Katsuaki Akaoka

Enhancement of intensity in microwave-assisted laser-induced breakdown spectroscopy for remote analysis of nuclear fuel recycling

An enhancement of emission intensity from a laser ablation plume, obtained by coupling a pulsed microwave using a simple wire antenna, is demonstrated to compensate the sensitivity reduction of a high resolution spectrometer that is required for nuclear fuel analysis. A gadolinium oxide sample was irradiated with 2.45 GHz, 250 W microwave pulse, and passed through a loop antenna. As a result, up to 50-fold enhancement of the emission signal was achieved for gadolinium ions. The enhancement enabled us to measure the mass concentration of europium per gadolinium, ranging from 5% to 100 ppm, and based on the extrapolation of the calibration curve the detection limit for microwave-assisted laser induced breakdown spectroscopy (MA-LIBS) was estimated to be 40 ppm. This offers a flexible and compact system of MA-LIBS for nuclear fuel analysis.

Ablation‐initiated Isotope‐selective Atomic Absorption Spectroscopy of Lanthanide Elements

For remote isotope analysis of low‐decontaminated trans‐uranium (TRU) fuel, absorption spectroscopy has been applied to a laser‐ablated plume of lanthanide elements. To improve isotopic selectivity and detection sensitivity of the ablated species, various experimental conditions were optimized. Isotope‐selective absorption spectra were measured by observing the slow component of the plume produced under low‐pressure rare‐gas ambient. The measured minimum line width of about 0.9 GHz was close to the Doppler width of the Gd atomic transition at room temperature. The relaxation rate of high‐lying metastable state was found to be higher than that of the ground state, which suggests that higher analytical sensitivity can be obtained using low‐lying state transition. Under helium gas environment, Doppler splitting was caused from particle motion. This effect was considered for optimization for isotope selection and analysis. Some analytical performances of this method were determined under optimum conditions an...

Effect of defocusing on laser ablation plume observed by laser-induced fluorescence imaging spectroscopy

We used laser-induced fluorescence imaging with a varying beam focal point to observe ablation plumes from metal and oxide samples of gadolinium. The plumes expand vertically when the focal point is far from the sample surface. In contrast, the plume becomes hemispherical when the focal point is on the sample surface. In addition, the internal plume structure and the composition of the ablated atomic and ionic particles also vary significantly. The fluorescence intensity of a plume from a metal sample is greater than that from an oxide sample, which suggests that the number of monatomic species produced in each plume differs. For both the metal and oxide samples, the most intense fluorescence from atomic (ionic) species is observed with the beam focal point at 3–4 mm (2 mm) from the sample surface.

Separation of an isotope as a precursor of a gamma-raylaser medium

The nuclear isomer 178Hfm2, expected to be the most promising candidate for the gamma-ray medium, is rather difficult to produce in large quantities. There are a few ways to create this isomer, such as the irradiation of 179Hf with high-energy neutrons through the (n,2n) reaction, the irradiation of 176Yb with high-energy α particles through the (α,2n) reaction, the irradiation of 181Ta with protons through the (p,2p2n) reaction. In some of these reaction schemes the isotopically pure target works better than the natural one from the viewpoint of spectroscopic purity, handling of radioactive materials and productivity. However, isotope separation of heavy elements for producing a precursor as a target material is difficult in terms of cost/effectiveness. The atomic vapor laser isotope separation (AVLIS) method is expected as the most efficient way compared with the normal electromagnetic separation method.

Time-resolved plasma imaging in microwave-assisted laser-induced breakdown spectroscopy

To study the dynamics of luminous plasma induced by a pulse laser and microwaves (MWs), time resolved imaging of microwave-assisted laser-induced plasma was carried out. In this study, a luminous plasma was induced by a second harmonic Nd:YAG laser (532 nm, 8 ns, 5 J) on calcium oxide (Ca2O3) pellet at low pressure (5 Torr) of Ar gas. The luminous plasma was enhanced by intensified microwaves (MWs) generated from a magnetron. The image of plasma induced by laser has different features from the plasma induced by the laser with MWs. For the case of laser only, the plasma lifetime is approximately 50 μs, the plasma size at 5 μs is approximately 3 mm, and the neutral Ca emission is much brighter than the ionic Ca emission. When the MWs was introduced into the laser-induced plasma, the plasma emission was enhanced, namely the plasma lifetime was elongated of approximately 8 times, the plasma size at 5 μs was enlarged of approximately 3 times, and the ionic Ca emission is much brighter than the case of neutral Ca emission, which indicated that the plasma temperature is much higher than the case of laser only. Therefore, the plasma induced by the microwave-assisted laser can be effectively used for the analysis of elemental composition in materials with high sensitivity.

Effect of Defocusing on Ablated Volume of Gadolinium Oxide

We used nanosecond (ns) and femtosecond (fs) laser pulses to ablate gadolinium oxide samples and measured the ablated volume as a function of the laser pulse focal position. The effect of defocusing on the ablated volume, which decreases as the ablation pulse focal position approaches the sample surface, was observed for both ns and fs pulses.

Fractional Distillation Characteristics of Duralumin

For the separation of radionuclide from the radioactive metallic waste generated by the decommissioning of nuclear facilities, a new method combined with the distillation and laser separation is being developed. The characteristics of fractional distillation for duralumin (Aluminum alloy 7075: Al-5.6Zn-2.5Mg-1.6Cu-0.25Cr) are studied experimentally and theoretically for the first step. In the experiment, the duralumin (378.7 mg) is heated to 1773 K with the rate of 200 K/h and vaporized. The ion current of its components within the vapor is measured using quadrupole mass spectrometer. In the simulation, the vaporization rate of the components from the melt is calculated by using the Langmuirs equation and the Henrys law. The results of the simulation agree well with the experimental ones, and it is indicated that Al, Mg and Zn could be fractionated from duralumin.