Technique Of Spin-exchange Optical Pumping Research Articles

A method for imaging and spectroscopy using γ-rays and magnetic resonance.

Magnetic resonance imaging (MRI) provides fine spatial resolution, spectral sensitivity and a rich variety of contrast mechanisms for diagnostic medical applications. Nuclear imaging using γ-ray cameras offers the benefits of using small quantities of radioactive tracers that seek specific targets of interest within the body. Here we describe an imaging and spectroscopic modality that combines favourable aspects of both approaches. Spatial information is encoded into the spin orientations of tiny amounts of a polarized radioactive tracer using pulses of both radio-frequency electromagnetic radiation and magnetic-field gradients, as in MRI. However, rather than detecting weak radio-frequency signals, imaging information is obtained through the detection of γ-rays. A single γ-ray detector can be used to acquire an image; no γ-ray camera is needed. We demonstrate the feasibility of our technique by producing images and spectra from a glass cell containing only about 4 × 10(13) atoms (about 1 millicurie) of the metastable isomer (131m)Xe that were polarized using the laser technique of spin-exchange optical pumping. If the cell had instead been filled with water and imaged using conventional MRI, then it would have contained more than 10(24) water molecules. The high sensitivity of our modality expands the breadth of applications of magnetic resonance, and could lead to a new class of radioactive tracers.

A high-pressure polarized 3He gas target for nuclear-physics experiments using a polarized photon beam

Following the first experiment on three-body photodisintegration of polarized $^3$He utilizing circularly polarized photons from High Intensity Gamma Source (HI$\gamma$S) at Duke Free Electron Laser Laboratory (DFELL), a new high-pressure polarized $^3$He target cell made of pyrex glass coated with a thin layer of sol-gel doped with aluminum nitrate nonahydrate has been built in order to reduce the photon beam induced background. The target is based on the technique of spin-exchange optical pumping of hybrid rubidium and potassium and the highest polarization achieved is $\sim$62% determined from both NMR-AFP and EPR polarimetry. The $X$ parameter is estimated to be $\sim0.06$ and the performance of the target is in good agreement with theoretical predictions. We also present beam test results from this new target cell and the comparison with the GE180 $^3$He target cell used previously at HI$\gamma$S. This is the first time that sol-gel coating technique has been used in a polarized $^3$He target for nuclear physics experiments.

A high-pressure polarized 3He gas target for the High Intensity Gamma Source (HI [formula omitted]S) facility at Duke Free Electron Laser Laboratory

A new polarized 3He target has been developed for nuclear physics experiments utilizing the High Intensity Gamma Source (HI γ S) at the Duke Free Electron Laser Laboratory (DFELL). This target is designed for a broad program of physics employing high intensity polarized photons and a polarized 3He target as an effective polarized neutron target. We report the performance of this target based on the technique of spin-exchange optical pumping (SEOP). Due to the significantly larger photon beam size at the HI γ S facility than that of a typical electron beam at electron accelerator laboratories, the HI γ S 3He target contains a larger number of 3He nuclei than any polarized 3He targets reported previously. A target polarization on the order of 33–46% has been achieved from both a regular 3He–Rubidium (Rb) target and a hybrid target which contains a mixture of Rb and potassium. The target polarization has been determined within 3 % using both the Electron Paramagnetic Resonance (EPR) technique and the NMR–AFP (Adiabatic Fast Passage) technique.

Laser-driven polarized H/D sources and targets

Traditionally, Atomic Beam Sources are used to produce targets of nuclear polarized hydrogen (H) or deuterium (D) for experiments using storage rings. Laser-Driven Sources (LDSs) offer a factor of 20–30 gain in the target thickness (however, with lower polarization) and may produce a higher overall figure of merit. The LDS is based on the technique of spin-exchange optical pumping where alkali vapor is polarized by absorbing circularly polarized laser photons. The H or D atoms are nuclear-polarized through spin-exchange collisions with the polarized alkali vapor and through subsequent hyperfine interactions during frequent H–H or D–D collisions.

EXPERIMENTAL STUDY OF SPIN POLARIZATION OF HYDROGEN ATOMS

Since the ground state first excited state resonance transition of H atoms lies in the VUV spectra region(λ=121.6 nm), and up to now, by the optical pumping direct orientation of H atoms is a complex and unsolved problem, we used the technique of spinexchange optical pumping to produce spin-polarized H atoms and to study the variations of polarization of H-atoms with temperature.

Hyperfine Splittings and Pressure Shifts ofLi6andLi7

The spin-exchange optical-pumping technique has been used to measure the hyperfine splittings in the ground states of ${\mathrm{Li}}^{6}$ and ${\mathrm{Li}}^{7}$ as a function of buffer-gas pressure. Measurements were made with He, Ne, and Ar buffer gases at temperatures near 390\ifmmode^\circ\else\textdegree\fi{}C. The fractional pressure shifts for Li were found to be (-5.34\ifmmode\pm\else\textpm\fi{}0.5) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$ /Torr in Ar, (40.5 \ifmmode\pm\else\textpm\fi{} 1.0) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$ /Torr in Ne, and (77.7\ifmmode\pm\else\textpm\fi{}1.0) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$ /Torr in He. The hyperfine splittings extrapolated to zero pressure are 228.205 261 (12) MHz for ${\mathrm{Li}}^{6}$ and 803.504 094 (25) MHz for ${\mathrm{Li}}^{7}$.

Pressure Shifts of Hyperfine Splitting of Hydrogen and Tritium in Argon

This paper reports new measurements of the pressure shifts in argon of the hyperfine splitting of hydrogen and tritium. A spin-exchange optical pumping technique was used to make these measurements. The fractional pressure shift (pressure shift in cps/mm Hg at 0\ifmmode^\circ\else\textdegree\fi{}C divided by the hyperfine splitting in kMc/sec for hydrogen in argon is -4.78 \ifmmode\pm\else\textpm\fi{} 0.03; the ratio of the fractional pressure shift for tritium to that for hydrogen is 1.007\ifmmode\pm\else\textpm\fi{}0.012; the temperature shift at constant density of the hydrogen hyperfine splitting is 0.012\ifmmode\pm\else\textpm\fi{}0.003 cps/\ifmmode^\circ\else\textdegree\fi{}K mm Hg. This new value for the hydrogen pressure shift is then used to reanalyze the Yale data for the hyperfine splitting of muonium, under the hypothesis that the fractional pressure shift for muonium is the same as that for hydrogen. This gives for the muonium hyperfine splitting an alternative value of 4463.23(2) Mc/sec. This value of the muonium hyperfine splitting gives for the fine-structure constant \ensuremath{\alpha} the alternative value ${\ensuremath{\alpha}}^{\ensuremath{-}1}=137.0367(10)$. This value of $\ensuremath{\alpha}$ is compared with the values obtained from the hydrogen fine structure, hydrogen hyperfine structure, and the ac Josephson-effect determination of $\frac{2e}{h}$.

Gyromagnetic Ratios of Hydrogen, Tritium, Free Electrons, andRb85

The spin-exchange optical pumping technique has been used to measure the gyromagnetic ratios of hydrogen, tritium, and free electrons in terms of the electronic gyromagnetic ratio of ${\mathrm{Rb}}^{85}$. A direct measurement was also made of the ratio of the electronic $g$ factors of tritium and hydrogen. The 60-G magnetic field in which these measurements were made was produced by a precision-wound solenoid which was surrounded by three concentric magnetic shields. The magnetic field varied by 5 parts in ${10}^{6}$ over the region occupied by a typical absorption flask. The free electrons were produced by ionization resulting from the beta decay of the radioactive tritium atoms. Measurements were made in various sizes of absorption flasks and in flasks containing different pressures of helium, argon, and neon buffer gases. The measured $g$-factor ratio did not depend upon the nature or pressure of the buffer gas. The results of these measurements were as follows: $\frac{{g}_{J}(\mathrm{Rb})}{g(e)}=1+(6.3\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}; \frac{{g}_{J}(\mathrm{Rb})}{{g}_{J}(\mathrm{H})}=1+(23.74\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6};$ $\frac{{g}_{J}(\mathrm{T})}{{g}_{J}(\mathrm{H})}=1\ensuremath{-}(0.11\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}; \frac{{g}_{J}(\mathrm{H})}{g(e)}=1\ensuremath{-}(17.4\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}.$