TOTAL CROSSS ECTIONS FOR ELECTRON SCATTERING FROM SIMPLE HYDROCARBON MOLECULES: C_2H_4,C_2H_6 AND C_3H_8

１ＩＮＴＲＯＤＵＣＴＩＯＮＳｉｍｐｌｅｈｙｄｒｏｃａｒｂｏｎｍｏｌｅｃｕｌｅｓａｓａｎｉｍｐｏｒｔａｎｔｃｏｍｐｏｎｅｎｔｉｎｔｈｅｐｌａｎｅｔａｒｙａｎｄｃｏｍｅｔａｒｙａｔｍｏｓｐｈｅｒｅａｎｄａｓａｄｏｍｉｎａｎｔｍａｔｅｒｉａｌｉｎｔｈｅｆｉ...     

A Study of Intermediate Energy Proton-^16O Elastic Scattering Based on the α-Particle Model

In the framework of KMT multiple scattering theory, an optical potential for the intermediate energy proton-160 elastic scattering is presented based on the α particle model of 160. The differential cross sections, the analyzing powers, and the total cross sections of the intermediate energy proton-160 scattering have been calculated by using the obtained optical potential. The main features of the measured angular distributions of the cross section and the analyzing power can be well described. The calculated total cross sections are in good agreement with the experimental data at energies below 0.7 GeV and underestimate the data about 8% at higher energies.     

Coupled-channel optical calculation for positron—lithium scattering

Positron scattering with atomic lithium is investigated by using a coupled-channel optical method.The ionization continuum and positronium formation channels are taken into account via a complex equivalent-local optical potential.The positronium formation cross sections and the ionization cross sections,as well as the total scattering cross sections,are reported at energies above 3 eV and compared with available experimental and theoretical data.     

Positron scattering and ionization of neon atoms—theoretical investigations

Although positron scattering with inert gas atoms has been studied in theory as well as in experiment, there are discrepancies. The present work reports all the major total cross sections of e+-neon scattering at incident energies above ionization threshold, originating from a complex potential formalism. Elastic and cumulative inelastic scatterings are treated in the complex spherical e+-atom potential. Our total inelastic cross section includes positronium formation together with ionization and excitation channels in Ne. Because of the Ps formation channel it is difficult to separate out ionization cross sections from the total inelastic cross sections. An approximate method similar to electron-atom scattering has been applied to bifurcate ionization and cumulative excitation cross sections at energies from threshold to 2000 eV. Comparisons of present results with available data are made. An important outcome of this work is the relative contribution of different scattering processes, which we have shown by a bar-chart at the ionization peak.     

硅烷与硅的质量衰减截面实验测量

用高能质子激发单元素靶或化合物靶产生的特征X射线源,系统地测量了1.486—15.165千电子伏能区里硅烷和8.041—29.109千电子伏能区里硅元素的质量衰减系数.不仅在实验上验证了布喇格相加规则在气体化合物中的适用性,而且得到了1.4一6千电子伏能区里硅元素的质量衰减截面,从而填补了硅元素在该能区的数据空白.从实验测得的总截面中减去康普顿散射和漫散射截面,便得到硅元素的光电截面值,并与理论值进行了比较. 关键词：     

A semi-empirical formula for total cross sections of electron scattering from diatomic molecules

A fitting formula based on the Born approximation is used to fit the total cross sections for electron scattering by diatomic molecules (CO, N₂, NO, O₂ and HCl) in the intermediate- and high-energy range. By analyzing the fitted parameters and the total cross sections, we found that the internuclear distance of the constituent atoms plays an important role in the e-diatomic molecule collision process. Thus a new semi-empirical formula has been obtained. There is no free parameter in the formula, and the dependence of the total cross sections on the internuclear distance has been reflected clearly. The total cross sections for electron scattering by CO, N₂, NO, O₂ and HCl have been calculated over an incident energy range of 10–4000 eV. The results agree well with other available experimental and calculation data.     

On studying energy dependences of π− p elastic scattering cross sections in the 33–55 GeV/c range

The π^? p differential elastic scattering cross sections have been measured for eight momenta in the 33–55 GeV/c range. The energy dependence of the slope and of the total elastic scattering cross sections has been determined experimentally. The results are compared with the known data. The experimental data are compared both with the Regge pole model and with the quasi-potential one.     

Total cross section prediction of the collisions of positrons and electrons with alkali atoms using Gradient Tree Boosting

A relatively new computational technique, namely gradient tree boosting (GTB), is presented for modeling the total cross sections of the scattering of positrons and electrons by alkali atoms in the low and intermediate energy regions. The calculations have been performed in the framework of gradient tree boosting (GTB). The GTB has been running based on the experimental data of the total collisional cross sections to produce the total cross sections for each alkali atom as a function of the incident energy of the projectile as well as the atomic number and the static dipole polarizability of the atom. Moreover our GTB model is used to predict the experimental data for total collisional cross sections that are not used in the training session. The calculated and predicted total collisional cross sections are compared with the experimental data. We find that the GTB technique shows a good match to the experimental data. To our knowledge, this is the first application of the GTB technique to the data of positron and electron collisions with alkali atoms at low and intermediate energies.     

Electron-impact total cross sections for inelastic processes for furan,tetrahydrofuran and 2,5-dimethylfuran

We report total inelastic, total ionisation and summed total excitation cross sections for electron scattering on furan, tetrahydrofuran (THF) and 2,5-dimethylfuran at energies between the ionisation threshold and 5 keV. We have employed the spherical complex optical potential formalism (SCOP) to calculate the total inelastic cross sections (Q_inel) and have used complex scattering potential-ionisation contribution (CSP-ic) method to derive total ionisation cross sections (Q_ion) and summed total excitation cross sections (∑Q_exc) from the calculated Q_inel. We have also computed Q_ion for these molecules using binary-encounter-Bethe (BEB) approach. We have compared our total cross sections (TCS) with available experimental as well as previous theoretical results and have found good agreement. The results are presented graphically as well as numerically.     

Absolute differential bremsstrahlung cross section for the scattering of 0.6-keV electrons by xenon atoms

The spectral distribution of the absolute differential cross section for total bremsstrahlung, including ordinary and polarization, for the scattering of 0.6-keV electrons from free xenon atoms has been measured. The bremsstrahlung photons have been detected at an angle of 97° with respect to the electron motion direction. The investigations have been carried out in the ultrasoft x-ray spectral region 60–240 eV. The results are compared with the total cross sections for bremsstrahlung calculated in several approximations for the scattering of 5-and 25-keV electrons by Xe atoms. Both the value and the spectral distribution of the experimental absolute cross sections are most satisfactorily reproduced by the calculations in the distorted partial wave approximation.     

Periodic structures in the Franck-Hertz experiment with neon: Boltzmann equation and Monte-Carlo analysis

A new experimental technique for the measurements of the total cross section for electron scattering from atoms and molecules at very low energy is described. Momentum transfer cross sections for scattering from Ar, Kr and Xe at very low energies were carefully derived using the modified effective range theory from the recently measured total cross sections, which were obtained with a new experimental technique utilizing the threshold photoelectron source. A significant discrepancy between the momentum cross sections derived from the present analysis and those determined in the previous electron swarm studies was found at energies below 100 meV. The findings emphasize the need of further high precision experiments in the very low energy region as well as re-analysis of the previous swarm data.     

Recent positron-atom cross section measurements and calculations

We review recent cross section results for low-energy positron scattering from atomic targets. A comparison of the latest measurements and calculations for positron collisions with the noble gases and a brief update of the newest studies on other atoms is presented. In particular, we provide an overview of the cross sections for elastic scattering, positronium formation, direct and total ionisation, as well as total scattering, at energies typically between about 0.1 and a few hundred eV. We discuss the differences in the current experimental data sets and compare those results to the available theoretical models. Recommended data sets for the total cross section are also reported for each noble gas. A summary of the recent developments in the scattering from other atoms, such as atomic hydrogen, the alkali and alkaline-earth metals, and two-electron systems is finally provided.     

250—1400eV能区N2分子的电子散射全截面测量

建立了一套直线透射式全截面测量装置,并测量了250—1400eV能区N₂分子的电子散射全截面,实验误差为3.5%。测量的结果与已报道实验和理论工作做了比较。 关键词：     

Measurements of positronium formation cross sections for positron-ar and-K scattering

We have made preliminary measurements of positronium (Ps) formation cross sections for 9 to 452 eV positrons scattered from Ar atoms and for 1 to 20 eV positrons scattered from K atoms. Our experimental approach involves setting lower and upper limits on Ps formation cross sections using a combination of (1) the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the wall of the scattering cell in which the Ps is formed, and (2) the determination of scattering cross sections associated with the measured transmission of the positron beam through the gas in our scattering cell with the angular discrimination of our apparatus deliberately made as poor as possible. The constraints placed by these lower and upper limits are used to check for consistency with prior experimental and theoretical results for Ar and to provide the first measurements of Ps formation cross sections for K, which are compared with available theoretical results.     

Glory undulations in the total cross section for scattering of heavy rare gas atoms

In a supersonic molecular beam apparatus the velocity dependence of the total cross section for scattering of argon and krypton beams by argon, krypton and xenon has been measured for relative velocities ranging from 0.55 to 4.30 km · s^-1. For all these systems a number of glory extrema were well resolved. The measured cross sections are compared with cross sections calculated on the basis of recently proposed pair potentials. For the systems Ar-Ar, Kr-Kr and Ar-Kr the glory structure is fairly well described by the potentials, however, the energy dependence of the cross sections is not. The available potentials for the systems Ar-Xe and Kr-Xe describe the glory structure less accurately. Rather severe changes of the potentials will be required to obtain agreement with the total cross section data. A qualitative analysis of the required changes is presented.     

Small-angle elastic scattering of 14.8 mev neutrons

The 14.8 MeV neutron elastic scattering differential cross sections of U, Pb, Hg, Ta, Sn and Al have been measured for angles extending from 10° down to 1.8° and for U and Pb down to 0.35°. Nuclear cross sections extrapolated to 0° have been compared with the Wick limit. The U nuclear cross sections did not rise as sharply toward 0°, and were not in as serious disagreement with the spherical optical model, as in earlier measurements. The smallest-angle data verified the Schwinger prediction.     

正电子被分子散射总截面的计算

将光学势方法与可加性规则（ａｄｄｉｔｉｖｉｔｙｒｕｌｅ）相结合，我们计算了能量在１０－１０００ｅＶ范围内正电子被分子（Ｈ２，Ｎ２，ＨＣｌ，ＮＨ３，ＣＨ４，ＳＦ６）散射的总截面，计算结果与已有的实验结果进行了比较。     

Elastic and inelastic scattering of neutrons from Fe and Cu : (I). Measurements from 8 to 14 MeV and a spherical optical model analysis

Differential cross sections were measured at 8, 10, 12 and 14 MeV for elastic scattering of neutrons from enriched samples of ⁵⁴Fe, ⁵⁶Fe, ⁶³Cu and ⁶⁵Cu. Inelastic scattering to the first excited state in ^{54, 56}Fe was also observed. For the ^{63, 65}Cu isotopes, the inelastic cross sections for scattering to the combined group of the three (five) states were determined at 8 and 10 MeV (12 and 14 MeV). The elastic scattering data are compared to predictions of earlier global optical models. New spherical optical model representations were obtained. These data were combined with data for nickel, tin and lead to generate a new global parametrization. Comparisons of derived volume integrals for the potentials, total cross sections and potential radii are made to available information.     

A Comprehensive Theoretical Analysis of <Superscript>6,7</Superscript>Li + <Superscript>64</Superscript>Zn Elastic Scattering in a Wide Angular Range Around the Coulomb Barrier

In this paper, the elastic scattering angular distributions of ^6,7Li on ⁶⁴Zn have been investigated by using various nuclear potentials. For this, we use the phenomenological Woods-Saxon potential, the real double folding potential with the density-independent M3Y effective interaction supplemented with an imaginary part in Woods-Saxon form and the double folding potentials multiplied with a normalization factor of the real and imaginary parts via the density-independent and CDM3Y6 density-dependent versions of the M3Y effective interaction have been used. The results have been compared with each other as well as with the experimental data. It has been observed that the agreement between the theoretical results and earlier reported data is perfect. Finally, the change of the total reaction cross sections with energy has been investigated.     

Multiple scattering effects for quasifree scattering in 3He(d,dd)1H breakup reaction

The differential cross sections for the ³He(d, dd)¹H breakup reaction have been measured in the kinematical region corresponding to quasifree scattering (QFS). The angular dependence of the cross section at the minimum laboratory energy of the unobserved proton has been obtained. The shapes of energy spectra are approximately reproduced by a calculation in the plane-wave impulse approximation (PWIA). As for the angular dependence of the cross section and for the absolute values, the calculation fails to reproduce the experimental results. A calculation with multiple scattering effects reproduces the experimental data well, not only for the shape of the energy spectra but also for the angular dependence. For the absolute cross sections, the ratio of the experimental values to the calculated ones with multiple scattering effects is 0.7 and this value is improved compared with the value of 0.3 obtained by the PWIA calculation.