Kimio Morimoto

Measurement of the parity violating asymmetry Aγ in n→+p→d+γ

The weak pion-nucleon coupling constant H{sub {pi}}{sup 1} remains poorly determined, despite many years of effort. The recent measurement of the {sup 133}Cs anapole moment has been interpreted to give a value of H{sub {pi}}{sup 1} almost an order of magnitude larger than the limit established in the {sup 18}F parity doublet experiments. A measurement of the gamma ray directional asymmetry A{sub {gamma}} for the capture of polarized neutrons by hydrogen has been proposed at Los Alamos National Laboratory. This experiment will determine H{sub {pi}}{sup 1} independent of nuclear structure effects. However, since the predicted asymmetry is small, A{sub {gamma}} {approximately} 5 x 10{sup {minus}8}, systematic effects must be reduced to < 5 x 10{sup {minus}9}. The design of the experiment will is presented, with an emphasis on the techniques used for controlling systematic errors.

Small-angle neutron scattering from dynamically polarized hydrogenous materials

Small-sngle neutron scattering from the hydrogenous materrials EHBA-Cr V and dicyclohexyl-18-crown-6 dissolved in the deuterated or partially deuterated propanediol was investigated with pulsed white thermal neutrons. The dynamical nuclear polarization technique was applied to polarize tFte nuclear spins of the samples. The typical small-angle scattering patterns and their enhancement by the nuclear polarization could be observed. The results are in good agreement with the theoretical calculations, indicating the feasibility of the combination of small-angle neutron scattering and dynamical nuclear polarization technique for the study of semi-macrostructures of hydrogenous materials.

A horizontal dilution refrigerator with high cooling power for a spin frozen target

Abstract A horizontal dilution refrigerator was constructed for a spin frozen proton and deuteron target at KEK (National Laboratory for High Energy Physics). It was designed to obtain very high cooling capacity over the wide temperature range, especially at rather high temperatures (50 mK ∼ 500 mK). It has a high gas flow rate (typically 4.5 × 10 −3 mol s −1 ), a powerful 4 He precooling system and an adequate heat exchange efficiency between the incoming stream and outgoing solution. It has double-tube heat exchangers, whose lower temperature parts are filled with sintered copper. The mixing chamber is made of PFA which is joined with a brass flange by a simple demountable seal. Typical cooling power was about 40 mW and 5 mW at 500mK and 200 mK respectively and the lowest temperature was about 20 mK.

Slow Neutron Polarization by Longitudinally Polarized Proton Filter

The neutron beam with the energy between 10-2 eV and 10 eV could be polarized by the longitudinally polarized proton filter. In this experiment, we found that the polarization cross section for the longitudinally polarized filter is approximately the same value as that for the transversely polarized one.

Bismuth silicate as a scintillating material for electromagnetic shower detectors

Abstract A BSO single crystal is evaluated with respect to the scintillation characteristics as a candidate alternative to BGO: the light output of BSO is 20% that of BGO and the flourescence lifetime is 0.1 μs at room temperature. Their temperature dependences were also measured from the room temperature down to 185 K.

Analysis of deuteron NMR spectrum in propanediol for polarization measurement

Abstract An analysis of the deuteron NMR spectrum is given to determine the deuteron polarization and the quadrupole coupling parameters in deuterated 1, 2-propanediol-D6 and 1, 2-propanediol-D8. Deuterons are polarized by the dynamic method in a spin frozen target. The deuteron line-shape function is calculated for a polycrystalline solid. Agreement between the theoretical and experimental spectrum is satisfactorily good. The following parameters are obtained for the deuteron quadrupole coupling; e2qQ/h = (166.3 ± 1.0) kHz, η = 0.03 ± 0.01 for the C-D bond, and e2qQ/h = (197.9 ± 3.0) kHz, η = 0.17 ± 0.02 for the O-D bond. The deuteron polarization reaches around 40% and is determined with a relative error less than 10%. A possible application of the dynamic polarization method to the study of molecular structure is discussed.

Measurement of Propagation Velocities of the Normal Zone in a 1 mφ×1 m Superconducting Solenoid Magnet

Propagation velocities of the normal zone in a 1 m×1 m superconducting solenoid magnet were unambiguously measured as a function of the magnet excitation current by inducing quenches with a heater. The magnet was built to study the feasibility of constructing thin, large solenoid magnets and it has a single layer aluminum-stabilized NbTi/Cu superconductor of 269 turns. The ratio of Al:NbTi:Cu of the conductor is 24:1:1. The design current of the conductor is 4.5 kA at 1.5 Tesla. Measured velocities are 30, 65, and 90 m/s in the direction of the conductor at 2020, 3030, and 3540 A, respectively. Thermal distributions inside the coil after quenches were quite uniform and no local overheating was observed.

Slow Neutron Polarization by Polarized Proton Filter Using Ethylene Glycol

A feasibility study of a polarized proton filter for slow neutrons was successfully carried out. Ethylene glycol containing a few percents of Cr V ions was used as filter material in which protons were dynamically polarized. Polarization of protons was varied between 20 and 72%. The maximum polarizability of 0.84±0.01 (flipping ratio of 11.5±0.5) was obtained for neutrons of 80 meV. This value corresponds to the polarization cross section of 27±1.4 b. The idea will open a way for the polarization of intense neutron beams of white spectra. In addition, this method does not impose serious restriction on the angular divergence of the incoming neutron beam.

A Spin-Frozen Polarized Target of Proton and Deuteron

A spin-frozen polarized target of proton and deuteron was constructed for the measurement of spin dependent parameters of hadron-hadron scatterings at the 12 GeV KEK proton synchrotron. The target was also used for experiments at LAMPF-HRS. As the proton and deuteron targets, 1,2-propanediol and fully deuterated propanediol (D-8) with stable Crv complex (EHBA) were used, respectively. The characteristics and performance of the targets are described. Data on the nuclear spin lattice relaxation time (Tln) with proton beam give us information on the Kapitza resistance between the target material and liquid 3He/4He mixture.

Dynamic nuclear polarization of irradiated targets

Polarized proton targets used in high energy physics experiments employ the method of dynamic nuclear polarization (DNP) to polarize the protons in an alcohol. DNP requires the presence of paramagnetic centers, which are customarily provided by a chemical dopant. These targets suffer from loss of polarization as the target is irradiated, and also the hydrogen fraction for the alcohols is relatively low, e.g., 0.13 for butanol. If the paramagnetic centers formed when the target is irradiated could be used in the DNP process, the resulting targets might be more radiation-resistant. Also it might be possible to use materials which have high hydrogen fractions, but are not easily doped, such as NH3 or HD.