1 / 16

Simulating G g Distributions

Simulating G g Distributions. What is G g ? How are G g ’s measured? What does the standard model predict? Simulating G g distributions. Constraining the Oslo method . Testing the Porter-Thomas distribution. What is G g ?.

Download Presentation

Simulating G g Distributions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Simulating Gg Distributions What is Gg? How are Gg’s measured? What does the standard model predict? Simulating Gg distributions. Constraining the Oslo method. Testing the Porter-Thomas distribution

  2. What is Gg? • Gg is the total radiation width.Sum of partial radiation widths, Ggi, for primary transitions from the capturing state (resonance).

  3. Neutron Capture Cross Sections:Neutron hits target and sticks • AZ(n,g)A+1Z

  4. (n,g) Measurements at ORELA Employ C6D6 Detectors Flux monitor g-ray detectors Neutron beam Sample

  5. How is Gg Measured? • Gg determined from R-matrix analysis of neutron-resonance data. • Typically need both neutron total (transmission) and capture data. • Capture area.Ag=gJGnGg/(Gn+Gg). • Depth of transmission dip proportional to Gn. • Total width.Gt=Gn+Gg

  6. What Does the Standard Model Predict? • Strengths of primaries Ggi follow the Porter-Thomas distribution (PTD).Same distribution as Gn0Follows from assumption of compound nucleus model and central limit theorem of statistics.The PTD is a c2 distribution with 1 degree of freedom (n=1). • Sum of samples from N c2 distributions having n = 1 is a c2 distribution with N degrees of freedom.Expect Gg to follow a c2 distribution with n equal to the number of independently-contributing channels, n≈100.

  7. Comparison of Gn0 and Gg Distributions • Neutrons, Gn0.Single channel, n=1.PTD.Very broad. • Gammas, Gg.n~100 channels.Very narrow.

  8. Comparison of Measured Gg to c2 Distributions • Example: 192,194,195,196Pt.Often seems to be an extra tail compared to c2 distribution.

  9. Simulating Gg Distributions: Step 1Generating a Level Scheme • DICEBOX “Nuclear Realization”. • From r(Ex) to set of Exi’s. • Use N(Sn) random numbers to pick Exi’s. • Throw away those below Ecut. • Add in known levels below Ecut. • Separate sets of Exi’s for each Jp that can be reached by dipole decay.e.g. 197Pt decay from ½+ resonances; ½+, 3/2+, ½-, and 3/2-.

  10. Simulating Gg Distributions: Step 2Calculating the Ggi’s • Egi = Sn – Exi. • Calculate fX1(Egi)’s. • Calculate “PTD” factor ξi2.ξi2 randomly chosen from the PTD.Generalize to allow n≠1. • Ggi = D0ξi2fX1(Egi) Egi3.Calculate Ggi ’s for each Jp reached by dipole decay.

  11. Simulating Gg Distributions: Steps 3 and 4Calculating Total Widths and Iterating • Sum Ggi’s to get total width. • Iterate.Use same level schemes, etc.New Ggi’s by varying ξi2 only.Yields distribution of Gg’s. • Shape of Gg distribution due to:Shapes of LD and PSF models.“PTD” fluctuations.

  12. Examples: LD and PSF Models in Talys • Five LD models.1 – Const. T + Fermi Gas.2 – Back-shifted Fermi Gas.3 – Generalized Superfluid.*4 – Goriely.5 – Hilaire. • Five PSF models.1 – Kopecky-UhlLorentzian.2 – Brink-Axel Lorentzian.3 – Hartree-Fock BCS.4 – Hartree-FockBogolyubov.5 – Goriely’s Hybrid.*Didn’t use. Couldn’t normalize.

  13. Talys Results for ‹Gg› • Talys calculation with 4 LD and 5 PSF models. • Normalized LD models to ORELA D0 = 153 eV.LD models 1 and 2 normalized using “a”, models 4 and 5 using “c” and “d”. • PSF models un-normalized. • Chose LD/PSF combinations which gave closest to ORELA value, ‹Gg› = 85.9±1.8 meV, for simulations.

  14. Simulation Results with Talys Models • All simulations using Talys models yielded Gg distributions significantly narrower than measured.Agrees with nuclear physics lore. • Decreasing n results in much better agreement between simulation and data.Another sign of violation of the PTD?

  15. Simulation Results with LD and PSF from the Oslo Method • What was the experimental spin distribution?Affects slopes of LD and PSF. • What is the true spin distribution?Affects normalization of PSF and shape of simulated distribution. • Would be better to know more about low-lying levels in 197Pt.Ecut= 0.269 MeV.Only 2 ½- and 2 3/2- levels.

  16. Problems, Improvements, and Future Plans • How to decompose PSF data into E1 and M1?Fit E1 and M1 is everything else?Vice versa? • How to normalize slopes of LD and PSF?s is correct when simulated Gg distribution matches data?Ohio U. method? • Simulating 194Pt+nGg distribution might be even more interesting.More widths/better statistics.Tail is more pronounced. • Simulate 95Mo+nGg distributions.Have 6 Jp’s.Sensitivity to upbend? • Simulate 88Sr, 116,120Sn, 134,136,137Ba,… Preliminary!

More Related