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Title: Study of Interference Effects in the 18F(p,alpha) 15O Reaction

Abstract

The {sup 18}F(p,{alpha}a){sup 15}O reaction plays a crucial role in understanding {gamma}-ray emission from novae. Because of the importance of understanding the {sup 18}F + p reactions, a number of studies of the A=19 isobars have been made using stable and exotic beams. The interference effects among J{sup {pi}} = 3/2{sup +} resonances in the {sup 18}F + p system, however, have never been measured, but they can change the S-factor by a factor of 20 at nova energies. R-matrix calculations indicate that the cross sections above the E{sub c.m.} = 665 keV resonance are sensitive to the interference between the E{sub c.m.} = 8, 38, and 665 keV resonances. In order to study the interference effects, an excitation function for the {sup 1}H({sup 18}F,{alpha}){sup 15}O reaction has been measured in the energy range of E{sub c.m.} = 663-877 keV using radioactive {sup 18}F beams at the Holifield Radioactive Ion Beam Facility. By measuring the {sup 18}F(p,{alpha}){sup 15}O cross section off resonance and comparing the cross section with theoretical calculations, we provide the first experimental constraints on the interference of 3/2{sup +} resonances.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Holifield Radioactive Ion Beam Facility
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC)
OSTI Identifier:
944098
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos IX, Geneva, Switzerland, 20060625, 20060630
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ASTROPHYSICS; CROSS SECTIONS; ENERGY RANGE; EXCITATION FUNCTIONS; NOVAE; NUCLEI; R MATRIX; RADIOACTIVE ION BEAMS; RESONANCE; UNIVERSE

Citation Formats

Chae, Kyung Yuk, Bardayan, Daniel W, Blackmon, Jeff C, Gregory, Darren R, Guidry, Mike W, Johnson, Micah, KOZUB, RAYMOND L, Livesay, Jake, Ma, Zhanwen, Nesaraja, Caroline D, Pain, Steven D, Paulauskas, Stanley V, Porter-Peden, Matthew D, Shriner, Jr., John F, Smith, Michael Scott, Smith, Nathan A, and Thomas, Jeffrey S. Study of Interference Effects in the 18F(p,alpha)15O Reaction. United States: N. p., 2006. Web.
Chae, Kyung Yuk, Bardayan, Daniel W, Blackmon, Jeff C, Gregory, Darren R, Guidry, Mike W, Johnson, Micah, KOZUB, RAYMOND L, Livesay, Jake, Ma, Zhanwen, Nesaraja, Caroline D, Pain, Steven D, Paulauskas, Stanley V, Porter-Peden, Matthew D, Shriner, Jr., John F, Smith, Michael Scott, Smith, Nathan A, & Thomas, Jeffrey S. Study of Interference Effects in the 18F(p,alpha)15O Reaction. United States.
Chae, Kyung Yuk, Bardayan, Daniel W, Blackmon, Jeff C, Gregory, Darren R, Guidry, Mike W, Johnson, Micah, KOZUB, RAYMOND L, Livesay, Jake, Ma, Zhanwen, Nesaraja, Caroline D, Pain, Steven D, Paulauskas, Stanley V, Porter-Peden, Matthew D, Shriner, Jr., John F, Smith, Michael Scott, Smith, Nathan A, and Thomas, Jeffrey S. Sun . "Study of Interference Effects in the 18F(p,alpha)15O Reaction". United States. doi:.
@article{osti_944098,
title = {Study of Interference Effects in the 18F(p,alpha)15O Reaction},
author = {Chae, Kyung Yuk and Bardayan, Daniel W and Blackmon, Jeff C and Gregory, Darren R and Guidry, Mike W and Johnson, Micah and KOZUB, RAYMOND L and Livesay, Jake and Ma, Zhanwen and Nesaraja, Caroline D and Pain, Steven D and Paulauskas, Stanley V and Porter-Peden, Matthew D and Shriner, Jr., John F and Smith, Michael Scott and Smith, Nathan A and Thomas, Jeffrey S},
abstractNote = {The {sup 18}F(p,{alpha}a){sup 15}O reaction plays a crucial role in understanding {gamma}-ray emission from novae. Because of the importance of understanding the {sup 18}F + p reactions, a number of studies of the A=19 isobars have been made using stable and exotic beams. The interference effects among J{sup {pi}} = 3/2{sup +} resonances in the {sup 18}F + p system, however, have never been measured, but they can change the S-factor by a factor of 20 at nova energies. R-matrix calculations indicate that the cross sections above the E{sub c.m.} = 665 keV resonance are sensitive to the interference between the E{sub c.m.} = 8, 38, and 665 keV resonances. In order to study the interference effects, an excitation function for the {sup 1}H({sup 18}F,{alpha}){sup 15}O reaction has been measured in the energy range of E{sub c.m.} = 663-877 keV using radioactive {sup 18}F beams at the Holifield Radioactive Ion Beam Facility. By measuring the {sup 18}F(p,{alpha}){sup 15}O cross section off resonance and comparing the cross section with theoretical calculations, we provide the first experimental constraints on the interference of 3/2{sup +} resonances.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Conference:
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  • The 18F(p, alpha)O-15 reaction rate is crucial for constraining model predictions of the gamma-ray observable radioisotope F-18 produced in novae. The determination of this rate is challenging due to particular features of the level scheme of the compound nucleus, Ne-19, which result in interference effects potentially playing a significant role. The dominant uncertainty in this rate arises from interference between J(pi) = 3/2(+) states near the proton threshold (S-p = 6.411 MeV) and a broad J(pi) = 3/2(+) state at 665 keVabove threshold. This unknown interference term results in up to a factor of 40 uncertainty in the astrophysical S-factormore » at nova temperatures. Here we report a new measurement of states in this energy region using the F-19(He-3, t)Ne-19 reaction. In stark contrast to previous assumptions we find at least 3 resonances between the proton threshold and E-cm = 50 keV, all with different angular distributions. None of these are consistent with J(pi) = 3/2(+) angular distributions. We find that the main uncertainty now arises from the unknown proton width of the 48 keV resonance, not from possible interference effects. Hydrodynamic nova model calculations performed indicate that this unknown width affects F-18 production by at least a factor of two in the model considered.« less
  • For the first time the {sup 18}F({ital p},{alpha}){sup 15}O reaction has been studied with a {sup 18}F beam at energies which are of interest to explosive nucleosynthesis. Utilizing the gas-filled magnet technique a clean identification of the reaction products was achieved. A resonance with spin 3/2{sup +} at an equivalent c.m. energy of 660 keV dominates the yield.
  • The cross section for the {sup 18}F(p,{alpha}) reaction at energies below 1 MeV/u, of interest to the breakout from the hot CNO cycle, was measured for the first time using a radioactive {sup 18}F beam. {sup 18}F (T{sub 1/2}=110 m) was produced at the cyclotron of the University of Wisconsin through the {sup 18}O(p,n){sup 18}F reaction, transported to Argonne and installed in the SNICS source of ATLAS. The (p,{alpha}) reaction was studied in inverse kinematics at energies below 1 MeV/u using the gas-filled Enge Split-Pole spectrograph for particle identification. Absolute cross sections were determined from the simultaneous measurements of themore » p({sup 18}F,{sup 15}N){alpha} reactions and Rutherford scattering from mass 18 projectiles.« less
  • Excited levels of /sup 19/F have been studied by the reaction /sup 18/ O(p, alpha )/sup 15/N using /sup 18/O-enriched self-supporting targets of Al/sub 2/O/sub 3/. Two simultaneously obtained excitation curves at theta /sub lab/ = 185 and 90 deg have been observed and tabulated. (auth)