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The radial stability and the irreversible transformation of triple-wall carbon nanotubes (TWCNTs) bundles are investigated at high pressure conditions both experimentally and theoretically (exp. up 72 GPa). The tubes having a mean internal diameter of 0.83 nm and graphite-like intertube distance, show an onset of the radial collapse evidenced by the evolution of optical phonons. The nanotube collapse onset is observed at ∼ 22 GPa completes for the two external tubes at ∼ 29 GPa, however the innermost tube remains stable up to ∼ 37 GPa. Molecular dynamic calculations performed on smaller diameter TWCNTs bundles, as a model system, confirmed the multiple-stage pressure-induced collapse process. An analytical expression for the collapse pressure of carbon nanotubes having an arbitrary number of walls is proposed. Our experiments and modelling show that for pressures beyond ∼ 60 GPa an irreversible structural transformation of TWCNTs takes place. Ex situ transmission electron microscopy characterization on the recovered sample from 72 GPa revealed the mechanical failure of carbon nanotubes which evolve towards ribbon-like structures as corroborated by Raman spectroscopy. Modelling the tubes evolution at high pressure and high temperature showed the formation of new structures ranging from ribbon-like to graphite-like with either different degrees of amorphization or s p 3 interlinking.

International audience; High-pressure resonance Raman experiments were performed on linear carbon chains Cn confined in double-wall carbon nanotubes (Cn@DWCNT). Our results indicate that the frequency of the chain mode undergoes a non-linear decreasing as pressure increases, in agreement with previous studies of the behavior of carbon chains into multi-wall carbon nanotubes. After the pressure cycle, the Cn modes present an irreversible frequency downshift together with an irreversible upshift (downshift) of the RBM modes (G+ band) of the inner tube. These spectral changes are interpreted as evidence of cross-linking between the carbon chain and the wall of the inner tube. Density functional theory (DFT) calculations were performed in order to shed light on the interpretation of the experimental data. The theoretical calculations show a pressure-induced charge transfer from the nanotube to the carbon chain, thus resulting in an increasing of the C≡C bond length, and consequently, a softening frequency of the Cn Raman mode. Furthermore, an irreversible cross-linking between the tube and Cn is observed when the maximum applied pressure is higher than the pressure of radial tube collapse is predicted by modelling, thus supporting the experimental results.

The particle size distribution of radioactive aerosols, which originated from the released radioactive materials from the Fukushima Daiichi nuclear power plant accident, has been observed using the Andersen-type classifier combined with a high volume air sampler. Estimated activity median aerodynamic diameters (AMADs) of 131I-, 134Cs- and 137Cs-aerosols were ranging from 0.56 to 0.60 μm, which were larger than that of 7Be-aerosols existing as an aerosol including cosmogenic radionuclide, about 0.2 μm.

From a series of Mossbauer measurements performed on a single crystal of FePSe3, we have observed the effect of electromagnetically induced transparency (EIT) in a second nuclear system, after a first experiment using the mineral siderite FeCO3. When the condition of nuclear level crossing was fulfilled, an obvious deficit in absorption was observed at the point of level crossing. This reduced absorption cannot be ascribed to saturation effects because of the specific geometry of the measurement. We conclude that the observed deficit in absorption is due to coherence and interference effects.

The vibrational properties of double-walled carbon nanotubes (DWNTs) is investigated by high-pressure resonance Raman scattering up to 30 GPa in two different pressure-transmitting media (PTM): paraffin oil and NaCl. The protection effect on the outer tube during compression is verified .The collapse of DWNTs is experimentally observed for the first time, showing to be two-step: the onset of the outer 1.56 nm diameter tube collapse at ∼21 GPa is followed by the collapse of the inner 0.86 nm diameter tube at a higher pressure of ∼25 GPa. This observation is supported by calculations. We show that filling a tube with another tube leads to a pressure stabilization against collapse, in strong opposition to what is observed when filling a tube with fullerenes or iodine. The collapse pressure in DWNTs appears to follow a 1/dtav3 law, where dtav is the average diameter from the inner and outer tubes, in agreement with predictions [Yang, X.;Appl. Phys. Lett. 2006, 89, 113101]. Contrary to SWNTs and peapods, for D...

We present a high temperature heat treatment study of CVD-grown graphene nanoribbons annealed up to 2800 °C, demonstrating a progressive annihilation of lattice defects as the heat treatment temperature is raised. Starting at 1500 °C, single and multiple loop formation were observed on the ribbons edges as the temperature was increased. The structural changes of the samples are documented by X-ray diffraction, Raman spectroscopy, TGA, SEM, and HRTEM. This work indicates that nanoribbon annealing eventually leads to defect-free samples, through graphitization and edge loop formation. The annealed material exhibits structural differences that could be tailored for a variety of specific applications.

Double-wall carbon nanotubes (DWCNTs) grown directly via a CVD method and DWCNTs produced by annealing C 60 and ferrocene filled single-wall carbon nanotubes were studied with X-ray, diffraction (XRD) and Raman spectroscopy. The samples showed the typical XRD patterns of hexagonally bundled tubes. The frequencies and linewidths of the inner tube radial breathing (RBMS) were (within experimental precision) equal in all three samples only the intensities differed. Finally, all samples showed the typical clustering of the inner tube RBMs due to the distribution of inner-outer tube pairs. The only difference was the population of specific inner-outer tube pairs where the CVD and ferrocene based DWCNTs were rather similar and both diffared from the C 60 based DWCNTs.

The concentration of 7Be in surface air at Nagano City has been measured during the period from August 2000 to March 2005. The average monthly concentrations of 7Be in surface air were in the range of 3.3–14 mBq/m3 with pronounced two peaks in spring and autumn. It took 30–40 hours to recover the 7Be concentrations observed before, once 7Be was washed out by wet precipitations. For a pronounced increase in the concentrations of 7Be found in winter, a low-pressure trough coming close to the Japanese Islands with high concentrations of 7Be is responsible under the characteristic distribution of atmospheric pressure around the Japanese Islands.

We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (

Hydrophilic endohedral 133Xe-fullerenols, [133Xe@C60(OH)xand 133Xe@C70(OH)x], were synthesized from hydrophobic endohedral 133Xe-fullerenes. The yield of endohedral 133Xe-fullerenols extracted in water was about 40% and 23% for C60and C70, respectively. The products stored in 0.9% NaCl solution at 20 °C were stable enough to be used in nuclear medicine.

We have observed the effect of electromagnetically induced transparency (EIT) in a nuclear system. A series of Mossbauer measurements was performed on a single crystal of natural FeCO3. When the condition of nuclear level crossing is fulfilled, a clear reduction in absorption or transparency is seen at the point of level crossing. This reduced absorption cannot be ascribed to saturation effects because of the specific geometry of the experiment. We present an explanation in terms of level mixing by a small non-axial component of the electric field gradient. It can be shown that such a scheme is equivalent, at least in principle, with the schemes considered for EIT in quantum optics.

The production yield of endohedral 133 Xe-fullerene by ion implantation has been studied by taking advantage of the radioactivity of 133 Xe. Fullerene targets, which were produced by vacuum evaporation of C 60 or C 70 on a Ni backing, were bombarded with 30–38 keV 133 Xe ions by using an isotope separator at doses ranging from 1 × 10 12 to 1 × 10 14 cm −2 . The production yield of endohedral 133 Xe-fullerene was determined by an high performance liquid chromatography analysis following the dissolution of the targets in o -dichlorobenzene. It was found that the production yield decreased with increasing dose and incident energy, and the production yield of 133 Xe@C 70 was higher than that of 133 Xe@C 60 for the same dose and incident energy. Those production yields are discussed in connection with amorphization of fullerene molecules in collisions with 133 Xe ions.

Ion implantation was applied to the production of endohedral 133Xe-fullerene. Using an isotope separator, 133Xe ions were implanted into a fullerene target of C60 and C70 produced by vacuum evaporation on a Ni backing. An HPLC analysis following dissolution of the fullerene targets in o-dichlorobenzene corroborated the formation of 133Xe@C60 and 133Xe@C70, showing a strong correlation between C60/C70 and 133Xe. The observed tailing following 133Xe peaks in the elution curves suggests a possibility of the isolation of endohedral 133Xe-fullerene from empty fullerene.

A significant reduction of absorption of single gamma photons has been observed using the Mossbauer spectra of 57Fe in a FeCO3 crystal. The absorption deficit can be ascribed to partially destructive interference for absorption because of two indistinguishable absorption paths. The necessary coherence is created by means of level mixing produced by a suitable combination of a magnetic dipole and electric quadrupole interaction.

The seasonal variation of 222Rn concentrations in the air of tunnels constructed during World War II at Nagano City has been investigated. The determination of 222Rn concentrations in tunnel air was performed using a solid-state nuclear track detector technique. The monthly radon concentrations changed smoothly, decreasing towards winter and increasing towards summer, and it was found that the concentrations strongly correlate with the temperature difference between the inside and the outside of the tunnel. In the innermost areas of the tunnel, the maximum concentration was observed in July, its value being about 6500 Bq m (-3). The concentrations of radon in the tunnel air decrease exponentially towards the openings of the tunnel, which indicates that the radon concentration in the tunnel is basically governed by diffusion and mixing of radon gas with air. These observations lead to the conclusion that the seasonal variation of the radon concentration in the tunnel air is mainly caused by a convection current due to a stack effect induced by the temperature difference between the tunnel air and the outside air.

The pion capture process in gas mixtures containing hydrogen was studied by measuring pionic X rays and π0 decays. A little difference in pion transfer process was found between the H2+D2 and H2O+D2O systems. Pressure-dependence of the transfer rates was also revealed in the CH4+Ar system by the measurements at several gas pressures. The mechanism of the pion transfer process was discussed based on a comparison between transfer parameters in the gas and liquid phases.

Positron annihilation lifetime (PAL) spectroscopy has been applied to polyvinyl alcohol (PVA) films prepared with commercially available PVA or from polyvinyl acetate (PVAc). The variation of lifetimes of ortho-positronium (o-Ps) formed in the films was investigated as a function of the degrees of polymerization, saponification, or crystallinity. For the fully saponificated samples, no dependence was found to exist on the degrees of polymerization or of crystallinity. For the partially saponificated samples, however, the dependence of the o-Ps lifetime on the degree of saponification was clearly observed, and this is explained by both the formation of hydrogen bonds among the polymer chains and the existence of acetyl group strongly inhibiting the hydrogen-bond formation due to steric hindrance.

Mossbauer effect measurements for the 81 keV transition in133Cs have been performed with133Xe-implanted sources prepared by means of an electromagnetic isotope separator. The behavior of the isomer shift of133Cs impurities was studied in various metals. Some correlations were found between measured isomer shifts and electronic properties of the host materials, and they show that the host conduction electrons have an important role in the determination of the isomer shift in metals.

Pionic X-rays and π0 decays were measured for gas mixtures of H2/D2/CH4+SF6/Ar and the individual pure gases. Chemical effects on the pion transfer process from pionic hydrogen to other atoms were revealed by the pionic X-ray spectrum. The changes of the intensity patterns of pionic X-rays were compared with the predictions by a cascade calculation taking the transfer process into account. The mechanism of pion transfer process was discussed based on the results for gas phase and the previous ones for liquid phase.

Annihilation γ-rays of π0 and pionic X-rays were measured in the gas mixtures of H2+Z and CH4+Z systems (Z=He, Ne, Ar and Kr). Pion capture probability of hydrogen atom was obtained from the annihilation γ-ray counts and the capture probability of Z atom was obtained from the pionic X-ray intensities. Transfer rates were determined from the data based on a combined large mesomolecular model. The transfer rates obtained were smaller than the systematics of the Russian group. Difference in the transfer rate between the gas and the liquid phases was found by a comparison of the present results with our previous ones.

In situ Raman scattering measurements of pristine and fluorinated double-walled carbon nanotube samples under high pressure have been performed. Due to the mechanical shielding effect of the outer tubes of the double-walls to the applied pressure, the Raman scattering lines from the inner tubes of both samples remained to be observed even at high pressure.

Endohedral 133Xe-higher fullerenes (133Xe@C76 and 133Xe@C84) were produced by implantation of 133Xe ions using an isotope separator. A high performance liquid chromatography (HPLC) analysis showed that the peak of endohedral 133Xe-higher fullerenes shifted backward from that of empty fullerenes, suggesting a possibility of the separation of endohedral 133Xe-higher fullerenes from empty fullerenes. The yields of endohedral 133Xe-fullerenes were in the order of 133Xe@C76

A simple retardation system has been constructed in order to realize low-energy ion-implantations using an electro-magnetic isotope separator (EMIS). Mass-separated ions are decelerated through a smoothly increasing potential which is produced in a box which is coated inside with a highly resistive film. To test the performance of the system, 133Xe ions retarded from 20 keV by a maximum of 15 keV were implanted into a nickel foil covered by a thin copper layer, and their mean range in copper was determined with a radiochemical technique. The observed ranges are in good agreement with theoretical prediction, which manifests that the system works well as expected.

The fascinating characteristic of carbon atoms to create multiple orbital hybridizations (e.g., sp, sp2, or sp3) provides the possibility to synthesize one-, two-, and three-dimensional carbon nano ...

Atomic capture probabilities of negative pions in some metal hydrides were measured. The capture by a hydrogen atom was detected by means of a pair of the annihilation γ rays of π0 which had been produced by the charge-exchange reaction of π− with the capturing hydrogen nucleus (proton). This method ensures a high sensitivity and reliability of the measurements. The probabilities obtained were in agreement with previous measurements except for palladium hydride, which showed a much smaller probability than that given in the literature. The atomic capture of π− is well described in the framework of the large mesic molecular model, in which the proportionality constant reflects the chemical states of the capturing atoms and also the neighboring ones.

Carbonaceous materials have been shown to graphitize up to different levels upon heat treatment, depending on the characteristics of their defects and the temperature reached during the heat treatment. In the literature there are reports on the annealing of materials, such as thin carbon films, graphite fibers, polyparaphenylene (PPP)-basedcarbons, cup-stacked carbon nanotubes, diamond-like carbon films, and more recently graphitic nanoribbons and flakes of highly oriented pyrolytic graphite (HOPG). The general behavior upon heat treatment is an increase of sp hybridization of the carbon atoms, an enlargement of the in-plane crystallite size (2D order of the

Pristine and molybdenum filled double walled carbon nanotubes (DWNTs) suspended in D2O show excellent ultrafast optical switching properties investigated through femtosecond Z-scan and degenerate pump-probe method using 50 fs pulses with central photon energy of 1.57 eV. For pristine-DWNT, the two photon absorption coefficient, beta and nonlinear refraction coefficient, n2 are 4.9×10−8 cm/W, and 9.5×10−11 cm2/W, respectively, which yield one photon figure of merit, W=133 and two photon figure of merit, T=0.4. The degenerate pump-probe measurements show strong photoinduced bleaching with biexponential decay with time constants ~150 and 600 fs. ©2009 American Institute of Physics

In this work, we performed a detailed study of the Raman spectra of double-wall carbon nanotube (DWNT) bucky paper samples. The effects of ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ doping on the electronic and vibrational properties of the DWNTs are analyzed and compared to the corresponding effects on single-wall carbon nanotubes (SWNTs). Analysis of the radial breathing mode (RBM) Raman spectra indicates that the resonance condition for the outer wall nanotubes and the SWNTs are almost the same, indicating that the effect of the inner-outer wall interaction on the transition energies of the outer walls is weak compared to the width of the resonance window for the RBM peaks. The effect of ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ on the RBM frequencies of the outer wall of the DWNTs is stronger for larger diameter nanotubes. In the case of the inner walls, only the metallic nanotubes were affected by the acid treatment, while the RBM peaks for the inner semiconducting nanotubes remained almost unchanged in both frequency and intensity. The ${G}^{+}$ band was seen to upshift in frequency with ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ doping for both DWNTs and SWNTs. However, the effect of the acid treatment on the ${G}^{\ensuremath{-}}$ band frequency for DWNTs was opposite to that of SWNTs in the $2.05--2.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ range, for which the acid treatment causes a ${\ensuremath{\omega}}_{{G}^{\ensuremath{-}}}$ upshift for SWNTs and a downshift for DWNTs. The ${G}^{\ensuremath{'}}$ band line shape of the DWNTs is explained in terms of four contributions from different components which are in resonance with the laser excitation. Two of these peaks are more related to the inner wall nanotube while the other two are more related to the outer wall.

Article, Physical Review B. 73(23):235413 (2006)

We study the resonance behavior of the unusual Raman feature known as the coalescence-inducing mode CIM, observed at 1850 cm^-1, in samples of double-wall carbon nanotubes annealed at high temperatures. Resonance Raman spectra taken with different laser energies show that the intensity of the CIM band exhibits a maximum around 2.20 eV. By comparing the resonance Raman experimental results with first-principles calculations for the vibrational frequency and the energy gap, we propose that the CIM feature is associated with short carbon chains with an odd number of atoms, interconnecting the nanotube surfaces., Article, Physical Review B. 73(19):193408 (2006)

This study presents experimental results on quantum interference phenomena observed in gamma-optics for the first time. The idea is to employ the interference phenomena typical for electromagnetically induced transparency found in quantum optics.

A significant reduction of absorption for single gamma photons has been experimentally observed by studying Mössbauer spectra of 57Fe in a FeCO3 crystal. The experimental results have been explained in terms of a quantum interference effect involving nuclear level anticrossing due to the presence of a combined magnetic dipole and electric quadrupole interaction., Journal Article, info:eu-repo/semantics/published

The survey of [sup 222]Rn concentration in the air of tunnels constructed during World War II has been performed using a solid-state nuclear track detector technique. For the practical application of this technique t the determination of [sup 222]Rn concentrations in air, some basic properties were experimentally examined on the cellulose nitrate film, Kodak LR 115 type II. The calibration coefficient of the cellulose nitrate film used is determined from a correlation between the [sup 222]Rn concentration in air and the observed number of perforated etched tracks for widespread radon concentrations. The slope of the linear relationship observed yields a calibration coefficient of (0.00209 [+-] 0.00018) tracks cm[sup [minus]2] (Bq m[sup [minus]3] h)[sup [minus]1]. From the survey of [sup 222]Rn concentration in the air of tunnels, the concentration of several thousand Bq m[sup [minus]3] was observed at the inner most area of the tunnel, and the seasonal variation was clearly observed. The exponential distribution of radon concentration as a function of distance from the openings of the tunnel suggests that the radon concentration in the tunnel is basically governed by diffusion and mixing of radon gas with air.

By using a simple air filter technique, the fractions of aerosol and gaseous components were measured for individual nuclides formed in the air of a high energy accelerator tunnel. The size distributions for 7Be, 24Na and 38S aerosols were also measured by using a diffusion battery and found to be log-normal with a geometric mean radius of about 28 nm; the radioactive aerosol formation was adequately explained by simple attachment reactions.

The production method of high specific 119 m Sn was studied by using the reaction of alpha particles with enriched cadmium. The excitation function for the 116 Cd( α , n ) 119 m Sn reaction and its thick-target yields were investigated with the stacked foil technique at the incident alpha particle energy of 25 MeV. When the incident alpha particle energy of 20 MeV was chosen, 0.1 μCi/μA·h of 119 m Sn could be produced at the end of bombardment. The procedure for the carrier-free separation of tin activity from the cadmium target and the copper backing by coprecipitation, organic solvent extraction and anion exchange is described.

The optimum irradiation conditions were investigated for the production of 61Cu and 62Zn by alpha and 3He particle bombardment of natural nickel. Formation cross sections and thick-target yields were obtained for reaction products in the energy range of 10 to 40 MeV. For the production of 61Cu and 62Zn, the alpha particle bombardment was found superior to the 3He particle bombardment in so far as the yield was concerned. When the incident alpha energy of 21 MeV was chosen, after 2.4 hours of cooling, 2.1 mCi/muA.h of 61Cu could be produced with less than 1% of 60Cu contamination. For the production of 62Zn, when the incident alpha energy of 35 MeV and the target thickness of 57 mg /cm2 were chosen, 97.5 muCi/muA.h of 62Zn could be produced. Radiochemical purity of 62Zn was the highest at 12 hours after the end of bombardment.

Radioactive119Sb was implanted into 6 different host matrices, Y, Β-Sn, Pt, Au, Pb and CaSnO3, and internal-conversion and Mossbauer spectra were measured for the same samples. The isomer-shift calibration constant of the Mossbauer transition of119Sn was derived as δR/R=(0.87±0.25)×10−4 for R=1.2×A1/3 fm or, δ〈r2〉=(3.6±1.0)×10−3 fm2.

Mean ranges of 119Sb in tin and 125I in copper have been measured for the energy region of 10 keV to 60 keV by using the samples prepared by ion-implantation of these nuclides into vacuum-evaporated layers of metals. The observed ranges are in good agreement with those predicted by the theory of Lindhard et al. for 0.1 > ϵ > 0.02, but they are slightly smaller for 0.02 > ϵ > 0.01 in terms of the dimensionless energy ϵ.

The 7Be, produced by nuclear spallation reactions in the air of high energy accelerator tunnels, is present in the form of an aerosol. The size distribution of the 7Be-aerosols was measured with a parallel plate diffusion battery and was found to be a log-normal distribution with a geometric mean radii of 27 nm and a logarithmic standard deviation of 0.36. The formation of the 7Be-aerosol is adequately explained by the attachment of 7Be to non-radioactive aerosols containing sulfates, which are produced by radiation induced oxidation reactions of SO2 present in the air.

Radioactive119Sb was implanted into six host matrices (CaSnO3, Pt, Y, Au,Β-Sn, Pb) and internal conversion electrons of the 23.87 keV transition in119Sn were measured with an iron-free magnetic spectrometer as well as Mossbauer spectra. In the analysis of the conversion spectra of outermost electrons, the overlapping K-LM Auger lines were subtracted using the Auger spectrum of tin measured with another source of117mSn, and the shake-off effect accompanying the conversion process was considered. From the correlation between the Mossbauer isomer shifts and the intensity ratios of O-shell to N1-shell conversion electrons, the change of the nuclear charge radius of the 23.87 keV transition of119Sn was deduced to be δR/R=(0.87 ± 0.25) × 10−4 for a uniform charge distribution ofR= 1.2 ×A1/3 fm or, equivalently, δ 〈r2>—=(3.6 ± 1.0) ×10−3 fm2.

The optimum conditions were investigated for the production of 61 Cu by the alpha-particle bombardment of natural nickel. Formation cross-sections and thick-target yields were obtained for most of the reaction products in the energy range from 10 to 40 MeV. When the incident alpha energy of 21 MeV was chosen, after 2 hr of cooling 2.1 mCi/μA·hr of 61 Cu could be produced with a 60 Cu contamination of less than 1%. The other reaction products were also analyzed in terms of the corresponding nuclear reactions, and excitation functions were deduced for the 58 Ni and 60 Ni target nuclides.

From a relation between the 5s (valence) electron contact density and the Mossbauer isomer shift, the contact density and the number of 5s electrons of Sn in \-Sn were evaluated to be 72.3±4.1 a.u. and 1.87±0.13, respectively, where the renormalization of solid-state effect was considered.