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New $γ$-ray Transitions Observed in $^{19}$Ne with Implications for the $^{15}$O($α$,$γ$)$^{19}$Ne Reaction Rate
Authors:
M. R. Hall,
D. W. Bardayan,
T. Baugher,
A. Lepailleur,
S. D. Pain,
A. Ratkiewicz,
S. Ahn,
J. M. Allen,
J. T. Anderson,
A. D. Ayangeakaa,
J. C. Blackmon,
S. Burcher,
M. P. Carpenter,
S. M. Cha,
K. Y. Chae,
K. A. Chipps,
J. A. Cizewski,
M. Febbraro,
O. Hall,
J. Hu,
C. L. Jiang,
K. L. Jones,
E. J. Lee,
P. D. O'Malley,
S. Ota
, et al. (12 additional authors not shown)
Abstract:
The $^{15}$O($α$,$γ$)$^{19}$Ne reaction is responsible for breakout from the hot CNO cycle in Type I x-ray bursts. Understanding the properties of resonances between $E_x = 4$ and 5 MeV in $^{19}$Ne is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2…
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The $^{15}$O($α$,$γ$)$^{19}$Ne reaction is responsible for breakout from the hot CNO cycle in Type I x-ray bursts. Understanding the properties of resonances between $E_x = 4$ and 5 MeV in $^{19}$Ne is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2$^-$ and 7/2$^-$, respectively. Gamma-ray transitions from these states were studied using triton-$γ$-$γ$ coincidences from the $^{19}$F($^{3}$He,$tγ$)$^{19}$Ne reaction measured with GODDESS (Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory. The observed transitions from the 4.14- and 4.20-MeV states provide strong evidence that the $J^π$ values are actually 7/2$^-$ and 9/2$^-$, respectively. These assignments are consistent with the values in the $^{19}$F mirror nucleus and in contrast to previously accepted assignments.
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Submitted 1 April, 2019;
originally announced April 2019.
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Key $^{19}$Ne states identified affecting $γ$-ray emission from $^{18}$F in novae
Authors:
M. R. Hall,
D. W. Barbadian,
T. Baugher,
A. Lepailleur,
S. D. Pain,
A. Ratkiewicz,
S. Ahn,
J. M. Allen,
J. T. Anderson,
A. D. Ayangeakaa,
J. C. Blackmon,
S. Burcher,
M. P. Carpenter,
S. M. Cha,
K. Y. Chae,
K. A. Chipps,
J. A. Cizewski,
M. Febbraro,
O. Hall,
J. Hu,
C. L. Jiang,
K. L. Jones,
E. J. Lee,
P. D. O'Malley,
S. Ota
, et al. (12 additional authors not shown)
Abstract:
Detection of nuclear-decay $γ$ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense $γ$-ray flux is thought to be annihilation radiation from the $β^+$ decay of $^{18}$F, which is destroyed prior to decay by the $^{18}$F($p$,$α$)$^{15}$O reaction. Estimates of $^{18}$F production had been uncertain, however, because key near-threshold levels in the compound nucleus,…
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Detection of nuclear-decay $γ$ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense $γ$-ray flux is thought to be annihilation radiation from the $β^+$ decay of $^{18}$F, which is destroyed prior to decay by the $^{18}$F($p$,$α$)$^{15}$O reaction. Estimates of $^{18}$F production had been uncertain, however, because key near-threshold levels in the compound nucleus, $^{19}$Ne, had yet to be identified. This Letter reports the first measurement of the $^{19}$F($^{3}$He,$tγ$)$^{19}$Ne reaction, in which the placement of two long-sought 3/2$^+$ levels is suggested via triton-$γ$-$γ$ coincidences. The precise determination of their resonance energies reduces the upper limit of the rate by a factor of $1.5-17$ at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.
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Submitted 31 January, 2019;
originally announced February 2019.
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Experimental investigation of a linear-chain structure in the nucleus 14C
Authors:
H. Yamaguchi,
D. Kahl,
S. Hayakawa,
Y. Sakaguchi,
K. Abe,
T. Nakao,
T. Suhara,
N. Iwasa,
A. Kim,
D. H. Kim,
S. M. Cha,
M. S. Kwag,
J. H. Lee,
E. J. Lee,
K. Y. Chae,
Y. Wakabayashi,
N. Imai,
N. Kitamura,
P. Lee,
J. Y. Moon,
K. B. Lee,
C. Akers,
H. S. Jung,
N. N. Duy,
L. H. Khiem
, et al. (1 additional authors not shown)
Abstract:
It is a well-known fact that a cluster of nucleons can be formed in the interior of an atomic nucleus, and such clusters may occupy molecular-like orbitals, showing characteristics similar to normal molecules consisting of atoms. Chemical molecules having a linear alignment are commonly seen in nature, such as carbon dioxide. A similar linear alignment of the nuclear clusters, referred to as linea…
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It is a well-known fact that a cluster of nucleons can be formed in the interior of an atomic nucleus, and such clusters may occupy molecular-like orbitals, showing characteristics similar to normal molecules consisting of atoms. Chemical molecules having a linear alignment are commonly seen in nature, such as carbon dioxide. A similar linear alignment of the nuclear clusters, referred to as linear-chain cluster state (LCCS), has been studied since the 1950s, however, up to now there is no clear experimental evidence demonstrating the existence of such a state. Recently, it was proposed that an excess of neutrons may offer just such a stabilizing mechanism, revitalizing interest in the nuclear LCCS, specifically with predictions for their emergence in neutron-rich carbon isotopes. Here we present the experimental observation of α-cluster states in the radioactive 14C nucleus. Using the 10Be+α resonant scattering method with a radioactive beam, we observed a series of levels which completely agree with theoretically predicted levels having an explicit linear-chain cluster configuration. We regard this as the first strong indication of the linear-chain clustered nucleus.
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Submitted 12 December, 2016; v1 submitted 20 October, 2016;
originally announced October 2016.
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$^{24}$Mg($p$, $α$)$^{21}$Na reaction study for spectroscopy of $^{21}$Na
Authors:
S. M. Cha,
K. Y. Chae,
A. Kim,
E. J. Lee,
S. Ahn,
D. W. Bardayan,
K. A. Chipps,
J. A. Cizewski,
M. E. Howard,
B. Manning,
P. D. O'Malley,
A. Ratkiewicz,
S. Strauss,
R. L. Kozub,
M. Matos,
S. D. Pain,
S. T. Pittman,
M. S. Smith,
W. A. Peters
Abstract:
The $^{24}$Mg($p$, $α$)$^{21}$Na reaction was measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory in order to better constrain spins and parities of energy levels in $^{21}$Na for the astrophysically important $^{17}$F($α, p$)$^{20}$Ne reaction rate calculation. 31 MeV proton beams from the 25-MV tandem accelerator and enriched $^{24}$Mg solid targets were used…
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The $^{24}$Mg($p$, $α$)$^{21}$Na reaction was measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory in order to better constrain spins and parities of energy levels in $^{21}$Na for the astrophysically important $^{17}$F($α, p$)$^{20}$Ne reaction rate calculation. 31 MeV proton beams from the 25-MV tandem accelerator and enriched $^{24}$Mg solid targets were used. Recoiling $^{4}$He particles from the $^{24}$Mg($p$, $α$)$^{21}$Na reaction were detected by a highly segmented silicon detector array which measured the yields of $^{4}$He particles over a range of angles simultaneously. A new level at 6661 $\pm$ 5 keV was observed in the present work. The extracted angular distributions for the first four levels of $^{21}$Na and Distorted Wave Born Approximation (DWBA) calculations were compared to verify and extract angular momentum transfer.
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Submitted 10 August, 2015;
originally announced August 2015.