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Clustering in 12 Be: Determination of the Enhanced monopole strength Yanlin Ye School of Physics and State Key Lab. of Nucl. Phys.&Tech. Peking University.

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Presentation on theme: "Clustering in 12 Be: Determination of the Enhanced monopole strength Yanlin Ye School of Physics and State Key Lab. of Nucl. Phys.&Tech. Peking University."— Presentation transcript:

1 Clustering in 12 Be: Determination of the Enhanced monopole strength Yanlin Ye School of Physics and State Key Lab. of Nucl. Phys.&Tech. Peking University ARIS, , Tokyo

2 Collaborators

3 Outline I. Some background II. Observation III.Discussion IV. Summary

4 4 alternating independent-particle and clustering structure — a unique feature of nuclear many- body system.

5 Idea of the relative tightness of a cluster inside a nucleus

6 for unstable nuclei Unstable nuclei: much more cluster configurations (and thresholds) within a small E x interval. — richness of nuclear clustering

7 7 Recent progress Theory: AMD, GCM(RGM), GTCM, FMD, TCSM, TCHO(DHO), … Experiment: (7.65 MeV) state in 12C, (6.05 MeV) and (12.05 MeV) in 16O; (8.03 MeV) in 20 Ne …...

8 8 AMD 6 He + 6 He resonance

9 9

10 10 Monopole excitation method T. Yamada et al., PRC85,034315(2012); PTP120,1139(2008) Isoscaler monopole excitation, a jump of about 35 MeV in a simple single-particle picture.

11 11 GTCM Explicit cluster-degree of freedom Good up to high excited levels

12 12

13 13

14 Outline I. Some background II. Observation III.Discussion IV. Summary

15 Main experimental observables for determining the cluster formation i)E x - spin systematics: high moment of inertia ii) Large cluster decay width: large Γ Cluster /Γ ; γ 2 Cluster ; θ 2 Cluster iii)Characteristic transition strength large M(IS) !! M(IS) Γ Cluster

16 Freer et al., PRL82(1999) 1383; PRC63 (2001) Charity et al., PRC76(2007) no small angle (low E rel ) detection 6 He+ 6 He,CH 2 4 He+ 8 He,with P 4 He+ 8 He, with C Freer Charity

17 A new exp. at Lanzhou

18 Beam : 12 Be , 29.0MeV/u , ~3000pps Target : Carbon, 100 mg/cm 2 DSSD : 32 2mm-stip, 300μm, covering Lab. CsI(Tl) : 4 x 4 , 2.5cm*2.5cm*3cm, Detection focused on the most forward angles

19 4He 6He 8He PID for 2- x He fragments Uniform calibration of the Si strips and treatment of PID under intense direct beam: [IEEE-NS 61(2014)596, NIMA728(2013)52]

20 E x = E rel + E thr 4 He+ 4 He 4 He+ 6 He 6 He+ 6 He 4 He+ 8 He 2- x He events for 12 Be Reconstruction (insensitive to E beam )

21 107.6KeV 8Be(g.s) 504.1KeV: 9Be->8Be(2+) Excitation Energy--- 4 He+ 4 He Ref1: PLB580(04) Be breakup Ref1 verification for 4 He + 4 He channel

22 22 Resolution and efficiency

23 Our exp: 6 He+ 6 He MeV 4 He+ 8 He MeV Large and unusual 10.3 MeV state;

24 Outline I. Some background II. Observation III.Discussion IV. Summary

25 Our exp: 6 He+ 6 He MeV 4 He+ 8 He MeV Large and unsual 10.3 MeV state; pure 0 + !! Determine the spin and MR band

26 Spin: Angular correlation analysis for the 10.3 MeV state in 4 He + 8 He channel For small angle inelastic scattering leading to a resonant state with an angular momentum J, which subsequently breaks up into spin-0 fragments, the projected angular correlation spectrum is proportional to | P J (cos(Ψ) | 2, with Ψ being the fragment c.m. angle relative to the beam direction. E x : MeV

27 13.6 MeV state 10.3 MeV state

28 |cosΨ| resolution MeV state

29 Confirming the MR band with large moment of inertia

30 Determining the monopole strength

31 Fraction: 0.034(10) x 2.2. EWSR : fm 4 MeV, M(IS) : 7.0 +/- 1.0 fm 2, DWBA calculation

32 Determining the cluster decay width 10.3 MeV (0 + ) state:

33 All possible decay channels 10.3 MeV(0+) state: Γ = 1.5(2) MeV; Γ = Γ He +Γ Be

34 Overall dominance of the 0 + state Kosheninnilov ours DWBA calculations for the excitation of 12Be from its ground state to the 10.3 MeV excited state, when interacting with a C target.

35 10.3 MeV(0+) state: Γ = 1.5(2) MeV; Γ = Γ He +Γ be Kosheninnilov[12]: Γ Be /Γ= 0.28±0.12 Γ He/ Γ = 1−Γ Be /Γ = 0.72(12); Γ He = 1.1(2) MeV γ 2 He = 0.50(9); θ 2 He = 0.53(10) ( comparable to 8 Be)

36 Outline I. Some background II. Observation III.Discussion IV. Summary

37 Summary i)For the first time a strong monopole strength has been determined in unstable nuclei, providing a clear evidence for cluster formation in 12 Be. ii)Angular-correlation method is very sensitive to the spin of the resonance. MR band in 12 Be has been justified based on the E x -spin systematics. iii) A large cluster-decay width, and consequently a large cluster SF, are obtained for the 10.3 MeV state in 12 Be. All these findings demonstrate a dominating cluster structure in 12 Be just above the 4 He+ 8 He threshold. iv) detection around 0-degrees is essential in in order to measure near-threshold resonances in breakup exp.

38 38

39 comparison Freer Charity ours

40 Korsheninnikov et al., 1995, 50 AMeV 12Be + p; inelastic 10 MeV state, L >= 4 Saito et al., 2004, 60 AMeV 12Be + α;

41 Recent comprehensive review 238 pages

42 42


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