Polymer films as indicator of hydrogen spillover through the gas phase

Films of poly-ε-caproamide (PA), polyethylene (PE), and polyethylene terephthalate (PET) were used for detection of hydrogen spillover through the gas phase. The hydrogen used in the experiments contained tritium activated by two procedures (W wire, 2000 K; 5% Pd/C, 335 K). The radioactivity of the films was recorded by classical and digital autoradiography and by liquid scintillation counting. Under the action of “hot” atoms generated on a W wire, the maximal specific radioactivity of the films, equal to 420, 415, and 330 mCi cm^–2 for PA, PE, and PET, respectively, was reached in 100 s. Preliminary thermalization of the atoms to a temperature of 77–335 K influenced the decrease in the film radioactivity differently. The effective activation energy of the reaction in the range 298–318 K was 21, 30, and 12.5 kJ mol–1 for PA. PE, and PET, respectively. Under the conditions of heating 5% Pd/C to 335 K for 25 min, the radioactivity of PA, PE, and PET was 1.6, 0.05, and 0.15 μCi cm^–2, respectively. The revealed difference in the radioactivity of the films suggests different mechanisms of the interaction of tritium with organic molecules at different activation methods.     

声致发光气泡中原子碰撞发光机制

文章导出一种由两个中性的惰性气体原子之间的碰撞引起的电四极辐射几率,对于热平衡的惰性气体系统,推导出由碰撞引起的总辐射能量的公式（单位体积,在给定波长的每单位波长）,考虑到气体的吸收和周围环境水的折射,用此公式拟合纯氙和纯氨的单气泡声致发光的实验光谱,拟合温度大约为5,000K,结果令人满意。     

Monitoring a Flow of “Hot” Tritium Atoms in the Course of Thermal Activation

The possibility of measuring a flow of reactive tritium atoms falling on a target during thermal activation using polyethylene (PE) films was studied. Procedures were developed for pretreatment of PE films before experiment, their subsequent treatment, and radioactivity measurements. The distribution of the flow of tritium atoms in a common reactor as influenced by various modes of atomizer arrangement and different experimental conditions was studied with PE films. The rate of formation of the labeled compound was maximal when the product of the tritium pressure in the system (Pa) by the distance from the atomizer to the target (cm) was 2.     

Nonequilibrium processes in reactions of hot tritium atoms with cooled solid targets. Influence of the atomizer temperature on formation of labeled substances

A system consisting of a cold target and “hot” atoms generated by dissociation of tritium on a tungsten wire was studied with the aim to determine conditions for preparing tritium-labeled organic compounds with the maximal radiochemical yield. The influence of the atomizer temperature on the result of the reaction of tritium atoms with amino acids and tetraalkylammonium bromides was studied; homological series of the substrates were examined with the aim to evaluate the contributions of functional groups and hydrocarbon tail to the processes occurring in the target. The dependence of the yield of the labeled parent compound on the atomizer temperature varied in the range 1600–2000 K was determined. The rates of decarboxylation and deamination sharply grew with increasing temperature of the tungsten wire. The highest yield of labeled amino acids was attained at an atomizer temperature of 1800–1900 K, and at higher temperature their yield decreased. The difference between the activation energies of the elimination of the carboxy and amino groups and of the isotope exchange of hydrogen for tritium in the C-H bond appeared to be 93 and 59 kJ mol^?1, respectively. For alkyltrimethylammonium bromides with the alkyl radicals C₁₂H₂₅, C₁₄H₂₉, and C₁₆H₃₃, the yield of the labeled parent compound reached 80–90% and was virtually independent of the atomizer temperature. The capability of tritium atoms to penetrate into the targets was evaluated. For the exponential model of the attenuation of the flow of tritium atoms inside the target, the attenuation factor for freeze-dried amino acids and alkyltrimethylammonium bromides as targets was 1.8 nm^?1.     

Comparison of the Results of Prediction of Transport Coefficients of Sodium Vapor with Experimental Data

The interatomic interaction potentials derived from new precision spectroscopic data are used to calculate averaged collision cross sections of two sodium atoms. The coefficients of viscosity and thermal conductivity of sodium vapor at temperatures from 700 to 2500 K and pressures from those corresponding to monatomic rarefied gas to the saturation curve (but not exceeding 1 MPa) are predicted. The prediction results are compared with the available experimental data about the transport coefficients of sodium vapor. Possible reasons for observed systematic discrepancy are discussed.     

Investigations of ion induced re-emission using the thermal desorption technique

The technique of thermal desorption of previously trapped inert gas atoms from polycrystalline tungsten has been used to continue our study of the ion-induced re-emission process. It is shown that preferential reduction in gas atom densities from different trapping centres below the target surface may be effected by bombardment with a suitable secondary ion type and energy. Results fit our model which suggests a maximum in the gas sputtering process when the collision cascade produced by the secondary ion overlaps the range distribution of the primary specie.     

A tritium gas-handling system for muon catalyzed fusion research at the RIKEN-RAL Muon Facility

A tritium gas-handling system has been constructed to produce a high-purity D–T target gas for precise measurements of the -sticking probability in the muon catalyzed fusion cycle at the RIKEN-RAL Muon Facility in the UK. At the experiment site, the system enables us to purify the D–T target gas by removing the ³He component, to adjust the D/T gas mixing ratio and to measure the hydrogen isotope components. The system is designed to handle D–T gas with a negative pressure; the total volume is 1.1 liter. The whole performance has been confirmed, and tritium gas with an inventory of 56 TBq (1500 Ci) has been operated in the system. We have completed a series of muon catalyzed fusion experiments at tritium concentrations of 99%, 70%, 60%, 50%, 40%, 28%, 20% and 10%, allowing a more precise determination of the -sticking probability.     

A Comparative Study of the Reactions of Thermally Activated Tritium with Sugars and Diazines and of Solid-Phase Catalytic Hydrogenation of These Compounds with Tritium

The feasibility of the labeling procedure involving thermal activation (TA) of tritium was examined with the substrates that are commonly labeled by solid-phase catalytic hydrogenation (SCH) with tritium. Comparative characteristics of SCH and TA as procedures for tritium labeling of sugars and diazines were obtained. These two methods ensure comparable rates of tritium incorporation into purine and pyrimidine bases. The SCH allows preparation of tritium-labeled compounds with the maximum possible molar radioactivity. The molar radioactivity of the same compounds labeled using TA did not exceed 37 TBq mol⁻¹, because only a small fraction of the substrate could react with atomic tritium. Longer reaction times and increased amounts of tritium taken into the reaction resulted in stronger degradation of the substrates. On the assumption that the reactive tritium atoms penetrate into the target to a depth of 0.5 nm, the actual specific radioactivity of the labeled compound in the zone accessible for atomic tritium reaches 0.2–2 PBq mol⁻¹. Ways are suggested to increase the molar radioactivity of compounds labeled using thermal activation of tritium.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 284–288.Original Russian Text Copyright © 2005 by Sidorov, Badun, Baitova, Baitov, Platoshina, Myasoedov, Fedoseev.     

Kinetic Features of Labeled Product Formation under the Action of Atomic Tritium on Frozen Solutions and Lyophilically Dried Mixtures of Amino Acids

Formation of labeled amino acids in reactions of their lyophilically dried mixtures and frozen solutions with atomic tritium generated by thermal activation was studied in relation to the reaction time and pressure of molecular tritium. The molar radioactivity of the amino acids is a complex function of the reaction time. At short reaction times, the radioactivity of the amino acid depends primarily on its concentration in the near-surface layer. At long labeling times, in the case of surfactants, the yield of labeled products can decrease owing to side reactions. The influence of water on the rate of formation of labeled products and its role in thermalization of hot tritium atoms in the target is discussed. An increase in the tritium pressure in the system increases the initial radioactivity of the target but affects the yield of the labeled amino acids insignificantly. Recommendations are formulated on optimizing the conditions for labeling of biological macromolecules in their structural studies by tritium planigraphy.     

Permeability of Lipid Membranes for Atomic Tritium or Atom “Slipping” Effect and Its Role in Tritium Planigraphy

The depth of penetration of tritium atoms capable of isotope substitution, generated by thermal dissociation on a tungsten wire (thermal activation of tritium), into a solid target is considered. On the basis of calculations used in the theory of recoil atom stopping, with a lipid bilayer as example, the possibility of penetration of reactive atoms to a depth of up to 5 nm was demonstrated. This result is nicely consistent with the available experimental data. The possibility of slipping of atomic tritium, without loss of its reactivity, into cavities with a decreased electron density was suggested. This phenomenon should be taken into account when interpreting the results of studying biological macromolecules and their complexes by tritium planigraphy.     

Efficiency of isotope exchange between sodium 4-phenylbenzoate and activated tritium

The efficiency of the protium–tritium isotope exchange in the sodium 4-phenylbenzoate (PBNa) molecule on activating the reaction on a tungsten filament at 1940 K (target temperature 77 and 295 K) and on heating the substrate supported on 5% Pd/C in the presence of gaseous tritium is compared. It is shown that the reaction mechanism is laregly determined by the properties of the material on which this reaction occurs and not only by the method of generation of activated tritium species. In the reaction of tritium atom with PBNa deposited on glass walls of the reaction vessel, the isotope substitution of tritium for protium occurred by the radical mechanism, leading to the formation of [³H]PBNa and hydrogenation products. It is assumed that the spillover of tritium atom over the support (carbon) surface is accompanied by polarization of the electronic shell and formation of the cluster (^{3 +})(\(\bar e\)), which leads to changes in the composition of the reaction products. The combined treatment of PBNa on 5% Pd/C allows estimation of the concentration of clusters on the carbon surface, which reaches 10.9 particles per 100 nm² (9.2 nm² per cluster).     

Transport of sputtered atoms investigated by Monte Carlo method

Increasing attention has been paid to the sputtering process as a tool to deposit films and to the study of the interaction between the film properties and the deposition parameters. It is obvious that the energy and direction of these particles arriving at the substrate is in close relation with the transport process from the target to the substrate. This work deals with the computer simulation of the sputtered Ag atoms trajectories through the background gas in a diode-sputtering configuration. For that, we have developed a numerical model to simulate the transport process. We followed the three-dimensional trajectory of each sputtered atom separately and calculated the scattering angle and the energy loss if a collision took place. A statistical method, Monte Carlo simulations is used. The model predicts the flux of Ag atoms arriving at the substrate, their energies and angular distribution. The dependence of the deposition rates of Ag atoms on the gas pressure and the distance between target to substrate were investigated.     

Comparative Study of Reaction of Atomic Tritium with Glucosamine and Amino Acids

Reaction of amino acids (glycine and serine) and amino sugar (glucosamine) with atomic tritium generated by thermal dissociation of molecular tritium on a tungsten filament was studied. A frozen aqueous solutions and a freeze-dried mixture of these compounds was bombarded with tritium atoms is a special vacuum unit. The relative yield of the labeled compounds was determined as influenced by the reaction conditions (residual pressure in the system and bombardment time) and target type (frozen solution and freeze-dried mixture). Formation of labeled products is almost independent of the tritium pressure. The ratio of the formation rates of labeled serine and glycine in the frozen solution and freeze-dried mixture bombarded with atomic tritium for 45–270 s was 1.66±0.15 and 1.44±0.13, respectively. At shorter reaction time (15 s), the ratio increases to 3.5±0.2 and 2.0±0.4, respectively. The formation rate of [³H]glucosamine in the mixture is higher at a shorter bombardment time. The radioactivity ratio of labeled glucosamine and glycine formed in frozen solutions and freeze-dried mixture in 15 s was 26.0±2.3 and 6.8±0.6, respectively. At longer reaction time, the relative yield of [³H]glucosamine sharply decreases owing to stronger radiolysis of labeled glucosamine on exposure to tritium beam.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 281–283.Original Russian Text Copyright © 2005 by Badun, Ksenofontov, Lukashina, Pozdnyakova, Fedoseev.     

Numerical estimates for energy of sputtered target atoms and reflected Ar neutrals in sputter processes

During the sputtering process in Ar gas, the sputtered target atoms and the reflected Ar neutrals from the target have much higher energy than the background gas. In this study, the Thompson distribution and an updated Meyer model based on the elastic energy transfer between two colliding particles were used to obtain energy distributions and average energies for the sputtered metal atoms and the reflected Ar neutrals. An energy dependent elastic collision cross section was incorporated into Meyer’s model and a thermalization criterion based on power balance was used. Under typical sputtering conditions (0.5 mTorr and 1000 K Ar, 400 eV incident Ar ion), the model predictions indicate that for Cu, Ti and Ta targets, the sputtered metal atoms have initial average energies from 15 to 22 eV and thermalize with the background Ar gas between 10 and 20 collisions. The reflected Ar neutrals thermalize after about 10 collisions. Depending on the number of collisions, the energy dependent mean free path values of the sputtered metal atoms range from 300 to 100 cm while the mean free path values for the reflected Ar neutrals range from 200 to 100 cm.     

Thermodynamic Calculation of the Characteristics of Metal Thermionic Emission

The thermodynamic equilibria of the “Fermi–Dirac gas–Maxwell gas–Boltzmann gas” and “metal–saturated vapor” systems are considered (with allowance for charged particles). It is shown that the work function of a metal at 0 K is equal to the Mulliken electronegativity of its atoms. For the latter case, it is proposed to take into account the relationship between the work-function thermal coefficient and the thermodynamic functions of positive and negative metal ions.     

Preparation of tritium-labeled modified single-walled carbon nanotubes for pharmacokinetic studies

Tritium was introduced by the thermal activation method into samples of single-walled carbon nanotubes modified with diaminotriethylene glycol. Chemical linking of the modifier considerably increased the specific radioactivity of the product. The maximal specific radioactivity was reached when “hot” (2000 K) tritium atoms acted on targets of modified nanotubes kept at 295 K. The main pharmacokinetic parameters of tritium-labeled modified carbon nanotubes upon intravenous administration into mongrel rats chosen as a model were determined.     

The influence of deuterium exposures on subsequent outgassing rate of an UHV system

The accuracy of results in experiments where a well-processed UHV system is exposed to hydrogen depends on the hydrogen absorption rate and kinetics of subsequent spontaneous release from the system itself. In experiments to date, the sensitivity required to detect very low rates has been achieved only when tritium has been used as a tracer gas. Unfortunately, tritiated water from the surface prevails among released gas species which is not expected for well-outgassed surfaces. In the present studies, UHV system behaviour at 303 K during three deuterium exposures of duration 92 and 72 h at an initial pressure of 1 mbar was explored. The rate of decrease of pressure was constant during the whole of these periods as monitored by non-ionizing vacuum gauges. It corresponded to an effective sticking probability of the order of 1×10^-12 and resulted in absorption of 5×10¹⁴ D atoms/cm². The release kinetics were observed for several days starting immediately after deuterium had been pumped from the system. Initially, the deuterium release rate exceeded the background hydrogen outgassing by more than three orders of magnitude. These results demonstrate that extremely high sensitivity for deuterium absorption and release can be achieved with a precise pressure measuring technique otherwise attributed exclusively to tritium scintillation methods.     

Scaling of the L-vacancy-production cross section at kiloelectronvolt-ion collisions

A method is proposed for determining the vacancy-production probability from the dependence of the emission cross section of Auger-electrons or characteristic radiation on the collision energy. Based on the generalization of the existing experimental data on the collisions of atomic particles in gas and solid phases, a universal character of the dependence of the vacancy production probability on the closest approach distance is established for the first time. Scaling is proposed that makes it possible to calculate an L-vacancyproduction cross section from the universal dependence.     

Thermal Expansion and Isothermal Compressibility of TlGaSe2

The thermal expansion and isothermal compressibility of TlGaSe₂were measured from 77 to 300 K. The results indicated a second-order phase transition around 110 K. The experimental data were used to calculate the Debye characteristic temperature, rms atomic displacement, and difference in the specific heats at constant pressure and volume.     

In-situ optical analysis of the gas phase during the formation of carbon nanotubes

A reactor has been developed at ONERA to investigate the gas phase during carbon nanotube formation by laser-induced fluorescence (LIF), Laser-induced incandescence (LII), coherent anti-Stokes Raman Scattering (CARS), and emission spectroscopy. Continuous vaporization is achieved with a continuous wave CO2 laser. Optimized conditions are used for single-walled nanotube growth, that is, a graphite target doped with 2 atom % Ni and 2 atom % Co, helium as buffer gas at a flow rate of 50 ml/s, and a pressure of 300 hPa. Temperature profiles are measured by CARS on H2, and soot images are obtained by LII in the hot carbonaceous flow. LIF and spontaneous emission of the C2 radical and Ni and Co atoms are presented. Spectral investigations are conducted at 3100 and 3200 K to have an optimized pair of excitation/detection wavelengths. Spatial investigations of the relative concentrations in the hot carbonaceous flow are performed up to 3500 K. The concentrations are measured as a function of target temperature. Two regimes of vaporization are observed. Vaporization is slow up to 3350 K and becomes much faster above this temperature. The fast regime in the 3350-3500 K range corresponds to the observed spatial extent of the metal vapors region. At 3500 K, the C2 profiles obtained with and without catalysts are very different as a result of carbon coalescence as well as carbon dissolution into the metal nanoparticles when these are present in the gas phase. The shape of the C2 profile can be related to nanotube formation and growth at a target temperature of 3500 K.