Estimation of external dose for wild Japanese macaques captured in Fukushima prefecture: decomposition of electron spin resonance spectrum.

The signal intensities of CO2- radicals in teeth can be utilised as an individual indicator of the cumulative external dose for animals. To accurately determine the external dose, it is desirable to analyse the CO2- radical intensity and improve its detection limit. We recently reported a dose-response in the range of 0-200 mGy and estimated the absorbed dose for seven wild Japanese macaques captured in/around the related areas to the Fukushima Daiichi Nuclear Power Plant accident. Herein, for further improvement of this method, we examined the electron spin resonance spectra of the teeth of these seven and an additional four macaques captured in Fukushima by applying two spectrum-decomposition algorithms.

Interlaboratory comparison of electron paramagnetic resonance tooth enamel dosimetry with investigations of the dose responses of the standard samples.

A total of seven Japanese laboratories participated in an intercomparison study to estimate the dose given to tooth enamel samples, using the electron spin resonance method. Each of four of the participating laboratories prepared a set of tooth enamel samples, using the electron spin resonance method. Four of the participating laboratories each prepared a set of tooth enamel samples, consisting of seven standard aliquots irradiated from 100 to 2000 mGy and three samples with an 'unknown' dose between 140 and 960 mGy, were intended to eliminate bias from sample preparation. Although not all seven laboratories measured all four sets of samples, the major finding was that systematic biases in estimating doses may be caused by differences in laboratory measurements rather than by the enamel extracting procedures. When doses were averaged by measurements made by multiple laboratories, the averaged values were close to the actual values. Scattering in the intercepts in the standard dose response would be a serious problem in actual dosimetry where no background sample is available.

Ultraviolet photodissociation of Mg+-NO complex: Ion imaging of a reaction branching in the excited states.

Ultraviolet photodissociation processes of gas phase Mg+-NO complex were studied by photofragment ion imaging experiments and theoretical calculations for excited electronic states. At 355 nm excitation, both Mg+ and NO+ photofragment ions were observed with positive anisotropy parameters, and theoretical calculations revealed that the two dissociation channels originate from an electronic transition from a bonding orbital consisting of Mg+ 3s and NO π* orbitals to an antibonding counterpart. For the NO+ channel, the photofragment image exhibited a high anisotropy (ß = 1.53 ± 0.07), and a relatively large fraction (∼40%) of the available energy was partitioned into translational energy. These observations are rationalized by proposing a rapid dissociation process on a repulsive potential energy surface correlated to the Mg(1S) + NO+(1Σ) dissociation limit. In contrast, for the Mg+ channel, the angular distribution was more isotropic (ß = 0.48 ± 0.03) and only ∼25% of the available energy was released into translational energy. The differences in the recoil distribution for these competing channels imply a reaction branching on the excited state surface. On the theoretical potential surface of the excited state, we found a deep well facilitating an isomerization from bent geometry in the Franck-Condon region to linear and/or T-shaped isomer. As a result, the Mg+ fragment was formed via the structural change followed by further relaxation to lower electronic states correlated to the Mg+(2S) + NO(2Π) exit channel.

Roles of resonant muonic molecule in new kinetics model and muon catalyzed fusion in compressed gas.

Muon catalyzed fusion ([Formula: see text]CF) in which an elementary particle, muon, facilitates the nuclear fusion between the hydrogen isotopes has been investigated in a long history. In contrast to the rich theoretical and experimental information on the [Formula: see text]CF in cold targets, there is relatively scarce information on the high temperature gas targets of deuterium-tritium mixture with high-thermal efficiency. We demonstrate new kinetics model of [Formula: see text]CF including three roles of resonant muonic molecules, (i) changing isotopic population, (ii) producing epi-thermal muonic atoms, and (iii) inducing fusion in-flight. The new kinetics model reproduces experimental observations, showing higher cycle rate as the temperature increasing, over a wide range of target temperatures ([Formula: see text] K) and tritium concentrations. Moreover, it can be tested by measurements of radiative dissociation X-rays around 2 keV. High energy-resolution X-ray detectors and intense muon beam which are recently available are suitable to reveal these dynamical mechanism of [Formula: see text]CF cycles. Towards the future [Formula: see text]CF experiments in the high-temperature gas target we have clarified the relationship between the fusion yield and density-temperature curve of adiabatic/shock-wave compression.

Photodissociation processes of a water-oxygen complex cation studied by an ion imaging technique.

Photochemistry of molecular complex ions in the atmosphere affects the composition, density, and growth of chemical species. Photodissociation processes of a mass-selected O2+(H2O) complex ion in the visible and ultraviolet regions were studied by ion imaging experiments and theoretical calculations. At 473 nm excitation, O2+ was the predominant photofragment ion produced. In this O2+ channel, the kinetic energy release was comparable to that estimated using a statistical dissociation model, and the anisotropy parameter was determined to be ß = 1.0 ± 0.1. On the other hand, the H2O+ photofragment ion was mainly produced at 355 nm excitation. The kinetic energy release for the H2O+ channel was large and nonstatistical, and the anisotropy parameter was ß = 1.9 ± 0.2. Theoretically, the 473 and 355 nm excitations were assigned to the B[combining tilde]2A''← X[combining tilde]2A'' and D[combining tilde]2A''← X[combining tilde]2A'' transitions, respectively, both of which were characterized by positive charge transfer from O2 to H2O subunits. To further investigate the dissociation mechanisms, potential energy curves (PECs) and surfaces (PESs) for the O2+(H2O) ion were calculated for the ground and excited states. As a result, the H2O+ channel at 355 nm excitation was explained by rapid dissociation on the repulsive PES of the D[combining tilde] state, while rapid electronic relaxation from the B[combining tilde] to X[combining tilde] state followed by dissociation in the ground state was inferred in the O2+ channel at 473 nm excitation.

Visible photodissociation of the CO2 dimer cation: fast and slow dissociation dynamics in the excited state.

Velocity and angular distributions of photofragment CO2+ ions produced from mass-selected (CO2)2+ at 532 nm excitation were observed in an ion imaging experiment. The velocity distribution was assigned to two components, fast and slow velocity components, which was consistent with the previous study by Bowers et al. The anisotropy parameters of the angular distributions for the fast and slow velocity components were experimentally determined to be ßfast = 1.52 ± 0.14 and ßslow = 0.46 ± 0.10, respectively. In the theoretical approach, potential energy surfaces (PESs) of (CO2)2+ were calculated along two coordinates, the intermolecular distance and mutual orientations of the CO2 monomers. In addition, molecular dynamics simulations were performed. The visible transition of the most stable staggered structure of (CO2)2+ was attributed to C[combining tilde]2Ag ← X[combining tilde]2Bu by an excited state calculation. On the PES of the C[combining tilde] state, a potential well was found in which the two CO2 monomers lay side by side to each other, in addition to a repulsive slope along the intermolecular distance. The results of the simulations confirmed that the fragment CO2+ ions with fast velocity and large anisotropy originated from the rapid dissociation of (CO2)2+ on the repulsive slope. Meanwhile, the fragment CO2+ ions with slow velocity and small anisotropy were expected to emerge from statistical dissociation after large amplitude libration of CO2 molecules which was caused by the potential well in the excited state PES.

Ion Imaging of MgI+ Photofragment in Ultraviolet Photodissociation of Mass-Selected Mg+ICH3 Complex.

We have observed images of MgI+ fragment ions produced in ultraviolet laser photodissociation of mass-selected Mg+ICH3 ions at 266 nm. Split distribution almost perpendicular to the polarization direction of the photolysis laser was observed in the photofragment image. Potential energy curves of Mg+ICH3 were obtained by theoretical calculations. Among these curves, the excited complex ion dissociated along almost repulsive potentials with several avoided crossings, which was connected to MgI+ + CH3. In the ground state of Mg+ICH3, the CH3I was bonded with Mg from the iodine side, and the Mg-I-C bond angle was calculated to be 101.1°. The theoretical results also indicated that the dissociation occurred after the 52A' ← 12A' photoexcitation, where the transition dipole moment was almost parallel to the Mg-I bond axis. The MgI+ and CH3 fragments dissociated each other parallel to the direction connecting those center-of-masses, which was 67° with respect to the transition dipole moment of 52A' ← 12A' photoexcitation. Therefore, the fragment recoil direction was assumed to approach perpendicular tendency against the polarization direction under the fast dissociation process. However, calculated potential energy curves showed a complicated reaction pathway for MgI+ production, including nonadiabatic processes, although the experimental results indicated the fast dissociation reaction.

Development of a linear-type double reflectron for focused imaging of photofragment ions from mass-selected complex ions.

An ion imaging apparatus with a double linear reflectron mass spectrometer has been developed, in order to measure velocity and angular distributions of mass-analyzed fragment ions produced by photodissociation of mass-selected gas phase complex ions. The 1st and the 2nd linear reflectrons were placed facing each other and controlled by high-voltage pulses in order to perform the mass-separation of precursor ions in the 1st reflectron and to observe the focused image of the photofragment ions in the 2nd reflectron. For this purpose, metal meshes were attached on all electrodes in the 1st reflectron, whereas the mesh was attached only on the last electrode in the 2nd reflectron. The performance of this apparatus was evaluated using imaging measurement of Ca+ photofragment ions from photodissociation reaction of Ca+Ar complex ions at 355 nm photoexcitation. The focused ion images were obtained experimentally with the double linear reflectron at the voltages of the reflection electrodes close to the predictions by ion trajectory simulations. The velocity and angular distributions of the produced Ca+ ([Ar] 4p1, 2P3/2) ion were analyzed from the observed images. The binding energy D0 of Ca+Ar in the ground state deduced in the present measurement was consistent with those determined theoretically and by spectroscopic measurements. The anisotropy parameter ß of the transition was evaluated for the first time by this instrument.

Photofragment ion imaging from mass-selected Mg+BrCH3 complex: Dissociation mechanism following photoinduced charge transfer.

We have observed fragment ion images produced by ultraviolet photodissociation of Mg+BrCH3 complex ions using a reflectron time-of-flight mass spectrometer combined with an imaging detector. The BrCH3+ fragment ion was produced after the 266-nm excitation of Mg+BrCH3. In the image of the BrCH3+ ions, a split distribution was observed parallel to the polarization direction of the photolysis laser. In calculated potential energy curves, we found a repulsive potential correlated with a dissociation limit of Mg + BrCH3+: The calculation results indicate that the dissociation and the charge transfer occurred via non-adiabatic process after the 52A' ← 12A' photoexcitation. The obtained energy and angular distributions of BrCH3+ photofragments were consistent with the fast BrCH3+ formation process on the repulsive potential energy curve.