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Cluster Formation Determination in 12Be Nuclei

Explore enhanced monopole strength in 12Be nuclei through nuclear clustering analysis using varying theories and experimental data. This research contributes to understanding unstable nucleus structure. Experimental findings highlight significant monopole characteristics and cluster decay width in 12Be nuclei, affirming a prevalent cluster structure near specific thresholds.

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Cluster Formation Determination in 12Be Nuclei

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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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