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Clustering in 12 Be: Determination of the Enhanced monopole strength

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, 2014.06.02, Tokyo. Collaborators. Outline. I. Some background. II. Observation. Discussion. IV. Summary.

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Clustering in 12 Be: Determination of the Enhanced monopole strength

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  1. Clustering in 12Be: Determination of the Enhanced monopole strength Yanlin Ye School of Physics and State Key Lab. of Nucl. Phys.&Tech. Peking University ARIS, 2014.06.02, Tokyo

  2. Collaborators

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

  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 Ex interval. — richness of nuclear clustering

  7. Recent progress Theory: AMD, GCM(RGM), GTCM, FMD, TCSM, TCHO(DHO), … Experiment: 0+2(7.65 MeV) state in 12C, 0+2(6.05 MeV) and 0+3 (12.05 MeV) in 16O; 0+4(8.03 MeV) in 20Ne …...

  8. AMD 6He + 6He resonance

  9. 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.

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

  11. Outline I. Some background II. Observation • Discussion IV. Summary

  12. Main experimental observables for determining the cluster formation • Ex - spin systematics: high moment of inertia ii) Large cluster decay width: large ΓCluster/Γ ; γ2Cluster ; θ2Cluster • Characteristic transition strength large M(IS) !! ΓCluster M(IS)

  13. Freer et al., PRL82(1999) 1383; PRC63 (2001)034301 Charity et al., PRC76(2007)064313 no small angle (low Erel) detection Freer Charity 4He+8He, with C 6He+6He,CH2 4He+8He,with P

  14. A new exp. at RIBLL1@HIRFL, Lanzhou

  15. Beam： 12Be，29.0MeV/u，~3000pps Target：Carbon, 100 mg/cm2 DSSD：32 2mm-stip, 300μm , covering 00-120 Lab. CsI(Tl)： 4 x 4， 2.5cm*2.5cm*3cm, Detection focused on the most forward angles

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

  17. Reconstruction (insensitive to Ebeam) Ex = Erel + Ethr 2-xHe events for 12Be

  18. verification for 4He + 4He channel 107.6KeV 8Be(g.s) 504.1KeV: 9Be->8Be(2+) Ref1 Excitation Energy---4He+4He Ref1: PLB580(04)129-14Be breakup

  19. Resolution and efficiency

  20. Large and unusual 10.3 MeV state; Our exp: 6He+6He 11.7 13.3 MeV 4He+8He 10.3 12.1 13.6 MeV

  21. Outline I. Some background II. Observation • Discussion IV. Summary

  22. Determine the spin and MR band Large and unsual 10.3 MeV state; pure 0+ !! Our exp: 6He+6He 11.7 13.3 MeV 4He+8He 10.3 12.1 13.6 MeV

  23. Spin: Angular correlation analysis for the 10.3 MeV state in 4He + 8He 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 | PJ(cos(Ψ) |2, with Ψ being the fragment c.m. angle relative to the beam direction. Ex: 10.0 - 11.4 MeV

  24. 10.3 MeV state 13.6 MeV state

  25. 10.3 MeV state |cosΨ| resolution 0.1 0.2 0.4

  26. Confirming the MR band with large moment of inertia 10.3 MeV state

  27. Determining the monopole strength

  28. DWBA calculation Fraction: 0.034(10) x 2.2. EWSR：6727.9 fm4 MeV, M(IS)： 7.0 +/- 1.0 fm2,

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

  30. All possible decay channels 10.3 MeV(0+) state: Γ = 1.5(2) MeV; Γ = ΓHe+ΓBe

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

  32. 10.3 MeV(0+) state: Γ = 1.5(2) MeV; Γ = ΓHe+Γbe Kosheninnilov[12]: ΓBe/Γ= 0.28±0.12 ΓHe/Γ = 1−ΓBe/Γ = 0.72(12); ΓHe = 1.1(2) MeV γ2He= 0.50(9); θ2He= 0.53(10) （comparable to 8Be)

  33. Outline I. Some background II. Observation • Discussion IV. Summary

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

  35. Thank you for your attention

  36. comparison ours Freer Charity

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

  38. Recent comprehensive review 238 pages

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