1. Beta-decay studies of sd-shell nuclei near proton drip-line
第十七届全国核物理大会 ，武汉
Beta-decay studies of sd-shell nuclei near proton drip-line
徐新星
中国科学院近代物理研究所

2. OUTLINE Introduction to the collaboration and our studies
22Si β-decay: Two-proton emission
Mirror asymmetry (compared with 22O)
27S β-decay: Astrophysical impact on Galactic 26Al
Summary and Outlook

3. 1. Introduction to the collaboration and our studies
More than 50 researchers from 15 institutions
X. X. Xu (徐新星) 1, C. J. Lin (林承键)2, J. Lee (李晓菁)3, Z. H. Li (李智焕)4, J. S. Wang (王建松)1,
D. Q. Fang(方德清)5, J. J. He (何建军)6，K. Kaneko 7，Y. Sun (孙杨) 8 ，L. J. Sun (孙立杰) 8, S. Q. Hou (侯素青)1, J. Jose 9, C. X. Yuan (袁岑溪)10, F. Herwig11,12, J. Keegans13, Y. H. Lam (蓝乙华) 1 , H. Y. Wu (吴鸿毅)4 , J. Li(李晶) 4, P. F. Liang (梁鹏飞)3, Q. Q. Zhao (赵青青)3, Y. Y. Yang (杨彦云)1 , P. Ma (马朋)1, J. B. Ma (马军兵)1, F. P. Zhong (钟福鹏)2, J. G. Wang (王建国)1, R. Li (李忍)1, C. G. Wu (武晨光)4, D. W. Luo (罗迪雯) 4 , Z. G. Hu (胡正国)1, R. F. Chen (陈若富)1, M. L. Liu (柳敏良)1, W. Q. Yang (杨维青)1 , D. X. Wang (王东玺)2, Q. Hu (胡强)1, G. Z. Shi (石国柱)1, H. M. Jia (贾会明)2, Z. Bai (白真)1, Y. Jiang (蒋颖)4, Y. Liu (刘洋)4, D. S. Hou (侯东升)1, N. R. Ma (马南茹)2, G. L. Zhang (张高龙)14, F. F. Duan (段芳芳)15, P. J. Li (李朋杰)3, Y. M. Zhao (赵玉民)8, and H. Q. Zhang (张焕乔) 2 et al.
1 Institute of Modern Physics, CAS, Lanzhou, China
2 China Institute of Atomic Energy, Beijing, China
The University of Hong Kong, Hong Kong, China
Peking University, Beijing, China
Fudan University, Shanghai, China
Beijing Normal University, Beijing , China
Department of Physics, Kyushu Sangyo University, Fukuoka , Japan
8 Shanghai Jiao Tong University, Shanghai, China
9 Universitat Politecnica de Catalunya, Barcelona, Spain
Sun Yat-Sen University, Zhuhai, China
Department of Physics & Astronomy, University of Victoria, Victoria, BC, V8W 2Y2, Canada
Joint Institute for Nuclear Astrophysics, Center for the Evolution of the Elements, Michigan State University, East Lansing, MI 48824, USA
E.A. Milne Centre for Astrophysics, Department of Physics & Mathematics, University of Hull, Hull HU6 7RX, UK
Beihang University, Beijing, China
Lanzhou University, Lanzhou, China

4. Where ? Primary Beam: 28Si, 75.8 MeV/u 32S, 80.6 MeV/u Target: 9Be
Detector Array

5. How ? Silicon Array 1 + Clover HPGe
L.J. Sun, X.X. Xu*, C.J. Lin*, et al, Nucl. Instrum. Methods Phys. Res., Sect. A 804 (2015) 1.
DSSD1 (149um), DSSD2(66um) for implantation-decay correlation
QSD2,QSDU,D,R,L(1500um) for β particles
Clover for γ rays
ΔE(SD, QSD),TOF(T1,T2) for particle identification

6. How ? Silicon Array 2 + Clover HPGe LaBr3
DSSD1 (142um), DSSD2(40um), DSSD3(304um) for implantation-decay correlation
QSD1(1500um) for β particles Clover and LaBr3 for γ rays
ΔE(QSD),TOF(T1,T2) for particle identification

7. Beta-decay studies of extremely proton-rich nuclei from Mg to S
Mass Number ~ 20 to 30
2017
2015
2017
Experiment in 2015:
23Al, 24Si: NIMA 804, 1 (2015).
22Si : PLB 766, 321 (2017).
20Mg: PRC 95, (2017).
23Si: IJMPE 27, (2018)
21Mg: EPJA 54, 107 (2018) .
22Al：PLB 784, 12 (2018).
Experiment in 2017:
27S：PRC 99, (2019).
2015

8. 2. 22Si β-decay 22Si the lightest nucleus Tz=-3 the sd-shell nucleus
high-quality shell-model calculations
β -delayed proton emission
candidate for β2p, β3p emission
possible βpα or direct 2p decay

9. Experiment in January, 2015
Si, purity at %, total 350 ions/sec RIBS

10. The decay of 22Si (The lightest nucleus with Tz=−3)βp
β2p
Charged-particle spectrum
Decay-time spectrum
X.X.Xu*, et al, Physics Letters B 766 (2017) 312–316

11. First observation of β2p in the decay of 22Si
Identification of particles at the energy of 5600keV
The atomic mass excess of 22Si :32163 (123)keV
Two-proton separation energy (S2p) for 22Si : −108(125)keV
22Si marginally situates beyond the two-proton drip line
X.X.Xu*, et al, Physics Letters B 766 (2017) 312–316

12. β-decay scheme of 22Si

13. 3. 27S β-decay ---Galactic 26Al Puzzle
The Puzzle about the origin of a large amount of 26Al
COMPTEL map of 26Al emission (1.809 MeV) (Oberlack et al. 1997)

14. The decay of 27S and Galactic 26Al Puzzle
The 26Si(p, γ)27P reaction competes with the β decay of 26Si to 26Alm, and the latter can produces 26Alg via thermal excitations. Thus, the production and destruction of 26Si by proton capture should be influential in determining the amount of the 26Alm and 26Alg produced by the equilibrium.
26Si(p, γ)27P
26Si(β+)26Alm
25Al(p, γ)26Si
Explosive hydrogen burning scenarios

15. The decay of 27S and Galactic 26Al Puzzle
Two-dimensional identification plot of ΔE and ToF
Ion
27S
26P
25Si
Intensity (pps)
0.137
0.879
20.73
Purity
2.45×10–4
1.57×10–3
3.7×10–2
Total number
4.7×104
3.0×105
7.1×106

16. The decay of 27S and Galactic 26Al Puzzle
Decay scheme of 27S
Mass of 27P
Literature
Δ(27P) (keV)
Audi_NPA2003
–717(26)
Wang_CPC2012
–722(26)
Wang_CPC2017
Benenson_PRC1977
–716(16)
Caggiano_PRC2001
–670(41)
Fu_PRC2018
Janiak_PRC2017
–685(42)
–640(30)
Present work
–659(9)
βp spectrum
βγ spectrum
L. J. Sun (孙立杰), X. X. Xu (徐新星)*, et al, PHYSICAL REVIEW C 99, (2019)

17. Precise 26Si(p, γ )27P Rate and mass of 27P
The astrophysical impact on Galactic 26Al :
1, Validating previous predictions of the nova contribution
2, Increasing more than 50% in x-ray burst compared with the previous calculation.
Ratios of various 26Si(p,γ)27P reaction rates

18. Summary and Outlook
1, Physics：a, Two-proton emission 22,23Si, 22Al, 27S,26P
b, Isospin symmetry breaking 22Si,27,28S
c, Galactic 26Al Puzzle 27S, 26,27P
2, Detectors, ASIC, DPP Techs:
4π Arrays of Silicon, Clover and LaBr3
GET SYSTEM
Digital Pulse Processing
3, More Collaborations needed

19. Thanks!