Spin polarized 3 He: From basic research to medical applications
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pin Polarized 3He: From Basic Research to Medical Applications1 S. Karpuka, F. Allmendingerb, M. Burghoffc, C. Gemmela, M. Güldnera, W. Heila, W. Kilianc, S. KnappeGrünebergc, Ch. Mrozika, W. Müllerc, E. W. Ottena, M. Repettoa, Z. Salhia, U. Schmidtb, A. Schnabelc, F. Seifertc, Yu. Soboleva, L. Trahmsc, and K. Tullneya a
Universität Mainz, Institut für Physik, 55128 Mainz, Germany Universität Heidelberg, Physikalisches Institut, 69120 Heidelberg, Germany cPhysikalischTechnische Bundesanstalt, 10587 Berlin, Germany email: karpuk@unimainz.de
b
Abstract—Polarization of 3He gas by means of optical pumping is well known since the early 1960s with first applications in fundamental physics. Some thirty years later it was discovered, that one can use hyperpolar ized 3He as contrast agent for magnetic resonance imaging of the lung. The wide interest in this new method made it necessary to find ways of polarizing 3He in large quantities with high polarization degrees. A high per formance polarizing facility has been developed at the University of Mainz, designed for centralized produc tion of hyperpolarized 3He gas. We present the Mainz concept as well as some examples of numerous appli cations of spin polarized 3He in fundamental research and medical applications. DOI: 10.1134/S1063779613060105 1
INTRODUCTION
3He
Since 1963, it is known that 3He gas can be spin polarized by means of optical pumping techniques [1]. Optical pumping transfers polarization from photons to atoms by resonant absorption of circularly polarized light. In spin exchange optical pumping (SEOP), angular momentum from a circularly polarized laser beam is indirectly transferred to the 3He nuclei via alkali metal atoms (usually rubidium). A second method to polarize 3He gas is metastability exchange optical pumping (MEOP) with direct transfer of angu lar momentum from resonant laser light to 3He atoms. Each technique has its own advantages and limita tions. For instance, SEOP directly operates at high pressure but is a relatively slow process, while MEOP is a much faster process, but only operates at low pres sures of about 1 mbar and usually requires mechanical compression for later applications. In MEOP only a small fraction of metastable 3He atoms is produced in a low pressure gas discharge. These metastable helium atoms can absorb resonant pump light at 1083 nm and be optically pumped. For the 3He isotope in the excited metastable state, the efficient hyperfine coupling between the nucleus and the electrons results in an almost instantaneous transfer of angular momentum into the nuclear system. This nuclear orientation is again rapidly transferred to the 3He ground state atoms by so called metastability exchange collisions [2]. The necessity of providing polarized 3He gas in large quantities was originally demanded by nuclear physics experiments, where nuclear spin polarized 1 The article is published in the original.
was needed as a target for polarized neutrons: the spin of the polarized 3He is essentially carried by the spin of the
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