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A new approach to estimating the probability for  delayed neutron emission

E. A. McCutchan A.A. Sonzogni T.D. Johnson National Nuclear Data Center Brookhaven National Laboratory, NY USA. A new approach to estimating the probability for  delayed neutron emission. Outline. Motivation Traditional systematics A new parameterization A closer look.

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A new approach to estimating the probability for  delayed neutron emission

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  1. E. A. McCutchan A.A. Sonzogni T.D. Johnson National Nuclear Data Center Brookhaven National Laboratory, NY USA A new approach to estimating the probability for  delayed neutron emission

  2. Outline • Motivation • Traditional systematics • A new parameterization • A closer look

  3. -delayed neutrons and their use • Basic structure physics • Reactor control and post-processing of fuel • r-process nucleosynthesis • and abundances

  4. Relevance of reliable systematics 214 nuclei with measured Pn values http://www.nndc.bnl.gov/nudat2

  5. Some terminology  Pn : the probability to emit a neutron following  decay AZ n Qn Q A-1Z+1 Sn AZ+1

  6. Traditional systematic studies Kratz-Herrmann Formula (KHF) Two parameter fit with ‘a’ and ‘b’ Cut off parameter C (MeV) even-even Log-log plot gives straight line with slope=b even-odd odd-odd K.-L. Kratz and G. Herrmann, Z. Phys. A 263, 435 (1973)

  7. The standard for systematic studies Linear regression a = 106(38) b = 5.5(6) red 2= 81 Weighted least-squares B. Pfeiffer et al., Prog. Nucl. Energy 41, 39 (2002).

  8. Effect of improved Q values Masses from : Audi and Meng (2011) Audi and Wapstra (1995) a = 106(38) b = 5.5(6) red 2= 81 a = 119(42) b = 5.45(48) red 2= 146

  9. A better parameterization? Strength function Fermi integral Applying same concept as KHF

  10. A more compact trajectory Light fission fragment region a = 119(42) b = 5.45(48) red 2= 146 a = 0.0097(9) b = 4.87(7) red 2= 35

  11. A more compact trajectory Heavy fission fragment region a = 0.016(2) b = 4.55(13) red 2= 55 a = 141(48) b = 5.08(37) red 2= 78

  12. A surprising correlation Light nuclei, Z <26 a = 45(6) b = 4.4(4) red 2= 280 a = 0.037(9) b = 4.11(9) red 2= 87

  13. A closer look Light fission fragment region • Very linear trend • Few outliers 102Rb 100Rb

  14. A closer look Heavy fission fragment region • Few outliers • Less linear trend • Possible shell effects?

  15. How do we do ?? KHF-2002: B. Pfeiffer et al., Prog. Nucl. Energy 41, 39 (2002). QRPA-1: P. Moller et al., Phys. Rev. C 67, 055802 (2003).

  16. Another surprising correlation P. Moller et al., Phys. Rev. C 67, 055802 (2003).

  17. Summary • New prescription for systematics of Pn values • Ratio of Pn to T1/2 • More compact trajectory • Works across nuclear chart • For the future • Extract information about strength function from slope ??

  18. Relevance to ENSDF • Some evaluators give Pfeiffer KHF results (2002Pf04) for cases where Pn has not been measured • Should we replace with values from new systematics ?

  19. Another surprising correlation P. Moller et al., Phys. Rev. C 67, 055802 (2003).

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