Integral Cross Section Measurements Research Articles

Production and magnetic analysis of beams of S atoms and SO radicals: a collisional study of their interactions with hydrogen molecules

An intense and stable continuous beam of S atoms and SO radicals has been produced with a microwave discharge source operating in the Torr range in mixtures of SO 2 with various gases. The beam emerging from the plasma source was velocity analyzed by a mechanical velocity selector and detected by a quadrupole mass filter. Stern-Gerlach magnetic analysis indicates that both species are mainly generated in their electronic ground state and in the case of sulfur atoms with fine-structure levels, populated according to their degeneracies. Total integral cross section measurements are reported, as a function of velocity in the range 1.0–2.5 km × s −1, for the scattering of S( 3P J ) atoms and SO ( 3Σ) radicals by D 2 molecules. The analysis of experimental data (cross sections and their velocity dependence, which exhibits glory interference patterns) allows a characterization of the spherically average component of the interaction potential for the investigated systems. A discussion of the effect of the Σ-Π splitting, spin-orbit, and electrostatic (including quadrupole–quadrupole) interaction on the dependence of the hydrogen molecule orientation is given for the S–H 2 potential energy surface.

Molecular Beam Scattering of Nitrogen Molecules in Supersonic Seeded Beams: A Probe of Rotational Alignment

Measurements of total integral cross sections for scattering of nitrogen molecules by Xe atoms in the glory collision energy range (40−600 meV) are reported under two different experimental conditions, using either a rotationally “hot” (most probable levels J = 8, 9) effusive beam of nitrogen (obtaining information on the isotropic component of the interaction potential) or rotationally “cold” N2 seeded beams emerging from supersonic expansions (obtaining quantitative information on rotational alignment of molecular nitrogen). The scattering results presented in this paper allow us to establish that the recently reported phenomenon of the strong correlation between the degree of collision-induced alignment and the speed of the molecules within a supersonic seeded velocity distribution, as previously observed for the first time in molecular oxygen, also occurs for the case of nitrogen molecules. Alignment parameters are reported for both the ortho and para forms of nitrogen, which are cooled down in the seeded supersonic expansion process to their lowest rotational levels J = 0, 1, 2.

Experimental studies and nuclear model calculations on the formation of radioactive products in interactions of medium energy protons with copper, zinc and brass: Estimation of collimator activation in proton therapy facilities

Excitation functions of (p,x) processes on collimator materials for radiation therapy (Cu, Zn and brass), leading to the formation of long-lived activation products, were measured over the proton energy range 70 to 350 MeV using the stacked-foil technique. In most of the cases the product activity could be measured non-destructively via γ-ray spectrometry; for studies on low-yield products, however, radiochemical separations were essential. A comparison of the data obtained via an integration of the differential data for Cu and Zn with integral cross-section measurements on brass showed an agreement within ±17%. The experimental data for natCu, natZn and brass were also compared with theoretical data obtained using the modified hybrid nuclear model code ALICE-IPPE (1996) for intermediate energies. The agreement was found to be good up to about 120 MeV. For products rather away from the target elements, large deviations were observed. Using the measured data, an estimation of collimator activation in proton therapy facilities was done.

Production, Characterization, and Scattering of a Beam of Sulfur Monoxide Radicals: The SO−Noble Gas Interactions

rotationally hot distribution and provides an upper limit ( e7%) on the concentration of electronic metastable states. Total integral cross-section measurements as a function of velocity in the range 0.9 -2.4 km‚s -1 for the scattering of ground-state SO radicals by Ne, Ar, and Kr have also been performed. The analysis of experimental data (cross sections and their velocity dependence, which exhibits glory interference patterns) allows a characterization of the interaction potential features for the investigated systems. Use of a correlation rule leads to an estimate of the average polarizability of the SO molecule and also of the potential features for SO-He and SO-Xe.

Reaction mechanisms and energy disposal in the [C2H2:OCS]+ system: A mode-selective differential cross section study

Charge transfer and S-atom transfer have been studied for reaction of both charge states of the [C2H2:OCS]+ system. Reactions have been studied as a function of six different modes of reactant nuclear motion, including relative motion and nine levels of five vibrational modes for the two reactant ions. Integral cross section measurements provide information on how total reactivity and product branching are affected by different forms of reactant excitation. Detailed insight into the reaction mechanism is obtained from differential scattering measurements—the first ever for mode-selectively excited reactants. The S-transfer reaction is found to be nearly identical for the two reactant charge states, which appear to be coupled by charge transfer in the collision entrance channel. In both charge states S transfer is dominated by two distinct direct scattering mechanisms, rebound and glancing/stripping, each of which are affected by collision energy and vibrational state. At collision energies below 0.5 eV, complex-mediated scattering becomes an important mechanism as well. It appears that the cis-trans symmetry of the C2H+2 bending vibration strongly affects formation of [C2H2:OCS]+ complexes. Charge transfer goes by very different mechanisms in the two charge states. For C2H+2+OCS, long-range electron hopping is the dominant mechanism, while for OCS++C2H2 the dominant mechanism requires impulsive collisions.

Guided-ion beam measurements of the O+(4S)+Xe charge-transfer reaction

Guided-ion beam integral cross section measurements, product ion time-of-flight (TOF) measurements, and doubly differential cross sections are presented for the O+(4S)+Xe→O+Xe+ charge-transfer reaction. The integral cross section is observed to increase monotonically with mean center-of-mass collision energy (ET) from 0.72 Å2 at 0.1 eV to 26.9 Å2 at 35.2 eV. Product ion TOF measurements show that the primary contribution to the charge-transfer cross section arises from a direct electron transfer at long range of the Demkov type. The collision energy dependence of the cross section for center-of-mass (c.m.) forward-scattered Xe+ ions reveals that this minor contribution to the total cross section arises from a hard-sphere-type scattering that primarily involves a Landau–Zener-type diabatic curve crossing at shorter range. Doubly differential cross sections at 4.4 eV indicate that translational to product internal energy transfer is inefficient even at small impact parameters and that the spin-allowed Xe+(2P)+O(3P) product channels are preferentially populated.

High accuracy determination of the shape of the efficiency curve of the HPGe detector in the energy range 900 to 1300 keV

A method for high accuracy characterization of the shape of a High Purity Germanium (HPGe) detector efficiency curve has been developed. Radionuclides with decay schemes having at least two γ lines, for which the yield ratio can be calculated accurately, are used to establish the shape of the detector efficiency curve. Measurements using 60Co and 46Sc sources show that the behavior of the efficiency curve of the detector on a log-log scale is indistinguishable from that of a straight line with a slope of −0.828 ± 0.004. Measurements using a 24Na source show that above 1368 keV this behavior no longer holds due to pair production and escape effects. The measured value of the slope in that case is −0.951 ± 0.002. The proposed method is to be used in measurements requiring the minimum calibration bias in the determination of the reaction rate ratios, such as reactor dosimetry applications, integral cross section measurements and k 0 determination for neutron activation analysis.

Test of local model potentials for positron scattering from rare gases.

We report calculations of differential and integral cross sections for positron (${\mathit{e}}^{+}$) scattering from He, Ne, Ar, Kr, and Xe rare gases. An optical-potential approach is employed in which the repulsive Coulombic interaction is calculated exactly at the Hartree-Fock level and the attractive polarization and correlation effects are included via a model potential determined from the use of a local density-functional theory (DFT). These model calculations are further compared with the results from two other local potentials, one based on determining the short-range correlation energy, ${\mathit{E}}_{\mathrm{C}}$, for a positron in an homogeneous electron gas and the other from the correlation-polarization potential of an electron interacting with a free-electron gas. We found that the present DFT-based, correlation-polarization treatment is fairly simple to implement computationally and appears to be the most accurate of all the models examined here. Our results are in fact compared with recent measurements of differential and integral cross sections for positron scattering with rare gases and are found to be remarkably close to both sets of experiments.

ChemInform Abstract: High‐Resolution Measurements of Integral Cross Sections in Ion‐ Molecule Reactions from Low‐Energy‐Guided Crossed‐Beam Experiments.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

High-resolution measurements of integral cross sections in ion-molecule reactions from low-energy-guided crossed-beam experiments

ADVERTISEMENT RETURN TO ISSUEPREVArticleHigh-resolution measurements of integral cross sections in ion-molecule reactions from low-energy-guided crossed-beam experimentsPaolo TosiCite this: Chem. Rev. 1992, 92, 7, 1667–1684Publication Date (Print):November 1, 1992Publication History Published online1 May 2002Published inissue 1 November 1992https://doi.org/10.1021/cr00015a009RIGHTS & PERMISSIONSArticle Views178Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts Get e-Alerts

The H+para-H2 reaction: Influence of dynamical resonances on H2 (v′=1, j ′=1 and 3) integral cross sections

We have measured integral rate constants for the reaction H+para-H2→H2(v′=1, j′=1 and 3)+H at 11 center-of-mass collision energies (Erel) between 0.88 and 1.01 eV, a region in which dynamical scattering resonances are present. We have also measured the H2(v′ = 1, j′ = 3)/H2(v′ = 1, j′ = 1) population ratio at two additional values of Erel outside of this range. Tunable uv laser photolysis of HI was used to generate translationally hot H atoms of variable kinetic energy. Quantum-state-specific detection of the H2 reaction product was accomplished via (2+1) resonance-enhanced multiphoton ionization and time-of-flight mass spectrometry. The integral rate constants have a smooth dependence on Erel, in agreement with the recent quantum-mechanical (QM) calculations of Zhang and Miller and contrary to the experimental results of Nieh and Valentini. The QM results are in nearly perfect agreement with the present measurements for the dependence on Erel of both the integral rate constants and the H2(v′ = 1, j′ = 3)/H2(v′= 1, j′ = 1) population ratio. It is concluded that measurements of integral cross sections as a function of collision energy are not highly sensitive to the presence of dynamical resonances in this system.

A generalized model for the ν-dependence of the anisotropic long-range attractive interaction of alkali dimer-atom systems

State-selective measurements of anisotropic integral cross sections for the scattering of highly vibrationally excited alkali molecules (Li 2, Na 2) with various atoms (He, Ne, Ar, Kr, Na) are used to model simple three-dimensional potential hypersurfaces for these systems by comparison with quantum mechanical IOS scattering calculations. The two necessary fitting parameters in the attractive and repulsive part of the potentials are remarkably similar for all investigated systems and give new insight into the variation of potential energy with vibrational excitation. On the basis of this manifold of improved hypersurfaces, it is possible to account for the net increase in total cross section, anisotropy, and rotational inelasticity for vibrationally hot molecules by a single, generalized expression with a scaling parameter that includes collision energy and vibrational ground state potential well depth.

Spark counting of particle damage tracks in neutron studies

As shown by trial experiments, neutron detectors based on fissile nuclides and thin Lavsan foils can be used successfully in combination with a spark counter of tracks in a variety of neutron studies: measurements of the spatial distributions of the spectral characteristics of neutron fields of various kinds; measurements of integral and differential fission cross sections; in personal neutron dosimetry; etc. This method ensures that information from a large number of neutron detectors is obtained rapidly.

Measurements of integral cross-sections of incoherent interactions of photons withL-shell electrons

Measurements of integral cross-sections of incoherent interactions of photons withL-shell electrons

Determination of the H–D2 spherically averaged potential and the H–Ne potential from absolute integral cross-section measurements

Absolute integral cross sections for the H–D2 and the H–Ne collisions were measured by means of atomic–hydrogen beam scattering for kinetic energies of the atom of 1.8–330 meV with high accuracy. Realistic potential models which have only two or three adjustable parameters were used for the interpretation of the data in order to remove arbitrariness of interpretation. The best fit potential for H–D2 has a well of depth ε = 2.02 meV at position rm = 3.43 Å, and crosses zero at r0 = 2.99 Å which agrees exactly with r0 obtained by Torello and Dondi from the D–H2 differential cross-section measurements. The best fit potential for H–Ne (ε = 1.46 meV, rm = 3.40 Å, r0 = 2.99 Å) is in good agreement with ab initio potentials calculated by Das et al. The low-energy repulsive part of the best fit H–D2 potential is consistent, in the internuclear distance region of 4a0⩽r⩽5a0, with recent theoretical results of Truhlar and Horowitz for the spherically symmetric term of the H–H2 potential. The best fit H–D2 potential is finally modified in the region of r⩽4.5a0 so that its extrapolation to the short distance region leads to Truhlar and Horowitz’s results for r⩽3.5a0.

Measurement of integral cross-sections of incoherent interactions of photons withK-shell electrons

Integral cross-sections of incoherent interactions of 662 and 1250 keV gamma-rays with L-shell electrons of different elements with 74 ≤Z ≤ 92 have been measured. The experimental results, when interpreted in terms of photoelectric and Compton interaction cross-sections, are found to agree with theory.

Neutron source characterization for fusion materials studies

Neutron flux and energy spectrum measurements are conducted for all major fusion materials irradiation facilities, including fission reactors and accelerators. Dosimetry characterization experiments and integral cross section measurements have been performed. Multiple activation and helium production measurements are performed routinely to provide materials experimenters with neutron exposure parameters including fluence, spectrum, displacements, gas production, and transmutation with typical accuracies of 10–15%. Such data are crucial to the fusion materials program in order to correlate materials property changes between irradiations and facilities and to confidently predict the performance of materials in fusion reactors.

Scattering of magnetically selected O(3P) atoms: Characterization of the low lying states of the heavy rare gas oxides

Measurements of absolute integral elastic cross sections for scattering of O(3P) atoms, magnetically selected in their sublevels mj=0, are reported at three collision energies in the thermal range for each of the target gases Ar, Kr, and Xe. Anisotropy effects, as measured by differences between cross sections with and without magnetic selection, are negligible for Ar, but of the order of a few percent for Kr and Xe: they show up in the glory structure of cross sections. These data and the dependence on velocity of cross sections without magnetic selection, suggest that in the regions of the very shallow van der Walals wells of KrO and XeO, Π-type electrostatic interactions are stronger than Σ ones.

H-D 2 potential from absolute integral cross section measurements at thermal energy

The H-D 2 absolute integral cross sections were measured for hydrogen atom energies of 1.8–330 meV with high accuracy. A well defined potential was obtained for separations r ≧ 4 a o with the aid of a realistic three-parameter model for the potential.

Measurement of integral cross sections for the electronic excitation in alkali-Hg collisions at energies between 15 eV and 1400 eV

Excitation cross sections for the interaction of Na, K and Rb with Hg have been measured by the observation of the light emitted from a scattering chamber. The spectra of this light are given for various collision energies. In these measurements the excitation of the resonance doublet of the alkali atoms is found to be dominant. For these states the energy dependence and the absolute value of the cross sections are reported. By a polarisation analysis the cross sections for the magnetic substate of the P3/2 component are determined.