21 research outputs found
Operation of a single mode external-cavity laser diode array near 780 nm
We have narrowed the spectral bandwidth of a commercial 2 W laser diode array to be less than 120 MHz near 780 nm. The external-cavity laser diode array system is a standard double-pass LittmanâMetcalf configuration operating on a dominant single longitudinal mode. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69845/2/RSINAK-73-12-4169-1.pd
The search for a permanent electric dipole moment using 129Xe and 3He
Time reversal and parity nonâinvariant interactions within an atom naturally give rise to an atomic permanent electric dipole moment (PEDM). For noble gas atoms, the size of such a PEDM scales as Z2 and higher powers of Z depending on the actual manifestation of T nonâinvariance, most importantly a distribution of electric dipole moment within the nucleus (Schiff Moment) and a Tâodd tensor interaction between the nucleus and atomic electrons. We have developed techniques to simultaneously measure the PEDMs of 129Xe and 3He in a single cell in order to mitigate systematic effects due to leakage currents and common mode problems such as magnetic field and time base noise. The philosophy of our approach is that PEDM of 3He is negligible compared to that of 129Xe and thus we use the 3He as a ââmagnetometerââ and monitor of systematic effects. Sensitivity of â10â25 eâcm per day has been demonstrated in preliminary work using a freeâinduction decay technique.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87703/2/73_1.pd
The search for a permanent electric dipole moment using 129Xe and 3He
Time reversal and parity nonâinvariant interactions within an atom naturally give rise to an atomic permanent electric dipole moment (PEDM). For noble gas atoms, the size of such a PEDM scales as Z2 and higher powers of Z depending on the actual manifestation of T nonâinvariance, most importantly a distribution of electric dipole moment within the nucleus (Schiff Moment) and a Tâodd tensor interaction between the nucleus and atomic electrons. We have developed techniques to simultaneously measure the PEDMs of 129Xe and 3He in a single cell in order to mitigate systematic effects due to leakage currents and common mode problems such as magnetic field and time base noise. The philosophy of our approach is that the PEDM of 3He is negligible compared to that of 129Xe and thus we use the 3He as a ââmagnetometerââ and monitor of systematic effects. Sensitivity of â10â25 eâcm per day has been demonstrated in preliminary work using a free induction decay technique.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87730/2/84_1.pd
Frequency shifts in noble-gas magnetometers
Polarized nuclei are a powerful tool in nuclear spin studies and in searches
for beyond-the-standard model physics. Noble-gas comagnetometer systems, which
compare two nuclear species, have thus far been limited by anomalous frequency
variations of unknown origin. We studied the self-interactions in a
He-Xe system by independently addressing, controlling and measuring
the influence of each component of the nuclear spin polarization. Our results
directly rule out prior explanations of the shifts, and demonstrate
experimentally that they can be explained by species dependent
self-interactions. We also report the first gas phase frequency shift induced
by Xe on He.Comment: v.
Polarized 129Xe129Xe optical pumping/spin exchange and delivery system for magnetic resonance spectroscopy and imaging studies
We describe the design and construction of a laser-polarized 129Xe129Xe production and delivery system that is used in our in vitro and in vivo magnetic resonance imaging (MRI) experiments. The entire apparatus including lasers and optics, rapidly actuated valves, heating and cooling, and transport tubing lies in the high magnetic field environment of a 2 T MRI magnet. With approximately 7.5% 129Xe129Xe polarization, 157 ccâatm of xenon gas is produced and stored as xenon ice every 5 min. Large quantities of polarized 129Xe129Xe can be obtained by cycling this process. The xenon is subsequently delivered in a controlled fashion to a sample or subject. With this device we have established the feasibility of using laser-polarized 129Xe129Xe as a magnetic tracer in MRI. This reliable, effective, and relatively simple production method for large volumes of 129Xe129Xe can be applied to other areas of research involving the use of laser-polarized noble gases. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69879/2/RSINAK-70-2-1546-1.pd
Magnetic Resonance Imaging with laser polarized 129Xe129Xe
Magnetic Resonance Imaging with laser-polarized 129Xe129Xe can be utilized to trace blood flow and perfusion in tissue for a variety of biomedical applications. Polarized xenon gas introduced in to the lungs dissolves in the blood and is transported to organs such as the brain where it accumulates in the tissue. Spectroscopic studies combined with imaging have been used to produce brain images of 129Xe129Xe in the rat head. This work establishes that nuclear polarization produced in the gas phases survives transport to the brain where it may be imaged. Increases in polarization and delivered volume of 129Xe129Xe will allow clinical measurements of regional blood flow. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87439/2/200_1.pd
The SLAC highâdensity 3He target polarized by spinâexchange optical plumbing
A new highâdensity 3He target polarized by spin exchange with optically pumped rubidium vapor has recently been used at the Stanford Linear Accelerator in an experiment to measure the longitudinal spinâdependent structure function of the neutron. The 3He target operated at a density of 2.3Ă1020 atoms/cm3 in a 30 cm long scattering region with polarizations between 30% and 40% measured with NMR techniques. Target cells with several day spinârelaxation times were developed in order to achieve these polarizations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87509/2/244_1.pd
Distribution and dynamics of laser-polarized 129 Xe magnetization in vivo
The first magnetic resonance imaging studies of laser-polarized 129 Xe, dissolved in the blood and tissue of the lungs and the heart of Sprague-Dawley rats, are described. 129 Xe resonances at 0, 192, 199, and 210 ppm were observed and assigned to xenon in gas, fat, tissue, and blood, respectively. One-dimensional chemical-shift imaging (CSI) reveals xenon magnetization in the brain, kidney, and lungs. Coronal and axial two-dimensional CSI show 129 Xe dissolved in blood and tissue in the thorax. Images of the blood resonance show xenon in the lungs and the heart ventricle. Images of the tissue resonance reveal xenon in lung parenchyma and myocardium. The 129 Xe spectrum from a voxel located in the heart ventricle shows a single blood resonance. Time-resolved spectroscopy shows that the dynamics of the blood resonance match the dynamics of the gas resonance and demonstrates efficient diffusion of xenon gas to the lung parenchyma and then to pulmonary blood. These observations demonstrate the utility of laser-polarized 129 Xe to detect exchange across the gas-blood barrier in the lungs and perfusion into myocardial tissue. Applications to measurement of lung function, kidney perfusion, myocardial perfusion, and regional cerebral blood flow are discussed. Magn Reson Med 42:1137â1145, 1999. © 1999 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34928/1/19_ftp.pd
Polarization and relaxation of radon
Investigations of the polarization and relaxation of Rn by spin
exchange with laser optically pumped rubidium are reported. On the order of one
million atoms per shot were collected in coated and uncoated glass cells.
Gamma-ray anisotropies were measured as a signal of the alignment (second order
moment of the polarization) resulting from the combination of polarization and
quadrupole relaxation at the cell walls. The temperature dependence over the
range 130C to 220C shows the anisotropies increasing with
increasing temperature as the ratio of the spin exchange polarization rate to
the wall relaxation rate increases faster than the rubidium polarization
decreases. Polarization relaxation rates for coated and uncoated cells are
presented. In addition, improved limits on the multipole mixing ratios of some
of the main gamma-ray transitions have been extracted. These results are
promising for electric dipole moment measurements of octupole-deformed
Rn and other isotopes, provided sufficient quantities of the rare
isotopes can be produced.Comment: 4 pages, 4 figure
Observation of the radiative decay mode of the free neutron
The theory of quantum electrodynamics (QED) predicts that beta decay of the neutron into a proton, electron and antineutrino should be accompanied by a continuous spectrum of soft photons. While this inner bremsstrahlung branch has been previously measured in nuclear beta and electron capture decay, it has never been observed in free neutron decay. Recently, the photon energy spectrum and branching ratio for neutron radiative decay have been calculated using two approaches: a standard QED framework(1-3) and heavy baryon chiral perturbation theory(4) (an effective theory of hadrons based on the symmetries of quantum chromodynamics). The QED calculation treats the nucleons as point-like, whereas the latter approach includes the effect of nucleon structure in a systematic way. Here we observe the radiative decay mode of free neutrons, measuring photons in coincidence with both the emitted electron and proton. We determined a branching ratio of (3.13 +/- 0.34) x 10(-3) (68 per cent level of confidence) in the energy region between 15 and 340 keV, where the uncertainty is dominated by systematic effects. The value is consistent with the predictions of both theoretical approaches; the characteristic energy spectrum of the radiated photons, which differs from the uncorrelated background spectrum, is also consistent with the calculated spectrum. This result may provide opportunities for more detailed investigations of the weak interaction processes involved in neutron beta decay.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62639/1/nature05390.pd