Total electron scattering cross-sections for nitrous oxide at low electron energies

Absolute total electron scattering cross sections for nitrous oxide have been measured at low electron energies using a photoelectron source. The measurements have been carried out at 19 electron energies varying from 0.73–9.14 eV with an accuracy of ±3%. The cross sections obtained in the present experiment have been compared with other measurements.     

低能电子入射电离He原子二重微分截面的理论研究

研究了低能电子入射单电离He原子的二重微分截面(DDCS)，通过对散射电子三重微分截面在全空间的角度积分得到敲出电子的DDCS.分别用DS3C模型和BBK模型计算了入射能为26.3，28.3，30.3，32.5，34.3，36.5和40.7eV时，低能电子入射电离He原子的DDCS；研究表明：DS3C的计算结果，除在低入射能(比如26.3eV)和小敲出角之外，均能与绝对测量的实验结果较好地符合.此外，对直接和交换效应也进行了研究，给出了交换效应对截面的贡献.     

Effects of electron screening on low-energy fusion cross sections

The effects of electron screening on the low-energy cross sections of nuclear fusion reactions of astrophysical interest have been studied within the Born-Oppenheimer approximation using a simplified model. These studies indicate that a significant enhancement of the cross sections can occur already at beam energies, which are about a factor 100 higher than the electron binding energies. Cross sections near such energies can now be measured, in some cases, and several examples are discussed. For an understanding of the low-energy data as well as for a reliable extrapolation of the cross sections (for bare nuclei) to lower energies, the effects of electron screening must be well understood.     

Ionization for Hf- and W-L-shell by electron impact

Electron-induced Hf-, W-L-shell partial, total production cross sections, mean ionization cross sections and Hf-L_3-shell ionization cross sections (at two energies) have been measured as functions of electron energies (from near threshold to 36keV). The influence of electrons reflected from the backing of the thin targets on measured results was corrected using a model to relate to the electron transport process. The mean paths of electron multi-scattered in the target itself (including forward and backward scattering) were calculated by means of Monte Carlo program (EGS4) and they were used to correct measured results. A comparison with both theoretical predictions was given.     

Total cross section for inclusive electron scattering in the lowQ 2 region

Absolute cross sections for inclusive electron scattering on H, D, Be, Al, and Si have been measured in the kinematical region 0.08 (GeV/c)²<Q ²<1.0 (GeV/c)² and 0.3 GeV<v<6.5 GeV. The measurements have been performed at incident energies of 3, 5, 6, and 7 GeV and at the fixed scattering angle of 10°. A careful treatment of radiative corrections due to elastic electron nucleus scattering, quasielastic and inelastic scattering on the bound nucleons has been applied to the measured cross sections. The comparison of the nuclear cross sections with the elementary ones leads to a value ofA _eff<A with a rapid onset of this effect at small values of the scaling variablex′.     

低能He2+-He反应中单电子俘获微分散射过程的实验研究

利用冷靶反冲离子动量谱仪装置系统研究了20—40 keV He²⁺-He碰撞体系的态选择单电子俘获过程,实验获得了单电子俘获过程的态选择截面以及角微分截面.在所研究的能区范围,电子俘获到L壳层的截面最大,为主要的反应道,这与分子库仑过垒模型的反应窗理论的预测一致.实验测量的态选择截面与原子轨道紧耦合的计算结果很好地符合,与光谱方法的测量结果存在一定的差别,主要原因是光谱方法不能测量完整的反应通道信息.实验结果表明,总角微分截面在小角度范围主要来源于电子俘获到基态的贡献,在大角度范围主要来自电子俘获到激发态的贡献;电子俘获到基态的和激发态的角微分截面均出现振荡结构,这种振荡来源于电子俘获反应中分子轨道之间的相干效应.实验测量的角微分截面与其他实验和紧耦合方法的计算结果进行了比较和分析. 关键词： 冷靶反冲离子动量谱仪 态选择电子俘获 态选择截面 角微分截面     

Absolute doubly differential cross sections for electron bremsstrahlung from rare gas atoms at 28 and 50 keV

Absolute doubly differential bremsstrahlung cross sections from Xe, Kr, Ar, and Ne have been measured for electron bombarding energies of 28 and 50 keV. Bremsstrahlung photons have been detected at 90 degrees to the incident electron beam at energies ranging from 5 keV up to the kinematic end point. The results are compared with predictions of ordinary bremsstrahlung and of total bremsstrahlung that include polarizational bremsstrahlung from the target atom calculated in the stripping approximation. All previous absolute cross sections have been from thin-film solid targets and have not shown any polarizational bremsstrahlung contribution. The present results, the first from free atoms, provide definitive evidence for the contribution of polarizational bremsstrahlung to the photon spectrum from electron bremsstrahlung.     

First state selective electron capture measurements with trapped highly charged ions

The first state selective electron capture cross section measurements at eV energies are reported for collisions between C⁴⁺ ions and H₂ molecules. The cross sections are measured in a crossed beam experiment by means of Photon Emission Spectroscopy. The ion beams are decelerated in an octopole ion trap where the trap is used to guide the ion beam through the collision region. The experimental results are in excellent agreement with previous measurements at higher energies. The 3-state atomic orbital calculations of Gargaud and McCarroll generally agree with our measurements although there are some discrepancies at lower energies. However, the results for C⁴⁺ are still on a relative scale. To put our measurements on an absolute scale the N⁴⁺+ H system is investigated at keV energies. These results are in good agreement with the data of previous experiments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cross section calculations for electron scattering from platinum chemotherapeutic compounds

Cross section for electron impact ionization of carboplatin, C₆H₁₂N₂O₄Pt, and oxaliplatin, C₈H₁₄N₂O₄Pt, have been calculated within binary-encounter-Bethe model for energies from the ionization threshold up to 5000 eV. Cross section for elastic electron scattering from carboplatin and oxaliplatin molecules have also been derived using independent atom method (IAM) and additivity rule for collision energies ranging from 50 eV to 3000 eV. Obtained cross sections have been compared with relevant cross sections for cisplatin molecules.     

Total electron scattering cross-sections for carbon monoxide at low electron energies

Absolute total electron scattering cross-sections for carbon monoxide have been measured at low electron energies using a photoelectron source. The measurements have been carried out at 22 electron energies varying from 0.73 to 9.14 eV with an accuracy of ±3%. The cross-sections obtained in the present experiment have been compared with other measurements and theoretical computations.     

Triple differential cross sections for low energy electron impact ionisation of helium

Measurements are reported of the triple differential cross sections for the ionisation of helium by electron impact. Data are presented for incident energies of 100 and 80.5 eV at several scattering angles and compared with previous measurements and theoretical calculations.     

Absolute electron scattering cross sections for the CF2 radical

Using a crossed electron-molecular beam experiment, featuring a skimmed nozzle beam with pyrolytic radical production, absolute elastic cross sections for electron scattering from the CF2 molecule have been measured. A new technique for placing measured cross sections on an absolute scale is used for molecular beams produced as skimmed supersonic jets. Absolute differential cross sections for CF2 are reported for incident electron energies of 30-50 eV and over an angular range of 20-135 deg. Integral cross sections are subsequently derived from those data. The present data are compared to new theoretical predictions for the differential and integral scattering cross sections, as calculated with the Schwinger multichannel variational method using the static-exchange and static-exchange plus polarization approximations.     

一种考虑几何屏蔽效应的计算“电子-分子”散射总截面的可加性规则修正方法

在考虑分子内原子间的几何屏蔽效应随电子入射能量变化的基础上, 提出了一种能够在中、高能区准确计算“电子-分子”散射总截面的可加性规则修正方法. 利用这一修正后的可加性规则并使用“电子-C, H, O, N原子”散射总截面的实验数据, 在50—5000 eV内计算了电子被NO, N₂O, NO₂和C₂H₆分子散射的总截面, 且将计算结果与实验结果及其他理论结果进行了比较. 结果表明, 利用这一方法修正过的可加性规则进行计 关键词： 电子散射 可加性规则 总截面 几何屏蔽效应     

Cross section calculations for electron impact ionization and elastic scattering from cisplatin

Total cross section for single electron-impact ionization of cisplatin (H₆N₂Cl₂Pt) molecule has been calculated with the binary-encounter-Bethe (BEB) model from the ionization threshold up to 5 keV. To obtain input data for the BEB calculations, geometric and electronic structures of the cisplatin have been studied with quantum chemical methods. Elastic cross section for electron collisions with cisplatin have also been evaluated using independent atom method with static-polarization model potential for incident energies ranging from 50 to 3000 eV. The obtained geometric structure of cisplatin is compared with available experimental and theoretical data. Calculated cross sections have been compared with related cross sections for selected purine and pirimidine bases.     

Oppenheimer-Phillips effect and electron screening ind+ d fusion reactions

Thed(d, n) ³He andd(d,p)t fusion reactions have been studied at center-of-mass energies E=1.6 to 130 keV using intense beam currents from 30, 100, and 450 kV accelerators in combination with detectors in close and far geometry. The cross sesction ratio,R(E)=σ(d,n)/σ(d, p), approaches unity (within 2%) at low energies; thus there is no experimental evidence for the Oppenheimer-Phillips effect at subcoulomb energies. The cross sections of d(d, p)t at E≦10keV show clear evidence for electron screening effects. However, the observed cross section enhancement is significantly larger than can be accounted for from available atomic physics models.     

Excitation of molecular vibrations by positron impact

Absolute cross sections for the vibrational excitation of CO, CO2, and H2 by positron impact are presented for incident positron energies from 0.5 eV to several electron volts. The measurements use a novel technique that exploits the adiabatic motion of a positron beam in a strong magnetic field. This work is the first systematic experimental study of vibrational excitation by positron impact, and extends to energies where positron measurements have traditionally been difficult. The measured cross sections are compared with available theoretical calculations.     

Double electron capture in H+ + Mg collisions

The cross section for double electron capture in H⁺ + Mg collisions has been measured over the proton energy range 1.1 keV to 80 keV. The cross section exhibits structure at low energies and is rising below 2.8 keV. Results are discussed and compared with recent multichannel Landau-Zener calculations and with previous measurements.     

Absolute cross sections for one electron capture into excited projectile states in collisions between He2+ (15–150 keV) and Li atoms

We have studied the He²⁺-Li collision system at laboratory energies between 15 and 150 keV using optical methods. From the measured emission cross sections we derive state-selective capture cross sections for n = 2,3,4 and n ? 5 states of the He⁺ ions. Our data are consistent with theoretical predictions of Bransden and Ermolaev. The total capture cross sections as evaluated from our emission cross section data, agree very well with the results of McCullough et al. obtained from projectile charge detection measurements. Near 15 keV our emission cross sections for 30.4 nm and 25.6 nm are much larger than those measured previously by Barrett and Leventhal at slightly lower energies.     

The Trojan Horse Method in nuclear astrophysics

The study of energy production and nucleosynthesis in stars requires an increasingly precise knowledge of the nuclear reaction rates at the energies of interest. To overcome the experimental difficulties arising from the small cross sections at those energies and from the presence of the electron screening, the Trojan Horse Method has been introduced. The method provides a valid alternative path to measure unscreened low-energy cross sections of reactions between charged particles, and to retrieve information on the electron screening potential when ultra-low energy direct measurements are available.     

Mn and Cu K-shell ionization cross sections by slow electron impact

Near the threshold energy, electron induced Mn and Cu K-shell ionization cross sections have been measured. Except for energies very close to threshold, the results are in good agreement with the semi-empirical formula of Green and Cosslett.