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Title: Strong one-neutron emission from two-neutron unbound states in β decays of the r -process nuclei Ga 86 , 87

Abstract

β-delayed one-neutron and two-neutron branching ratios (P$$_{1n}$$ and P$$_{2n}$$) have been measured in the decay of A = 84 to 87 Ga isotopes at the Radioactive-Isotope Beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of 3He neutron counters (BRIKEN). Two-neutron emission was observed in the decay of 84, 85, 87Ga for the first time and the branching ratios were measured to be P$$_{2n}$$ = 1.6 (2)%, 1.3 (2)%, and 10.2 ( 28 ) stat( 5 ) sys %, respectively. One-neutron branching ratio of 87Ga (P$$_{1n}$$= 81 (9) stat (8) sys %) and half-life of 29(4) ms were measured for the first time. The branching ratios of 86Ga were also measured to be P$$_{1n}$$ = 74 (2) stat (8) sys % and 16.2 (9) stat ( 6 ) sys % with better precision than a previous study. The observation that P$$_{1n}$$ > P$$_{2n}$$ for both 86,87Ga was unexpected and is interpreted as a signature of dominating one-neutron emission from the two-neutron unbound excited states in 86, 87Ge. In order to interpret the experimental results, shell-model and Hauser-Feshbach statistical model calculations of delayed particle and γ-ray emission probabilities were performed. This model framework reproduces the experimental results. The shell model alone predicts P$$_{2n}$$ significantly larger than P$$_{1n}$$ for the 87Ga decay, and it is necessary to invoke a statistical description to successfully explain the observation that P$$_{1n}$$ > P$$_{2n}$$. Our new results demonstrate the relevance and importance of a statistical description of neutron emission for the prediction of the decay properties of multineutron emitters and that it must be included in the r-process modeling.

Authors:
 [1];  [2];  [3];  [3];  [4];  [5];  [6];  [7];  [7];  [8];  [4];  [6];  [7];  [9];  [10];  [5];  [11];  [12];  [11];  [10] more »;  [6];  [13];  [7];  [7];  [10];  [14];  [10];  [15];  [1];  [7];  [10];  [16];  [17];  [18];  [1];  [19];  [16];  [7];  [12];  [12];  [20];  [21];  [22];  [1];  [23];  [16];  [24];  [6];  [12];  [13];  [15];  [25];  [16];  [26];  [12];  [27];  [6];  [5];  [7];  [7];  [12];  [1];  [4];  [7];  [28];  [7];  [7];  [11];  [26];  [6];  [16];  [10];  [29] « less
  1. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy
  2. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. TRIUMF, Vancouver, BC (Canada)
  6. Consejo Superior de Investigaciones Cientificas (CSIC), Valencia (Spain)
  7. Inst. of Physical and Chemical Research (RIKEN), Wako (Japan)
  8. Consejo Superior de Investigaciones Cientificas (CSIC), Valencia (Spain); MTA Atomki, Debrecen (Hungary)
  9. Seoul National Univ. (Korea, Republic of)
  10. Univ. of Edinburgh, Scotland (United Kingdom)
  11. Univ. Politècnica de Catalunya (UPC), Barcelona (Spain)
  12. Science and Technology Facilities Council (STFC), Daresbury (United Kingdom). Daresbury Lab.
  13. Central Michigan Univ., Mount Pleasant, MI (United States)
  14. Seoul National Univ. (Korea, Republic of); Inst. of Physical and Chemical Research (RIKEN), Wako (Japan)
  15. Univ. of Liverpool (United Kingdom)
  16. Univ. of Warsaw (Poland)
  17. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  18. Vietnam Academy of Science and Technology, Ha Noi (Vietnam)
  19. Inst. of Physical and Chemical Research (RIKEN), Wako (Japan); MTA Atomki, Debrecen (Hungary)
  20. McMaster Univ., Hamilton, ON (Canada)
  21. Univ. of Hong Kong (China). Dept. of Physics; Inst. of Physical and Chemical Research (RIKEN), Wako (Japan)
  22. National Physical Lab. (NPL), Teddington, Middlesex (United Kingdom); Univ. of Surrey, Guildford (United Kingdom); Inst. of Physical and Chemical Research (RIKEN), Wako (Japan)
  23. Inst. of Physical and Chemical Research (RIKEN), Wako (Japan); Univ. of Tokyo (Japan). Dept. of Physics
  24. Michigan State Univ., East Lansing, MI (United States)
  25. Inst. of Physical and Chemical Research (RIKEN), Wako (Japan); VNU Univ. of Science, Hanoi (Vietnam)
  26. Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab. (RAL)
  27. Tennessee Technological Univ., Cookeville, TN (United States)
  28. Univ. of Notre Dame, IN (United States). Dept. of Physics
  29. Univ. of Hong Kong, Pokfulam Road (Hong Kong)
Publication Date:
Research Org.:
Univ. of Tennessee, Knoxville, TN (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1566761
Alternate Identifier(s):
OSTI ID: 1562737
Grant/Contract Number:  
FG02-96ER40983; AC05-00OR22725; NA0002132; PHY-1430152; PHY-1565546; PHY-1714153; 14F04808; 17H06090; 25247045; 19340074; 89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 100; Journal Issue: 3; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Yokoyama, R., Grzywacz, R., Rasco, B. C., Brewer, N., Rykaczewski, K. P., Dillmann, I., Tain, J. L., Nishimura, S., Ahn, D. S., Algora, A., Allmond, J. M., Agramunt, J., Baba, H., Bae, S., Bruno, C. G., Caballero-Folch, R., Calvino, F., Coleman-Smith, P. J., Cortes, G., Davinson, T., Domingo-Pardo, C., Estrade, A., Fukuda, N., Go, S., Griffin, C. J., Ha, J., Hall, O., Harkness-Brennan, L. J., Heideman, J., Isobe, T., Kahl, D., Karny, M., Kawano, T., Khiem, L. H., King, T. T., Kiss, G. G., Korgul, A., Kubono, S., Labiche, M., Lazarus, I., Liang, J., Liu, J., Lorusso, G., Madurga, M., Matsui, K., Miernik, K., Montes, F., Morales, A. I., Morrall, P., Nepal, N., Page, R. D., Phong, V. H., Piersa, M., Prydderch, M., Pucknell, V. F. E., Rajabali, M. M., Rubio, B., Saito, Y., Sakurai, H., Shimizu, Y., Simpson, J., Singh, M., Stracener, D. W., Sumikama, T., Surman, R., Suzuki, H., Takeda, H., Tarifeño-Saldivia, A., Thomas, S. L., Tolosa-Delgado, A., Wolińska-Cichocka, M., Woods, P. J., and Xu, X. X. Strong one-neutron emission from two-neutron unbound states in β decays of the r -process nuclei Ga86,87. United States: N. p., 2019. Web. doi:10.1103/PhysRevC.100.031302.
Yokoyama, R., Grzywacz, R., Rasco, B. C., Brewer, N., Rykaczewski, K. P., Dillmann, I., Tain, J. L., Nishimura, S., Ahn, D. S., Algora, A., Allmond, J. M., Agramunt, J., Baba, H., Bae, S., Bruno, C. G., Caballero-Folch, R., Calvino, F., Coleman-Smith, P. J., Cortes, G., Davinson, T., Domingo-Pardo, C., Estrade, A., Fukuda, N., Go, S., Griffin, C. J., Ha, J., Hall, O., Harkness-Brennan, L. J., Heideman, J., Isobe, T., Kahl, D., Karny, M., Kawano, T., Khiem, L. H., King, T. T., Kiss, G. G., Korgul, A., Kubono, S., Labiche, M., Lazarus, I., Liang, J., Liu, J., Lorusso, G., Madurga, M., Matsui, K., Miernik, K., Montes, F., Morales, A. I., Morrall, P., Nepal, N., Page, R. D., Phong, V. H., Piersa, M., Prydderch, M., Pucknell, V. F. E., Rajabali, M. M., Rubio, B., Saito, Y., Sakurai, H., Shimizu, Y., Simpson, J., Singh, M., Stracener, D. W., Sumikama, T., Surman, R., Suzuki, H., Takeda, H., Tarifeño-Saldivia, A., Thomas, S. L., Tolosa-Delgado, A., Wolińska-Cichocka, M., Woods, P. J., & Xu, X. X. Strong one-neutron emission from two-neutron unbound states in β decays of the r -process nuclei Ga86,87. United States. doi:10.1103/PhysRevC.100.031302.
Yokoyama, R., Grzywacz, R., Rasco, B. C., Brewer, N., Rykaczewski, K. P., Dillmann, I., Tain, J. L., Nishimura, S., Ahn, D. S., Algora, A., Allmond, J. M., Agramunt, J., Baba, H., Bae, S., Bruno, C. G., Caballero-Folch, R., Calvino, F., Coleman-Smith, P. J., Cortes, G., Davinson, T., Domingo-Pardo, C., Estrade, A., Fukuda, N., Go, S., Griffin, C. J., Ha, J., Hall, O., Harkness-Brennan, L. J., Heideman, J., Isobe, T., Kahl, D., Karny, M., Kawano, T., Khiem, L. H., King, T. T., Kiss, G. G., Korgul, A., Kubono, S., Labiche, M., Lazarus, I., Liang, J., Liu, J., Lorusso, G., Madurga, M., Matsui, K., Miernik, K., Montes, F., Morales, A. I., Morrall, P., Nepal, N., Page, R. D., Phong, V. H., Piersa, M., Prydderch, M., Pucknell, V. F. E., Rajabali, M. M., Rubio, B., Saito, Y., Sakurai, H., Shimizu, Y., Simpson, J., Singh, M., Stracener, D. W., Sumikama, T., Surman, R., Suzuki, H., Takeda, H., Tarifeño-Saldivia, A., Thomas, S. L., Tolosa-Delgado, A., Wolińska-Cichocka, M., Woods, P. J., and Xu, X. X. Thu . "Strong one-neutron emission from two-neutron unbound states in β decays of the r -process nuclei Ga86,87". United States. doi:10.1103/PhysRevC.100.031302.
@article{osti_1566761,
title = {Strong one-neutron emission from two-neutron unbound states in β decays of the r -process nuclei Ga86,87},
author = {Yokoyama, R. and Grzywacz, R. and Rasco, B. C. and Brewer, N. and Rykaczewski, K. P. and Dillmann, I. and Tain, J. L. and Nishimura, S. and Ahn, D. S. and Algora, A. and Allmond, J. M. and Agramunt, J. and Baba, H. and Bae, S. and Bruno, C. G. and Caballero-Folch, R. and Calvino, F. and Coleman-Smith, P. J. and Cortes, G. and Davinson, T. and Domingo-Pardo, C. and Estrade, A. and Fukuda, N. and Go, S. and Griffin, C. J. and Ha, J. and Hall, O. and Harkness-Brennan, L. J. and Heideman, J. and Isobe, T. and Kahl, D. and Karny, M. and Kawano, T. and Khiem, L. H. and King, T. T. and Kiss, G. G. and Korgul, A. and Kubono, S. and Labiche, M. and Lazarus, I. and Liang, J. and Liu, J. and Lorusso, G. and Madurga, M. and Matsui, K. and Miernik, K. and Montes, F. and Morales, A. I. and Morrall, P. and Nepal, N. and Page, R. D. and Phong, V. H. and Piersa, M. and Prydderch, M. and Pucknell, V. F. E. and Rajabali, M. M. and Rubio, B. and Saito, Y. and Sakurai, H. and Shimizu, Y. and Simpson, J. and Singh, M. and Stracener, D. W. and Sumikama, T. and Surman, R. and Suzuki, H. and Takeda, H. and Tarifeño-Saldivia, A. and Thomas, S. L. and Tolosa-Delgado, A. and Wolińska-Cichocka, M. and Woods, P. J. and Xu, X. X.},
abstractNote = {β-delayed one-neutron and two-neutron branching ratios (P$_{1n}$ and P$_{2n}$) have been measured in the decay of A = 84 to 87 Ga isotopes at the Radioactive-Isotope Beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of 3He neutron counters (BRIKEN). Two-neutron emission was observed in the decay of 84, 85, 87Ga for the first time and the branching ratios were measured to be P$_{2n}$ = 1.6 (2)%, 1.3 (2)%, and 10.2 ( 28 )stat( 5 ) sys %, respectively. One-neutron branching ratio of 87Ga (P$_{1n}$= 81 (9)stat (8)sys %) and half-life of 29(4) ms were measured for the first time. The branching ratios of 86Ga were also measured to be P$_{1n}$ = 74 (2)stat (8) sys % and 16.2 (9)stat ( 6 ) sys % with better precision than a previous study. The observation that P$_{1n}$ > P$_{2n}$ for both 86,87Ga was unexpected and is interpreted as a signature of dominating one-neutron emission from the two-neutron unbound excited states in 86, 87Ge. In order to interpret the experimental results, shell-model and Hauser-Feshbach statistical model calculations of delayed particle and γ-ray emission probabilities were performed. This model framework reproduces the experimental results. The shell model alone predicts P$_{2n}$ significantly larger than P$_{1n}$ for the 87Ga decay, and it is necessary to invoke a statistical description to successfully explain the observation that P$_{1n}$ > P$_{2n}$. Our new results demonstrate the relevance and importance of a statistical description of neutron emission for the prediction of the decay properties of multineutron emitters and that it must be included in the r-process modeling.},
doi = {10.1103/PhysRevC.100.031302},
journal = {Physical Review C},
number = 3,
volume = 100,
place = {United States},
year = {2019},
month = {9}
}

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