Cluster Dscay of the High-lying Excited States in 14 C

Transcription

1 Cluster Dscay of the High-lying Excited States in 14 C Yanlin Ye School of Physics and State Key Lab of Nuclear Physics and Technology, Peking University INPC2016, Sept , 2016, Adelaide, Australia

2 Collaborators

3 Outline I. Some background II. The experiment III. Preliminary results IV. Summary

4 The threshold rule in cluster formation Ikeda diagram 4

5 Clustering in unstable nuclei a new area W.Von Oerttzen et al., Phys. Report 432(06)43 Y. Kanada-En yo et al., Prog. Theor. Exp. Phys., 2012, 01A202

6 Possible chain states based on α-cores 8 Be(2α) W.Von Oerttzen et al., Z. Phys. A357(97)355.

7 Example of studies for x Be

8 x C: triangle, and π-bond or σ-bond linear-chain states π-bond or σ-bond most exotic one: σ-bond linear-chain state T. Baba and M. Kimura arxiv:1605/05567v1

9 Major improvements: Latest AMD calculations for 14 C T. Baba and M. Kimura arxiv:1605/05567v1 Ø Gogny D1S force to better describe E x ; Ø Projected single particle wave function for valence neutrons to distinguish the π-bond or σ-bond states; Ø core excitation included and the reduced decay-width deduced accordingly.

10 T. Baba and M. Kimura arxiv:1605/05567v1

11 Decay width is related to the cluster-configuration T. Baba and M. Kimura arxiv:1605/05567v1

12 10 Be*(~6 MeV) α + 10 Be* σ-bond linear-chain π-bond linear-chain triangle 10 Be Experimental probes 14 C

13 Previous 14 C experiments with 10 Be*(~6 MeV) selection N. Soic, M. Freer et al., PRC68(2003) ; 7 Li( 9 Be, 4 He 10 Be) 2 H, E beam =70 MeV D.L. Proce, M. Freer et al., PRC75(2007) ; 14 C( 14 C, 4 He 10 Be) 14 C, E beam =98.2 MeV

14 Recently reported results: no selection on 10 Be*(~6 MeV) M. Freer et al., PRC90(2014) ; α( 10 Be, α) 10 Be, E x =13 to 24 MeV A. Fritsch et al., PRC93(2016)014321; α( 10 Be, α) 10 Be, E x =15.0 to 20.7 MeV Possible observation of the triangle-like and π-bond linear-chain states, but not σ-bond states.

15 Outline I. Some background II. The experiment III. Preliminary results IV. Summary

16 Basic considerations for experimentation Ø Projectile and target in favor of cluster formation Ø Large Q-value reaction in order to excite high lying states in 14 C and to have a good selection of the states in 10 Be fragment; Ø MM + IM measurements in order to extract the reduced cluster-decay width from branching ratio.

17 selected reaction (5 AMeV beam; 185 ug/cm 2 target) : Be + Be He + C Q=17.25 MeV C 10Be α α main contamination in Q-value: a He + Be Q=5.239 MeV Be + Be Be + Be Q = MeV 10Be 8Be a He + He α α can be removed via kinematics analysis

18 Experiment setup at CIAE Detector Segmentation Thickness (µm) Covering angle (degree) Purpose Telescope U0&D0 U0&D0 are symmetrical Be&alpha from 14C Alpha(14C) DSSD 16 x ΔE DSSD 32x E SSD 1500 E(4He) Telescope U1&D1 U0&D0 are symmetrical Alpha(14C) DSSD 16*16 60 ΔE SSD 1500 E Telescope U2&D2 symmetrical Alpha(14C) DSSD ΔE SSD 1500 E Beam 9 Be 45MeV ~7enA Target 9 Be 0.9um

19 Typical PID at forward angles 9 Be( 9 Be, 14 C[ 10 Be+α])α 19

20 Outline I. Some background II. The experiment III. Preliminary results IV. Summary

21 Missing mass method (inelastic or transfer) 3 B* A T A 3 B* B* T A 3 Q T T T m m m m m m m m Q = + = + = + ( ) B B 3 A B A cos m T T m m E m m T m m Q A A θ + + =

22 Invariant mass method r r r EB* = E1 + E2, pb* = p1 + p2 r r m c = [ E c p ] = [( E + E ) c p + p ] / /2 B* B* B* E =( m + m m ) c S 1 1 B E = m c - m c = E + E 2 2 x B* B S rel 2

23 Comparison of Q-values Soic et al.: 7 Li( 9 Be, α 10 Be ) d, E beam =70 MeV, PID for forward 10 Be + α, deduced recoil α. Present work: 9 Be( 9 Be, α 10 Be ) α, E beam =45 MeV, PID for forward 10 Be + α, deduced recoil α.

24 Kinematics check 9 Be+ 9 Be 14 C * (18MeV)+α 9 Be+ 9 Be 10 Be * (6MeV)+ 8 He deduced recoil α angle vs measured 14 C angle

25 Comparison of IM spectra for various 10 Be states Tentative: π-bond chain? 18.5 MeV (new) σ-bond chain? (new) Consistent with predictions

26 Simulated energy resolution T. Baba and M. Kimura arxiv: 1605/05567v1

27 Outline I. Some background II. The experiment III. Preliminary results IV. Summary

28 Ø A reaction with very large Q-value was carried out, allowing to excite 14 C to very high lying states and to clearly separate the various states in 10 Be fragment. Ø Three highly excited states in 14 C are observed which decay primarily into 10 Be*(~6 MeV), corresponding likely to the σ-bond linear-chain states according to the latest AMD model predictions. Ø Further analysis of the cluster-decay branching ratio, related to the cluster reduced width, are underway in order to make quantitative comparison with theoretical calculations. 28

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