Koichi Nittoh

Extension of dynamic range in X-ray radiography using multi-color scintillation detector

Abstract A new imaging system using the multi-color scintillator Gd 2 O 2 S:Eu has been developed for the X-ray radiography. In this method a color Charge Coupled Device detects the weak blue and green photons associated with the transitions from the terms like 5 D 1 and 5 D 2 in the Eu-ions as well as the dominant red photons. As these transitions become appreciable and saturate at quite different intensity levels of the X-ray, we can realize a big extension of the dynamic range of the imaging almost by hundred times in comparison with the conventional monochromatic method. As a result, the new system makes it possible to take a clear image of any complex object, which consists of various parts of the different X-ray penetrability, from plastic to heavy metal, at a single shot.

Discriminated neutron and X-ray radiography using multi-color scintillation detector

Abstract A new conversion screen Gd2O2S:Eu is developed, which emits red light on irradiation by thermal neutrons. By applying this in combination with the currently used Gd2O2S:Tb, a green-light scintillator, in the radiography under a neutron + X-ray coexisting field, we can easily separate the neutron image and the X-ray image by simple color-image processing. This technique enables a non-destructive and detailed inspection of industrial products composed both of light elements (water, plastics, etc.) and heavy elements (metals), widening the horizon of new applications.

Photoionization polarization spectroscopy of complex atoms

An improved method for the angular momentum measurement of autoionizing levels of complex atoms based on photoionization polarization spectroscopy is reported. In this method, a variation of the ion yield is measured as a function of the combination of the polarizations of the lasers used to excite the autoionizing level through a ladder of intermediate resonant states. Here, eight combinations of different polarizations in three lasers are used, which include not only circular but also linear polarizations. It has been confirmed that the angular momentum of the autoionizing level can be determined uniquely by relative ion-yield measurements for any combination of angular momenta of the levels of the excitation ladders by choosing appropriate intensities of the lasers.

High-temperature operation of high-power InGaAlP visible laser diodes

High-power InGaAlP lasers operating at high temperature have been realized by using a strained active layer, a highly doped p-cladding layer, and a long cavity structure. The maximum operating temperature has been increased to 80 degree(s)C for a 50 mW operation of transverse-mode stabilized laser diodes, and also for a 100 mW operation of broad-stripe laser diodes. This improvement in the temperature characteristics has led to a highly reliable operation at a high output power. Transverse-mode stabilized InGaAlP lasers oscillating at 698 nm have exhibited a stable operation for 2,000 hours at a high output power of 40 mW with an ambient temperature of 40 degree(s)C. A highly reliable operation of broad-stripe structure lasers has also been achieved. A stable 100 mW operation for 1,500 hours at a temperature of 50 degree(s)C was obtained for InGaAlP lasers with a stripe width of 25 micrometers .

Neutron radiography used on a mono-propellant thruster

Most mono-propellant thruster technologies were developed in the 1960s and the basic principles and fundamental structures, such as the catalyst and propellant, have remained in use without major technical innovation. Conversely, much remains to be identified in terms of the concrete mechanisms and quantitative limitations of the phenomena inside the monopropellant thruster. One of our studies to improve the reliability of propulsion systems involved visualization, facilitating the direct observation of the physical and chemical phenomena occurring within the catalyst bed of the mono-propellant thruster. In this paper, we introduce the visualization test results of the mono-propellant thruster utilizing Neutron Radiography. This paper shows an overview of the non-destructive imaging technique using Neutron Radiography and the visualization hot-firing test result of the mono-propellant thruster through the application of Neutron Radiography.

Measurement of Dipole-Moment in Atomic Transitions under Strong External Magnetic Field

Obtaining an accurate value of the electric dipole moment μ is essential in the fields of laser application technologies. A direct way of measuring the electric dipole moment μ is to observe the Rabi-oscillation which manifests itself in the coherent photo-excitation behavior of atoms. In the case of the elements which have large angular momenta, identifying the Rabi-oscillation in their excitation behavior becomes rather difficult. We proposed an accurate and straightforward method of determining the electric-dipole moment μ between multifold degenerate levels. The point is to remove the degeneracy by applying an external magnetic field with the aid of the Zeeman effect and, then, to realize a degeneration free coherent excitation. As a result, we can observe the Rabi-oscillations explicitly in the excitation vs. laser-fluence curves. The present method provides a reliable basis of experimental determination of μ. As an example, we applied the present method to a transition to 0–17,362 cm−1 level in uran...

Polarized laser spectroscopy of two-step electric-dipole excitation of atoms

A simple and accurate method of measuring the total angular momentum J of atomic energy levels is described. The method is essentially based on the J and photon-polarization dependence of the laser-induced two-step excitation in a three-level system. Four different combinations of polarizations in two lasers, which are tuned to each of the two Bohr frequencies, are utilized. They are co-circulating, counter-circulating polarizations and mutually parallel and perpendicular linear polarizations. It has been confirmed that the J-value of a level in the three-level system can be determined uniquely from relative strengths of the fluorescence originating in the top level. The determination of J is carried out by recognition of patterns in the excitation behaviour, which is peculiar to each J-value. The merit of the present method lies in the high reliability inherent in the pattern recognition procedure and also in the relative ease of the experiment.

New Device for Discriminated Neutron and X-Ray Radiography using Multi-Color Scintillators

Abstract A new conversion screen Gd2O2S: Eu has been developed which emits red light on thermal neutron irradiation. By using this in combination with the current green-light scintillator (Gd2O2S: Tb) in radiography under a neutron+X-ray field, we can easily separate the neutron and the X-ray images on PC with any color-graphic software in the market. This technique leads us to a new possibility of non-destructive and high-precision inspection of industrial products composed both of light elements (organic compounds and plastics) and heavy elements (metals).

Photo resonance excitation and ionization characteristics of atoms by pulsed laser irradiation

The authors report on obtaining generation of a CO2 laser with a phase- anisotropy three-mirror cavity operating in a linear orthogonal polarized double-mode regime. Power and frequency characteristics of a double-mode three-mirror laser are also studied. It was proved that in a double mode CO2 laser with an internal absorbing cell the saturation of the absorbing medium can be significantly reduced with the help of a three-mirror telescopic cavity. Narrow nonlinear resonances of high amplitude were obtained in a CO2/SF6 laser with the help of phase-anysotropy three-mirror telescopic cavity.

Observation of dynamic Stark effect in Zeeman-split absorption lines and determination of dipole moment

A simple and straightforward method is presented for determining the electric-dipole moments of phototransitions between degenerate levels in atoms. In the present method, the dynamic Stark effect (DSE) is induced by a high-fluence laser light in the presence of a strong external magnetic field. The energy splitting caused by the DSE is measured by sweeping the frequency of the probe laser. As the separation width of the DSE peak is essentially given by a product of the dipole moment , the relevant Wigner 3-j symbol and the square root of the laser intensity, we are able to determine the value of in a direct way. As the DSE is induced between a pair of non-degenerate Zeeman sublevels, which is singled out by the external magnetic field, the result is free from any ambiguities brought about by the degeneracy such as the smoothing out of DSE peaks caused by the overlapping of the sublevel contributions. The method was tested against the transition between the 17 362 and levels in atomic uranium, giving the electric dipole moment .