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Neutron beam effects on spin-exchange-polarized 3He
M Sharma1, E Babcock, K H Andersen
1FOCUS Center and Physics Department, University of Michigan, Ann Arbor, Michigan 48104, USA.
Physical Review Letters
|September 4, 2008
Summary
High-intensity neutron beams cause depolarization in helium-3 (³He) spin filters. A new alkali-metal spin-relaxation mechanism, dependent on neutron flux, was discovered, impacting filter performance.
Area of Science:
- Atomic, Molecular, and Optical Physics
- Nuclear Physics
- Materials Science
Background:
- Spin-exchange-polarized helium-3 (³He) cells are crucial for neutron spin filtering.
- Depolarization effects in these cells can reduce their efficiency.
- Previous studies suggested alkali-metal polarization decrease as a cause for ³He depolarization.
Purpose of the Study:
- To investigate depolarization effects in alkali-metal spin-exchange-polarized ³He cells under high-intensity cold neutron beams.
- To directly measure alkali-metal polarization and spin relaxation rates as a function of neutron flux.
- To identify and characterize the underlying spin-relaxation mechanism.
Main Methods:
- Experiments conducted at Los Alamos Neutron Science Center and Institute Laue-Langevin.
- Direct measurement of alkali-metal polarization and spin relaxation.
- Varying neutron capture-flux density (φn) incident on the ³He cells.
Main Results:
- Observed depolarization effects correlating with reduced maximum ³He polarization.
- Identified a novel alkali-metal spin-relaxation mechanism.
- This mechanism's rate scales approximately as the square root of the neutron capture-flux density (√φn).
Conclusions:
- A new neutron-flux-dependent spin-relaxation mechanism in alkali-metals within ³He cells has been discovered.
- The observed relaxation is significantly larger than predicted by existing models, suggesting a new interaction.
- This finding has implications for optimizing neutron spin filter performance and understanding spin dynamics in polarized targets.
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