Masabumi Miyabe

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.

Highly excited odd-parity levels of atomic uranium

An extensive energy level survey of atomic uranium was performed in the 31 300-36 400 cm-1 region using a two- or three-colour RIMS scheme; over 450 odd-parity levels, including about 150 new ones, were revealed. The J-value assignment was also performed by the method based on the J-momentum selection rule.

Development of RIMS apparatus for isotope analysis of calcium in nuclear waste materials

We have developed a frequency stabilized laser system for RIMS analysis of a long-lived radionuclide of calcium (41 Ca) in concrete waste materials. A stable reference laser has been developed using magnetically induced circular dichroism of atomic rubidium. The frequency stability was estimated to be 50 kHz over 8-h period from beat frequency measurement. Furthermore, a computer-controlled fringe offset lock system has been developed to transfer the high frequency stability to the other lasers for three-step excitation of atomic calcium. By using the system precise frequency tuning of 1 MHz error over 1 GHz scan was realized. The overall frequency tuning precision was also confirmed by a multistep fluorescence and resonance ionization spectroscopy of calcium.

Analysis of the even-parity Rydberg series of Gd I to determine its ionization potential and isotope shift

Three-step resonance ionization mass spectroscopy has been performed to observe the even-parity Rydberg series converging to four states of (, , and ). Using low-angular-momentum states as the second-step intermediate levels, simple and unperturbed series structures have been obtained. From an analysis of these structures, the first ionization potential of atomic Gd has been determined with improved accuracy as . In addition, on the basis of the isotope shifts of the Rydberg states the isotope shift (-) of the ionization potential of has been found.

Pressure Shifts of Valence and Core Exciton Peaks in Potassium Iodide

Hydrostatic pressure shifts of valence and core exciton peaks in KI are measured with a modulation method at about 120 K. The pressure coefficients are determined to be, in units of 10 -3 meV/bar, 17.0 and 4.7 for the valence excitons at 5.73 and 7.22 eV, and 18.8, 17.0 and -38.7 for the core excitons at 19.95, 20.20 and 21.05 eV, respectively. The pressure shifts of the lowest exciton at 5.73 eV and the core excitons are discussed with a simple model of localized transitions. Experimental results for the lowest exciton and the core excitons at 19.95 and 20.20 eV are explained well in this model, but the shift of the core exciton at 21.05 eV does not agree with the theoretical expectation. The exciton-phonon interaction term contributing to thermal shifts of the excitons is deduced from the present pressure coefficients.

Total angular momenta of even-parity autoionizing levels and odd-parity high-lying levels of atomic uranium

Using three-step resonance ionization spectroscopy, over 200 even-parity autoionizing (AI) levels of atomic uranium, including Rydberg series converging to the second lowest ionic level (6L 11/2o), were observed in the 49 930–51 200 cm−1 energy range. Total angular momenta (J values) of these levels were determined by a polarization combination method as well as a method based on the J-momentum selection rule. Using the AI levels of which J values were determined unambiguously, unique J values were also assigned for about 70 high-lying odd-parity levels. The observed J-dependence on autoionization linewidth is interpreted as being due to a centrifugal potential barrier.

Ultra Trace Isotope Determination in Environmental, Bio-Medical and Fundamental Research by High Resolution Laser-Mass Spectrometry

The introduction of resonance ionization using continuous wave narrowband lasers into mass spectrometry has lead to the successful development of an efficient technique for ultra trace atom determination with outstanding specifications regarding isobaric and isotopic selectivity. Due to these features this compact laser-based method is just becoming competitive to conventional ultra trace detection techniques like accelerator mass spectrometry or low level decay counting and gives access to a variety of demanding investigations. Starting from high resolution atomic spectroscopy on high lying Rydberg states or autoionizing levels, selective determination for a number of ultra trace istopes becomes feasible. Experimental prerequisites as well as a number of challenging applications concerning in particular 41Cadetermination for environmental, bio-medical as well as fundamental investigations are presented.

Identification of single-colour multiphoton ionization transitions of atomic gadolinium

Single-colour resonant multiphoton ionization transitions of atomic gadolinium have been investigated by resonance ionization mass spectrometry. A total of 72 transitions have been found in the wavelength range of 530 - 635 nm. The wavelengths, relative intensities, linewidths and isotope shifts have been obtained for most of these transitions. In addition, the initial state for each transition has also been assigned employing the multicolour pump - probe technique. From the analysis of these transitions, it is found that most of the observed transitions arise from the three-photon process via the resonant first or second state and their isotope shifts correspond well with those of the resonant states. Based on these results, we have proposed new high-lying states and have determined isotope shifts of several excited states.

Highly excited odd-parity states of atomic gadolinium

An energy level survey of atomic gadolinium was performed in the 31 000 - region using simultaneous detection of optogalvanic and resonance photoionization signals; over 90 odd states, including 38 new ones, were revealed. The J-values of several new states were also determined by a method based on the J momentum selection rule.

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...