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Study of the  -decay of 12 B

Study of the  -decay of 12 B. Spokesperson H.O.U. Fynbo Contactperson U.C. Bergmann. Proposal to INTC 25th February 2002. Why is that interesting ?. Isn’t that all known ?. Region probed by b -decay. Region probed by delayed a -emission. What we know of 12 C.

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Study of the  -decay of 12 B

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  1. Study of the -decay of 12B Spokesperson H.O.U. Fynbo Contactperson U.C. Bergmann Proposal to INTC 25th February 2002

  2. Why is that interesting ? Isn’t that all known ?

  3. Region probed by b-decay Region probed by delayed a-emission What we know of 12C Latest evaluation 1990

  4. Recent interest Shell-model, cluster model, Group theory ……… What do they predict?

  5. Model Predictions -“Exact” 12-body calculations coming in 1-2 years time - Improved shell-model on its way

  6. The NACRE compilation Nucl. Phys. A656 (1999) 3. The triple-a reation rate

  7. Previous Experiments Why it isn’t all known

  8. 12B b-decay Studies • In beam ->energyloss • Evidence for energetic • a-particles

  9. The 10.3 MeV state E = 10.1(2) MeV, G = 2.5 MeV Singles spectra E=10.3(3) MeV, G = 3.0(7) MeV

  10. Evidence for new state near 13MeV The -decay of 12N • Unpublished data from Heidelberg from 1978 (Schwalm) • Main experimental problems are • Energy loss in target • Summing

  11. Reaction studies ? Eyrich et al. PRC36 (1987) 416. Lewis et al. Nucl. Phys. A474 (1987) 499. Youngblood et al. PRC57 (1998) 2748. Overlapping positive and negative parity states -> 0+ strength present

  12. Why we can do better Now Illustrated with results from 12N experiment at JYFL

  13. Main experimental Improvements • Modern segmented Si-Detectors • Large Solid Angle • detect all particles • High Segmentation • no summing • ISOL beams • Low energy isotope separated beam • Can be stopped in a thin collection foil (carbon) • Well-defined source • Little energyloss of emitted particles Previous studies using this setup 31Ar 2p Nucl. Phys. A677 (2000) 38 9C 2p Nucl. Phys. A692 (2001) 427 12N 3a Under analysis R.R.Betts IL NOUVO CIMENTO 110A (1997) 975

  14. - Resolution - Statistics 12N results from JYFL experiment

  15. 12N Results : “The 10.3MeV state” • Select 8Be 0+ branches by gating on diagonal • Use Monte-Carlo to correct for detection efficiency • Fit

  16. Dalitz plot E2 E3 E1 12N Results : The 12.71MeV state • Motivation for previous proposal to INTC • Break-up mechanism ? • Sequential of simultaneous • What is the role of 8Be 2+ • 12N Data : • Simultaneous gives best description of the data

  17. Proposed experiment Dedicated measurement of the b-decay of 12B for the question of 0+ and 2+ states in 12C

  18. 5 cm 10 cm Setup and Production • Detectors : 2 DSSSDs • New DSSSD with reduced deadlayer is ordered. • ISOLDE ball of single detectors is under construction, and will be included if ready. • Dedicated thin detector for singles • New improved electronics • Production • 12B can be produced with high yield indirectly via 12Be. • Analysis • Reduced contribution of 12.71MeV • Measure ba-angular distribution • Measure singles • Decays via 8Be 2+ is applicable

  19. Summary and beam-time Request • Strong indications for • both 0+ and 2+ states at 8-11 MeV • new state near 13 MeV • New experimental possibilities • ISOL beams (reduced energy loss) • Segmented Si-detectors • We ask for 15 shifts

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