1. An Ultra-Cold Neutron Source at the NCState Pulstar Reactor A.R. Young NCState University

2. The Collaboration Physics Department: C. Gould, A. R. Young Nuclear Engineering Department: B. W. Wehring, A. Hawari Hahn-Meitner Institute (plan: NCState in Jan, 2004) R. Golub, E. Korobkina new NCState physics faculty in fundamental neutron physics (offer being made now…) H. Gao & D. Dutta (in the EDM collaboration) H. Karwowski and T. Clegg (weak interactions res.) Local research groups with overlapping interests:

3. R. Golub: co-invented superthermal source technique B. Wehring: constructed a CN source at the Nuclear Engineering Teaching Laboratory TRIGA Mark II reactor at University of Texas, Austin A. Hawari: active research program in neutron moderator modeling All of the collaboration members have experience with neutron- related physics research and/or UCN production PULSTAR facility is ideal for exploring new ideas for UCN production and experimentation

4. The PULSTAR UCN Source Project Establish a university-based UCN facility with a strong focus on nuclear physics applications for UCN Integrate the UCN facility into the undergraduate curriculum Involve the local nuclear physics groups (NCState, UNC and Duke, through TUNL) in fundamental physics with cold and ultracold neutrons.

5. NCSU PULSTAR Reactor Sintered UO 2 pellets 4% enriched 1-MW power Light water moderated and cooled Just issued a new license for about 10 years of operation. PULSTAR design has several advantages for a UCN source: -high fast flux leakage -long core lifetime Source located in thermal column 28 ft Core

6. Takes advantage of: large fast flux leakage – channel fast and thermal neutrons into D 2 O tank very low heating – use solid methane moderator Conceptual Design I (top view)

7. Parametric design calculations –CN fluxes in the UCN converter and heating rates by MCNP simulations –UCN production rates by integrating the converter CN energy spectrum with the UCN production cross sections—physics based on LANSCE measurements. –UCN intensity at end of an open UCN guide using UCN-transport calculations. UCN Converter –Solid ortho D 2 –4-cm thick –18-cm diameter CN Source –Solid methane –1-cm thick cup around SD 2 Details of UCN Source

8. Averaged over UCN converter Integrated, 0 to 10 meV CN energies φ = 0.9 x 10 12 CN/cm 2 -s CN Flux (MCNP)

9. UCN converter, 200 g 1.7 W UCN converter chamber, 696 g 3.1 W CN source, 558 g 5.6 W CN source chamber, 1529 g 6.0 W I o = 2.7 x 10 7 UCN/s For  SD2 = 43 ms,  = 1,160 UCN/cm 3 Neutron and Gamma Heating Rates (MCNP) UCN Production Rate and Limiting Density Lifetime assumes SD 2 at 5K, 1.5% para-deuterium, no H 2 Low!

10. CN flux averaged over UCN converter –4-cm thick x 18-cm diameter φ = 1.0 x 10 12 CN/cm 2 -s UCN intensity at end of open Ni-58 guide –50-cm rise, 2-m level I o = 1.0 x 10 7 UCN/s UCN limiting density  = 1,290 cm 3 Partially Optimized Design (side view)

11. SD 2 Source Summary For 1MW reactor operating power: I o = 3.0  10 7 UCN/s  = 1,300 UCN/cm 3 Very small heat loads (1.7 W total to UCN converter) -cryostat designs straightforward (D. G. Haase) -lower operating temperatures feasible Accessibility of source is excellent, available year- round, reactor operable by students Upgrade of reactor power to 2MW being planned

12. Rough Comparison with Other Sources PULSTAR (1MW, SD 2 )1.3UCN current I P =10 7 at shielding wall UCNA source (4  A) 1-2(funded) MAINZ 11I  I P /10 (funded) PSI3-4(partially funded) FRM II>10Reactor not operational (partially funded) KEK>100LHe PULSTAR (1MW,LHe)>100I < I P, even with 20l of LHe Facility  UCN (  1000/cm 3 ) Comments

13. Observed baryon-antibaryon asymmetry  physics beyond the standard model How do we explore these issues at a university-based facility? Measure T invariance in neutron decay (D coefficient) Contribute to the UCN EDM project Perform source development work as a part of implementing a UCN neutron-antineutron oscillations experiment (NNbar) A Nuclear Physics Science Program T non-invariance Baryon number violating interactions

14. Measurement of T-noninvariance in  -decay Experiments go here Polarizer/spin-flipper UCN guide UCN source Envisioned facility (He liquifier not shown) Neutron decay directional angular correlations: PPT The term proportional to D violates T symmetry: need to observe decay  ’s and protons in coincidence  use a cell geometry with UCN

15. A Potential D Measurement with UCNs.  D =2  10 -4 1  10 9 decays 25 UCN/cc -10 days Why this experiment is suitable for a small, university facility: Relatively compact (about 3m long) Detectors are inexpensive and relatively straightforward to implement Does not require a large superconducting spectrometer magnet Does not require high precision polarimetry From complete PENELOPE MC: Much higher densities ultimately available…up to ~ 1000 with this source

16. Possible Contributions to the UCN EDM Project (M. Cooper and S. K. Lamoreaux, PIs) Local members of the EDM collaboration: H. Gau, D. Dutta, R. Golub, E. Korobkina Possible measurement programs using the NCState source as a test facility: UCN storage UCN depolarization UCN production of scintillation light Dressed UCN interaction with polarized 3 He

17. NNbar and source development NNbar workshop at the IUCF/LENS facility, Sept. 2002: Evaluated idealized geometry & conclusion: Need more UCN  Source R&D (At NCState: 4 years of running produce factor of 7 improvement over ILL results (PSI or US national facility somewhat more effective)

18. Source Development Projects: Solid Oxygen and Liquid He Solid oxygen (part of thesis of Chen-Yu Liu): Freeze out magnons at 2K UCN lifetime  9 x  SD2 Optimal production w/CN at 8-10K ~ 1.8 R SD2 Limiting UCN density  SO2 ~ 16  SD2 If UCN elastic scattering length is long in SO 2, more gains possible! gap

19. Liquid He: R. Golub and E. Korobkina NCState CN flux well-suited to UCN production in liquid He Korobkina et al. calculate contribution from single and multiphonon prod for various CN distributions Large gains possible (need to do pilot experiments)

20. Easy access (by students, staff, etc…) excellent for exploring performance of various source geometries Low heating rate makes possible the investigation of more “fragile” moderators and converters Low heating rate also permits straightforward cryostat design Source Development in a University Setting A Systematic investigation of source parameters is required to optimize UCN production rates and densities -CN moderators  optimize temperature and total flux of CN -UCN converters  explore physics of production, lifetimes, cooling, engineering issues University facilities such as NCState PULSTAR and LENS:

21. Educational Program Undergraduate students: already mechanism for integrating research projects at the reactor into the curriculum: Every undergraduate in the NE program must do project at the reactor Physics department’s advanced physics lab (PY 452) involves students doing projects in research labs; only requirement is “measure something with an error bar” (two in my lab this semester) Nuclear Engineering Enrollment at NCSU 19981999200020012002 Undergrad4052375372 Masters19121615 PhD1815131422

22. Graduate students: local facilities are a powerful draw for students. Fundamental neutron physics is being established as one of the primary activities at TUNL, providing exposure to a large pool of nuclear physics graduate students Training in neutron science and engineering is being established as a priority in the NE department (a director of reactor research is being created to expand the neutron research capabilities of the PULSTAR facility) Faculty: NCState is committed to expanding its role at the SNS, and both the NE and physics departments are seeking to make joint hires in neutron/nuclear physics related research—this is explicitly stated in the “compact plan” for each of these departments, in which departmental funding priorities are established.

23. Facilities and Operations Costs Reactor operations: funded by State of North Carolina director: A. Hawari budget: $490,000/y staff: 7 technical staff, 1 secretary adequate for daily operations: 1 shift of 8 hr/day Rennovation costs requested in compact plan

24. Source Equipment Costs & Operating Grant Costs $1,035,905 over 3 years -$392,315 for cryostat & related equipment (year 1) -$408,700 for Model 1410 He liquifier (year 2) -$234,890 for polarizer/spin-flipper magnet (year 3) increase to operating costs for nuclear physics group ~$80,000/year (materials and supplies, LHe and at least one more student)

25. Conclusion There is now the nucleus of a strong fundamental neutron physics group at NCState, with more faculty and staff to be joining Two unique local resources: the PULSTAR reactor and TUNL Timing is perfect to begin building a strong user group and training students for the SNS and future experiments We should build this source