Yasuhiro Masuda

beta. -ray angular distribution from aligned /sup 12/B and /sup 12/N

The coefficients ..cap alpha../sub minus-or-plus/ in the alignment-correlation terms A..cap alpha../sub minus-or-plus/EP/sub 2/(costheta), in /sup 12/B and /sup 12/N decays have been determined; ..cap alpha../sub -/(/sup 12/B) =+(0.006 +- 0.018) %/MeV, and ..cap alpha../sub +/(/sup 12/N) =-(0.273 +- 0.041) %/MeV. The sign of ..cap alpha../sub +/(/sup 12/N) was determined for the first time, by use of an NMR method and measurements on ..beta..-..gamma.. correlation in aligned /sup 12/N. The (..cap alpha../sub -/-..cap alpha../sub +/) result is consistent with strong conservation of vector currents without second-class currents and the (..cap alpha../sub -/+..cap alpha../sub +/) result gives unique information on the time component of the axial-vector current.

A resonance detector spectrometer at KENS

Abstract We have tested a resonance detector spectrometer at the KENS neutron source, using 181Ta, 121Sb and 149Sm resonances and bismuth germanate (BGO) scintillators. In the process we encountered and solved numerous background problems, and discovered a time-focussing principle. We measured the scattering from a number of materials and have so far analyzed results for bismuth, vanadium and graphite, which we present. Tests of cooled absorbers indicate that resolution of 70 meV is possible with 181Ta.

A High-Rate Detection System to Study Parity Violation with Polarized Epithermal Neutrons at LANSCE

Abstract We describe an apparatus for studies of parity violation in neutron-nucleus scattering. This experiment requires longitudinally polarized neutrons from the Los Alamos Neutron Scattering Center over the energy range from 1 to 1000 eV, the ability to reverse the neutron spin without otherwise affecting the apparatus, the ability to detect neutrons at rates up to 500 MHz and an appropriate data acquisition system. We will discuss the neutron polarizer, fast neutron spin reverser, detector for transmitted neutrons and high rate data acquisition system.

Neutron spin rotation and P-violation

A new apparatus to measure the neutron spin rotation due to interaction with matter has been developed at KEK. The present apparatus enables us to measure the parity violating neutron spin rotation in the p-wave resonance in the energy region of eV.

Response of a large CsI(Tl) crystal to electrons and pions below 1.5 GeV/c

Abstract A CsI(Tl) crystal of 9.5 cm diameter and 30 cm length was tested with electrons and pions in the momentum range from 0.2 to 1.5 GeV/ c . Photodiode and photomultiplier readouts were used for comparison. In the photodiode readout, the fwhm energy resolution for electrons was 6.7% at 1 GeV in agreement with the EGS simulation. The e/π separation for momentum analyzed particles was found to be 1/1000 at 1 GeV/ c with a simple energy cut. The pulse heith nonuniformity along the longitudinal position, scanned with a pencial beam of 1 GeV/ c pions, was smaller than ±4% between 4 and 27 cm from photomultiplier.

An EDM measurement with a new comagnetometer and a high density UCN source

We discuss a new neutron EDM measurement of 10−28 e cm. For the improved UCN density, we will apply a new spallation UCN source of superfluid He. For magnetometry, 129Xe nuclear spins are injected into a EDM cell, to supress GPE. Performance of the prototype KEK-RCNP UCN source, and the obtained Ramsey resonance spectra are presented.

Determination of the gamma-ray background in a pulsed epithermal neutron beam

Abstract The γ-ray background in the pulsed neutron beam at the Los Alamos Neutron Scattering Center was measured with an array of 10 B-loaded liquid scintillators. With the method employed the γ-ray contribution in the neutron beam can be determined without knowledge of the energy spectrum of the γ-rays. The ratio of γ-ray to neutron intensities in the beam was determined during the time interval following the beam burst that corresponds to neutron energies from E n = 1 to 340 eV. The γ-ray content in the beam ranges from 2% at 1 eV to 10% at 340 eV.

A Ramsey's Method With Pulsed Neutrons for a T-Violation Experiment

A Ramsey’s method with pulsed neutrons is discussed for neutron spin manipulation in a time reversal (T) symmetry violation experiment. The neutron spin (sn) is aligned to the direction of a vector product of the nuclear spin (I) and the neutron momentum (kn) for the measurement of a T-odd correlation term, which is represented as sn · (kn × I), during propagation through a polarized nuclear target. The phase control and amplitude modulation of separated oscillatory fields are discussed for the measurement of the T-odd correlation term.

Test of parity violation and time reversal invariance in slow neutron absorption reactions

Abstract Measurements of helicity asymetries in slow neutron absorption reactions have been performed by detecting capture γ-rays. Large enhancements of parity-violation effect observed in these reactions are explained by interference between s- and p-wave resonances. The weak matrix element in hadronic reaction has been deduced from the results. Violation of time reversal invariance is being searched for in reactions in which large enhancement of the parity violation effect occurs. The same order of enhancement is expected in violation of time reversal invariance. The difference between the probability for helicity flip (+ → −) and that for (− → +) during transmission through a transversely polarized target is being measured. Recently, 139 La nuclei in LaAlO 3 crystal have been polarized successfully. The crystal is useful for the target, since the highest enhancement of the parity violation effect has been found for the 139 La target. The perspective of the experiment is shown.

Measurement of nEDM with a He-II Spallation UCN Source

A neutron EDM measurement by means of a He-II spallation UCN source is discussed. For an improvement in the statistical error, a proton beam power is increased up to 20 kW so that a UCN density in an EDM measurement cell becomes 800 UCN/cm. The  heating in a He-II bottle is removed by using a He cryostat. Polarized UCN are extracted from the He-II bottle through an aluminum window by using a superconducting magnet for Ramsey resonance in the EDM cell. For an improvement in the systematic error, Xe nuclear spins are used for magnetic field monitoring in the EDM cell. A geometric phase effect is suppressed by a buffer gas effect.