Title : Compact hyper-polariser of 129Xe
Abstract:
Hyper-polarised 129Xe is a highly sensitive agent used with the technologies of Nuclear Magnetic Resonance (NMR) in many applications [1]. Conventionally, in order to produce hyper-polarised amounts of this gas, large and complex high-throughput (10–1,000 l/day) plants are used, which are mostly oriented to medical applications. On the other hand, however, there exists a broad class of problems that may be solved by access to comparatively small amounts of hyper-polarised gas (several ml).
The present work considers ways of making a compact inexpensive hyper-polariser relying on commercially available components. The possibilities of a simple and small-footprint device for hyper-polarisation of small doses of the gas sufficient for one or two NMR measurements are analysed. A prototype is presented of such a compact hyper-polariser of 129??.
The proposed prototype is based on the following: hyper-polarisation of 129?? is carried out by spin-exchange optical pumping; pumping radiation is provided by a 4-W laser diode with the output line width of 2 nm; hyper-polarisation of 129?? is performed in a compact (~100-mm long) high-pressure test tube (up to 6 atm) designed to last for several dozens of cycles.
The present report explains the design of the proposed prototype and discusses ways of its further improvement. The experimentally achieved hyper-polarisation degree of 129?? exceeds the equilibrium level by 3–4 orders of magnitude. Among the unexpected findings is the discovered possibility of Rb vapour pumping with radiation that has a line width exceeding the Doppler contour width in Rb vapour by over an order of magnitude. This effect enables the hyper-polariser to use relatively broad-band laser radiation. This report studies this effect and provides an explanation. Also, we studied the influence of the buffer gas (in our case, nitrogen) on fluorescence quenching of the polarised alkali metal atoms. The effects are demonstrated that emerge when the buffer gas pressure deviates from the optimum.
A novel design of a compact 129?? hyper-polariser is proposed that uses an optical cell fabricated from a commercially sourced test tube and an affordable diode laser pump. The measured xenon hyper-polarisation level of 1.34% is sufficient for many applications, including characterisation of various porous materials.
1. Hyperpolarized Xenon-129 magnetic resonance: concepts, production, techniques and applications (new developments in NMR, volume 4) (edts: T. Meersmann, E. Brunner). Royal Society of Chemistry, 504p., 2015. ISBN 978-1-849-73889-7.
What will audience learn from your presentation?
• This report demonstrates that technologies of hyper-polarisation of noble gas atoms may become considerably more accessible and affordable
• In the near future, compact hyper-polarisers of 129?? may become standard devices in both scientific and practical applications
• Broad adoption of the proposed inexpensive technology of 129?? hyper-polarisation by spin-exchange optical pumping will enable solving of many problems through NMR measurements
