Quantitative analysis of deuterium using laser-induced plasma at low pressure of helium

It was proved that the analysis of deuterium can be conducted using laser-induced plasma spectroscopy. By selecting the appropriate surrounding gas, its pressure, and gating time of the detection system, it was shown that the emission lines of both hydrogen (H(alpha)) and deuterium (D(alpha)), separated by only 0.179 nm, can be fully resolved. A linear calibration curve was also obtained, indicating that this technique has the potential for quantitative analysis of deuterium. The minimum detection limit achieved in this stage of research was estimated to be 50 ppm. We have also shown that this technique can be used as a simple and rapid method for D and H analysis in solid samples.     

The emission characteristics of low-pressure water vapor discharge UV emitters

We have studied the characteristics of UV emission sources operating on low-pressure normal (H₂O) and heavy (D₂O) water vapor excited by periodic-pulsed and glow discharges. The emission in a 300–330 nm wavelength interval has been studied in detail for water vapor pressures ranging from 50 to 2500 Pa. A comparison of the characteristics of emission from discharge plasma at low (50–150 Pa) and elevated (2.0–2.5 kPa) water vapor pressures reveals significant differences in the character of emission spectra, which can be related to the different types of emitting species (hydroxy radicals versus small clusters of such radicals and water molecules). Discharge current and emission intensity pulses in the periodic-pulsed discharge regime have been measured.     

Quantitative analysis of deuterium in zircaloy using double-pulse laser-induced breakdown spectrometry (LIBS) and helium gas plasma without a sample chamber

A crucial safety measure to be strictly observed in the operation of heavy-water nuclear power plants is the mandatory regular inspection of the concentration of deuterium penetrated into the zircaloy fuel vessels. The existing standard method requires a tedious, destructive, and costly sample preparation process involving the removal of the remaining fuel in the vessel and melting away part of the zircaloy pipe. An alternative method of orthogonal dual-pulse laser-induced breakdown spectrometry (LIBS) is proposed by employing flowing atmospheric helium gas without the use of a sample chamber. The special setup of ps and ns laser systems, operated for the separate ablation of the sample target and the generation of helium gas plasma, respectively, with properly controlled relative timing, has succeeded in producing the desired sharp D I 656.10 nm emission line with effective suppression of the interfering H I 656.28 nm emission by operating the ps ablation laser at very low output energy of 26 mJ and 1 μs ahead of the helium plasma generation. Under this optimal experimental condition, a linear calibration line is attained with practically zero intercept and a 20 μg/g detection limit for D analysis of zircaloy sample while creating a crater only 10 μm in diameter. Therefore, this method promises its potential application for the practical, in situ, and virtually nondestructive quantitative microarea analysis of D, thereby supporting the more-efficient operation and maintenance of heavy-water nuclear power plants. Furthermore, it will also meet the anticipated needs of future nuclear fusion power plants, as well as other important fields of application in the foreseeable future.     

Field emission characteristics of CuO nanowires by hydrogen plasma treatment

CuO nanowires were formed on copper-coated silicon substrates by a wet chemical process, immersing them in a hot alkaline solution. The effect of hydrogen plasma treatment on the field emission characteristics of the CuO nanowires was investigated. The results showed that hydrogen plasma treatment enhanced the field emission characteristics of the CuO nanowires showing a decrease in turn-on voltage as well as an increase of field enhancement factor. It is believed that hydrogen plasma treatment plays an important role in the improvement of field emission characteristics of CuO emitters.     

Quantitative hydrogen analysis of zircaloy-4 in laser-induced breakdown spectroscopy with ambient helium gas

This experiment was carried out to address the need for overcoming the difficulties encountered in hydrogen analysis by means of plasma emission spectroscopy in atmospheric ambient gas. The result of this study on zircaloy-4 samples from a nuclear power plant demonstrates the possibility of attaining a very sharp emission line from impure hydrogen with a very low background and practical elimination of spectral contamination of hydrogen emission arising from surface water and water vapor in atmospheric ambient gas. This was achieved by employing ultrapure ambient helium gas as well as the proper defocusing of the laser irradiation and a large number of repeated precleaning laser shots at the same spot of the sample surface. Further adjustment of the gating time has led to significant reduction of spectral width and improvement of detection sensitivity to ~50 ppm. Finally, a linear calibration curve was also obtained for the zircaloy-4 samples with zero intercept. These results demonstrate the feasibility of this technique for practical in situ and quantitative analysis of hydrogen impurity in zircaloy-4 tubes used in a light water nuclear power plant.     

The influence of longitudinal magnetic field on recombination radiation of low-pressure glow discharge in hydrogen and helium

We study the influence of longitudinal magnetic field on the radiation of low-pressure glow discharges in hydrogen and helium. We conducted experiments under a pressure in a discharge chamber of 10–20 Pa and a discharge current of 10–20 mA. A 0–1600 G magnetic field influenced only the cathode parts of the discharge, negative glow, and the dark Faraday space. The electron temperature and density were measured by the two-probe method as a function of magnetic field. We studied the dependence of the intensity of radiation in the spectral lines and continuous spectrum on magnetic field induction. We discovered that, under the action of magnetic field, discharge in hydrogen and helium is compressed and its glow volume increases by a factor of 20–25. In contrast, the radiation intensity in the lines and continuous spectrum increase by a factor of 100–200. We found a strong discrepancy in the measured intensity of the continuous spectrum into spectral ranges with calculation of electron-ion recombination.     

In-situ optical emission spectroscopy of laser-induced vanadium oxide plasma in vacuum

This study aims to analyze the elemental composition, and temporal- and spatial distributions of vanadium atoms and ions in the laser-induced vanadium oxide plasma under high vacuum using optical emission spectroscopy. Neutral atoms and singly charged V ions were detected under high vacuum in the emission spectra. The mean translational velocity of neutral V atoms in their first 25 mm propagation was estimated to be 15.7 km/s using the temporal- and spatial dynamics investigation of neutral V species in the plasma.     

Application of fluorescence microscopy for noninvasive detection of surface contamination and precursors to laser-induced damage

We present an experimental investigation to evaluate fluorescence microscopy as a tool to detect surface contamination as well as reveal surface damage precursors on optical components for large-aperture laser systems. We performed fluorescence imaging experiments using 351-nm laser excitation, whereas in situ damage testing was performed at laser fluences well below the dielectric breakdown threshold of the pure material. The experimental results demonstrated the potential of this technique to address both aforementioned technical issues.     

氢、氧等离子体处理对氮化硼薄膜场发射特性的影响

用RF磁控溅射的方法在Si(100)基底上沉积了纳米氮化硼薄膜,然后分别用氢、氧等离子体对薄膜表面进行了处理,用红外光谱、原子力显微镜、光电子能谱以及场发射试验对薄膜进行了研究,结果表明氢等离子体使BN薄膜表面NEA增加,阈值电场降低,发射电流明显增大.氧等离子体处理对BN薄膜的场发射特性影响不大,只是发射电流略有降低,这只能是由于氧化层存在的原因.     

On the mechanism of electric breakdown under low-pressure discharge in helium

It us shown that the left branch of the Paschen curve is determined by the gas phase breakdown, which is caused by the electron avalanche at pD ≥ (pD)_e and by the gas ionization by fast positive ions at pD < (pD)_e. The (pD)_e threshold value is evaluated, and it is established that the E/p ratio is the main parameter determining the gas breakdown.     

ERD facility for analysis of hydrogen and deuterium in solids

Hydrogen is the lightest element in nature, and so, its detection and quantitative analysis is difficult by the conventional methods utilized for other elements. In the recent years the technique of elastic recoil detection analysis (ERD) using 1–2 MeV He⁺ beam has been developed to quantitatively and simultaneously analyze hydrogen and its isotopes in solids. Such a facility has been set up using the 2 MeV Van-de-Graaff accelerator at IIT Kanpur. It facilitates H and D analysis in a material up to a depth of ∼ 1μm with a detection sensitivity of 0·1 at.% and depth resolution of about 300 ?. The application potential of this setup is illustrated by presenting the results of measurements performed on Al:H:D systems prepared by plasma source ion implantation and highT _c YBCO pellets exposed to humid atmosphere.     

Influence of optical aberrations on laser-induced plasma formation in water and their consequences for intraocular photodisruption

The influence of spherical aberrations on laser-induced plasma formation in water by 6-ns Nd:YAG laser pulses was investigated for focusing angles that are used in intraocular microsurgery. Waveform distortions of 5.5lambda and 18.5lambda between the optical axis and the 1/e(2) irradiance values of the laser beam were introduced by replacement of laser achromats in the delivery system by planoconvex lenses. Aberrations of 18.5lambda increased the energy threshold for plasma formation by a factor of 8.5 compared with the optimized system. The actual irradiance threshold for optical breakdown was determined from the threshold energy in the optimized system and the spot size measured with a knife-edge technique. For aberrations of 18.5lambda the irradiance threshold was 48 times larger than the actual threshold when it was calculated by use of the diffraction-limited spot size but was 35 times smaller when it was calculated by use of the measured spot size. The latter discrepancy is probably due to hot spots in the focal region of the aberrated laser beam. Hence the determination of the optical-breakdown threshold in the presence of aberrations leads to highly erroneous results. In the presence of aberrations the plasmas are as much as 3 times longer and the transmitted energy is 17-20 times higher than without aberrations. Aberrations can thus strongly compromise the precision and the safety of intraocular microsurgery. They can further account for a major part of the differences in the breakdown-threshold and the plasma-transmission values reported in previous investigations.     

Optical emission from laser-induced breakdown plasma of solid and liquid samples in the presence of a magnetic field

The optical properties of laser-induced plasma generated firm solid (Al alloy) and liquid (Mn, Cr, Mg, or Ti solutions) samples expanded across an external, steady magnetic field have been studied by atomic-emission spectroscopy. Various line emissions obtained from the constituents of the Al alloy and of the aqueous solution show an enhancement in intensity in the presence of an approximately 5-kG magnetic field. The enhancement of the signal was nearly a factor of 2 for the minor constituents of the solid samples and a factor of 1.5 for the elements in liquid phase. Temporal evolution of the emission from the solid sample showed maximum enhancement in emission intensity at 3-10-micros time delay after plasma formation in the laser energy range 10-50 mJ. However, for the liquid sample the maximum signal was for a gate delay of 3-25 micros the energy range 50-200 mJ. This enhancement in the emission intensity was found to be due to an increase in effective density of the plasma as a result of magnetic confinement when the plasma cooled after expansion. This enhanced emission was due to an increase in the rate of radiative recombination in the plasma.     

表面等离子共振氢敏传感器理论和模拟

提出了一种钯(Pd)膜氢敏感表面等离子共振传感器结构,该传感器以镀在棱镜端面的 Pd作为氢敏感膜。Pd 膜吸氢以后发生化学反应,生成的 PdHx使折射率发生变化,同时,它作为金属膜产生 SPW,当折射率变化时又在金属和介质表面产生表面等离子共振。利用 Fortran 语言程序进行了表面等离子共振氢敏传感器的 Pd 膜厚度和传感器灵敏度数值模拟。氢气浓度的变化引起折射率的变化,数值模拟表明,表面等离子共振氢敏传感器的灵敏度与 Pd 膜厚度有关,当 Pd膜的厚度在 10-30nm 时,氢气浓度在 1%-10%范围内具有较高的灵敏度。这种传感器结构将用于监测氢气作燃料的商用和军用机车的氢气泄漏。     

Correlations and effective potential in the ground state of a one-dimensional model for solid helium and deuterium

The ground-state energyE can be calculated exactly by the transfer-integral method if the total wave function is assumed to be a product of single-particle functions and nearest-neighbor correlation functionsf. The variation ofE with respect tof for fixed leads to a Schrödinger equation for the relative motion of two particles which is coupled to the transfer integral equation by an effective potential V. For the case of a Gaussian the optimalf, the one- and two-particle probability amplitudes, and other quantities are computed by iteration of the Schrödinger equation with the transfer integral equation until self-consistency is achieved. The minimum ofE as a function of the Gaussian width is obtained for different values of the lattice parameter. The shape of V andf is discussed. The self-consistentf describes both short- and long-range correlations.     

Reference wavelengths for strong lines of atomic hydrogen and deuterium

Wavelengths of the individual fine-structure components of the n = 1-2 (Ly(alpha)), n = 1-3 (Ly(beta)), n = 1-4 (Ly(gamma)), n = 1-5 (Ly(delta)), n = 1-6 (Ly(epsilon)), n = 1-7 (Ly(zeta)), n = 2-3 (H(alpha)), n = 2-4 (H(beta)), n = 2-5 (H(gamma)), n = 2-6 (H(delta)), and n = 2-7 (H(epsilon)) transitions of H and D are determined from theoretical values for the binding energies. Theoretical line strengths are used to obtain recommended values for the peaks of unresolved blends of these components as likely to be observed with discharge light sources and spectrometers with low to moderate resolution.     

Phonons in a linear chain with hard-core potentials of helium and deuterium

The phonon theory is formulated in terms of transfer functions, which are solutions of the transfer integral equation. Since these functions already implicitly contain the effects of anharmonicities and of the hard core, no further difficulties occur from these properties of the potential. The only assumption to be made is a Hartree-Jastrow form of the wave functions, where the Jastrow factors describe both short- and long-range correlations. Numerical results are given for Lennard-Jones potentials with data from helium and deuterium.     

Chemical sputtering and surface damage of graphite by low-energy atomic and molecular hydrogen and deuterium projectiles

We present experimental methane production yields for H⁺, ions incident on ATJ graphite in the energy range 10–250 eV/H. Below about 60 eV/H, the molecular H species give higher methane yields/H when compared with isovelocity H⁺, similar to our earlier measurements for incident deuterium atomic and molecular ions. For both D and H atomic and molecular projectiles, the yields/atom coalesce onto a single curve below projectile energies of 60 eV/atom, when plotted as a function of maximum energy transfer, under the assumption that, below this energy, the incident molecular species are largely undissociated when undergoing C–C bond breaking collisions during their collision cascade and thus produce more damage. Raman spectroscopy of a graphite sample exposed to high fluences of D⁺ and beams at high and low energies qualitatively confirmed the assumption that more surface damage is produced by the low-energy incident molecular species than by isovelocity atomic ions. While the two high-energy beam-exposed spots showed similar damage, the low-energy molecular-beam-exposed spot showed slightly more damage than the corresponding D⁺-beam-exposed spot.