performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The level properties above the proton separation energy of the nuclei 30S, 36K and 37Ca were measured with precision of < 10 keV. This will allow a reduction in the determination of the astrophysical (p,γ) reaction rate under rp-process conditions.
Journal of Physics Conference Series 02/2010; 202(1):012009.
-
J. Pereira,
S. Hennrich,
A. Aprahamian,
O. Arndt,
A. Becerril,
T. Elliot, A. Estrade,
D. Galaviz,
R. Kessler,
K.-L. Kratz, [......],
F. Montes,
B. Pfeiffer,
H. Schatz,
F. Schertz,
L. Schnorrenberger,
E. Smith,
A. Stolz,
M. Quinn,
W. B. Walters,
A. Wöhr
[show abstract]
[hide abstract]
ABSTRACT: Measurements of β-decay properties of A≲110 r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory at Michigan State University. β-decay half-lives for 105Y, 106,107Zr, and 111Mo, along with β-delayed neutron emission probabilities of 104Y, 109,110Mo and upper limits for 105Y, 103-107Zr, and 108,111Mo have been measured for the first time. Studies on the basis of the quasi-random-phase approximation are used to analyze the ground-state deformation of these nuclei.
Phys. Rev. C. 03/2009; 79(3).
-
J. Pereira,
S. Hennrich,
A. Aprahamian,
O. Arndt,
A. Becerril,
T. Elliot, A. Estrade,
D. Galaviz,
R. Kessler,
K. -L. Kratz, [......],
F. Montes,
B. Pfeiffer,
H. Schatz,
F. Schertz,
L. Schnorrenberger,
E Smith,
A. Stolz,
M Quinn,
W. B. Walters,
A. Wohr
[show abstract]
[hide abstract]
ABSTRACT: Measurements of the beta-decay properties of r-process nuclei below A=110 have been completed at the National Superconducting Cyclotron Laboratory, at Michigan State University. Beta-decay half-lives for Y-105, Zr-106,107 and Mo-111, along with beta-delayed neutron emission probabilities of Y-104, Mo-109,110 and upper limits for Y-105, Zr-103,104,105,106,107 and Mo-108,111 have been measured for the first time. Studies on the basis of the quasi-random phase approximation are used to analyze the ground-state deformation of these nuclei.
03/2009;
-
J. Pereira,
A. Aprahamian,
O. Arndt,
A. Becerril,
T. Elliot, A. Estrade,
D. Galaviz,
S. Hennrich,
P. Hosmer,
R. Kessler, [......],
P. Santi,
B. Pfeiffer,
M Quinn,
H. Schatz,
F. Schertz,
L. Schnorrenberger,
E Smith,
B. E. Tomlin,
W. Walters,
A. Wohr
[show abstract]
[hide abstract]
ABSTRACT: The impact of nuclear physics on astrophysical r-process models is discussed, emphasizing the importance of beta-decay properties of neutron-rich nuclei. Several r-process motivated beta-decay experiments performed at the National Superconducting Cyclotron Laboratory are presented. The experiments include the measurement of beta-decay half-lives and neutron emission probabilities of nuclei in regions around Ni-78; Se-90; Zr-106 and Rh-120, as well as spectroscopic studies of Pd-120. A summary on the different experimental techniques employed, data analysis, results and impact on model calculations is presented.
02/2009;
-
J. B. Stoker,
P. F. Mantica,
D. Bazin,
A. Becerril,
J. S. Berryman,
H. L. Crawford, A. Estrade,
C. J. Guess,
G. W. Hitt,
G. Lorusso,
M. Matos,
K. Minamisono,
F. Montes,
J. Pereira,
G. Perdikakis,
H. Schatz,
K. Smith,
R. G. T. Zegers
[show abstract]
[hide abstract]
ABSTRACT: A half-life of 2.2 $\pm$ 0.2 s has been deduced for the ground-state $\beta$ decay of $^{84}$Mo, more than 1$\sigma$ shorter than the previously adopted value. $^{84}$Mo is an even-even N = Z nucleus lying on the proton dripline, created during explosive hydrogen burning in Type I X-ray bursts in the rapid proton capture ($rp$) process. The effect of the measured half-life on $rp$-process reaction flow is explored. Implications on theoretical treatments of nuclear deformation in $^{84}$Mo are also discussed.
02/2009;
-
D Bazin,
F Montes,
A Becerril,
G Lorusso,
A Amthor,
T Baumann,
H Crawford, A Estrade,
A Gade,
T Ginter, [......],
K Minamisono,
G Perdikakis,
J Pereira,
J Pinter,
M Portillo,
H Schatz,
K Smith,
J Stoker,
A Stolz,
R G T Zegers
[show abstract]
[hide abstract]
ABSTRACT: The beta-decay properties of the N=Z nuclei 96Cd, 98In, and 100Sn have been studied. These nuclei were produced at the National Superconducting Cyclotron Laboratory by fragmenting a 120 MeV/nucleon 112Sn primary beam on a Be target. The resulting radioactive beam was filtered in the A1900 and the newly commissioned Radio Frequency Fragment Separator to achieve a purity level suitable for decay studies. The observed production cross sections of these nuclei are lower than predicted by factors of 10-30. The half-life of 96Cd, which was the last experimentally unknown waiting point half-life of the astrophysical rp process, is 1.03_{-0.21};{+0.24} s. The implications of the experimental T_{1/2} value of 96Cd on the abundances predicted by rp process calculations and the origin of A=96 isobars such as 96Ru are explored.
Physical Review Letters 01/2009; 101(25):252501. · 7.37 Impact Factor
-
D. Bazin,
F. Montes,
A. Becerril,
G. Lorusso,
A. Amthor,
T. Baumann,
H. Crawford, A. Estrade,
A. Gade,
T. Ginter, [......],
K. Minamisono,
G. Perdikakis,
J. Pereira,
J. Pinter,
M. Portillo,
H. Schatz,
K. Smith,
J. Stoker,
A. Stolz,
R. G. T. Zegers
[show abstract]
[hide abstract]
ABSTRACT: The β-decay properties of the N=Z nuclei Cd96, In98, and Sn100 have
been studied. These nuclei were produced at the National Superconducting
Cyclotron Laboratory by fragmenting a 120MeV/nucleon Sn112 primary beam
on a Be target. The resulting radioactive beam was filtered in the A1900
and the newly commissioned Radio Frequency Fragment Separator to achieve
a purity level suitable for decay studies. The observed production cross
sections of these nuclei are lower than predicted by factors of 10 30.
The half-life of Cd96, which was the last experimentally unknown waiting
point half-life of the astrophysical rp process, is
1.03-0.21+0.24s. The implications of the
experimental T1/2 value of Cd96 on the abundances predicted
by rp process calculations and the origin of A=96 isobars such as Ru96
are explored.
Physical Review Letters 11/2008; 101(25):252501. · 7.37 Impact Factor
-
D Bazin,
F Montes,
A Becerril,
G Lorusso,
A Amthor,
T Baumann,
H Crawford, A Estrade,
A Gade,
T Ginter, [......],
K Minamisono,
G Perdikakis,
J Pereira,
J Pinter,
M Portillo,
H Schatz,
K Smith,
J Stoker,
A Stolz,
R G T Zegers
11/2008;
-
D Galaviz,
A M Amthor,
D Bazin,
B A Brown,
A Cole,
T Elliot, A Estrade,
Zs Fülöp,
A Gade,
T Glasmacher, [......],
W Müller,
J Pereira,
H Schatz,
B Sherrill,
F Schertz,
Y Shimbara,
E Smith,
A Tamii,
M Wallace,
R G T Zegers
[show abstract]
[hide abstract]
ABSTRACT: The level structure just above the proton threshold of the nucleus 30S has been studied using the neutron removal process on fast radioactive beams at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. In this work we provide a description of the experimental setup. The present status of the analysis is also discussed.
Journal of Physics G Nuclear and Particle Physics 12/2007; 35(1):014030. · 4.18 Impact Factor
-
M. Matos, A. Estrade,
M Amthor,
A. Aprahamian,
D. Bazin,
A. Becerril,
T. Elliot,
D. Galaviz,
A Gade,
S Gupta,
G. Lorusso,
F. Montes,
J. Pereira,
M. Portillo,
A M Rogers,
H. Schatz,
D. Shapira,
E Smith,
A. Stolz,
M. Wallace
[show abstract]
[hide abstract]
ABSTRACT: Atomic masses play a crucial role in many nuclear astrophysics calculations. The lack of experimental values for relevant exotic nuclides triggered a rapid development of new mass measurement devices around the world. The Time-of-Flight (TOF) mass measurements offer a complementary technique to the most precise one, Penning trap measurements, the latter being limited by the rate and half-lives of the ions of interest. The NSCL facility provides a well-suited infrastructure for TOF mass measurements of very exotic nuclei. At this facility, we have recently implemented a TOF-Brho technique and performed mass measurements of neutron-rich nuclides in the Fe region, important for r-process calculations and for calculations of processes occurring in the crust of accreting neutron stars. Comment: 8 pages, 4 figures, submitted to Journal of Physics G, proceedings of Nuclear Physics in Astrophysics III
07/2007;
-
J. Pereira,
S. Hennrich,
M Quinn,
A. Aprahamian,
O. Arndt,
A. Becerril,
T. Elliot, A. Estrade,
D. Galaviz,
L. Kern, [......],
G. Lorusso,
P. Mantica,
M. Matos,
F. Montes,
B. Pfeiffer,
H. Schatz,
F. Schertz,
E Smith,
W. Walters,
A. Woehr
[show abstract]
[hide abstract]
ABSTRACT: A JINA/VISTARS r-process campaign was completed at the A1900 Fragment Separator of the National Superconducting Cyclotron Laboratory in the fall of 2005. The purpose of the campaign was the measurement of the beta-decay half-lives and beta-delayed neutron-emission probabilities of different unknown neutron-rich nuclei participating in the r-process. Details of this campaign will be presented.
09/2006;
-
F. Montes, A. Estrade,
P. T. Hosmer,
S. N. Liddick,
P. F. Mantica,
A. C. Morton,
W. F. Mueller,
M. Ouellette,
E. Pellegrini,
P. Santi,
H. Schatz,
A. Stolz,
B. E. Tomlin,
O. Arndt,
K.-L. Kratz,
B. Pfeiffer,
P. Reeder,
W. B. Walters,
A. Aprahamian,
A. Wöhr
[show abstract]
[hide abstract]
ABSTRACT: β-delayed neutron emission branchings (or upper limits) for neutron rich 116-120Rh, 120-122Pd, and 124Ag have been measured. These branching ratios serve as direct inputs to astrophysical rapid neutron capture process models and affect the final abundances calculated in these models. In addition, half-lives for neutron rich 114-115Tc, 114-118Ru, 116-121Rh, and 119-124Pd near the proposed path of the r-process have also been measured. The results agree with theoretical quasiparticle random-phase approximation calculations within model uncertainties; the only exception is the delayed neutron branching in the decay of 120Rh, which is found to be much smaller than predicted.
Phys. Rev. C. 03/2006; 73(3).
