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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;
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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).
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[show abstract]
[hide abstract]
ABSTRACT: The $^{32}$Cl(p,$\gamma$)$^{33}$Ar reaction rate is of potential importance in the rp-process powering type I X-ray bursts. Recently Clement et al. \cite{CBB04} presented new data on excitation energies for low lying proton unbound states in $^{33}$Ar obtained with a new method developed at the National Superconducting Cyclotron Laboratory. We use their data, together with a direct capture model and a USD shell model calculation to derive a new reaction rate for use in astrophysical model calculations. In particular, we take into account capture on the first excited state in $^{32}$Cl, and also present a realistic estimate of the remaining uncertainties. We find that the $^{32}$Cl(p,$\gamma$)$^{33}$Ar reaction rate is dominated entirely by capture on the first excited state in $^{32}$Cl over the whole temperature range relevant in X-ray bursts. In the temperature range from 0.2 to 1 GK the rate is up to a factor of 70 larger than the previously recommended rate based on shell model calculations only. The uncertainty is now reduced from up to a factor of 1000 to a factor of 3 at 0.3-0.7 GK and a factor of 6 at 1.5 GK.
12/2005;
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P T Hosmer,
H Schatz,
A Aprahamian,
O Arndt, R R C Clement,
A Estrade,
K-L Kratz,
S N Liddick,
P F Mantica,
W F Mueller, [......],
M Ouellette,
E Pellegrini,
B Pfeiffer,
P Reeder,
P Santi,
M Steiner,
A Stolz,
B E Tomlin,
W B Walters,
A Wöhr
[show abstract]
[hide abstract]
ABSTRACT: Nuclei with magic numbers serve as important benchmarks in nuclear theory. In addition, neutron-rich nuclei play an important role in the astrophysical rapid neutron-capture process (r process). 78Ni is the only doubly magic nucleus that is also an important waiting point in the r process, and serves as a major bottleneck in the synthesis of heavier elements. The half-life of 78Ni has been experimentally deduced for the first time at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University, and was found to be 110(+100)(-60) ms. In the same experiment, a first half-life was deduced for 77Ni of 128(+27)(-33) ms, and more precise half-lives were deduced for 75Ni and 76Ni of 344(+20)(-24) ms and 238(+15)(-18) ms, respectively.
Physical Review Letters 04/2005; 94(11):112501. · 7.37 Impact Factor
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R R C Clement,
D Bazin,
W Benenson,
B A Brown,
A L Cole,
M W Cooper,
P A DeYoung,
A Estrade,
M A Famiano,
N H Frank, [......],
P T Hosmer,
W G Lynch,
F Montes,
W F Mueller,
G F Peaslee,
P Santi,
H Schatz,
B M Sherrill,
M-J van Goethem,
M S Wallace
[show abstract]
[hide abstract]
ABSTRACT: A new experimental approach was developed that can reduce the uncertainties in astrophysical rapid proton capture (rp) process calculations due to nuclear data. This approach utilizes neutron removal from a radioactive ion beam to populate the nuclear states of interest. Excited states were deduced by the gamma-decay spectra measured in a semiconductor Ge-detector array. In the first case studied, 33Ar, excited states were measured with uncertainties of several keV. The 2 orders of magnitude improvement in the uncertainty of the level energies resulted in a 3 orders of magnitude improvement in the uncertainty of the calculated 32Cl(p,gamma)33Ar rate that is critical to the modeling of the rp process. This approach has the potential to measure key properties of almost all interesting nuclei on the rp-process path.
Physical Review Letters 05/2004; 92(17):172502. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: A search for 19Mg was performed using projectile fragmentation of a 150 MeV/nucleon 36Ar beam. No events of 19Mg were observed. From the time-of-flight through the fragment separator an upper limit of 22 ns for the half-life of 19Mg was established.
10/2003;
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W. A. Peters,
T. Baumann,
D. Bazin,
B. A. Brown, R. R. C. Clement,
N. Frank,
P. Heckman,
B. A. Luther,
F. Nunes,
J. Seitz,
A. Stolz,
M. Thoennessen,
E. Tryggestad
[show abstract]
[hide abstract]
ABSTRACT: The ground state and first excited state of 15F were measured by the method of elastic resonance scattering in inverse kinematics. A secondary beam of 115 MeV/nucleon 14O was slowed down to 8 MeV/nucleon and energy bunched before stopping in a C2H4 target. The 15F excitation energy spectrum was extracted from elastically scattered protons at 0°. The 1/2+ ground state resonance of 15F was determined to be unbound with respect to single-proton emission by 1.51±0.11MeV, corresponding to a mass excess of 16.81±0.11MeV. The 5/2+ first excited state resonance is unbound by 2.853±0.045MeV leading to an excitation energy of 1.34±0.15MeV. A comparison with systematics of single-nucleon separation energies and theoretical models suggests that 11N should be unbound by about 1.5±0.15MeV.
Phys. Rev. C. 09/2003; 68(3).
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ABSTRACT: One-proton and two-proton separation energies are calculated for proton-rich nuclei in the region $ A=41-75 $. The method is based on Skyrme Hartree-Fock calculations of Coulomb displacement energies of mirror nuclei in combination with the experimental masses of the neutron-rich nuclei. The implications for the proton drip line and the astrophysical rp-process are discussed. This is done within the framework of a detailed analysis of the sensitivity of rp process calculations in type I X-ray burst models on nuclear masses. We find that the remaining mass uncertainties, in particular for some nuclei with $N=Z$, still lead to large uncertainties in calculations of X-ray burst light curves. Further experimental or theoretical improvements of nuclear mass data are necessary before observed X-ray burst light curves can be used to obtain quantitative constraints on ignition conditions and neutron star properties. We identify a list of nuclei for which improved mass data would be most important.
02/2002;
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[show abstract]
[hide abstract]
ABSTRACT: The stopping of Ar beams at energies up to 100 MeV/nucleon in a combination of Al energy degrader and He gas volume was investigated. The range straggling was not largely enhanced by the energy degrader. A Monte Carlo simulation was applied in order to calculate the spatial distribution of stopped ions in the gas. 2002 Elsevier Science B.V. All rights reserved.
Nuclear Physics A. 01/2002; 701:282-285.
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[show abstract]
[hide abstract]
ABSTRACT: The 32Cl(p,γ)33Ar reaction rate is of potential importance in the rp process powering type I x-ray bursts. Recently, Clement et al. [Phys. Rev. Lett. 92, 172502 (2004)] [1] presented new data on excitation energies for low-lying proton unbound states in 33Ar obtained with a new method developed at the National Superconducting Cyclotron Laboratory. We use their data, together with a direct capture model and a shell model calculation, to derive a new reaction rate for use in astrophysical model calculations. In particular, we take into account capture on the first excited state in 32Cl, and we also present a realistic estimate of the remaining uncertainties. We find that the 32Cl(p,γ)33Ar reaction rate is dominated entirely by capture on the first excited state in 32Cl over the whole temperature range relevant in x-ray bursts. In the temperature range from 0.2 to 1 GK the rate is up to a factor of 70 larger than the previously recommended rate based on shell model calculations only. The uncertainty is now reduced from up to a factor of 1000 to a factor of 3 at 0.3–0.7 GK and a factor of 6 at 1.5 GK.
Phys. Rev. C. 72(6).
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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
Physical Review C, v.82 (2010).
