Annihilation of positrons in helium, neon, and argon

1970 ◽  
Vol 48 (11) ◽  
pp. 1288-1302 ◽  
Author(s):  
R. E. Montgomery ◽  
R. W. LaBahn
Keyword(s):  
Cross Sections ◽  
Orbital Method ◽  
Scattering Process ◽  
Electron Atom ◽  
Atom Scattering ◽  
Energy Behavior ◽  
The Cross ◽  
Helium Neon ◽  
Atom Collision ◽  
Good Agreement

The electric field dependences of the direct annihilation rates for positrons in helium, neon, and argon are calculated. This is done by using a systematic description of the scattering process. The momentum transfer and direct annihilation cross sections are calculated within the framework of the polarized-orbital method which has worked well for electron–atom scattering. The cross sections are then used in the appropriate diffusion equation to determine the experimentally observable annihilation rates appropriate to the exponential decay region of the spectrum. The resulting annihilation rates are found to be extremely sensitive to the low-energy behavior of the cross sections. Best agreement between calculated and experimental annihilation rates is obtained for helium where fairly rigorous calculations of the cross sections are available. Good agreement between theory and experiment for neon and argon is obtained only by making judicious choices for the components of the distortion included in the calculations. It is thus concluded that the positron–atom scattering process is considerably more sensitive to the details of the mutual distortion interaction than is observed in the corresponding electron–atom collision process.

Elastic and inelastic scattering of 40 MeV polarized protons from 90Zr and 92Zr

1979 ◽  
Vol 57 (4) ◽  
pp. 540-549 ◽  
Author(s):  
R. de Swiniarski ◽  
Dinh-Lien Pham ◽  
G. Bagieu ◽  
H. V. Geramb
Keyword(s):  
Inelastic Scattering ◽  
Cross Sections ◽  
Imaginary Component ◽  
Spin Orbit ◽  
Model Calculations ◽  
Analyzing Powers ◽  
Elastic And Inelastic Scattering ◽  
Polarized Protons ◽  
The Cross ◽  
Good Agreement

Analyzing powers and cross sections have been measured for elastic and inelastic scattering of 40 MeV polarized protons from 90Zr and 92Zr. The analysis has been carried out in the DWBA within the framework of the macroscopic and microscopic models. Furthermore, the coupled-channels calculations using the vibrational model and the full Thomas form for the spin–orbit potential give a very good description for both the cross sections and the analyzing powers of the iow-lying2+, 3−, 5−, and 4+ states in 92Zr and the 2+ and 3− in 90Zr. The cross section and analyzing power for the first 2+ state in these nuclei were compared with previous results at 30 and 20.3 MeV, and from this comparison a certain energy dependence of the relative strength of the spin–orbit deformation to the central deformation could be observed. Microscopic model calculations with tensor and spin–orbit components included in the projectile–target real interaction and with an exact treatment of knock-on' exchange have been performed for the 2+ states in these nuclei. An attempt has also been made in order to include the imaginary component in the N–N interaction. For these calculations, rather good agreement was obtained especially for the 2+ state in 92Zr but poor agreement for 90Zr. Finally, valence plus core polarization calculations have also been done and showed a very good agreement between theory and experiment for those 2+ transitions.

Importance of coupling for inelastic collisions between protons and hydrogen atoms

1965 ◽  
Vol 283 (1392) ◽  
pp. 100-114 ◽  
Keyword(s):  
Cross Sections ◽  
Intermediate State ◽  
Relative Velocity ◽  
Inelastic Collisions ◽  
Hydrogen Atoms ◽  
Resonance Reactions ◽  
The Cross ◽  
Good Agreement

The importance of coupling for fast collisions between protons and hydrogen atoms is examined with the two-centred expansion in atomic eigenfunctions proposed by Bates (1958 a ). Cross-sections are evaluated for reactions H + + H (I s ) → H(I s ) + H + , H + + H( I s ) → H(2 s ) + H + , and H + + H(l a ) → H + + H(2 s ). The effect of a single intermediate state, either I s or 2 s , is considered. For the non-resonance processes, it is found that the cross-sections may be substantially increased by passage through intermediate state for incident energies less than about 10 keV, tending towards equality with decrease in relative velocity. Results obtained for the symmetrical resonance reactions are in good agreement with the two-state solutions of McCarroll (1961).

A new empirical formula for cross-sections of (n,nα) reactions

2020 ◽  
Vol 29 (08) ◽  
pp. 2050062
Author(s):  
Mustafa Yiğit
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Empirical Formula ◽  
Nuclear Reactions ◽  
Measured Cross Section ◽  
Future Studies ◽  
Present Formalism ◽  
The Cross ◽  
Neutron Cross Sections ◽  
Good Agreement

Studies on the cross-sections of (n,n[Formula: see text]) reactions which are energetically possible, about 14 MeV neutrons are quite scarce. In this paper, the cross-sections of (n,n[Formula: see text] nuclear reactions at [Formula: see text]14–15 MeV are analyzed by using a new empirical formula based on the statistical theory. We show that neutron cross-sections are closely related to the [Formula: see text]-value of nuclear reaction, in particular for (n,n[Formula: see text]) channels. Results obtained with this empirical formula show good agreement with the available measured cross-section values. We hope that the estimations on the cross-sections using the present formalism may be helpful in future studies in this field.

scholarly journals Cross Section Ionization By Electron Impact Of Helium Like Ions

2021 ◽  
Author(s):  
Manel Hariz Belgacem ◽  
Elhabib Guedda ◽  
Haikel Jelassi
Keyword(s):  
Electron Impact ◽  
Cross Section ◽  
Cross Sections ◽  
Ground State ◽  
The Cross ◽  
State 1 ◽  
Unstable States ◽  
Good Agreement

<sub></sub> In this paper we present our calculation of the cross section ionization by electron impact of C V, N VI and O VII. Using the Flexible Atomic Code (FAC), we obtain the cross sections for the ionization of these ions from the ground state 1<sup>1</sup>S, and from the unstable states 2<sup>1</sup>S and 2<sup>3</sup>S. Our results are in good agreement with those based on the Coulomb Born (CB) approximation and the available measurements.

scholarly journals 14.8 MeV Neutron Activation Cross Section Measurements for Ge Isotopes

2009 ◽  
Vol 1 (2) ◽  
pp. 173-181 ◽  
Author(s):  
M. M. Haque ◽  
M. T. Islam ◽  
M. A. Hafiz ◽  
R. U. Miah ◽  
M. S. Uddin
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Gamma Ray ◽  
Reaction Cross ◽  
Activation Cross Section ◽  
Section Data ◽  
Gamma Ray Spectroscopy ◽  
24Na Reaction ◽  
The Cross ◽  
Good Agreement

The cross sections of Ge isotopes were measured with the activation method at 14.8 MeV neutron energy. The quasi-monoenergetic neutron beams were produced via the 3H(d,n)4He reaction at the 150 kV J-25 neutron generator of INST, AERE. The characteristics γ-lines of the product nuclei were measured with a closed end coaxial 17.5 cm2 high purity germanium (HPGe) detector gamma ray spectroscopy. The cross sections were determined with reference to the known 27Al(n,α)24Na reaction. Cross section data are presented for 72Ge(n,p)72Ga, 74Ge(n,α)71mZn and 76Ge(n,2n)75m+gGe reactions. The cross section values obtained for the above reactions were 24.78±1.75 mb, 1.69±0.11 mb and 860±50 mb, respectively. The results obtained were compared with the values reported in literature as well as theoretical calculation performed by the statistical code SINCROS-II. The experimental data were found fairly in good agreement with the calculated and literature data.  Keywords: Activation cross section; Neutron induced reaction; Gamma-ray spectroscopy; 14.8 MeV. © 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v1i2.1532  

Many-Electron Correlations in the Photoionization of a Nitrogen Atom

1974 ◽  
Vol 52 (4) ◽  
pp. 349-354 ◽  
Author(s):  
N. A. Cherepkov ◽  
L. V. Chernysheva ◽  
V. Radojević ◽  
I. Pavlin
Keyword(s):  
Nitrogen Atom ◽  
Cross Section ◽  
Cross Sections ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Electron Correlations ◽  
Sum Rule ◽  
Hartree Fock ◽  
The Cross ◽  
Good Agreement

Photoionization cross sections for the outer shell of the nitrogen atom ground state are calculated in the single-particle Hartree–Fock approximation and, in order to take into account many-electron correlations, also in the Random Phase Approximation with Exchange (RPAE). To be able to apply the RPAE, its modification for the half-filled shell atom, such as nitrogen atom, is presented. Calculation of length and velocity forms of the cross section in both approximations are compared with the available experimental data, and a good agreement is obtained. It has been found that in the RPAE the influence of many-electron correlations in a nitrogen atom is not great, but it is very important since, in contrast to the Hartree–Fock approximation, it results in the validity of the sum rule and the coincidence of the length and velocity forms of the cross sections, in agreement with the requirement of the general theory. The angular distribution of photoelectrons is also calculated in the RPAE, which has not been measured so far.

Positron lifetime spectra for gases

1982 ◽  
Vol 60 (4) ◽  
pp. 503-516 ◽  
Author(s):  
G. R. Heyland ◽  
M. Charlton ◽  
T. C. Griffith ◽  
G. L. Wright
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Inert Gases ◽  
Gas Density ◽  
Molecular Gases ◽  
Free Positron ◽  
To Receive ◽  
Helium Neon ◽  
Limiting Value ◽  
Good Agreement

Recent observations on the lifetime spectra for gases are presented and discussed. There is little to report on the inert gases helium, neon, and argon and the spectra for these gases are thought to be understood. New lifetime data for krypton and xenon have revealed two fast components which, although probably connected with the low positronium fractions for these gases, have yet to receive a satisfactory interpretation.The polarized orbital calculations for Zeff's and momentum transfer cross sections for all the inert gases by the York group are now complete and are generally in good agreement with experiment.For the molecular gases some information on rotational excitation cross sections has been obtained from thermalization times for nitrogen, hydrogen, and deuterium. In general, the [Formula: see text] parameter is dependant on gas density and temperature with some gases showing a pronounced maximum in the density dependance. The gases C3H8, C4H10, and CH3Cl have very large values of [Formula: see text] which indicate localization or capture of the positron by one or more molecules. These three gases exhibit a maximum in the instantaneous decay rate of the "free" positron component at low densities from which a "capture" cross section can be estimated.The positronium fraction, F, generally increases with the gas density, usually approaching a limiting value asymptotically, but for nitrogen this density dependance has a maximum at ~ 140 amagat. No satisfactory explanation has been offered for this behaviour.Positronium formation cross sections for several gases have been deduced from measurements of the variation of F with the concentration of the gas in helium. These cross sections are similar in magnitude to those deduced from the total cross section beam measurements.

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