Charge-stripping system for 238U ion beam with recirculating He gas

Recent developments in a charge-stripping system employing high-flow rate He gas circulation (~200 L/min) for ²³⁸U³⁵⁺ beams injected at 10.8 MeV/u are reported. He gas is confined in a target section and is separated from a vacuum duct using five-stage differentially-pumped sections. To minimize the gas leakage rate via beam apertures, a high-performance differential pumping was required. To avoid huge gas consumption, a clean gas recycling with high-flow rate was simultaneously required. To realize these, we developed multi-stage mechanical booster pump array. The recycling rate of He gas was achieved as more than 99 %. The system performance has been checked with the present maximum beam current up to 13 eμA (~1 kW beam power).     

Effect of atmosphere on collinear double-pulse laser-induced breakdown spectroscopy

Double-pulse laser-induced breakdown spectroscopy (DP-LIBS) has been shown to enhance LIBS spectra. Several researchers have reported significant increases in signal-to-noise and/or spectral intensity compared to single-pulse (SP) LIBS. In addition to DP-LIBS, atmospheric conditions can also increase sensitivity. Thus, in this study, a collinear DP-LIBS scheme was used along with manipulation of the atmospheric conditions. The DP-LIBS scheme consisted of an initial 45-mJ pulse at 1,064-nm fired into a sample contained in a controlled atmospheric/vacuum chamber. A second analytical 45-mJ pulse at 1,064-nm was then fired 0 to 200 μs after and along the same path of the first pulse. Ar, He, and air at pressures ranging from atmospheric pressure to 1 Torr are introduced during DP-LIBS and SP-LIBS experiments. For a brass sample, significant increases in the spectral intensities of Cu and Zn lines were observed in DP-LIBS under Ar compared to DP-LIBS in air. It was also found that Cu and Zn lines acquired with SP-LIBS in Ar are nearly as intense as DP-LIBS in air. While collinear DP-LIBS is effective for increasing the sensitivity for some reduced atmospheres (i.e., Ar and air at 630 to 100 Torr and He at 300 Torr), the enhanced spectral intensity ultimately dropped off as the pressure was reduced below 10 Torr for all atmospheric compositions in the experimental arrangement used in this study. At all pressures of air and Ar, the plasma temperature remained rather constant with increased inter-pulse delays; however, the plasma temperature was more variable for different He gas pressures and inter-pulse delays.     

Atmospheric-pressure Penning ionization of aliphatic hydrocarbons

A study has been made of the atmospheric-pressure Penning ionization (APPeI) of aliphatic hydrocarbons (pentane, hexane, heptane, and octane) with long-lived rare gas atoms (Rg*). The metastable rare gas atoms (He*, Ne*, Ar* and Kr*) were generated by the negative-mode corona discharge of atmospheric-pressure rare gases. In the Rg*APPeI mass spectra for aliphatic hyrocarbons, the relative abundances of fragment ions were found to increase in the order of He* --> Ne* --> Ar* --> Kr*. The order is in the opposite direction to the internal energies of the Rg*. The less fragmentation observed for He* may be because the nascent molecular ions [M(+.)]* formed by Penning ionization have lifetimes long enough for them to be collisionally deactivated in the atmospheric-pressure ion source. It was found that the relative abundances of fragment ions in Ar*APPeI increased when the sample pressure in the ion source was reduced. This is attributed to the collision of Ar* with molecular ions followed by fragmentation.     

Differential cross sections for collisional neutralisation of H− by rare gases

Measurements are presented of the differential cross section for neutralisation of H⁻ in collisions with He, Ar and Xe. The measurements are carried out in the energy range 500–2000 eV. The angular range is 0–4.2 degree with an ultimate resolution of 0.02 degree. The H⁻ beam is formed in an electron impact source, mass selected, and focused by means of two electrostatic lenses through a collision chamber onto a position-sensitive channelplate detector. The results show a strong forward peaking of the cross section and a double peak structure when the results are plotted on a reduced ϱ(θ) = σ(θ) sin(θ)θ versus τ=Eθ scale. It is shown that forward peaking can be accounted for by a model based on the impulse approximation.     

Quantum scattering and adiabatic channel treatment of the low-energy and low-temperature capture of a rotating quadrupolar molecule by an ion

The capture rate coefficients of homonuclear diatomic molecules (H(2) and N(2)) in the rotational state j=1 interacting with ions (Ar+ and He+) are calculated for low collision energies assuming a long-range anisotropic ion-induced dipole and ion-quadrupole interaction. A comparison of accurate quantum rates with quantum and state-specific classical adiabatic channel approximations shows that the former becomes inappropriate in the case when the cross section is dominated by few partial contributions, while the latter performs better. This unexpected result is related to the fact that the classical adiabatic channel approximation artificially simulates the quantum effects of tunneling and overbarrier reflection as well as the Coriolis coupling and it suppresses too high values of the centrifugal barriers predicted by a quantum adiabatic channel approach. For H2(j=1)+Ar+ and N(2)(j=1)+He+ capture, the rate constants at T-->0 K are about 3 and 6 times higher than the corresponding values for H2(j=0)+Ar+ and N(2)(j=0)+He+ capture.     

MCM-41负载钨磷杂多酸催化剂的性能研究

制备并表征MCM-41负载H~3PW~1~2O~4~0(PW)催化剂.PW杂多酸在MCM-41上负载量高达70%(质量分数)时,XRD中仍未检测到其晶相峰.PW杂多酸与MCM-41载体的相互作用要比与SiO~2载体的强.PW杂多酸中的质子位是非常强的酸中心,它们对NH~3的微分吸附热在160-180kJ/mol的范围.与PW杂多酸相比,PW/MCM-41催化剂的酸中心强度变弱并且分布不均匀,其酸量和酸中心分布可以通过改变PW杂多酸的负载量来调节.PW/MCM-41是一类适合于中强酸和弱酸催化反应的新型固体酸催化剂。     

Cr cluster deposition by plasma—gas-condensation method

Transmission electron microscopy observation was carried out for nanometric Cr clusters deposited on microgrids at room temperature using plasma–gas-condensation (PGC) method. In order to obtain optimum conditions for monodisperse cluster formation we have studied effects of an Ar gas pressure, an Ar gas flow rate, and a mixing rate of He gas with Ar gas on the size distribution of formed clusters. It has been found that monodisperse clusters with the size rage of 9–13 nm in diameter are producible at a low Ar gas pressure (≤1.3 Torr) and a low Ar gas flow rate (≤600 sccm). The mean cluster size decreases with decreasing Ar gas pressure, while it is not sensitive to the Ar gas flow rate. When He gas is mixed with Ar gas, the mean cluster size further decreases to 6 nm and the cluster beam intensity becomes stronger probably because He gas with the high thermal conductivity enhances supersaturation for cluster nucleation.     

Collision-induced Rotational Energy Transfer in an Atom-Diatom System

As a further theoretical study of the collision-induced quantum interference on rotational energy transfer in an atom-diatom system, based on the first-Born approximation of time-dependent perturbation theory, taking into account the anisotropic Lennard-Jones interaction potential and the long-range interaction potential, the differential interference angles in singlet-triplet mixed states of CO A1Ⅱ(v=0)～e3∑-(v=1)system in collision with He, Ne, Ar, and other partners were calculated theoretically. The relationships of differential interference angle versus impact parameters, including collision parameter b and velocity, are obtained.     

Depopulation of low‐Rydberg Na atom in collisions with rare gases: A molecular‐state treatment

Total quenching of the low‐Rydberg state of Na in collision with thermal Ne and Ar was investigated, for the first time, employing a molecular approach in the impact parameter formalism. A large basis set of Slater‐type orbitals was used to calculate the molecular structure of the transient quasimolecule formed during the collision; pseudopotentials were used to incorporate the effective binding of the distant electron. A 14‐channel calculation was carried out to evaluate the total depopulation cross sections for Na(9s) colliding with the ground‐state Ne and Ar atoms in the thermal‐energy region. The two colliding pairs not only differ from each other, but also show wide variations from the previously studied Na He pair, in terms of details of the collision dynamics. In the case of the Na Ar system, a unique feature that leads to appreciably larger quenching cross sections shows qualitative agreement with the measurement. A comparative study of three (He/Ne/Ar Na) colliding pairs reveals that the simplified approach like the free‐electron model or the impulse approximation fails to provide details of such state‐changing reactions. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 307–316, 1999     

The effect of collisions on the intensity and polarization of laser-induced D1π → X1Σ+ + fluorescence from NaK

Laser-induced fluorescence was applied for determining total deactivation cross sections of the level (17,94) D¹Π of NaK molecules in collisions with He, Ne, Ar, Kr, Xe, as well as with K atoms. Relaxation cross sections of population and alignment were found to coincide within experimental error. The kinetics of the transient process was used for determining the cross section of thermalization of the optically depopulated level of the electronic ground state (5,67) X¹Σ⁺ in NaK + Ar collisions.     

Development of an on-line low gas pressure cell for laser ablation-ICP-mass spectrometry.

An on-line low gas pressure cell device has been developed for elemental analysis using laser ablation-ICP-mass spectrometry (LA-ICPMS). Ambient gas in the sample cell was evacuated by a constant-flow diaphragm pump, and the pressure of the sample cell was controlled by changing the flow rate of He-inlet gas. The degree of sample re-deposition around the ablation pit could be reduced when the pressure of the ambient gas was lower than 50 kPa. Produced sample aerosol was drawn and taken from the outlet of the diaphragm pump, and directly introduced into the ICP ion source. The flow rate of He gas controls not only the gas pressure in the sample cell, but also the transport efficiency of the sample particles from the cell to the ICP, and the gas flow rate must be optimized to maximize the signal intensity of the analytes. The flow rates of the He carrier and Ar makeup gas were tuned to maximize the signal intensity of the analytes, and in the case of (238)U from the NIST SRM610 glass material, the signal intensity could be maximized with gas flow rates of 0.4 L/min for He and 1.2 L/min for Ar. The resulting gas pressure in the cell was 30 - 35 kPa. Using the low gas pressure cell device, the stability in the signal intensities and the resulting precision in isotopic ratio measurements were evaluated. The signal intensity profile of (63)Cu obtained by laser ablation from a metallic sample (NIST SRM976) demonstrated that typical spikes in the transient signal, which can become a large source of analytical error, were no longer found. The resulting precision in the (65)Cu/(63)Cu ratio measurements was 2 - 3% (n = 10, 2SD), which was half of the level obtained by laser ablation under atmospheric pressure (6 - 10%). The newly developed low-pressure cell device provides easier optimization of the operational conditions, together with smaller degrees of sample re-deposition and better stability in the signal intensity, even from a metallic sample.     

Syntheses and characterization of the MF6- (M = As, Sb) salts of the simple trithietanylium PhCS3+ cation and the identity of PhCS3Cl

MF6- (M = As or Sb) salts of a simple derivative of the trithietanylium PhCSSS+, 1, were synthesized for the first time by the reaction of PhCS3Cl and AgMF6 in liquid SO2. 1SbF6 was characterized by IR, FT-Raman, and NMR spectroscopy, elemental analysis, and a preliminary X-ray crystal structure. 1AsF6 was characterized by 1H NMR and FT-Raman spectroscopy. The calculated (MPW1PW91/3-21G* or 6-31G*) geometries, 1H and 13C chemical shifts (MPW1PW91/6-311G(2DF)//MPW1PW91/3-21G*), and vibrational frequencies and intensities (MPW1PW91/6-31G*) were in satisfactory agreement with the observed values. The calculated pi type molecular orbitals of HCSSS+ (MPW1PW91/6-311+G*) and 1 (MPW1PW91/3-21G*) imply that the 6pi-CSSS+ ring has some aromatic character. 1SbF6 undergoes a metathesis reaction with NBu4Cl in liquid SO2 to give PhCS3Cl, which was characterized by vibrational spectroscopy and mass spectrometry. The evidence indicates that PhCS3Cl has the ionic formulation PhCSSS+ Cl- with significant cation-anion interactions in the solid state. ArCSSS+ SbF6- (Ar = 1-naphthyl), 14SbF6, was prepared from ArCS3Cl and AgSbF6, suggesting that the synthesis of MF6- (M = As or Sb) salts of RCSSS+ is potentially general for aryl derivatives. The structure of 14SbF6 was established by 1H and 13C NMR, IR, and FT-Raman spectroscopy, and theoretical calculations gave values in agreement with the experimental data.     

The 3d←3p endothermic collisional population transfer of Li in He and Ar at 298 K

The 3p state of Li was excited in He and Ar buffer gases at room temperature (298 K) and the time profiles of sensitized fluorescence from the 3s and 3d states were measured. The 3d←3p endothermic population transfer rates determined from the pressure dependence of the time profiles were 6.5×10⁻¹¹ cm³ s⁻¹ for He and less than 10⁻³ cm³ s⁻¹ for Ar. The origin of this large difference between He and Ar is discussed in terms of non-adiabatic transitions between the 3p and 3d molecular states of the Li–He and Li–Ar molecules.     

The total ionisation cross section and the large angle differential cross section for the system He(21S, 23S) + Ar,N2

We have measured the total ionisation cross section Q_ion(g) and the large angle differential cross section σ(θ, g) for the system He(2¹S, 2³S)+ Ar, N₂ at energies 0.05 < E_c.m. (eV) < 6. This energy range is covered by applying two different discharge sources for the production of metastable atoms. In the atomic beam the He(2³S) level is most abundant with relative populations C = 0.91±0.01 and C = 0.96±0.01 for thermal energy range and the superthermal energy range, respectively. A quench lamp is used for the quenching of the (2¹S) level population. In the thermal energy range, σ(θ, g) and Q_ion(g) are in fair agreement with experimental results of other authors and with calculated cross sections based on the optical potential given by Siska. In the superthermal energy range, the He(2³S)+Ar optical potential is modified to describe our experimental data. The slope of the repulsive branch of the real potential is increased for r < 2.85 Å; in the imaginary potential a saturation to a constant (or even decreasing) value for internuclear distances less than 2.5 Å is introduced.     

A Simple Method for Estimating Effective Ion Source Residence Time

A method is presented that uses the well-understood O₂/Ax ion-molecule reaction system to determine the effective ion source residence time of a chemical ionization source. The process consists of: (1) defining the kinetic system in terms of reactions, reaction rates, and ionization cross sections; (2) solving the differential equations that describe the time evolu-tion of the kinetic system, and (3) comparing the calculated results to experimentally measured relative ion intensities. These steps are repeated for a variety of 0₂/Ar sample ratios and inlet pressures. The method leads to a simple relationship between inlet pressure and effective ion source residence time, independent of the 0₂/Ar sample ratio.     

Theoretical Study of Decomposition Pathways for Rare-gas-containing Compounds HRgX （Rg = He, Ne, Ar, Kr; X = Cl, Br）

1 INTRODUCTION transfer species with common formula H-Rgδ -Xδ, where X represents a strongly electrone-gative atom Since xenon hexafluoraplatinate, XePtF6 , the [1] or fragment, and Rg is a rare-gas atom. These species first rare gas-containing compound was discovered have linear equi- librium geometries and are mainly by Bartlett in 1962, rare gases are getting more and bound up by strong columbic attraction between (H- more attention and have been found to be possible to Rg) and…     

Computational tests of the factorization of cross sections in the sudden approximation

The factorization expressions for cross sections reported by Goldflam, Green and Kouri and independently by Khare are tested using accurate close coupling input for e^? + H₂, H + H₂, He + (HF, DF, HCl, DCl) and Ar + N₂. The results at the degeneracy averaged cross section level are used to illustrate accuracy criteria given for the factorization. Effects studied include variation of the projectile reduced mass, influence of initial and final rotor state, collision energy and potential anisotropy.     

Emission spectroscopic studies of Grimm-type glow discharge plasma with argon-helium gas mixtures

The effect of argon/helium pressure ratios on the emission intensity of various Ar II lines is investigated for a Grimm-type glow discharge radiation source, operated with Ar-He mixtures. The relative intensities of the Ar II lines are altered significantly by mixing helium with argon. It is found that the population of the Ar⁺ excited states can be redistributed through He-Ar collisional energy transfer. The energy level of the He singlet metastable state (¹S₀,20.62 eV) is very important for these processes. If the excitation energy of Ar II lines is higher than that of the He singlet metastable, strong quenching of the Ar II line intensity is observed. However, when the excitation energy is slightly lower, some of the Ar II lines are enhanced by adding helium to the argon plasma. Energy exchanges between the Ar⁺ doublet term states and the He singlet metastable are favoured because the total spin remains unchanged before and after the He-Ar collisions. Furthermore, the helium mixing also exerts a great influence on the emission intensities of the elements sputtered from the cathode of the discharge lamp. The enhancement of Al I and Al II emission intensities at suitable Ar-He mixture ratios is discussed for when aluminum is employed as a cathode material.     

Collision transfers between CdH A 2Πυ′ = 0 rotational states induced by He or Ar

CdH is obtained by radiofrequency discharge in Cd vapor mixed with 5% H₂ in He or Ar. It is selectively excited by a pulsed dye laser to A ²Π_{$\text{1}\text{2}$,$\text{3}\text{2}$} υ′ = 0, J′ = 0.5–16.5. Collision cross sections are measured from several J′ values corresponding to rotational transfers observed up to ΔJ′ = ±7. The total collision cross sections are smaller with He than with Ar. They decrease as J′ increases. The levels of the same electronic parity as the initial level are strongly privileged for high J′ with He, much less with Ar. The polarization of the initial lines decreases appreciably for high J′ with the Ar pressure, much less with the He pressure. Small spin transfers are observed from Π_{$\text{3}\text{2}$} to Π_{$\text{sol:1}\text{2}$}. The experimental results, especially the propensities, are justified using the Born approximation as developed in previous papers. Its validity is discussed in comparing the effects of He and Ar.     

Characterization of an annular helium inductively coupled plasma generated in a low-gas-flow torch

Atomic emission detection limits of Br, C, Cl and I measured for gaseous and aqueous samples with a low-gas-flow, annular He ICP were lower than those obtained with an Ar 1CP. Measurements of electron number density, excitation temperature and rotational temperature revealed that the extent of departure from local thermal equilibrium for the He ICP was larger than that for the Ar ICP.