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Copy/paste from Seville, with some news Status of Mg(n, g ) with C 6 D 6 in nTOF-Ph1

Copy/paste from Seville, with some news Status of Mg(n, g ) with C 6 D 6 in nTOF-Ph1 CERN, 12.04.2011 Cristian Massimi. Intoduction. Mg data in literature. Activation (thermal) Walkiewicz and Ranan Phys. Rev. C 45, 4 (1992). Activation (MACS) Mohr et. al., Phys. Rev. C 58, 2 (1998).

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Copy/paste from Seville, with some news Status of Mg(n, g ) with C 6 D 6 in nTOF-Ph1

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  1. Copy/paste from Seville, with some news Status of Mg(n,g) with C6D6 in nTOF-Ph1 CERN, 12.04.2011 Cristian Massimi

  2. Intoduction Mg data in literature Activation (thermal) Walkiewicz and Ranan Phys. Rev. C 45, 4 (1992) Activation (MACS) Mohr et. al., Phys. Rev. C 58, 2 (1998) • Charged particle reaction • Denhard et al., Phys. Rev. 160, 964 (1967) • Hardy et al., Academic • Photo-neutron (g,n) • Baglan et al. Phys. Rev. C 3, 672 (1971) • Same experiment, Phys. Rev. Lett. 24, 319 (1970) • Neutron induced reactions A) Transmission • Singh et al. Phys. Rev. C 10 2150 (1976) • Newson, Block et al., Ann. Phys.8, 211 (1959) B) Capture • Macklin et al., Rev. Mod. Phys. 37, 166 (1965) • Bergquist et al., Phys Rev. 158, 1049 () • Block et al., RPI technical report • Nystrom et al., Phys. Scr. 4, 95 (1971) Transmission + Capture + elastic: Weigmann, Macklin and Harvey, Phys. Rev. C 14, 4 (1976) + D.J. Horen, J.A. Harvey, N.W. Hill, Phys. Rev. C 3, 1168 (1976) + Koehler, Phys. Rev. C 66, 055805 (2002) ORELA

  3. Introduction Mg data in literature • Nutron induced reactions The available experimental data for 24,25,26Mg are essentially based on a time-of-flight measurement performed at ORELA: • very high-resolution transmission measurement (200-m flight path, metallic natMg sample, plastic scintillator) • high-resolution capture measurement (40-m flight path, 97.9% 25Mg enriched sample, fluorocarbon scintillators) • Elastic neutron scattering at 200-m flight path (angular momentum) Capture data on 24,26Mg from ORELA are missing

  4. Introduction • Evaluation does not consider: • - the photoneutron cross-section measurement 26Mg(,n)25Mg by Berman et al.(PRL 1969),  J • - a recent work by P. E. Koehler (PRC, 2002)  R-matrix analysis of existing measurements •  News: the mass of the natMg sample was wrong by > 10% Mg data evaluation • Existing evaluations are based on JENDL3.3 (by T. Asami) • JENDL 4 (2010) isnot updated • Resonance parameters in resolve resonance region are taken from BNL (Mughabghab) and negative resonances were added to reproduce the measured thermal cross-section

  5. Experiment Mg samples 2.2-cm in diameter. Oxide sample sealed in an aluminum canning. Al canning is 0.35 g (1.127E-03 at/b). First TOF measurement on an enriched 26Mg sample  News: it can not be used for RSA, anyway it adds important information concerning resonance identification News: 25Mg sample shows an areal density 30%lower than decleared !!!

  6. Data analysis • Detector energy calibration: g-ray sources • Weighting Function (F. Gunsing) News: threshold = 200KeV • Normalization: C6D6 and SiMon calibrated to 3% accuracy by saturating the 4.9-eV resonance in Gold with a 0.25-mm thick sample  News: added g-ray attenuation in WF (for Au) • Time-energy calibration: • TOF = Tn - T0 • Where T0 = Tγ – L / C • L = 185.07 m, from resonances in Au • News: a constant offset of 14 ns has been observed respect to ORELA data

  7. Resonance shape analysis News: we assign this resonance to 26Mg, it was thought to belong to 24Mg n + 26Mg ORELA n_TOF When data are not available, EVALUATION uses average reaction width  Gg = 3 eV This resonance was doubtful, thought to belong to 24Mg.

  8. Resonance shape analysis News: we confirm that these resonances belong to 26Mg n + 26Mg n_TOF n_TOF Huge discrepancy between Weigmann [TOF at ORELA] and Mohr [ACTIVATION]. “Resonance strength should be a factor 2.8 lower than the result from ORELA”.

  9. 26Mg MACS n + 26Mg MACS at 30 keV from present measurement: 0.106 ± 0.01 mb NEWS: Probably nonsense. No way to check for the areal density Negative resonance changed to reproduce the thermal neutron cross section  New value for the Radius

  10. Resonance shape analysis n + 24Mg Evaluation ≈ ORELA n_TOF ORELA

  11. Resonance shape analysis n + 24Mg Evaluation ≈ ORELA n_TOF ORELA

  12. Resonance shape analysis n + 24Mg

  13. Resonance shape analysis n + 24Mg

  14. Resonance shape analysis n + 24Mg

  15. Resonance shape analysis n + 24Mg

  16. Resonance shape analysis n + 24Mg

  17. 24Mg MACS n + 24Mg News: from present measurement: MACS at 30 keV 3.7 ± 0.2 mb MACS at 90 keV 2.4 ± 0.2 mb Preliminary calculations (A. Mengoni): Direct capture component to the MACS < 1 mb Negative resonance changed to reproduce the thermal neutron cross section  New value for the Radius

  18. Problem with 25Mg n + 25Mg, the large s-wave resonance at 20 keV In capture, when Gn >> Gg the RSA is sensitive to ngGg News: from natMg sample, 25Mg enrichment 95%  70% Uncertainty 10 - 15%

  19. Resonance shape analysis n + 25Mg

  20. Resonance shape analysis n + 25Mg

  21. Resonance shape analysis n + 25Mg

  22. Resonance shape analysis n + 25Mg

  23. Resonance shape analysis n + 25Mg

  24. Resonance shape analysis n + 25Mg

  25. Resonance shape analysis n + 25Mg

  26. Resonance shape analysis n + 25Mg

  27. 25Mg MACS n + 25Mg News: from present measurement: MACS at 30 keV 4.2 ± 0.2 ± ? mb MACS at 90 keV 1.5 ± 0.2 ± ? mb Preliminary calculations (A. Mengoni): Direct capture component to the MACS < 1 mb Negative resonance changed to reproduce the thermal neutron cross section  New value for the Radius

  28. Results • Resonance parameters of the 24Mg(n,) and 26(?)Mg(n,) reaction cross-sections have been determined. • Sizable differences have been found respect to the existing evaluation, JENDL4 (2010). • Smaller differences respect to ORELA data (in average 10%). • Direct capture component is an important mechanism, upper limit: 1 mb to the MACS.

  29. Conclusions • The present (n,) measurements improve the cross section data on 24,26(?)Mg isotopes. New value for the MACS are available. • From this analysis we find that the MACS of 25Mg isotope is lower than reported previously because of a problem with the sample. • The contribution of the direct capture mechanism should be investigated experimentally. • Is 26Mg sample thickness correct? • Is it worth to repeat the measurement on 25,26Mg using a metallic sample

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

  31. Experiment Mg samples 2.2-cm in diameter. Oxide sample sealed in an aluminum canning. Mg isotopes Gold Lead Carbon same diameter

  32. Capture

  33. Elastic

  34. 25Mg

  35. 25Mg and 26Mg

  36. Data analysis

  37. WF Weigthing Functions

  38. WF

  39. Problem with 25Mg n + 25Mg

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