Tetsuji Nishikawa

Rietveld Refinement of the Structure of Ba2YCu3O7-x with Neutron Powder Diffraction Data

The crystal structure of a high Tc superconductor, Ba2YCu3O7-x, has been refined by the Rietveld analysis of TOF neutron powder diffraction data. Two polymorphs of Ba2YCu3O7-x are contained in the sample: orthorhombic (74%) and tetragonal (26%) forms. The two forms have nearly the same structure closely related to that of perovskite-type compounds. In the orthorhombic form, the occupation factor of an oxygen atom on the a axis differed greatly from that on the b axis, which is the main reason why Ba2YCu3O7-x crystallizes in the orthorhombic form.

Fine Structure of J=1←0 Transition due to Internal Rotation in Methyl Alcohol

The fine structure of J =1←0 lines in various isotopic species of methyl alcohol has been explained by a combination method of Itohs theory for a rigid asymmetric hinded rotor and Kivelsons theory for a nonrigid symmetric hindered rotor. All lines have been fitted within errors of 2 Mc by this method. From the analysis the height of potential barrier to internal rotation for CH 3 OD has been determined to be 371±5 cm -1 . The molecular structure of methyl alcohol has also been calculated and discussed.

Coherent Bremsstrahlung from Si Single Crystal : I. Experiment

The interference effects in the production of bremsstrahlung in a silicon single crystal have been studied by using 720 MeV electrons. The energy spectrum of the bremsstrahlung has exhibited interference maxima of the first five orders. The intensity variation of the 150 MeV photons with the rotation of the crystal has shown also three interference Maxima on each side of the central minimum. The observed interference conditions for the photon energy and angles of incidence of electrons relative to crystal axes are in good agreement with the theory.

The Production Asymmetry in γ+n→π-+p Process with Polarized Photons

The production asymmetry in the reaction γ+ n →π - + p is measured at 90° in the center-of-mass system and at five photon energies from 357 to 555 MeV. Linearly polarized photons are obtained by means of the coherent breamsstrahlung process from a silicon single crystal. Negative pions and recoiling protons from a liquid-deuterium target are detected simultaneously so that events originated from neutrons almost at rest in the deuterons are selected. The asymmetry data are compared with the dispersion-relation calculation of Berends, Donnachie, and Weaver, and with that of Schmidt et al. It is shown that the contribution from the Roper P 11 (1470) resonance is small in the pion photoproduction process.

The Hyperfine Structure of Sodium by a Microwave Absorption Method.

The hyperfine structure of the ground state 2 S 1/2 of sodium atom, Na 23 ( I =3/2), has been measured by a microwave absorption method by means of a Zeeman modulation spectrograph. Among seven lines of the Zeeman components, F =1→ F =2, six lines have been observed. The remaining one has not been obserbed since it is not affected by weak magnetic field. The hyperfine structure separation at zero magnetic field has been obtained from the results, and it is \begin{aligned} \varDelta\nu{=}1771.70{\pm}0.15 Mc/\text{sec}. \end{aligned} This is in good agreement with the known value measured by the atomic beam magnetic resonance method in the Paschen-Back region.

Tristan project and KEK activities

Abstract An outline of recent activities of the National Laboratory for High Energy Physics in Japan (KEK) is given with an emphasis on its TRISTAN Project.

ANALYSIS OF PION PHOTOPRODUCTION ON NUCLEONS BELOW 500 MeV.

The differential cross sections, asymmetry ratios and recoil-nucleon polarizations of pion photoproduction on protons and neutrons below 500 MeV have been studied. It is shown that the dispersion theory of Berends, Donnachie and Weaver is unfavorable because of their inadequate treatments of the P 11 (1470) and D 13 (1518) resonances. The phenomenological analysis shows that the effect of the Roper P 11 (1470) resonance is negligible and the isovector amplitude is dominant in the multipole amplitudes leading to the final D 13 state. The experimental data are also favorably explained by the crude dispersion-theoretical model of Schmidt et al.

Coherent Bremsstrahlung from Si Single Crystal. II

The observed interference effect of bremsstrahlung produced by high energy electrons in a single crystal of silicon is analyzed. Numerical calculations have been carried out on the total cross section and the linear polarization. The interference part of the cross section is sensitive to the value of atomic form factor at a small momentum transfer. Assuming the form factor of Si atoms determined by the x-ray diffraction, one obtains a good agreement between the theory and the experiment. From the observed fine structure of bremsstrahlung spectrum. a path length of electron in which the interaction is coherent is estimated. Effects of photon beam collimation, temperature of the crystal, and inelastic process due to atomic electrons are discussed.

Photoproduction of Positive Pions from Carbon Nuclei

Positive pions with energies ranging from 30 MeV to 150 MeV were produced on a carbon target by the bremsstrahlung beam from the 750-MeV electron-synchrotron and detected by means of a π-µ decay counter telescope at an angle of 90° in the laboratory. The counts were corrected for the electronic efficiency of the pion counting system and for the loss of pions in the detection system by decay in flight, nuclear absorption, nuclear scattering and multiple Coulomb scattering. Absolute cross sections of the pion production are given as a function of the peak bremsstrahlung energies extending from 180 MeV to 550 MeV. Applying the photon difference method to the cross section per equivalent quantum, the differential cross sections, (\(d^{2}\sigma/d\varOmega dT_\pi\)) and (\(d\sigma/d\varOmega\)), are obtained, and compared with theoretical values, which are calculated on the bases of the impulse and closure approximation, the nuclear momentum distribution of a Gaussian type of the average kinetic energy of 19 Me...

MONOCHROMATIZATION OF COLLIMATED COHERENT BREMSSTRAHLUNG FROM A THIN SILICON CRYSTAL.

Collimation effects on the coherent bremsstrahlung produced in a thin silicon crystal have been studied by using 1 BeV electrons whose angular divergence is suppressed by scrapers in synchrotron orbit. The energy spectra of the bremsstrahlung exhibited narrow spikes and large enhancement ratios. The full width at half-maximum of the enhanced spike of 15% has been obtained at the photon energy of 435 MeV. The observed spectra were fitted to the theoretical ones calculated by the least square method. The fit gives the effective collimation angle \(\varTheta_{\text{eff}}\) of 0.54 reduced angles. The continuous part was 1.85 times as large as the theoretical prediction. Considering that the mechanical collimation angle \(\varTheta_{c}\) is 0.32 reduced angles, \(\varTheta_{\text{eff}}\) is mainly ascribed to the calculated multiple scattering angle \(\varTheta_{\text{ms}}\) of 0.65 reduced angles as well as \(\varTheta_{c}\).