Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.     

Further study and analysis of the <Superscript>7</Superscript>Li on <Superscript>56</Superscript>Fe reaction at 50 MeV incident energy

We present deuteron and triton spectra measured at 12 laboratory angles from the reaction of 50 MeV ⁷Li on ⁵⁶Fe together with evaporative components as modeled by CASCADE and fitted to the backward angle data. The deuteron and triton “break-up” spectra obtained by subtracting the evaporative components from the measured spectra are also presented. The break-up of the ⁷Li projectile near the surface occurs with high probability and the major fraction of the break-up cross-section is taken by (⁷Li,α) transfer process. A crude estimate of the fraction of the total cross-section is found to be of the same order of magnitude as the overall spectroscopic factor determined by the diffraction model. The value of the estimated fraction of total cross section at 50 MeV incident energy is compared to that at 68 MeV incident energy for the same reaction. However, these values of estimated fraction of total cross section are found very much consistent with the measured yields at both incident energies. The importance of the level density parameter in locating the maximum of excitation energy is indicated in the diffraction model.     

Energy spectra of geomagnetically trapped oxygen ions

In a series of COSMOS satellite flights plastic nuclear track detectors have been exposed in low-earth orbits to monitor anomalous cosmic rays (ACR) at energies below 25 MeV/nuc. The analysis of energy spectra has now been extended to energies up to 40 MeV/nuc for two exposures aboard COSMOS 2260 in 1993 and COSMOS 2311 in 1995. Our data on trapped ACR (TACR) oxygen energy spectra might indicate the influence of energy-dependent stripping probabilities and the presence of multiply charged ACR oxygen at high energies as reported by latest SAMPEX observations.     

Laser field induced interband absorption in a strained GaAs/GaAlAs double quantum well system

Effect of laser field intensity on exciton binding energies is investigated in a GaAs/ GaAlAs double quantum well system. Calculations have been carried out with the variational technique within the single band effective mass approximations using a two parametric trial wave function. The interband emission energy as a function of well width is calculated in the influence of laser field. The laser field induced photoionization cross-section for the exciton placed at the centre of the quantum well is computed as a function of normalized photon energy. The dependence of the photoionization cross-section on photon energy is carried out for the excitons. The resulting spectra are brought out for light polarized along and perpendicular to the growth direction. The intense laser field dependence of interband absorption coefficient is investigated. The results show that the exciton binding energy, interband emission energy, the photoionization cross-section and the interband absorption coefficient depend strongly on the well width and the laser field intensity. Our results are compared with the other existing literature available.     

Three-body final state breakup in the27Al(14N,X) reaction at 116 MeV bombarding energy

The energy spectra and angular distributions of products in the reaction²⁷Al(¹⁴N,X) have been measured at 116 MeV bombarding energy. It is shown that the energy spectra of the products lighter than the projectile, are well described by a three-body breakup calculation. The experimental total breakup cross-section estimated in the present work, together with Glas-Mosel calculation of the fusion cross-section, are in a reasonable agreement with the optical model total reaction cross-section.     

高能带电粒子直接产生电子对

本文叙述利用场强为6200高斯的磁云室,对级联簇射中的能量大于30兆电子伏的电子在铝中直接产生电子对的平均总截面进行了测量。实验上总共找到真正由电子产生的电子三岔8.1个,相应于三岔产生的平均自由路程为672±585厘米或平均总截面为(0.25±0.22)×10^-25厘米²。在数据处理中,对假三岔数目的除去作了应有的适当考虑。此外对Bhabha及Murota等的总截面公式也作了适合于于我们实验具体情况的修正,并算出总截面值,最后将它同实验值作了比较。结果我们认为实验上测得的值和Murota等的总截面值较为接近,但也不与Bhabha的截面值矛盾。     

The energy dependence of the proton-proton total cross-section for centre-of-mass energies between 23 and 53 GeV

Measurements of proton-proton elastic scattering at angles around 6 mrad have been made at centre-of-mass energies of 23, 31, 45 and 53 GeV using the CERN Intersecting Storage Rings. The absolute scale of the cross-section was established by determination of the effective density of the colliding beans in their overlap region. Proton-proton total cross sections were deduced by extrapolation of the elastic differential cross-section to the forward direction and by application of the optical theorem. The results indicate that over the energy range studied the proton-proton total cross-section increases from about 39 to about 43 mb.     

Photo-neutron cross-section calculations of 142,143,144,145,146,150Nd rare-earth isotopes for (γ, n) reaction

The theoretical photo-neutron cross sections for (γ, n) reaction have been calculated on ^{142,143,144,145,146,150}Nd rare-earth isotopes at photon energies of 8–23 MeV using the PCROSS, TALYS 1.2, and EMPIRE 3.1 computer codes. TALYS 1.2 two-component exciton model and EMPIRE 3.1 exciton model has been used to calculate the pre-equilibrium photo-neutron cross sections. PCROSS Weisskopf-Ewing model has been used for the reaction equilibrium cross-section calculations. The obtained cross sections have been compared with each other and against the experimental values existing in the EXFOR database. Generally, pre-equilibrium model cross-section calculations are in good agreement with the experimental data for all reactions along the incident photon energy in this study.     

Branching ratios and the partial photoionization cross-section for the 3s electron of argon

Binding-energy spectra obtained using the dipole (e, 2e) electron impact coincidence method have been used to derive the 3s/3p cross-section ratios for the photoionization of argon up to 75 eV. The 3s and 3p photoionization branching ratios have been obtained by making use of recently determined double photoionization yields. The partial photoionization cross-section (oscillator strength) for 3s ionization, obtained using the branching ratio and the known total photoionization cross-section, shows the deep minimum ca. 10 eV above threshold which has been predicted by those theoretical calculations which include electron correlation effects. Below 50 eV the cross-section is in excellent agreement with the SRPAE calculation. The results are in close agreement with recent measurements made using synchrotron radiation but are consistently smaller below the minimum and larger at the higher energies.     

Total hadronic cross-section of photon-photon interactions at LEP

The total hadronic cross-section for the interaction of real photons, hadrons, is measured for centre-of-mass energies GeV. The cross-section is extracted from a measurement of the process hadrons, using a luminosity function for the photon flux together with form factors for extrapolating to real photons ( GeV). The data were taken with the OPAL detector at LEP at centre-of-mass energies , 172$ and 183 GeV. The cross-section is compared with Regge factorisation and with the energy dependence observed in p and pp interactions. The data are also compared to models which predict a faster rise of compared to p and pp interactions due to additional hard interactions not present in hadronic collisions. Received: 3 June 1999 / Published online: 6 April 2000     

Scattering of electrons with formyl radical

A detailed theoretical study is carried out for electron interactions with formyl radical (HCO) with incident energies ranging from 0.01 to 5000 eV. This wide range of energy has allowed us to investigate a variety of processes and report data on vertical electronic excitation energies, dissociative electron attachment (DEA) and total cross-section along with scattering rate coefficients. We observed Ramsaur–Townsend minimum at 0.59 and 0.74 eV using DZP and cc-pDVZ basis sets, respectively. HCO has large number of low-lying excited states and the present study finds an overall good agreement with earlier reported data. In order to compute total cross-section, we have employed ab initio R-matrix method (0.01 to ～ 20 eV) and the spherical complex optical potential method (～ 10 to 5000 eV) employing static-exchange plus polarisation potential. The R-matrix calculations are performed using a close coupling method with the aid of 21 target states, 1191 configuration state functions and 195 channels. The DEA cross-sections of fragmentation of H^?, excitation cross- sections and scattering rate coefficients are reported for the first time. Total cross section presented here will provide a reference data set over an extensive impact energy range.     

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 130–172 GeV at LEP

Production of events with hadronic and leptonic final states has been measured in collisions at centre-of-mass energies of 130–172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z events, and compared to Standard Model expectations. The ratio of the cross-section for production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of -Z interference. The energy dependence of has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for -channel contributions from new massive particles and to place limits on gaugino pair production with subsequent decay of the gaugino into a light gluino and a quark pair. Received: 30 July 1997 / Published online: 10 March 1998     

Rydberg states of HCN observed by electron impact spectroscopy

The electron energy loss spectrum of HCN has been determined in the energy region 8–13.6 eV at impact energies of 100, 50 and 30 eV. It is shown that energy loss spectra of HCN at intermediate impact energies can be satisfactorily analysed unlike the diffuse unassigned optical absorption spectra that have previously been reported. Rydberg series have been assigned using term values and quantum defects together with ionization potentials obtained by photoelectron spectroscopy.     

Energy dependence of fission probabilities induced by negative pions in Sn,Au and Bi

Fission probabilities induced by negative pions in Sn, Au and Bi at different energies using variety of nuclear track detectors have been studied. The target-detector assemblies in 4π-geometric configuration were irradiated at the AGS facility of Brookhaven National Laboratory, USA. After etching the exposed detectors at appropriate etching conditions the detectors have been scanned for the tracks of fission fragments produced as a result of interaction of pions with the target nuclei. Based on the track counts, the values of fission cross sections have been measured and fission probabilities have been calculated using the reaction cross-section calculated with the help of the cascade-exciton model code CEM95. The values of fission probability based on experimental fission cross-sections have been compared with the theoretically calculated values of fission probabilities obtained using the CEM95 code. Theoretical values of fission probability have been computed for incident pion energy up to 2500 MeV in Sn, Au and Bi for comparison to fission data for high energy negative pions at 500, 672, 1068, 1665 MeV and 2300 MeV energies for the same targets. The values of fission probability based on the experimental fission cross section and theoretically calculated values of fission probability have been compared. Reasonable agreement has been observed among the experimentally measured and theoretically computed values of fission probabilities. A saturation of probabilities has been observed for Au and Bi at higher energies, but for Sn an increase of probability with the increase of pion beam momentum up to 1665 MeV has been observed.     

The definition of the effective interaction energy for astrophysical relevant reactions

Experimental studies of nuclear reactions of astrophysical interest are hampered by the exponential drop of the cross-section with decreasing energy. Generally, the effects of the projectile energy loss in the target cannot be neglected and the reaction yield is proportional to the average value of the cross-section over the interaction energies inside the target. Local cross-section values, instead of averaged, are needed to evaluate stellar reaction rates. To deal with this, several different effective interaction energy definitions have been introduced during the years, leading to potentially discrepant results. Thus, a well-defined procedure for data reduction is required. This work briefly reviews the theoretical ground for the experimental cross-section data reduction and the effective interaction energies definitions up to now introduced. The self-consistent approach introduced by B.W. Filippone et al. is discussed and its application to the data analysis of non-resonant and narrow-resonant reactions is presented. A comparison of the results obtained using the different approaches is also reported.     

Total cross section,inelasticity, and multiplicity distributions in proton-proton collisions

Multiparticle production in high-energy proton-proton collisions has been analyzed in the framework of the strongly correlated quark model of the hadron structure elaborated by the author. It is shown that inelasticity decreases at high energies and the violation of KNO scaling is a consequence of total cross-section growth and increases with collision energy masses of intermediate clusters.     

Magnetic field-modulated magnetoreflectance of europium chalcogenides

The optical constants of EuO and EuS single crystals have been determined at 300 K by means of a Kramers-Kronig analysis of the reflectivity for photon energies up to 12 eV. For EuS the optical constants have also been determined above and below the Curie temperature in the energy region from 1.5 to 5.7 eV. A first tentative assignment of optical structure to interband transitions has been attempted on the basis of recent orthogonal plane wave (OPW) and earlier augmented plane wave (APW) band structure calculations. For photon energies from 1.2 to 3.8 eV a low magnetic field-modulated magnetoreflectance has been measured using circularly polarized light. By use of the Kramers-Kronig relation for the differential reflectance spectra in conjunction with our data of the optical constants, a detailed analysis of the magnetoreflectance spectra of EuS was carried out for the first time.     

Elastic scattering and fusion cross-sections in 7Li + 27Al reaction

With an aim to understand the effects of breakup and transfer channels on elastic scattering and fusion cross-sections in the ⁷Li + ²⁷Al reaction, simultaneous measurement of elastic scattering angular distributions and fusion cross-sections have been carried out at various energies (E _lab?=?8.0–16.0 MeV) around the Coulomb barrier. Optical model (OM) analysis of the elastic scattering data does not show any threshold anomaly or breakup threshold anomaly behaviour in the energy dependence of the real and imaginary parts of the OM potential. Fusion cross-section at each bombarding energy is extracted from the measured α-particle evaporation energy spectra at backward angles by comparing with the statistical model prediction. Results on fusion cross-sections from the present measurements along with data from the literature have been compared with the coupled-channels predictions. Detailed coupled-channels calculations have been carried out to study the effect of coupling of breakup, inelastic and transfer, channels on elastic scattering and fusion. The effect of 1n-stripping transfer coupling was found to be significant compared to that of the projectile breakup couplings in the present system.     

Cross sections for electron collision with five-membered ring heterocycles

The absolute total cross-section (TCS) for electron scattering from isoxasole, (CH)₃NO, molecule has been measured using the linear transmission technique for impact energies ranging from 1 to 400 eV. The measured TCS energy dependence appears typical for highly polar targets; over whole energy range applied, the magnitude of TCS generally decreases as the energy increases. Some narrow features located near 1.2 and 2.7 eV have been observed in the TCS curve as well as a broad enhancement spanned between 5 and 15 eV. The TCS for electron-isoxazole scattering has been compared with TCS data for furan, (CH)₄O; differences and similarities in the appearance of both TCSs energy functions are indicated and discussed. In addition, for several five-membered ring heterocycle molecules: isoxazole, pyrrole [(CH)₄NH] and tiophene [(CH)₄S], integral elastic (ECS) and ionization (ICS) cross sections have been calculated at intermediate and high electron-impact energies in the additivity rule approximation and the binary-encounter-Bethe approach, respectively. For isoxazole and furan the sums of ECS and ICS are in very good agreement with the respective measured TCSs above 50 − 60 eV.     

Total electron ionization cross-sections for molecules of astrochemical interest

ABSTRACT

We describe a newly upgraded instrument for measuring absolute total electron ionization cross-sections over the energy range from 0 to 300?eV, and present cross-sections for nine previously unstudied molecules, as well as several small molecules for which comparison data is available. The measured cross-sections are compared with the predictions of the BEB model, and show reasonable agreement with the model, albeit peaking at higher electron energies than predicted by the model. We show that the maxima in the cross-sections follow an additivity model, such that the molecular cross-sections can be expressed as a sum over contributions from the constituent atoms. These contributions have been determined from a global fit to the data for all molecules studied, and allow maximum cross-sections to be predicted for molecules that have not been studied to date. We demonstrate the expected correlation between the maximum ionization cross-section and the molecular polarisability, and show that the atomic contributions to the cross-section show a similar dependence on the atomic polarisability. The observed correlation can be used as an alternative method for predicting unknown maximum cross-sections.