Masayoshi Tamaki

Development of imaging techniques for fast neutron radiography in Japan

Abstract Neutron radiography with fast neutron beams (FNR) has been studied at the fast neutron source reactor “YAYOI” of the University of Tokyo since 1986. Imaging techniques for FNR have been developed for CR-39 track-etch detector, electronic imaging system (television method), direct film method, imaging plate and also fast and thermal neutron concurrent imaging method. The review of FNR imaging techniques and some applications are reported in this paper.

Electrical resistivities of the uranium carbides

Abstract Electrical resistivities of arc-melted uranium carbides, UC, UC2, U2C3 and UC + UC2, were measured over the temperature range between 4 and 1900 K. The monocarbide, dicarbide and the mixture of carbides showed metallic character in their resistivity dependence on temperature above 30 K, while below this the resistivities were constant. U2C3 showed a knee in the resistivity curve at 54.0 K corresponding to a magnetic transition. Above 1100 K, the resistivity of U2C3 did not vary with temperature. The resistivity of the mixture (UC + UC2 with U2C3 precipitates) showed an arrest between 800 and 950 K.

Neutron irradiation effects in uranium monosulfide

Uranium monosulfide (US) was irradiated to investigate the effects of fission damage. Post-irradiation examinations were done by measuring the electrical resistivity, and partly the magnetic properties, at low temperature. The lattice parameter and the electrical resistivity measured at room temperature just after the irradiations showed an increase starting at a fission dose of 1 × 1016 fissions/cm3 and attaining a maximum at 3 × 1016 fissions/cm3. After that, a saturation of both increases persiste until 3 × 1017 fissions/cm3. The low-temperature electrical resistivity in the magnetic ordered state (ferromagnetic transition, Tc, at about 180 K) increased remarkably, while decreasing drastically in the magnetization, with increasing fission dose, apparently corresponding to the lattice expansion. In addition, the Curie point (Tc) shifted to lower temperatures with accumulating fission damage.

Visualization and correlation analysis of counter-current two-phase flow in a thermosyphon by neutron radiography

Abstract We visualized the working fluid behavior in a bent thermosyphon by a neutron radiography and analyzed it quantitatively with an image processing technique. Working fluid velocity was evaluated by the two-point correlation function and also the spatio-temporal correlation was calculated, which led to a clarification of the pass route of working fluid in the thermosyphon. The probability density function of the void fraction was calculated.

Magnetic character of us with fission damage

Abstract Effects of neutron irradiation (fission damage) and successive annealing on the magnetic character of ferromagnetic uranium monosulphide (US) are evamined. Fission-induced defects reduce drastically the magnetivation of US in the ordered state, accompanied with a remarkable increase in the electrical resistivity due to magnetic disordering. The magnetic parameters also changed with fission damage. Successive annealing showed a recovery in all the magnetic parameters and the disordered magnetivation and resistivity, in accordance with an annealing of fission damage.

Mass spectrometric studies of lithium-containing oxides at high temperature

Abstract The sublimation and vaporization of various lithium containing oxides have been studied by high temperature mass spectrometry. The installed Knudsen cell apparatus gave some useful information about the vapor species, appearance potentials, partial pressures and heats of reactions involved. The investigated oxides are Li 2 O, Li 2 O-Al 2 O 3 , Li 2 O-MoO 2 and Li 2 O-SiO 2 systems. This paper mainly presents the most recent data for the Li 2 O-SiO 2 system. A relationship for the decomposition reaction of ortho -Li 4 SiO 4 was deduced. The heat of the reaction was determined by the third law method. The activity of the Li 2 O component in the double oxides was estimated from the partial pressures of the vapor species. γ-LiAlO 2 and meta-Li 2 SiO 3 showed fairly low activities in comparison with Li 2 O oxide. The activity coefficients decreased with the Li 2 O mole fraction in the lithium compounds. The heats of formation and atomization of LiO and Li 2 O gaseous species were determined.

Magnetic properties of uranium mononitride with fission fragment damage

Abstract Magnetic disorder in neutron-irradiated (fission fragment damage) uranium mononitride (UN) has been investigated by magnetic susceptibility measurements. The Neel point (TN ) shifted to lower temperatures with increasing fission dose and attained the lowest value at a dose of around 1018 f/cm3. After further irradiations, however, it recovered to the non-irradiated value. The shift of TN was in accordance with the change of the concentration of fission-induced vacancies. Other magnetic parameters showed a similar trend. These fission-fragment damage results are discussed in terms of the electronic state of 5 f electrons.

Transmittance measurements of cold neutrons for some materials by means of neutron radiography

Abstract We examined cold neutron radiography (CNR) to determine its characteristics with respect to the ability to obtain the quantitative measurements. In order to describe the complicated transmission phenomena in CNR, a thickness dependent attenuation coefficient μ ( t ) is introduced instead of an average attenuation coefficient. A simple function using a linear approximation model to μ ( t ) is proposed to express transmission curves in CNR. This function agreed well with the experimental data for materials having deep and shallow Bragg cutoffs and for a 1 / ν dependent material. Thus, the linear approximation to μ ( t ) is effective for describing the transmission phenomena in CNR.

STUDY ON NEUTRON IMAGING TECHNIQUES AND PROCESSINGS FOR DEVELOPING QUANTITATIVE NEUTRON RADIOGRAPHY

Abstract Four kinds of existing arrangements of neutron radiography techniques and a newly proposed arrangement were examined to evaluate the removing efficiency of the scattered neutron and gamma-ray contaminant. Techniques of dispersion, channel and umbra arrangement were evaluated to obtain quantitative neutron attenuation coefficient. A new combination technique of the neutron absorbing honeycomb collimator and the double X-ray films has verified that the relationship between the neutron transmittance and object thickness is fairly expressed by a single exponential curve in a transmission range from 1.0 to 0.01.

Correction of scattering neutron effects on neutron CT

Abstract Correction of the scattering neutron effects in neutron computed tomography (CT) has been carried out. By subtracting the component of scattering neutrons in CT projection data, only the corrected direct transmitting component through objects is treated. By using the correction of the scattering component on neutron CT, the relatively low contrast on them by neutron electronic imaging method (TV) has been improved. Quantitative analyses with neutron CT have shown a better linear relationship between the neutron macroscopic cross sections and the CT outputs of metal objects.