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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. - PowerPoint PPT Presentation
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A new approach to estimating the probability for delayed neutron emission
E. A. McCutchanA.A. SonzogniT.D. Johnson
National Nuclear Data CenterBrookhaven National Laboratory, NY USA
Outline
• Motivation
• Traditional systematics
• A new parameterization
• A closer look
-delayed neutrons and their use• Reactor control and
post-processing of fuel
• r-process nucleosynthesis and abundances
• Basic structure physics
214 nuclei with measured Pn values
http://www.nndc.bnl.gov/nudat2
Relevance of reliable systematics
Some terminology
AZ+1
Q
AZ
Sn
A-1Z+1
Qn
n
Pn : the probability to emit a
neutron following decay
6
Kratz -Herrmann Formula (KHF)
𝑃𝑛≈𝑎 [𝑄 𝛽−𝑆𝑛
𝑄𝛽−𝐶 ]𝑏
Cut off parameter C (MeV)
𝐶=0𝐶=
13√𝐴
𝐶=26√𝐴
even-even
even-odd
odd-odd
Traditional systematic studies
K.-L. Kratz and G. Herrmann, Z. Phys. A 263, 435 (1973)
Two parameter fit with ‘a’ and ‘b’
Log-log plot gives straight linewith slope=b
B. Pfeiffer et al., Prog. Nucl. Energy 41, 39 (2002).
The standard for systematic studies
Linear regression
Weighted least-squares
a = 106(38)b = 5.5(6)
red 2 = 81
a = 119(42)b = 5.45(48)red 2 = 146
Audi and Meng (2011)
Effect of improved Q values
a = 106(38)b = 5.5(6)
red 2 = 81
Masses from :Audi and Wapstra (1995)
A better parameterization?Strength function Fermi integral
𝑃𝑛
𝑇1 /2𝑎(𝑄 𝛽𝑛)
𝑏
Applying same concept as KHF
A more compact trajectory
a = 0.0097(9)b = 4.87(7)red 2 = 35
a = 119(42)b = 5.45(48)red 2 = 146
Light fission fragment region
Heavy fission fragment region
a = 141(48)b = 5.08(37)red 2 = 78
a = 0.016(2)b = 4.55(13)red 2 = 55
A more compact trajectory
A surprising correlation
a = 45(6)b = 4.4(4)
red 2 = 280
a = 0.037(9)b = 4.11(9)red 2 = 87
Light nuclei, Z <26
A closer lookLight fission fragment region
• Very linear trend• Few outliers
100Rb102Rb
A closer lookHeavy fission fragment region
• Few outliers• Less linear trend• Possible shell
effects?
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).
Another surprising correlation
P. Moller et al., Phys. Rev. C 67, 055802 (2003).
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 ??
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 ?
Another surprising correlation
P. Moller et al., Phys. Rev. C 67, 055802 (2003).