A New UltraCold Neutron Source at LANSCE

1
A New Ultra-Cold Neutron Source at LANSCE
A. Saunders, T. Bowles, R. Hill, G. Hogan, K.
Kirch, S. Lamoreaux, C. L. Morris, A.
Pichlmaier, S. Seestrom, W. Teasdale (Los Alamos
National Laboratory) S. Hoedl, C.-Y. Liu, D. A.
Smith, A. Young (Princeton University) B.
Filippone, T. M. Ito, J. Martin, B. Tipton, J.
Yuan (California Institute of Technology) P.
Geltenbort (Institut Laue-Langevin) M. Hino
(University of Kyoto)

• A new prototype UCN source is operating at
  LANSCE.
• We have stored up to 30 UCN/cc in a stainless
  bottle.
• Development to scale the source up for
  experimental work continues.

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Bottled UCN
8 Proton Pulses
0.5 s Storage Time
Emptying Bottle
1000
800
600
UCN/8 ms
400
200
0
0
5
10
15
20
25
Time (sec)
3
UCN Source Layout
SS UCN Bottle
58Ni coated stainless guide
Liquid N2
Flapper valve
Be reflector
LHe
Solid D2
UCN Detector
77 K poly
Tungsten Target
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Superthermal UCN Sources(Golub and Pendlebury)

• UCN can be produced by inelastic interaction of
  higher energy neutrons with a cold medium
• For neutron energies well below molecular binding
  energies, single phonon scattering is the
  dominant inelastic process
• Cold neutrons can create a phonon and be
  down-scattered to near zero energy (creation of
  UCN)
• UCN can absorb a phonon and be up-scattered to
  cold or thermal energies (destruction of UCN)
• These rates can be different if the moderator
  temperature and the neutron temperature are not
  equal!
• Gain factors over the thermal UCN density can be
  as large as 104!

5
Volume Dependence
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SD2 Lifetime Measurements

• UCN trapped in bottle with SD2
• Valve opened to release UCN at different times

7
UCN Lifetime in SD2

• Minimum and Maximum measurable lifetimes
• Minimum because it takes time to drain UCN
• Maximum caused by bottle lifetime

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Para Contaminations Effect
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Proton Current Scaling
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Further Tests

• Continue lifetime measurements
• Other source materials
• Oxygen
• Nitrogen15
• Lead208
• Test bottles, UCN guides
• First experiments with new source

11
Conclusions

• We have successfully tested the new source at
  LANSCE.
• We have observed stored UCN densities of up to
  30/cc.
• UCN production and lifetime depend on para
  contamination and temperature as expected.
• Work continues to optimize full scale source
  design and experiments!