1. UCN transport and NN experiments
R. Young and B. Wehring
NCState University

2. The geometry:
How do we model transport?

3. Transport Data: Where Does It Come From?
Raw Data:
TOF – proton start, detector stop
LANSCE Prototype Source:
Modeling strategy, model date using fit parameters:
specularity (TOF very sensitive)
loss per bounce, shape of SD2 and UCN lifetime in SD2 (use “bottle lifetime between source and valve A)
For lifetime: study thin films so mfp in SD2 not important

4. Prototype Results
Specularity: average probability that a reflection will be mirror-like
Loss per bounce: average probability that UCN will be absorbed
or upscattered during a collision
58Ni/Mo coated guides (approx. 305 neV)
Specularity: % ( roughly 2% uncertainty)
agrees with measurements of straight and curved guides we
have performed at ILL
Loss per bounce: conservative, set by 58Ni bottle lifetimes and source
data
PLD diamond coatings ( neV, with 300 neV measured for
at SPEAR)
Specularity: >99% (data obtained at ILL recently for drawn quartz tubes)
Loss per bounce < (data from ILL expts – negligible for our purposes)

5. The Monte Carlo Runge-Kutta numerical integration
Gravity, magnetic fields (if needed), and wall reflections
Non-specular reflections via various models (Gaussian, isotropic and Lambertian—(from Golub, Richardson, Lamoreaux)
Spin dynamics if needed (depolarization on surfaces and spin dynamics in rf fields)
(future effort: n-n phase evolution)
Assume n annihilated on each collision

6. Preliminary results for base case (det eff = 1):
A possible base case: NCState geometry, 4 cm thick SD2, 18 cm guides,
.050s SD2 lifetime, a UCN energy cutoff of 430 neV initally
Primary flux: 6.0 x (below 305 neV)
Box loading efficiency: 20 –32%
Best case: diffuse walls, specular floor x10^9 discovery pot.
325 s avg. residency
Straightforward gains:
Source thickness x2 (see Serebrov’s geom): x 2
Source lifetime  .075s %
Running time: 4 years (“real”)
Speculative gains:
Multiphonon: x1.5(?)
Coherent amplification: x2 (?)
Solid Oxygen: x5 (?) 
5.5 – 7 x 109
Various diffuse regions, wall potentials, same “best” case as above