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Title: Identification of {gamma}-decaying Resonant States in {sup 26}Mg and their Importance for the Astrophysical {ital s} Process

Abstract

The Ne-22(alpha, n) reaction is expected to provide the dominant neutron source for the weak s process in massive stars and intermediate-mass (IM) Asymptotic Giant Branch (AGB) stars. However, the production of neutrons in such environments is hindered by the competing Ne-22(alpha,gamma)Mg-26 reaction. Here, the B-11(O-16,p) fusion-evaporation reaction was used to identify gamma-decay transitions from Ne-22 + alpha resonant states in Mg-26. Spin-parity restrictions have been placed on a number of alpha-unbound excited states in (26) Mg and their role in the Ne-22(alpha,gamma)Mg-26 reaction has been investigated. In particular, a suspected natural-parity resonance at E-c.m. = 557(3) keV, that lies above the neutron threshold in Mg-26, and is known to exhibit a strong alpha-cluster character, was observed to gamma decay. Furthermore, a known resonance at Ec.m.=466(4) keV has been definitively assigned 2(+) spin and parity. Consequently, uncertainties in the Ne-22(alpha,gamma) stellar reaction rate have been reduced by a factor of similar to 20 for temperatures similar to 0.2 GK.

Authors:
; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science - Office of Nuclear Physics; Science and Technologies Facilities Council (STFC-UK)
OSTI Identifier:
1603662
Grant/Contract Number:  
[AC02-06CH11357]
Resource Type:
Accepted Manuscript
Journal Name:
European Physical Journal. A
Additional Journal Information:
[ Journal Volume: 55; Journal Issue: 7]
Country of Publication:
United States
Language:
English

Citation Formats

Lotay, G., Doherty, D. T., Seweryniak, D., Almaraz-Calderon, S., Carpenter, M. P., Chiara, C. J., David, H. M., Hoffman, C. R., Janssens, R. V. F., Kankainen, A., and Lauritsen, T. Identification of {gamma}-decaying Resonant States in {sup 26}Mg and their Importance for the Astrophysical {ital s} Process. United States: N. p., 2019. Web. doi:10.1140/epja/i2019-12791-5.
Lotay, G., Doherty, D. T., Seweryniak, D., Almaraz-Calderon, S., Carpenter, M. P., Chiara, C. J., David, H. M., Hoffman, C. R., Janssens, R. V. F., Kankainen, A., & Lauritsen, T. Identification of {gamma}-decaying Resonant States in {sup 26}Mg and their Importance for the Astrophysical {ital s} Process. United States. doi:10.1140/epja/i2019-12791-5.
Lotay, G., Doherty, D. T., Seweryniak, D., Almaraz-Calderon, S., Carpenter, M. P., Chiara, C. J., David, H. M., Hoffman, C. R., Janssens, R. V. F., Kankainen, A., and Lauritsen, T. Thu . "Identification of {gamma}-decaying Resonant States in {sup 26}Mg and their Importance for the Astrophysical {ital s} Process". United States. doi:10.1140/epja/i2019-12791-5.
@article{osti_1603662,
title = {Identification of {gamma}-decaying Resonant States in {sup 26}Mg and their Importance for the Astrophysical {ital s} Process},
author = {Lotay, G. and Doherty, D. T. and Seweryniak, D. and Almaraz-Calderon, S. and Carpenter, M. P. and Chiara, C. J. and David, H. M. and Hoffman, C. R. and Janssens, R. V. F. and Kankainen, A. and Lauritsen, T.},
abstractNote = {The Ne-22(alpha, n) reaction is expected to provide the dominant neutron source for the weak s process in massive stars and intermediate-mass (IM) Asymptotic Giant Branch (AGB) stars. However, the production of neutrons in such environments is hindered by the competing Ne-22(alpha,gamma)Mg-26 reaction. Here, the B-11(O-16,p) fusion-evaporation reaction was used to identify gamma-decay transitions from Ne-22 + alpha resonant states in Mg-26. Spin-parity restrictions have been placed on a number of alpha-unbound excited states in (26) Mg and their role in the Ne-22(alpha,gamma)Mg-26 reaction has been investigated. In particular, a suspected natural-parity resonance at E-c.m. = 557(3) keV, that lies above the neutron threshold in Mg-26, and is known to exhibit a strong alpha-cluster character, was observed to gamma decay. Furthermore, a known resonance at Ec.m.=466(4) keV has been definitively assigned 2(+) spin and parity. Consequently, uncertainties in the Ne-22(alpha,gamma) stellar reaction rate have been reduced by a factor of similar to 20 for temperatures similar to 0.2 GK.},
doi = {10.1140/epja/i2019-12791-5},
journal = {European Physical Journal. A},
number = [7],
volume = [55],
place = {United States},
year = {2019},
month = {7}
}

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