Oak Ridge National Laboratory

1
Oak Ridge National Laboratory In-situ Polarized
3He Based Analyzer for SNS Magnetism Reflectometer
Wai-Tung Hal Lee,1 Xin (Tony) Tong,1 Joshua
Pierce,1 Michael Fleenor,1 J. Lee Robertson,1
Wang Chun Chen,2 Tom Gentile,2 Ambaye
Hailemariam,1 Richard J. Goyette,1 Andre
Parizzi,1 Valeria Lauter,1 Frank klose,3 Helmut
Kaiser,4 Christopher Lavelle,4 David V. Baxter,4
Larry W. McCollum1 1Oak Ridge National
Laboratory, 2National Institute of Standards and
Technology, 3Australian Nuclear Science and
Technology Organisation, 4Indiana University
Cyclotron Facility
Introduction
Polarized 3He neutron spin filter is based on the
spin-dependence of the neutron absorption of 3He.
If the 3He nuclear spin and the neutron spin are
anti-parallel, the absorption is very strong sa
(??) 5931 b for l1 Å neutrons. If the spins
are parallel, there is virtually no absorption.
sa (??) 0. The absorption cross-section is
proportional to the neutron wavelength l.
We have constructed a polarized 3He based
analyzer for the SNS Magnetism Reflectometer. The
analyzer is based on the Spin-Exchange Optical
Pumping (SEOP) method. The system consist of a
Aluminosilica glass cell that is filled with 3He
gas, nitrogen, and a small amount of rubidium and
potassium. The cell is placed in an oven that is
heated to 200ºC to control the alkali vapor
pressure. A magnetostatic cavity enclose the oven
and the cell to provide a uniform magnetic field
to maintain the 3He polarization. High-power
circularly polarized laser light with wavelength
tuned to the Rb D1
transition impinges on the 3He cell and optically
pumped the alkali. The optical pumping polarized
the alkali atoms. When polarized alkali atoms
collide with 3He atoms, spin-exchange hyper-fine
interaction between the atomic electron and the
3He nuclei polarizes the 3He.
Measurements and Results 73 3He polarization
reached on line at the instrument. 20 hours to
reach 73. In-situ polarizing keeps the
polarization stable during neutron measurements.
The 3He analyzer system at the SNS Magnetism
Reflectometer
Analyzing efficiency and neutron transmission
measurement results.