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UCN Source at the NCSU PULSTAR Reactor

UCN Source at the NCSU PULSTAR Reactor. Bernard Wehring and Albert Young North Carolina State University International Workshop on Neutron-Antineutron Transition Search with Ultra Cold Neutrons 13-14 September 2002 Bloomington, Indiana. Outline. NCSU PULSTAR Reactor Desirable Attributes

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UCN Source at the NCSU PULSTAR Reactor

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  1. UCN Source at theNCSU PULSTAR Reactor Bernard Wehring and Albert Young North Carolina State University International Workshop on Neutron-Antineutron Transition Search with Ultra Cold Neutrons 13-14 September 2002 Bloomington, Indiana

  2. Outline • NCSU PULSTAR Reactor • Desirable Attributes • NCSU UCN Source • Conceptual Designs • Conclusion

  3. NCSU PULSTAR Reactor

  4. NCSU PULSTAR Core • 5 x 5 array of fuel assemblies • 5 x 5 array of pins • Sintered UO2 pellets • 4% enriched • 1-MW power • Graphite, Be reflected • Light water moderated and cooled

  5. Desirable Attributes • Properties • Heavy loading of U-235 -- 12.5 kg • Low ratio of H to U-235 atoms • High ratio of fast to thermal flux in the core • Benefits • High fast-flux leakage • High sensitivity to reflector material • Long core lifetime

  6. PULSTAR Flux

  7. 1-MW TRIGA Mark II • U-ZrH fuel • 19.7% enrichment • 3.5 kg U-235 mass • ~ 64 liter core volume • 1013 n/cm2s core avg thermal flux • 6.4 x 1012 n/cm2s core avg. fast flux Thermal flux

  8. UCN Source at PULSTAR • Parametric design calculations • CN fluxes in the UCN converter and heating rates by MCNP simulations of the PULSTAR reactor, CN source, and UCN converter. • UCN production rates by integrating the converter CN energy spectrum with the UCN production cross sections. • UCN intensity at end of an open UCN guide using lumped-parameter and UCN-transport calculations.

  9. NCSU UCN Source Details • UCN Converter • Solid ortho D2 • 4-cm thick • 18-cm diameter • CN Source • Solid methane • 1-cm thick • Cup shape around UCN converter

  10. Conceptual Design I(top view)

  11. CN Flux (MCNP) • Averaged over UCN converter • Integrated, 0 to 10 meV CN energies φ = 1.0 x 1012 CN/cm2-s

  12. Neutron and Gamma Heating Rates (MCNP) • UCN converter, 86 g 0.7 W • UCN converter chamber, 484 g 2.1 W • CN source, 408 g 4.0 W • CN source chamber, 1164 g 4.4 W

  13. UCN Production Rate • P = N<σ>φ V • <σ> = <σsingle> + <σmulti> • <σsingle> = 5 x 10-7 b/D • <σmulti> = 1 x 10-7 b/D • V = 1000 cc P = 3.6 x 107 UCN/s

  14. UCN Intensity at End of Open Ni-58 Guide • Io = f P • f = absorption leak / (absorption + leak) • absorption = 50 ms • leak = 4 V / (S<v>) = 4 t /<v> = 32 ms • f = 0.6 • Io = 2.2 x 107 UCN/s

  15. Conceptual Design II(side view) • CN flux averaged over UCN converter • 4-cm thick x 18-cm diameter φ = 1.0 x 1012 CN/cm2-s • UCN intensity at end of open Ni-58 guide • 50-cm rise, 2-m level Io = 1.2 x 107 UCN/s

  16. Conceptual Design III(side view) • CN flux averaged over UCN converter • 4-cm thick x 18-cm diameter φ = 1.2 x 1012 CN/cm2-s • UCN intensity at end of open Ni-58 guide • 50-cm rise, 2-m level Io = 1.5 x 107 UCN/s

  17. N-N Bar Experiment

  18. Conclusion • UCN intensity at bottle entrance (2 MW) Io = 3 x 107 UCN/s • Bottle equivalent radius, R = 150 cm • Avg. chord length, L = 4/3 x R = 200 cm • L / (avg. UCN speed), t = 0.5 s • Bottle lifetime,  = 300 s • Discovery potential, coherent free path > 2L > Io x (/2t) x (2t)2 = 9 x 109 s (> 6 ILL)

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