A. R. Young
NCState University

•
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
Local research groups with overlapping interests:
• 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.)

All of the collaboration members have experience with neutronrelated physics research and/or UCN production
• 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
PULSTAR facility is ideal for exploring new ideas for UCN production and experimentation

• 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.

28 ft
Source located in thermal column
• Sintered UO
2
• 4% enriched pellets
• 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
Core

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

• UCN Converter
– Solid ortho D
2
– 4-cm thick
– 18-cm diameter
• CN Source
– Solid methane
– 1-cm thick cup around
SD
2
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.

• Averaged over UCN converter
• Integrated, 0 to 10 meV
CN energies
φ = 0.9 x 10 12
CN/cm 2 -s

• UCN converter, 200 g
• UCN converter chamber, 696 g
1.7 W
3.1 W
• CN source, 558 g
• CN source chamber, 1529 g 6.0 W
5.6 W
Low!
For

SD2
o
7

= 1,160 UCN/cm 3
Lifetime assumes SD
2 at 5K, 1.5% para-deuterium, no H
2

• 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

2
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 yearround, reactor operable by students
• Upgrade of reactor power to 2MW being planned

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

Observed baryon-antibaryon asymmetry
 physics beyond the standard model
T non-invariance
Baryon number violating interactions
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)


Polarizer/spin-flipper
Envisioned facility
(He liquifier not shown)
Experiments go here
UCN guide
UCN source
WdE e
Neutron decay directional angular correlations: d
 e d


 p e
E e
( E
0

E e
) 2

 1
 a
 p e
E e
 ˆ

 b m e
E e

A
 
 p e
E e

B
  ˆ


D
 
 p e

E e
ˆ



P P T
The term proportional to D violates T symmetry: need to observe decay
 ’s and protons in coincidence
 use a cell geometry with UCN

D
From complete PENELOPE MC:

D
=2

10 -4
1

10 9 decays
25 UCN/cc -10 days
Much higher densities ultimately available…up to ~ 1000 with this source
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

(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

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)

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

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)

•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:
• 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

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
Nuclear Engineering Enrollment at NCSU
1998 1999 2000 2001 2002
Undergrad
Masters
PhD
40
19
18
52
12
15
37
16
13
53
15
14
72
15
22
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)

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.

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

• $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)

•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