46570120
Relaxation of gaseous spin-polarized 3He targets due to ionizing radiation.
The theory of spin-polarized /sup 3/He relaxation due to hyperfine coupling in /sup 3/He/sup +/ and due to spin-rotation coupling in /sup 3/He/sub 2//sup +/ is presented. Comparison is made between the theory and recent experiments which utilized spin-polarized /sup 3/He as a charged-particle beam target. The theory predicts that at low He pressures applying a magnetic field significantly reduces the /sup 3/He depolarization rate due to formation of /sup 3/He/sub 2//sup +/. At high He pressures the relaxation rate decreases with pressure. In addition, charge-transfer processes with foreign gases suppress /sup 3/He depolarization by reducing the /sup 3/He/sup +/ and /sup 3/He/sub 2//sup +/ concentrations.
350710
Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array.
We present a portable four-channel atomic magnetometer array operating in the spin-exchange relaxation-free regime. The magnetometer array has several design features intended to maximize its suitability for biomagnetic measurement, specifically foetal magnetocardiography, such as a compact modular design and fibre-coupled lasers. The modular design allows the independent positioning and orientation of each magnetometer. Using this array in a magnetically shielded room, we acquire adult magnetocadiograms. These measurements were taken with a 6-11 fT Hz(-1/2) single-channel baseline sensitivity that is consistent with the independently measured noise level of the magnetically shielded room.
8930049
Spin-exchange optical pumping of noble-gas nuclei
Spin-exchange optical pumping of mixtures of alkali-metal vapors and noble gases can be used to efficiently polarize the nuclei of the noble-gas atoms. Liters of noble gases at standard temperature and pressure and with nuclear spin polarizations of several tens of percent are now used in many applications. The authors describe the basic phenomena that govern the spin-exchange process and review the physics of angular momentum transfer and loss in optical pumping and spin-exchange collisions. {copyright} {ital 1997} {ital The American Physical Society}
55911739
Spin exchange collisions and their consequences for spin polarized gas targets of hydrogen and deuterium
Abstract The effects of spin-exchange collisions on the polarization of dense spin-polarized samples of hydrogen and deuterium are analyzed. It is shown that even in large magnetic fields spin-exchange collisions transfer angular momentum between the electrons and the nuclei. This effect has important implications for the operation of densed spin-polarized targets and sources of hydrogen and deuterium. For tensor polarized targets care will be required to obtain a high tensor polarization, especially at low fields. For the specific case of sources that are spin-polarized by spin-exchange collisions with optically pumped alkali atoms, spin-exchange not only polarizes the hydrogen and deuterium electron spins, but polarizes the nuclear spins as well. For high-density vector-polarized targets this may eliminate the need for rf transitions to polarize the nuclei.
32501332
Hybrid spin-exchange optical pumping of 3He.
We demonstrate spin-exchange optical pumping of 3He using a "hybrid" K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and 3He atoms then transfer the angular momentum to the 3He with much greater efficiency than Rb-3He. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches 1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.
27418106
Analyzing powers in pi +p elastic scattering at intermediate energies.
The analyzing power, A/sub N/, has been measured for ..pi../sup +/p elastic scattering at p/sub ..pi../ = 471, 547, 625, and 687 MeV/c on a transversely polarized target. The results are compared with three recent partial-wave analyses for the isospin (3/2) channel. The agreement with our data for all three analyses is good at 471 MeV/c and reasonable at 547 and 625 MeV/c. At 687 MeV/c two of the analyses show a sharp maximum near costheta = -0.4 which is not seen in the data. There is no indication in our data of the existence of new, narrow ..delta.. resonances.
8649559
Interactions of ultrahigh-energy neutrinos.
Cross sections for the charged-current interactions of ultrahigh-energy neutrinos with nucleons are evaluated in light of recent improvements in our knowledge of nucleon structure functions. For 10/sup 19/-eV neutrinos, the cross section is an order of magnitude larger than the values traditionally used in astrophysical calculations. Some consequences for event rates from generic astrophysical neutrino sources are noted.
36572119
Radiative decays of massive relic particles and the submillimeter background.
We consider the interaction of the decay photons of an unstable relic particle species with the microwave background radiation. The radiative decays of these particles delay recombination and serve as an energy source for the resultant plasma. Nonrelativistic Compton scattering by these electrons couples the decay photons to the microwave background, producing submillimeter distortions. If the decay products close the Universe, they must decay with a radiative branching ratio larger than 2.5/times/10/sup /minus/5/ in order to produce recently observed excess submillimeter background radiation. To be consistent with measurements of the uv background, their mass /ital m//much gt/114 keV and their decay redshift /ital Z//sub /ital d///much gt/5200.
36463805
Resonant solar neutrino oscillation experiments.
The results of a detailed calculation of the effects of resonant neutrino oscillations in the sun on the current and proposed solar neutrino experiments are presented. Analytic results are used for the electron-neutrino survival probability so that a sophisticated model for both the production distribution of the solar neutrino sources and the solar electron-number density can be employed. Contour plots for the electron-neutrino capture rate, in the mass-difference-squared versus vacuum-mixing-angle plane, are given for the current /sup 37/Cl experiment and the proposed /sup 71/Ga detector.
43916778
Constraints on 17-keV neutrinos.
Recent experiments indicate that a 17-keV neutrino mixes with {nu}{sub {ital e}} with 1% probability. We discuss the constraints from neutrinoless double {beta} decay, cosmology, and astrophysics that any model possessing a 17-keV neutrino must obey. Several recently proposed models are shown to be incompatible with these constraints.
1721570
Time variation of fundamental constants, primordial nucleosynthesis, and the size of extra dimensions.
In theories with extra dimensions, the dependence of fundamental constants on the volume of the compact space allows one to use primordial nucleosynthesis to probe the structure of compact dimensions during the first few minutes after the big bang. Requiring the yield of primordial sup4He to be within acceptable limits, we find that in ten-dimensional superstring models the size of the extra dimensions during primordial nucleosynthesis must have been within 0.5% of their current value, while in Kaluza-Klein models the extra dimensions must have been within 1% of their current value.