Polarized He3 gas compression system using metastability-exchange optical pumping

Abstract

Dense samples (10–100barcm) of nuclear spin polarized He3 are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high He3 polarizations (≈80%) at low pressures (few mbar). We describe a polarized He3 gas compressor system which accepts 0.26barlh−1 of He3 gas polarized to 70% by a 4W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5barcm target with final polarization of 55%. The spin relaxation rates of the system’s components have been measured using nuclear magnetic resonance and a model of the He3 polarization loss based on the measured relaxation rates and the gas flow is in agreement with a He3 polarization measurement using neutron transmission.

Polarized neutron diffraction and its application to spin density studies

“…When the unpolarized neutron beam is scattered from the polarizing crystal, the Bragg [111] diffraction gives rise to a monochromatic beam of polarized neutrons with spins parallel (↑) to the magnetic field. A 3 He spin filter polarizes a broad energy range of neutrons and is thus suitable for pulsed neutrons [23,24] . There are two protons and one neutron in the 3 He isotope, and the 3 He nuclear polarization is dominated by the unpaired neutron [24] .…”

“…A 3 He spin filter polarizes a broad energy range of neutrons and is thus suitable for pulsed neutrons [23,24] . There are two protons and one neutron in the 3 He isotope, and the 3 He nuclear polarization is dominated by the unpaired neutron [24] . In an optical cell filled with 3 He gas, polarized light is used to optically pump the 3 He isotope continuously in order to maintain polarization [23] .…”

“…PND is experimentally similar to a neutron diffraction experiment, except that a polarized neutron beam is used [20][21][22][23][24][25] . To obtain a polarized neutron beam, an unpolarized neutron beam first passes through a spin filter that is made of either a polarizing crystal [22] , which also acts as a monochromator (polarizing monochromator), or a 3 He spin filter for pulsed neutrons [23,24] , so that neutrons with, e.g., up spin (m s = +1/2) are obtained. A polarizing crystal of a ferromagnetic material, such as Heusler alloy Cu 2 MnAl, is often used for polarized neutrons generated from reactors [22] .…”

Magnetic Resonance Imaging: From Spin Physics to Medical Diagnosis

“…More compact systems, in which cell size, laser power, and compressor flow rate are all consistently lower, have of course a significantly reduced performance, yielding e.g. 0.2-0.3 bar×liter/hour of 50%-polarized 3 He [67,68]. Still, for less demanding applications such as methodological developments in MRI, lung imaging in small animals, or imaging with a limited number of patients, these systems might offer an increased ease of use by providing locally-polarized gas on demand.…”

“…Mechanical compression attempts resumed only after the first multi-watt lasers for MEOP have been developed in the late 1980s [63], this time succeeding in reaching sufficient polarization and pressure for use in various experiments [64,65], in particular to prepare polarized 3 He targets for the measurement of the neutron electric form factor in scattering experiments of polarized electron beams [66]. Since then, various non-relaxing mechanical compression techniques have been applied to polarized 3 He, using a diaphragm pump [67], a peristaltic pump [68], or a piston compressor [69,70] for applications in lung MRI, in more accurate electron scattering experiments, and in neutron spin filters [71,72].…”