Isotope Effects in Thermal Neutron Scattering

This research discusses isotope effects in thermal neutron scattering, presented at the ORNL Cross Section Evaluation Working Group Meeting in November 2021. The study explores the impact of different isotopes on neutron scattering behavior, shedding light on valuable insights for neutron scattering research applications.

• Neutron Scattering
• Isotope Effects
• ORNL
• Research
• Cross Section

jayk539 Follow

Uploaded on Mar 07, 2025 | 0 Views

Download Presentation

Please find below an Image/Link to download the presentation.

The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.

You are allowed to download the files provided on this website for personal or commercial use, subject to the condition that they are used lawfully. All files are the property of their respective owners.

The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author.

Presentation Transcript

1. Isotope Effects in Thermal Neutron Scattering Chris W. Chapman, Andrew Holcomb, Doro Wiarda Oak Ridge National Laboratory Cross Section Evaluation Working Group Meeting 15-19 November 2021 ORNL is managed by UT-Battelle, LLC for the US Department of Energy

2. Background AMPX links Thermal Scattering Law (TSL) libraries to isotopes in the resolved resonance region TSL eval explicitly names isotope, we only bind TSL data to that isotope tsl-013_Al_027, tsl-026_Fe_05 Otherwise, assumes all isotopes can apply the TSL eval tsl-reactor-graphite-10P -> 12C-10p-graphite, 13C-10p-graphite U-UO2 -> 233UO2+ 234UO2 + 235UO2 + Zr-ZrH -> 90ZrH + 91ZrH + 92ZrH + No guidance is given in the TSL files or the ENDF format if this is acceptable or advised This can lead to some issues Isotope Effects in Thermal Neutron Scattering 2 2

3. Different Scattering Lengths Isotopes of the same element can have significantly different scattering lengths and, therefore, different bound/free scattering cross sections Element-specific bound/free scattering cross section given in File 7, but not sub-divided into isotopic distribution User must rely on either description in the ENDF file or references, which may not provide necessary description Different from issue in incoherent elastic bound scattering cross section issue (#13) Isotope Effects in Thermal Neutron Scattering 3 3

4. Different Scattering Lengths Comparison of Elemental and Isotopic Free Scattering Cross Sections Examples [1]: Isotope/ Material Weight pct. 51.45 11.32 17.19 17.28 2.76 Free Scattering xs [b] 4.99 9.49 6.75 8.22 3.72 6.32 6.34 Isotope/ Material Weight pct. 92.23 4.67 3.1 Free Scattering xs [b] 1.98 2.60 2.47 2.02 2.042 90Zr 28Si 91Zr 29Si 92Zr 30Si 94Zr natSi Si-SiC 96Zr natZr Zr-ZrH Up to 50% difference between isotopic & elemental scattering xs Isotope Effects in Thermal Neutron Scattering 4 4

5. Different Scattering Lengths Isotope Effects in Thermal Neutron Scattering 5 5

6. Resonances Some isotopes have resonances near (or sometimes IN) the thermal range Resonance theory is not currently incorporated into thermal scattering evaluations These can have a noticeable effect on the thermal scattering cross section Isotope Effects in Thermal Neutron Scattering 6 6

7. Resonances Isotope Effects in Thermal Neutron Scattering 7 7

8. Discussion Should information about the isotopic composition be provided in ENDF TSL files? Can anything be done regarding low-lying resonances? Try and match the TSL cross section with the resonance at a specific cutoff energy (tricky, but doable)? Implement resonances in thermal scattering (very difficult)? Isotope Effects in Thermal Neutron Scattering 8 8

9. Acknowledgements This work was supported by the Nuclear Criticality Safety Program, funded and managed by the National Nuclear Security Administration for the Department of Energy Isotope Effects in Thermal Neutron Scattering 9 9

10. References [1] https://www.ncnr.nist.gov/resources/n-lengths/ Isotope Effects in Thermal Neutron Scattering 10 10