Cross Sections For Electron Production Research Articles

The FLUKA cross sections for cosmic-ray leptons and uncertainties on current positron predictions

Cosmic-ray (CR) antiparticles have the potential to reveal signatures of unexpected astrophysical processes and even new physics beyond the Standard Model. Recent CR detectors have provided accurate measurements of the positron flux, revealing the so-called positron excess at high energies. However, the uncertainties related to the modelling of the local positron flux are still very high, significantly affecting our models of positron emission from pulsars and current dark matter searches.In this work, we report a new set of cross sections for positron and electron production derivedfrom the FLUKA code. We compare them with the most extended cross-section data-sets and showthe impact of neglecting the positron production from heavy CRs. Then, we review the mostsignificant sources of uncertainties in our current estimations of the secondary positron flux atEarth and examine for the first time the impact of considering the spiral arm structure of theGalaxy in these estimations. Finally, we provide state-of-the-art predictions of the local positronflux and discuss the limitations of our dark matter searches with positrons and difficulties todetermine the contribution from pulsars to the positron flux at low energies.

Charge Transfer and Electron Production in Proton Collisions with Uracil: A Classical and Semiclassical Study.

Cross sections for charge transfer and ionization in proton-uracil collisions are studied, for collision energies 0.05<E<2500 keV, using two computational models. At low energies, below 20 keV, the charge transfer total cross section is calculated employing a semiclassical close-coupling expansion in terms of the electronic functions of the supermolecule (H-uracil)+. At energies above 20 keV, a classical-trajectory Monte Carlo method is employed. The cross sections for charge transfer at low energies have not been previously reported and have high values of the order of 40 Å2, and, at the highest energies of the present calculation, they show good agreement with the previous results. The classical-trajectory Monte Carlo calculation provides a charge transfer and electron production cross section in reasonable agreement with the available experiments. The individual molecular orbital contributions to the total electron production and charge transfer cross sections are analyzed in terms of their energies; this permits the extension of the results to other molecular targets, provided the values of the corresponding orbital energies are known.

Development and validation of proton track-structure model applicable to arbitrary materials

A novel transport algorithm performing proton track-structure calculations in arbitrary materials was developed. Unlike conventional algorithms, which are based on the dielectric function of the target material, our algorithm uses a total stopping power formula and single-differential cross sections of secondary electron production. The former was used to simulate energy dissipation of incident protons and the latter was used to consider secondary electron production. In this algorithm, the incident proton was transmitted freely in matter until the proton produced a secondary electron. The corresponding ionising energy loss was calculated as the sum of the ionisation energy and the kinetic energy of the secondary electron whereas the non-ionising energy loss was obtained by subtracting the ionising energy loss from the total stopping power. The most remarkable attribute of this model is its applicability to arbitrary materials, i.e. the model utilises the total stopping power and the single-differential cross sections for secondary electron production rather than the material-specific dielectric functions. Benchmarking of the stopping range, radial dose distribution, secondary electron energy spectra in liquid water, and lineal energy in tissue-equivalent gas, against the experimental data taken from literature agreed well. This indicated the accuracy of the present model even for materials other than liquid water. Regarding microscopic energy deposition, this model will be a robust tool for analysing the irradiation effects of cells, semiconductors and detectors.

Diffractive incoherent vector meson production off protons: a quark model approach to gluon fluctuation effects

Fluctuations play an important role in diffractive production of vector mesons. It was in particular recently suggested, based on the Impact-Parameter dependent Saturation model (IPSat), that geometrical fluctuations triggered by the motion of the constituent quarks within the protons could explain incoherent diffractive processes observed at HERA. We propose a variant of the IPSat model which includes spatial and symmetry correlations between constituent quarks, thereby reducing the number of parameters needed to describe diffractive vector meson production to a single one, the size of the gluon cloud around each valence quark. The application to J/varPsi , rho and phi diffractive electron and photon production cross sections reveal the important role of geometrical fluctuations in incoherent channels, while other sources of fluctuations are needed to fully account for electroproduction of light mesons, as well as photo production of J/varPsi mesons at small momentum transfer.

On the use of additivity rules to estimate electron production cross sections in proton-biomolecule collisions

Additivity rules are employed to estimate electron production cross sections for proton collisions with nucleobases and amino acids, using as input experimental data for proton collisions with atoms and small molecules. Cross sections (total and single differential, in electron energy) are calculated for collision energies 10 keV ≤ E ≤ 2 MeV. The results show that this simple procedure yields cross sections in good agreement with the available experimental and theoretical cross sections at high collision energies and it is able to reproduce the energy dependence of the total cross sections, including the presence of maxima at intermediate energies.

A study of electron production in proton-biomolecule collisions using additivity rules

SynopsisAdditivity rules are employed to estimate electron production cross sections for proton collisions with nucleobases and amino acids at collision energies 10 keV ≤ E ≤ 2 MeV. Total and differential cross sections agree with the available theoretical and experimental cross sections, and the method can be easily applied to estimate electron production cross sections for collisions with other biomolecules.

Measurement of electrons from heavy-flavour hadron decays in pp and p-Pb collisions with ALICE

ALICE measured electrons from inclusive heavy-flavour hadron decays and beauty-hadron decays at mid-rapidity in pp collisions at = 7 TeV and 2.76 TeV and p-Pb collisions at = 5.02 TeV. For both pp collision energies, pT-differential electron production cross sections are presented and compared to pQCD predictions. For p-Pb collisions, the pT-dependent nuclear modification factor of electrons from inclusive heavy-flavour hadron decays is presented.

Double and single differential cross sections for secondary electron production in 6.0 MeV/u O8+ + H2O collisions

We discuss double and single differential cross sections (DDCSs and SDCS) for secondary electron production (30-1000 eV and 20-160°) in collisions of 6.0 MeV/u O8+ ions with water vapor. All the DDCSs and SDCS were compared with previous experimental results obtained with 6.0 MeV/u C6+ ions. The DDCSs of O8+ ions showed nearly symmetric angular distributions around 90° in the energy range of 30-700 eV, which was quite consistent with those of C6+ ions, while the SDCS of O8+ ions showed about 1.7 times larger yield than that of C6+ ions, due to a greater ionizing power of high-Z projectile. Comparison with theoretical calculations using CDW-EIS is also presented at the conference.

Radial Secondary Electron Dose Profiles and Biological Effects in Light-Ion Beams Based on Analytical and Monte Carlo Calculations using Distorted Wave Cross Sections

To speed up dose calculation, an analytical pencil-beam method has been developed to calculate the mean radial dose distributions due to secondary electrons that are set in motion by light ions in water. For comparison, radial dose profiles calculated using a Monte Carlo technique have also been determined. An accurate comparison of the resulting radial dose profiles of the Bragg peak for (1)H(+), (4)He(2+) and (6)Li(3+) ions has been performed. The double differential cross sections for secondary electron production were calculated using the continuous distorted wave-eikonal initial state method (CDW-EIS). For the secondary electrons that are generated, the radial dose distribution for the analytical case is based on the generalized Gaussian pencil-beam method and the central axis depth-dose distributions are calculated using the Monte Carlo code PENELOPE. In the Monte Carlo case, the PENELOPE code was used to calculate the whole radial dose profile based on CDW data. The present pencil-beam and Monte Carlo calculations agree well at all radii. A radial dose profile that is shallower at small radii and steeper at large radii than the conventional 1/r(2) is clearly seen with both the Monte Carlo and pencil-beam methods. As expected, since the projectile velocities are the same, the dose profiles of Bragg-peak ions of 0.5 MeV (1)H(+), 2 MeV (4)He(2+) and 3 MeV (6)Li(3+) are almost the same, with about 30% more delta electrons in the sub keV range from (4)He(2+)and (6)Li(3+) compared to (1)H(+). A similar behavior is also seen for 1 MeV (1)H(+), 4 MeV (4)He(2+) and 6 MeV (6)Li(3+), all classically expected to have the same secondary electron cross sections. The results are promising and indicate a fast and accurate way of calculating the mean radial dose profile.

Single Electrons from Heavy-Flavor Decays inp+pCollisions ats=200 GeV

The invariant differential cross section for inclusive electron production in p+p collisions at [FORMULA: SEE TEXT] has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4<or=pT<OR=5.0 GeV/c in the central rapidity region ([FORMULA: SEE TEXT]). The contribution to the inclusive electron spectrum from semileptonic decays of hadrons carrying heavy flavor, i.e., charm quarks or, at high , bottom quarks, is determined via three independent methods. The resulting electron spectrum from heavy-flavor decays is compared to recent leading and next-to-leading order perturbative QCD calculations. The total cross section of charm quark-antiquark pair production is determined to be [FORMULA: SEE TEXT].

Compton profiles of multiply ionized oxygen atoms

We have calculated Compton profiles of multiply ionized oxygen atoms with electronic configurations 1 s m 2 s n 2 p q , m=1−2, n=0−2, q=0−4 . The values of the Compton profiles from the present calculation can be used to determine the doubly differential electron production cross sections in recent ion–atom collision experiments with oxygen ions in the rest frame of the target atoms. The calculations have been performed in impulse approximation using numerical Hartree–Fock wave functions. Compton profiles of neutral oxygen atoms, available in the literature, are in excellent agreement with the present calculation. The variation of Compton profile with the degree of ionization is investigated.

Fully differential cusp electron production cross sections for 75-keVH2++Hecollisions

Fully differential cusp electron production cross sections for 75-keV<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:mrow><mml:mo>+</mml:mo><mml:mi mathvariant="normal">H</mml:mi><mml:mi mathvariant="normal">e</mml:mi></mml:math>collisions

Differential electron-Cu5+elastic scattering cross sections extracted from electron emission in ion-atom collisions

We present a method of deriving energy and angle-dependent electron-ion elastic scattering cross sections from doubly differential cross sections for electron emission in ion-atom collisions. By analyzing the laboratory frame binary encounter electron production cross sections in energetic ion-atom collisions, we derive projectile frame differential cross sections for electrons elastically scattered from highly charged projectile ions in the range between 60{degree} and 180{degree}. The elastic scattering cross sections are observed to deviate strongly from the Rutherford cross sections for electron scattering from bare nuclei. They exhibit strong Ramsauer-Townsend electron diffraction in the angular distribution of elastically scattered electrons, providing evidence for the strong role of screening played in the collision. Experimental data are compared with partial-wave calculations using the Hartree-Fock model. {copyright} {ital 1999} {ital The American Physical Society}

Binary-encounter electron emission after fast heavy-ion impact on complex rare- and molecular-gas targets

Doubly differential cross sections (DDCSs) for electron emission have been measured for collisions of 3.6 MeV/u Ne{sup 10+}, Xe{sup 40+} and 5.9 MeV/u U{sup 29+} on neon, xenon, water, ethanol, methanol, propanol, C{sub 2}F{sub 6}, SF{sub 6}, and C{sub 3}F{sub 8}. Electrons ejected with emission angles between 0{degree} and 180{degree} with respect to the ion beam axis have been recorded simultaneously using a toroidal electron spectrometer. We analyze the singly differential cross section (SDCS) for binary encounter electron (BE{ital e}) production as a function of target electron number and laboratory emission angle. We find that there exists a linear scaling of the BE{ital e} SDCS with the number of electrons bound in the target with an energy lower than the reduced projectile energy. The enhancement of BE{ital e} production in the forward direction in collisions with partially stripped ions is studied for the different projectiles and targets and compared to theoretical calculations. {copyright} {ital 1998} {ital The American Physical Society}

Production of the O 5+(1s2s2p 4P J) states by electron excitation in 10–34 MeV collisions of O 5+ ions with H 2, He, Ne, Ar, Kr and Xe targets

Absolute double differential cross sections (DDCS) for electron production were determined for the Auger-decay of the (1s2s2sp 4P) state in 10–34 MeV collisions of O 5+(1s 22s) ions with H 2, He, Ne, Ar, Kr, Xe targets using zero-degree projectile Auger-electron spectroscopy. Due to spin conservation, e-n interaction mechanisms are excluded to first order and thus the e-e interaction is expected to dominate the (1s 22s 2S) a ̊ (1s2s2p 4P) excitation. Auger electrons from the decay of the O 5+(1s2s2p 4P) state to the O 6+(1s 2) ground state were observed. The electron scattering model, using calculated direct electron-ion impact excitation cross sections, was compared to the measured DDCS. These calculations included the effects of the alignment of the 4P J ( J = 1 2 , 3 2 , 5 2 ) states and their subsequent angular-dependent Auger electron emission.

Recoil-ion charge-state-resolved electron-production cross sections at 55 degrees for 1 MeV/u C5+ on He and Ar.

Recoil-ion charge-state-resolved doubly differential cross sections for ejecting electrons at \ensuremath{\sim}55\ifmmode^\circ\else\textdegree\fi{} with respect to the incident beam direction in collisions between 1 MeV/u ${\mathrm{C}}^{5+}$ projectiles and Ar and He targets have been measured. Electrons with kinetic energies between 100 and 1250 eV have been detected. A prominent feature in the electron energy distributions is the binary-encounter peak. Experimental results are compared with binary-encounter electron production cross sections obtained using the impulse approximation and with theoretical predictions from many-body classical trajectory Monte Carlo calculations. An enhancement in the fraction of electrons detected with singly charged He recoil ions and a corresponding decrease in the fraction detected in coincidence with doubly charged He recoil ions as a function of the electron energy have been observed near the binary-encounter electron energy. This structure has been predicted by recent many-body classical trajectory Monte Carlo calculations. \textcopyright{} 1996 The American Physical Society.

Binary encounter electron production at relativistic velocities

Relativistic binary-encounter electrons produced in very fast collisions of bare and H-like Ar with carbon foils are studied as a function of laboratory frame emission angle. It is found that the velocity of the binary-encounter peak is consistent with a relativistic billiard ball model. The cross section for binary-encounter electron production is not in good agreement with a simple Rutherford scattering model. It is also found that the ratio of H-like to bare projectile cross sections is 1 at 0 degrees and becomes less than 1 at large emission angles.

Transport‐theoretic model for the electron‐proton‐hydrogen atom aurora: 2. Model results

In the companion paper (Basu et al., this issue), a self‐consistent transport‐theoretic model for the combined electron‐proton‐hydrogen atom aurora was described. In this paper, numerical results based on the model are presented. This is done for the pure electron aurora, the pure proton‐hydrogen atom aurora, and finally for the combined aurora. Adopting commonly used types of energy distributions for the incident particle (electron and proton) fluxes, we give numerical solutions for the precipitating electron, proton, and hydrogen atom differential number fluxes. Results are also given for ionization yields and emission yields of the following features: N2+ first negative group (3914 Å), N2 second positive group (3371 Å), selected N2 Lyman‐Birge‐Hopfield bands (1325 Å, 1354 Å, 1383 Å, 1493 Å, and all bands between 1700 and 1800 Å), O I (1356 Å), Lα (1216 Å), Hβ (4861 Å), and Hα (6563 Å). The yield at 1493 Å also contains a contribution from N I (1493 Å), which in fact dominates LBH emission. A major new result of this study is that the secondary electron flux produced by the proton‐hydrogen atom aurora is much softer than that produced by the electron aurora. This increased softness is due to the fact that (for energies of auroral interest) cross sections for secondary electron production by proton and hydrogen atom impact decrease exponentially with increasing secondary electron energy, whereas the cross sections for electron impact decrease as an inverse power law with increasing secondary energy. In our study of the pure electron aurora (no primary protons or hydrogen atoms present) and the pure proton‐hydrogen atom aurora (no primary electrons present), two important results obtain. First, certain emission features (for example, 3371 Å) are excited in completely different ways for the two kinds of aurora. Second, the "eV per electron‐ion pair" as a function of the characteristic energy E0 is nearly constant for the pure electron aurora, with a value of about 34, but varies by about 20% for the pure proton‐hydrogen atom aurora. In our study of the combined electron‐proton‐hydrogen atom aurora, two additional results obtain. Since the proton‐hydrogen atom contribution to the total incident energy flux in the midnight sector is, on the average, about 20 to 25% of that of the electrons, we find that when it is neglected, the ionization yield as well as the yields of many emission features will be underestimated, on the average, by about the same percentage. We also find that in the morning sector of the combined aurora, a double bump in the altitude profile of the E region electron density is possible for certain auroral conditions.

Doubly differential electron-production cross sections for 200-1500-eV e-+H2 collisions.

Ionization cross sections differential in the angle and energy of the detected electrons were measured for electron impact on hydrogen gas at 200, 500, 1000, and 1500 eV. Measurements were made from 15\ifmmode^\circ\else\textdegree\fi{}--150\ifmmode^\circ\else\textdegree\fi{} and from a few eV to T-I where T is the primary electron energy and I the ionization potential of hydrogen. The results are compared to earlier measurements and to available calculations.

Application of the trajectory method for the solution of the time-dependent Thomas-Fermi-Dirac equation to H++Ar collisions

A trajectory method for the solution of the time-dependent Thomas-Fermi-Dirac equation is applied to atomic scattering processes. The time evolution of the electron density is described by trajectories of test particles. This method is studied in the case of proton-impact ionization of an argon atom. Various cross sections for electron production, also differential in the emission angle and energy, are calculated and compared with experimental data.