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Results on 24,25,26 Mg(n, g ) and proposals Lisboa, 13-15 December 2011

Results on 24,25,26 Mg(n, g ) and proposals Lisboa, 13-15 December 2011. Introduction / Motivation Results on 24,25,26 Mg(n, g ) Astrophysical implications s-process Constraints on 22 Ne( a ,n) 25 Mg Proposal for future measurements 25 Mg(n, g ) and 25 Mg(n,tot)

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Results on 24,25,26 Mg(n, g ) and proposals Lisboa, 13-15 December 2011

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  1. Results on 24,25,26Mg(n,g) and proposals Lisboa, 13-15 December 2011

  2. Introduction / Motivation Results on 24,25,26Mg(n,g) Astrophysical implications s-process Constraints on 22Ne(a,n)25Mg Proposal for future measurements 25Mg(n,g) and 25Mg(n,tot) 25Mg(n,a)  CHALLENGE! Outline

  3. Introduction The s-process and Mg stable isotopes

  4. Introduction The s-process and Mg stable isotopes “Main component” 22Ne(,n)25Mg is a neutron source in AGB stars: 1Msun < M < 3Msun • kT=8 keV and kT=25 keV

  5. Introduction The s-process and Mg stable isotopes “Main component” 22Ne(,n)25Mg is a neutron source in AGB stars: 1Msun < M < 3Msun • kT=8 keV and kT=25 keV “Weak component” 22Ne(,n)25Mg is the mainneutron source in massive stars: M > 10 – 12Msun • kT=25 keV and kT=90 keV Other important reactions:22Ne(,g)26Mg, 25Mg(n,g)26Mg, 26Al (n,p)26Mg

  6. Motivations • (24),25,26Mg are the most important neutron poisons due to neutron capture on Mg stable isotopes in competition with neutron capture on 56Fe that is the basic s-process seed for the production of heavy isotopes. • Several attempts to determine therate for the reaction 22Ne(,n)25Mg either through direct 22Ne(,n)25Mg measurement or indirectly, via 26Mg(,n)25Mg or charged particle transfer reactions. In both cases the cross-section is very small in the energy range of interest. • The main uncertainty of the reaction rate comes from the poorly known property of the states in 26Mg. Information can come from neutron measurements (knowledge of J for the 26Mg states). • The production of 26Al in the cosmos  the main production mechanism is affected by uncertainties of several cross sections, in particular 24Mg(n,g)

  7. Resonance shape analysis Transmission ORELA Capture n_TOF

  8. MACS of 24Mg KADoNis This work (Resonance + DRC) sg(kT=5 keV)= 0.11 mb sg(kT=30 keV)= 3.3±0.4 mb sg(kT=80 keV)=2.7 mb sg(kT=5 keV)= (0.17+0.04)±0.04 mb sg(kT=30 keV)=(3.7+0.1)±0.2 mb sg(kT=80 keV)=(2.6+0.2)±0.2 mb • Uncertainty reduced to 5% • p-wave Direct Radiative Capture (DRC) included

  9. MACS of 25Mg KADoNis This work (Resonance + DRC) sg(kT=5 keV)= 4.8 mb sg(kT=30 keV)= 6.4±0.4 mb sg(kT=80 keV)=4.4 mb sg(kT=5 keV)= (4.9+0.03)±0.6 mb sg(kT=30 keV)=(4.0+0.1)±0.6 mb sg(kT=80 keV)=(1.8+0.1)±0.3 mb • Uncertainty INCREASED to 15 % • p-wave Direct Radiative Capture (DRC) included

  10. MACS of 26Mg KADoNis This work (Resonance + DRC) sg(kT=5 keV)= 0.1 mb sg(kT=30 keV)= 0.126±0.009 mb sg(kT=80 keV)=0.226 mb sg(kT=5 keV)= (0.067+0.02)±0.001 mb sg(kT=30 keV)=(0.09+0.05)±0.01 mb sg(kT=80 keV)=(0.29+0.08)±0.04 mb Activation • p-wave Direct Radiative Capture (DRC) included

  11. MACS of 26Mg

  12. MACS of 26Mg Activation Experiment • Normalization of the DRC calculations

  13. MACS of 26Mg TOF Experiment • Check on the mass of the sample

  14. Astrophysical implication s-process abundances Reduced poisoning effect. Lower MACS of 25Mg  higher neutron density • KADoNiS • Present work Abundance distribution of the weak s-process Small impact on AGB abundances

  15. Astrophysical implication Constraints for the 22Ne(a,n)25Mg reaction MeV Only natural-parity (0+, 1-, 2+, 3-, 4+, …) states in 26Mg can participate in the 22Ne(,n)25Mg reaction

  16. Astrophysical implication Constraints for the 22Ne(a,n)25Mg reaction MeV MeV s-wave  Jp= 2+, 3+ p-wave Jp= 1-, 2-, 3-, 4- d-wave Jp= 0+, 1+,2+, 3+, 4+, 5+ States in 26Mg populated by 25Mg(n,g)reaction

  17. Astrophysical implication 22Ne(a,n)25Mg • a-particle energy • Lab.

  18. Astrophysical implication 22Ne(a,n)25Mg T= (0.1-1.0)×109K • a-particle energy • Lab.

  19. Astrophysical implication 22Ne(a,n)25Mg 0.5 0.6 0.9 1

  20. Astrophysical implication 22Ne(a,n)25Mg 11.037 11.207 11.376 Ex (MeV) • 26Mg* energy • CM 0.5 0.6 0.9 1

  21. Astrophysical implication 22Ne(a,n)25Mg 11.037 11.207 11.376 Ex (MeV) • 26Mg* energy • CM • 25Mg(n,a)22Ne, • 25Mg(n,g)26Mg, • 25Mg+n • Neutron energy Lab. 30 117 294 0 En (keV) 0.5 0.6 0.9 1

  22. Astrophysical implication 22Ne(a,n)25Mg ? En (keV) 25Mg(n,a)22Ne 0 20 234 0.5 0.6 0.9 1

  23. Astrophysical implication 25Mg(n,g)26Mg Constraints for the 22Ne(a,n)25Mg reaction

  24. Astrophysical implication 25Mg(n,g)26Mg Constraints for the 22Ne(a,n)25Mg reaction

  25. Astrophysical implication 25Mg(n,g)26Mg Constraints for the 22Ne(a,n)25Mg reaction R. Longland et al., Phys. Rev. C 80, 055803, 2009 “Nuclear resonance fluorescence” Before the 62.727-keV resonance was thought to be 1-

  26. Astrophysical implication 25Mg(n,g)26Mg Constraints for the 22Ne(a,n)25Mg reaction Jp uncertain NO constraint for 22Ne(a,n)25Mg ?

  27. Astrophysical implication 25Mg(n,g)26Mg Constraints for the 22Ne(a,n)25Mg reaction The reaction rate of the neutron source can be calculated:

  28. Astrophysical implication 25Mg(n,g)26Mg Constraints for the 22Ne(a,n)25Mg reaction • The reaction rate of the neutron source can be calculated: • ER from (n,g) • Ga No information from neutron spectroscopy  different values assumed

  29. Astrophysical implication Constraints for the 22Ne(a,n)25Mg reaction With respect to recommended value from NACRE Upper limit for Ga Lower limit for Ga

  30. Conclusions • Resonance parameters improved: • thermal cross section • doubtful resonances • corrected previous results • MACS and related Astrophysical implication • Constraints on the s-process neutron source 22Ne(a,n)25Mg

  31. Future measurements Capture and transmission experiment on ENRICHED 25Mg (metallic!) sample: • Improve uncertainties • Determine Jp 24Mg

  32. 25Mg(n,a)22Ne The 25Mg(n,a)22Ne (Q-value=480 keV) cross-section is linked to the 22Ne(a,n)25Mg A B a b • Energy region of interest: • 0 < En < 300 keV

  33. 25Mg(n,a)22Ne • Energy region of interest: • 0 < En < 300 keV

  34. 25Mg(n,a)22Ne • Range of 480-keVa-particle  few µm The corresponding areal density of a 1-µm thick 25Mg sample is 4.2×10-6 atoms/barn.

  35. 25Mg(n,a)22Ne n = 4.2×10-6 atoms/barn • = 1 mb • = 50% (using a thin magnesium layer and a 2p a particle detector) Pa = 80% the resulting counting rate, as a function of the neutron fluence is: CR=2×10-8 ×f For instance in • EAR-1, fEAR-1 = 7.1×104 neutrons are delivered per proton burst in the 10-100 keV energy range • EAR-2, fEAR-2 ≈ 1.8×106 • 1 signal / 25 bunches • 30 signals / hour

  36. Detector • Diamond • MicroMegas • Silicon • Compensated ionization chamber • …

  37. Conclusion GOOD IDEAS are WELCOME

  38. Cristian Massimi Dipartimento di Fisica massimi@bo.infn.it www.unibo.it

  39. Neutron sensitivity

  40. Neutron sensitivity

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