Polarization of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi>He</mml:mi></mml:math>by Spin Exchange with Optically Pumped Rb and K Vapors

“…A pure Rb vapor was used to polarize 3 He prior to the development of hybrid cells. However, it was found that K is far more efficient than Rb at transferring its polarization to 3 He nuclei [37]. Hybrid mixtures of Rb and K have subsequently been used to improve the efficiency of the polarization process [37,50,51].…”

Section: Development Of Hybrid Targetsmentioning

confidence: 99%

“…However, it was found that K is far more efficient than Rb at transferring its polarization to 3 He nuclei [37]. Hybrid mixtures of Rb and K have subsequently been used to improve the efficiency of the polarization process [37,50,51]. In alkali-hybrid spin-exchange optical pumping (AHSEOP), the Rb vapor is polarized by circularly polarized laser light, but the polarization of Rb valence electrons is then rapidly shared with the K [29].…”

Section: Development Of Hybrid Targetsmentioning

confidence: 99%

Next-Generation Polarized 3He Targets for Electron Scattering Experiments

Wang¹,

Kaluarachchi²,

Matyas³

et al.

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Historically, 3 He targets for electron scattering experiments have been polarized through spin-exchange optical pumping (SEOP). Polarized laser light passes its circular polarization to alkali metal vapor, which then transfers its polarization to 3 He through spin-exchange collisions.This thesis discusses the basics of SEOP and the polarimetry techniques used in our lab. Narrowband laser and alkali-hybrid SEOP have improved the performance of targets significantly. In alkali-hybrid SEOP, potassium is used together with rubidium for transferring polarization to 3 He nuclei. We discussed the data collected over many pure-rubidium targets and alkali-hybrid targets. In the course of analyzing the data, we also studied the "X factor" which limits the highest achievable polarization of 3 He.Because the experiments planned for the 12GeV era in Jefferson National Laboratory (JLAB) will use much higher electron beam current, we are exploring the possibility of using metal (instead of glass) as the entry points (commonly referred to as "end windows") for future targets. We established the metal composition and developed the techniques to incorporate metal to targets without introducing significant spin-relaxation rates. We have successfully demonstrated that future targets can be constructed with metal end windows and are very close to making such targets.iii

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“…and the spin-exchange rate constant for helium-rubidium has been measured to be κ se = 6.7 ± 0.610 −20 cm 3 /s [46]. At the operating temperatures of helium-3 SEOP polarizers utilizing rubidium alone (T ∼ 190 • C), [Rb] ≈ 6.2 * 10 14 atoms/cm 3 and γ se ≈ 1 6.7 hours.…”

Section: Spin-exchange Optical Pumpingmentioning

confidence: 99%

Hyperpolarized Gas Diffusion MRI using Steady State Free Precession Pulse Sequences

Mooney¹

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Hyperpolarized noble gas magnetic resonance imaging (MRI) provides a unique view of the airspaces in human lungs. However, images created with this technique have a fundamental resolution limit due in part to the gas diffusion within the air spaces during the image acquisition. The process of diffusion can be used to provide a method for extracting structural information below the resolution limit, via short-time diffusion MR. In free space, the area a gas particle explores in a given amount of time (the diffusion coefficient) is a constant that does not depend on the duration over which the measurement is made. In a highly restrictive area like the lung airspaces, the diffusion coefficient varies greatly with the duration of the measurement.For very short times measurement times, the diffusion coefficient approaches the free space value, while at longer measurement times the surrounding walls prevent the particle from traveling. This time dependence is related to the surface to volume ratio of the confining space.The goal of this work was to develop a method of making diffusion-weighted measurements at diffusion times less than ∼ 1 ms to detect this time dependence in restrictive environments such as the human lung. In order to make measurements at these short times, we turned to an MRI technique known as Steady State Free Precession (SSFP). SSFP pulse sequences are coherent, which means the transverse magnetization is not zero at the application of the next RF pulse. An advantage of iii using an SSFP pulse sequence is that it produces a very high signal level on which to measure the small diffusion attenuation imparted by short-time measurements.We developed several modifications to an SSFP pulse sequence which include diffusion sensitization, and investigated the behavior of each of these methods through the use of a magnetization simulation. We made global apparent diffusion coefficient (ADC) measurements, as well as created images with the resulting pulse sequences. In the global version, we were able to make ADC measurements over a range of diffusion times from 300-800 µs in glass-bead phantoms and fit the time-dependent ADC to extract the packing volume fraction φ for each of the phantoms. Multiple diffusion-time global ADC measurements made in human subjects highlighted the differences between healthy and emphysmatic lungs. In the imaging experiments, we generated ADC maps at a diffusion time of 500 µs in several human subjects.

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Polarization of3Heby Spin Exchange with Optically Pumped Rb and K Vapors

Cited by 110 publications

References 21 publications

Enhancement of surface and biological magnetic resonance using laser-polarized noble gases

Enhancement of surface and biological magnetic resonance using laser-polarized noble gases

Next-Generation Polarized 3He Targets for Electron Scattering Experiments

Hyperpolarized Gas Diffusion MRI using Steady State Free Precession Pulse Sequences

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