Spin Exchange Optical Pumping Method Research Articles

Hyperpolarised gas filling station for medical imaging using polarised 129Xe and 3He

We report the design, construction, and initial tests of a hyperpolariser to produce polarised 129Xe and 3He gas for medical imaging of the lung. The hyperpolariser uses the Spin-Exchange Optical Pumping method to polarise the nuclear spins of the isotopic gas. Batch mode operation was chosen for the design to produce polarised 129Xe and polarised 3He. Two-side pumping, electrical heating and a piston to transfer the polarised gas were some of the implemented techniques that are not commonly used in hyperpolariser designs. We have carried out magnetic resonance imaging experiments demonstrating that the 3He and 129Xe polarisation reached were sufficient for imaging, in particular for in vivo lung imaging using 129Xe. Further improvements to the hyperpolariser have also been discussed.

A high volume, batch mode 129Xe polarizer

Numerous designs of optical gas polarizers have been proposed, broadening possible applications of the hyperpolarized gases as contrast agents in magnetic resonance imaging. We present a home–made 129Xe polarizer based on the spin exchange optical pumping method. The polarizer operates under 1bar of the gas mixture (at the maximum temperature of 160°C) in a high volume optical cell (5025cm3). Approximately 100cm3 of 129Xe polarized at 1.50±0.37% is produced in a single cycle of polarization. Operation under standard pressure imposes polarization transfer mainly via van der Waals molecules, resulting in the efficient spin exchange between rubidium and 129Xe atoms. The design, construction and operation of the polarizer are described in details.

Development of portable polarized 3He neutron spin filter and its application to magnetic field imaging at J-PARC

In order to expand the measurable neutron energy range up to the energy of epithermal neutrons in polarized neutron experiments, a portable polarized 3He neutron spin filter (NSF) was developed in the Materials and Life science experimental Facility (MLF) at J- PARC. After the generation of 3He polarization through a spin exchange optical pumping method, the NSF was used as a neutron spin polarizer and flipper in a beam line. We constructed a simple neutron spin analysis apparatus with two 3He NSFs and made a preliminary attempt to visualize magnetic fields generated by a coil. The results represented that our apparatus could function for neutron wavelengths between approximately 0.5-5 Å through the use of a neutron time-of-flight method.

Spin exchange optical pumping based polarized 3He filling station for the Hybrid Spectrometer at the Spallation Neutron Source

The Hybrid Spectrometer (HYSPEC) is a new direct geometry spectrometer at the Spallation Neutron Source at the Oak Ridge National Laboratory. This instrument is equipped with polarization analysis capability with 60° horizontal and 15° vertical detector coverages. In order to provide wide angle polarization analysis for this instrument, we have designed and built a novel polarized (3)He filling station based on the spin exchange optical pumping method. It is designed to supply polarized (3)He gas to HYSPEC as a neutron polarization analyzer. In addition, the station can optimize the (3)He pressure with respect to the scattered neutron energies. The depolarized (3)He gas in the analyzer can be transferred back to the station to be repolarized. We have constructed the prototype filling station. Preliminary tests have been carried out demonstrating the feasibility of the filling station. Here, we report on the design, construction, and the preliminary results of the prototype filling station.

Polarized 129Xe Production by Using the Spin Exchange Optical Pumping Method

Polarized 129Xe Production by Using the Spin Exchange Optical Pumping Method

Basic Concepts of Polarisation Analysis for Neutron Chopper Spectrometer POLANO at J-PARC

The basic concept underlying the use of neutron polarisers and analysers in a polarised neutron spectrometer which will be constructed in J-PARC/MLF is discussed. The spectrometer, named POLANO, is a compact chopper spectrometer for polarisation analysis in the energy region up to Ei ~200 meV. In the first stage of this project, a 3He spin filter polarised by the spin exchange optical pumping method will be used as the polariser. Based on the optimisations of the filter parameters, we confirm that the designed optimised 3He spin filters will be feasible for use up to 80 meV.

In situ polarized 3He system for the Magnetism Reflectometer at the Spallation Neutron Source

We report on the in situ polarized (3)He neutron polarization analyzer developed for the time-of-flight Magnetism Reflectometer at the Spallation Neutron Source at Oak Ridge National Laboratory. Using the spin exchange optical pumping method, we achieved a (3)He polarization of 76% ± 1% and maintained it for the entire three-day duration of the test experiment. Based on transmission measurements with unpolarized neutrons, we show that the average analyzing efficiency of the (3)He system is 98% for the neutron wavelength band of 2-5 Å. Using a highly polarized incident neutron beam produced by a supermirror bender polarizer, we obtained a flipping ratio of >100 with a transmission of 25% for polarized neutrons, averaged over the wavelength band of 2-5 Å. After the cell was depolarized for transmission measurements, it was reproducibly polarized and this performance was maintained for three weeks. A high quality polarization analysis experiment was performed on a reference sample of Fe/Cr multilayer with strong spin-flip off-specular scattering. Using a combination of the position sensitive detector, time-of-flight method, and the excellent parameters of the (3)He cell, the polarization analysis of the two-dimensional maps of reflected, refracted, and off-specular scattered intensity above and below the horizon were obtained, simultaneously.

Polarized 3He neutron spin filter program at the JCNS

Polarized neutron instruments will occupy about 80% of the Jülich Centre for Neutron Science (JCNS) instrument park. A successful polarized 3He program will be integral to many of these instruments. We have been focusing the developments on spin-exchange optical pumping (SEOP) to polarize the 3He gas in situ. Where possible, in situ polarization using the SEOP method will provide higher time averaged performance of the instruments. Further this allows a custom-built and independent source of polarized 3He to be developed optimized for each instruments demands. In this paper we will: present an argument for the advantages of in situ polarization; describe an in situ polarizer we have constructed, and initial tests of its performance; describe testing of polarization analysis for small angle neutron scattering on biological samples, and our plans for an in situ polarizer for this application.

In-situ Polarized 3He-Based Neutron Polarization Analyzer for SNS Magnetism Reflectometer

We report here the construction and neutron transmission test results of an in-situ polarized 3He-based neutron polarization analyzer system for the Magnetism Reflectometer at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyzer uses the Spin-Exchange Optical Pumping method to polarize the 3He nuclei of a cell of 3He gas. Polarized neutrons scattered from the sample are intercepted by the polarized 3He gas which strongly absorbs neutrons in one spin-state while allowing most neutrons in the other spin-state to pass through. To maintain a stable analyzing efficiency during an experiment, the 3He gas is continuously polarized in-situ on the instrument. Neutron transmission measurements showed that 73% 3He polarization was reached in this setup.

Effects of high-flux neutron beams onH3ecells polarizedin situwith spin-exchange optical pumping

Polarized $^{3}\text{H}\text{e}$ produced by spin-exchange optical pumping (SEOP) has potential as a neutron spin filter for polarization and polarization analysis in many neutron-scattering and neutron particle physics applications. The advantage of the SEOP method is its suitability for providing continuous stable polarization over the course of long experiments. However, we have discovered that exposure to high neutron flux leads to additional strong relaxation mechanisms in the optically polarized alkali-metal vapor used to polarize the $^{3}\text{H}\text{e}$. At a neutron flux density of $4.7\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }{\text{cm}}^{\ensuremath{-}2}\text{ }{\text{s}}^{\ensuremath{-}1}$, the alkali-metal relaxation rate increased from 100 to $1000\text{ }{\text{s}}^{\ensuremath{-}1}$ leading to reduced alkali-metal polarization. Other effects such as time dependence and gas composition dependence were explored to help understand the processes. In this paper we discuss our observations and present possible solutions for practical use of SEOP as a neutron spin filter for high-flux density applications.

Increasing the pump-up rate to polarize 3He gas using spin-exchange optical pumping method

In recent years, polarized 3 He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the 3 He gas are the spin-exchange optical pumping (SEOP) method and the meta-stable exchange optical pumping (MEOP) method. At present, the SEOP setup is comparatively compact due to the fact that it does not require the sophisticated compressor system used in the MEOP method. The temperature and the laser power available determine the speed, at which the SEOP method polarizes the 3 He gas. For the quantity of gas typically used in neutron scattering work, this speed is independent of the quantity of the gas required, whereas the polarizing time using the MEOP method is proportional to the quantity of gas required. Currently, using the SEOP method to polarize several bar-liters of 3 He to 70% polarization would require 20−40 h. This is an order of magnitude longer than the MEOP method for the same quantity of gas and polarization. It would therefore be advantageous to speed up the SEOP process. In this article, we analyze the requirements for temperature, laser power, and the type of alkali used in order to shorten the time required to polarize 3 He gas using the SEOP method.

Polarized neutron reflectometry of a patterned magnetic film with a He3 analyzer and a position-sensitive detector

We have employed a polarized He3 spin filter in conjunction with a position-sensitive detector (PSD) to perform efficient polarization analysis of neutron diffuse reflectivity. This work was carried out on the NG-1 polarized neutron reflectometer at the National Institute of Standards and Technology Center for Neutron Research. We measured the specular and diffuse reflectivity of a patterned magnetic array that has periodic square holes in a Co film. Analysis of the data yielded spin-analyzed two-dimensional Qx−Qz reciprocal space maps for the sample in magnetized and demagnetized states. We compared the measurements obtained with a 3He analyzer and a PSD with those obtained using a conventional supermirror analyzer and a 3He proportional counter. The results are in good agreement. For this experiment, 3He gas was polarized by the spin-exchange optical pumping method and stored in a uniform magnetic field provided by a shielded solenoid. Improved optical pumping using a spectrally narrowed diode laser array yielded an initial 3He polarization of 70% in a 3He cell volume of 280 cm3.