Yuzuru Matsumoto

Elastic scattering of electrons by water molecules over the range 100-1000 eV

Relative values of differential cross sections (DCS) are measured by the crossed-beam method. Two cylindrical-mirror energy analysers are employed. One of them is moved to detect scattered electrons at every angle, and the other is fixed at an angle to monitor the elastic scattering events. The effects of target gas distributions in a molecular beam flowing out from a multicapillary array are taken account of to correct the relative values. The DCS are also measured at an angle for water molecules and helium atoms by using gas chamber. On the basis of the absolute DCS for He measured by Jansen et al. (1976), the relative DCS for water molecules are converted into absolute values. In addition, the DCS are calculated by the partial-wave method for the double Yukawa potential. The values of its three adjustable parameters are determined by comparison with the experimental DCS. A spherically symmetric realistic potential is also inferred without adjustable parameters from the charge distribution that was derived from molecular-orbital theory. The DCS calculated for this potential reproduce the experimental values fairly well.

Ionization chamber system to eliminate the memory effect of tritium

Abstract The memory effect due to the adsorption of tritium onto the electrodes of an ionization chamber sometimes reduces the accuracy of the results. Ionization chambers are generally used to monitor the tritium level in a gas stream because of their reliability, flexibility and wide range of measurement. In this paper we shown that the memory effect is mainly brought about by the transfer of tritium from the gas stream to surface water on the electrode wall by adsorption or isotope exchange reactions. A way to simulate the extent of the memory effect is proposed. An ionization chamber system which can eliminate the memory effect by applying an isotope exchange reaction is also proposed.

Tritium mass balance in the piping system of a fusion reactor

This paper discusses the behavior of tritium on the surface of various piping materials considering the various mass transfer steps. It is observed in this study that the isotope exchange reaction between gaseous hydrogen in gas stream and surface water and transfer of hydrogen isotopes and water through surface layer formed on materials or pores are most effective when an oxide film layer is formed on a material surface such as stainless steel. The amount of tritium sorbed on the stainless steel is correlated and compared with that observed for copper or quartz. The memory effect observed for an ionization chamber having stainless steel electrodes is also compared with that having copper electrodes.

Characteristics of Nb-based Josephson junctions at a temperature below 1 K

A lithographic technique for Josephson LSI (large scale integrated) circuits was applied to the production of a superconducting tunnel junction for radiation detection. Nb-Al/aluminum oxide/Nb tunnel junctions with different junction sizes and barrier oxidation times have been fabricated. The current-voltage curves were measured in the temperature range from 4.2 to 0.45 K. The junctions showed some amounts of leakage current, which remained below 2 K. The behavior of the leakage current was successfully understood from its experimental dependence on the junction size. >

Plane multiwire-electrode ionization chamber for measurements of radon concentration in air

A continuous measuring system has been developed, which uses a plane multiwire‐electrode ionization chamber and obtains radon concentrations by measuring in situ alpha energy spectra due to alpha‐active nuclei in the air. The chamber has three rigid plane multiwire electrodes in a box of aluminum plates which have holes for the air to flow freely through them. The concentration measurements do not disturb the distribution of radon in the air. Values of concentration are obtained with good statistical errors because of the use of a large volume for the ionization chamber. The slow rise‐time pulses of alpha particles from the chamber are analyzed with a specially designed analog‐to‐digital converter which is controlled with a microcomputer. The energy spectra have been obtained with a FWHM of about 600 keV. Time variations of radon concentrations have been measured in a room in a ferroconcrete building.

Possible use of bulk superconductor with tunnel junctions for nuclear radiation spectroscopy

Abstract Nuclear radiation detectors with Josephson junctions, as hitherto reported, were composed of thin superconducting strips and had a poor energy resolution. A conceptual study is made on improvement of these detectors, with special consideration of quasiparticle collection. A bulk superconductor is shown to be appropriate as a radiation detector. Superconducting tunnel junctions of two types are proposed for superconducting radiation detectors of excellent energy resolution. These have high barrier penetrability and large area in order to collect all the quasiparticles generated in the superconductor by nuclear radiation.

Output signal from Nb-based tunnel junctions by irradiation of 6 keV X-rays

Large-size tunnel junctions with a Nb-Al-AlO/sub x/-Nb structure have been fabricated in order to study their performance in X-ray detection. The junction detected 5.9-keV X-rays with an energy resolution of 1 keV. The output signal was analyzed by the use of coupled Boltzmann equations. The method based on these equations clarifies the basic behavior of the quasiparticles and phonons, and the average energy for producing a single electron is 3.2 Delta .

Characteristics of a seven-element electrostatic lens system studied by an exact beam-tracing method

A lens system has been designed for an electron energy analyzer by the numerical beam‐tracing method using the paraxial equation of motion for electrons. Three new modes are investigated, in addition to a usual one, as methods for applying voltages to the lens electrodes. The emittance diagrams are obtained for the system by solving the exact equation of motion, and they clearly show the effects of aberrations. The transmission for electrons is calculated for each of the four modes by using the diagrams. The lens system can be used with considerable efficiency in the different energy regions appropriate to the respective modes.

Detection of 6 keV X-rays by Using Large-Size Nb-Based Tunnel Junctions

Nb-based tunnel junctions may be applicable to a high resolution x-ray measurement. Large-size tunnel junctions with a Nb/Al/AlOx/Nb structure have been fabricated to study their performance in x-ray detection. The lithographic technique was employed to make the junctions. The niobium layer being sensitive to x rays had a large size of 100 μm□ width X 1.2 μm thickness. The junction detected 5. 9 keV x rays with an energy resolution of 1 keV. The detector characteristics such as the pulse height spectrum and the signal to noise ratio were well understood.

Method to calibrate an ionization chamber for measuring indoor radon concentrations with standard gamma‐ray sources

Most instruments for measuring radon concentrations in the air should be calibrated using air with known radon concentrations, obtained from a solution of radium. However, safe handling of such a solution of alpha‐active elements can be troublesome. Standard gamma‐ray sources of low activity are handled more safely and typically used to obtain the absolute detection efficiency of a Ge detector with high accuracy. A new method has been developed to calibrate a radon detector with such sources. A radon exhalation rate for a substance containing a small amount of radium is measured with the radon detector to be calibrated. After this, the vessel containing the radium is sealed so that the radon does not escape from it. The buildup of the activity of  214Bi in it is obtained from gamma‐ray measurements and gives the radon exhalation rate on the basis of the activity of the standard sources. From the comparison between the two values of the exhalation rate, the radon detector is calibrated. A plane multiwire‐e...