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Simulating   Distributions What is   ? How are   ’s measured? What does the standard model predict? Simulating   distributions. Constraining the.

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Presentation on theme: "Simulating   Distributions What is   ? How are   ’s measured? What does the standard model predict? Simulating   distributions. Constraining the."— Presentation transcript:

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

2 What is   ?

3 Neutron Capture Cross Sections: Neutron hits target and sticks A Z(n,  ) A+1 Z

4 (n,  ) Measurements at ORELA Employ C 6 D 6 Detectors  -ray detectors Sample Neutron beam Flux monitor

5 How is   Measured?   determined from R- matrix analysis of neutron-resonance data. Typically need both neutron total (transmission) and capture data. Capture area. A  =g J  n   /(  n +   ). Depth of transmission dip proportional to  n. Total width.  t =  n +  

6 What Does the Standard Model Predict?

7 Comparison of  n 0 and   Distributions Neutrons,  n 0. Single channel, =1. PTD. Very broad. Gammas,  . ~100 channels. Very narrow.

8 Comparison of Measured   to  2 Distributions Example: 192,194,195,196 Pt. Often seems to be an extra tail compared to  2 distribution.

9 Simulating   Distributions: Step 1 Generating a Level Scheme

10 Simulating   Distributions: Step 2 Calculating the   i ’s E  i = S n – E xi. Calculate f X1 (E  i )’s. Calculate “PTD” factor ξ i 2. ξ i 2 randomly chosen from the PTD. Generalize to allow ≠1.   i = D 0 ξ i 2 f X1 (E  i ) E  i 3. Calculate   i ’s for each J  reached by dipole decay.

11 Simulating   Distributions: Steps 3 and 4 Calculating Total Widths and Iterating

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-Uhl Lorentzian. 2 – Brink-Axel Lorentzian. 3 – Hartree-Fock BCS. 4 – Hartree-Fock Bogolyubov. 5 – Goriely’s Hybrid. * Didn’t use. Couldn’t normalize.

13 Talys Results for ‹   › Talys calculation with 4 LD and 5 PSF models. Normalized LD models to ORELA D 0 = 153 eV. LD models 1 and 2 normalized using “a”, models 4 and 5 using “c” and “  ”. PSF models un-normalized. Chose LD/PSF combinations which gave closest to ORELA value, ‹   › = 85.9±1.8 meV, for simulations.

14 Simulation Results with Talys Models All simulations using Talys models yielded   distributions significantly narrower than measured. Agrees with nuclear physics lore. Decreasing 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 197 Pt. E cut = 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?  is correct when simulated   distribution matches data? Ohio U. method? Simulating 194 Pt+n   distribution might be even more interesting. More widths/better statistics. Tail is more pronounced. Simulate 95 Mo+n   distributions. Have 6 J  ’s. Sensitivity to upbend? Simulate 88 Sr, 116,120 Sn, 134,136,137 Ba,… Preliminary!


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