scholarly journals Collective Oscillations in Many Electron Atoms. III. Photoabsorption

1974 ◽  
Vol 27 (5) ◽  
pp. 667 ◽  
Author(s):  
JJ Monaghan
Keyword(s):  
Cross Section ◽  
Atomic Number ◽  
Cross Sections ◽  
Reasonable Agreement ◽  
Time Dependent ◽  
Photoabsorption Cross Section ◽  
Thomas Fermi ◽  
Experimental Cross ◽  
Collective Oscillations

The generalization by Bloch of the Thomas-Fermi atom to time-dependent motion is applied to the calculation of the photoabsorption cross section. The results are in reasonable agreement with the experimental cross sections in the range of photon energies 0�3 Z e V < lim < 300 Z e V, where Z is the atomic number of the atom.

Note on the production of positron-electron pairs during the passage of β-particles through matter

1938 ◽  
Vol 34 (3) ◽  
pp. 435-441 ◽  
Author(s):  
N. Feather ◽  
J. V. Dunworth
Keyword(s):  
Cross Section ◽  
Atomic Number ◽  
Cross Sections ◽  
High Energy ◽  
Coincidence Counting ◽  
Electron Pairs ◽  
Radioactive Substances

The method of coincidence counting has been applied to an investigation of the possible production of positron-electron pairs by the high energy β-particles from a source of uranium X in absorbers of aluminium, brass and lead. The results are not inconsistent with the high values recently reported for atomic cross-sections for the effect, nor with the suggestion that the atomic cross-section is proportional to the first power of the atomic number rather than the second. Suggestions are made for the use of the β-particles from artificially radioactive substances in an attempt to increase the sensitivity of the method.

Total-to-K-shell photoelectric cross-section ratios in some rare-earth and high-Z elements

1989 ◽  
Vol 67 (2-3) ◽  
pp. 139-142 ◽  
Author(s):  
S. Chandra Lingam ◽  
K. Suresh Babu ◽  
V. Prakash Kumar ◽  
D. V. Krishna Reddy
Keyword(s):  
Rare Earth ◽  
Cross Section ◽  
Atomic Number ◽  
Cross Sections ◽  
Cross Section Ratio ◽  
Section Ratio ◽  
Photoelectric Cross Section ◽  
Normal Transmission ◽  
Experimental Values ◽  
Good Agreement

The total photoelectric cross-sections in the elements gadolinium, dysprosium, erbium, lutetium, tantalum, tungsten, gold, and lead have been obtained by using the normal transmission experiments, and the results are reported. Using these total photoelectric cross sections, we have found the K-shell photoelectric cross sections, the K-jump ratios, and the total-to-K-shell photoelectric cross-section ratios at the K edges for the above elements. These values are compared with the available theoretical and experimental values. The results are in good agreement with the Storm and Israel results and the Scofield theoretical values, within the limits of experimental uncertainties. Furthermore, the variation of the total-to-K-shell photoelectric cross-section ratio with energy and atomic number is discussed.

GLUON SATURATION AND THE TOTAL PROTON-AIR CROSS SECTION

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1685-1689
Author(s):  
F. CARVALHO ◽  
F. O. DURÃES ◽  
S. SZPIGEL ◽  
F. S. NAVARRA
Keyword(s):  
Simple Model ◽  
Cross Section ◽  
Cross Sections ◽  
Cosmic Ray ◽  
Dipole Model ◽  
Perturbative Calculations ◽  
Experimental Cross ◽  
Energy Behavior ◽  
Gluon Saturation

In this work we propose a simple model for the total proton-air cross section, which is an improvement of the minijet model with the inclusion of a window in the pT-spectrum associated to the saturation physics. Our approach introduces a natural cutoff for the perturbative calculations which modifies the energy behavior of this component. The saturated component is calculated with a dipole model. The results are compared with experimental cross sections measured in cosmic ray experiments.

The Scattering of Positrons by Helium: Total Cross Sections up to 270 eV

1975 ◽  
Vol 53 (10) ◽  
pp. 962-967 ◽  
Author(s):  
B. Jaduszliwer ◽  
A. Nakashima ◽  
D. A. L. Paul
Keyword(s):  
Energy Range ◽  
Cross Section ◽  
Cross Sections ◽  
Born Approximation ◽  
Reasonable Agreement ◽  
Experimental Results ◽  
Formation Cross Section ◽  
Sum Rule ◽  
Total Cross Sections ◽  
High Energies

The total cross sections for the scattering of positrons by helium have been measured by the method of transmission in the 16 to 270 eV energy range. The experimental results are higher than those of Canter et al. but are in reasonable agreement with recent results of Griffith et al., and at high energies tend towards Born approximation calculations. The integral of the cross section over positron momentum is smaller than the sum rule estimate made by Bransden et al. A tentative value of (0.034 ± 0.017)πa02 is assigned to the positronium formation cross section at threshold.

Giant dipole resonance in 4He

1980 ◽  
Vol 58 (11) ◽  
pp. 1555-1559 ◽  
Author(s):  
J. J. Bevelacqua
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Giant Dipole Resonance ◽  
Reasonable Agreement ◽  
Center Of Mass ◽  
Nucleon Nucleon ◽  
Nucleon Interaction ◽  
R Matrix ◽  
Dipole Resonance ◽  
Nucleon Nucleon Interaction

The 4He giant dipole resonance is calculated with the generalized R-matrix method of Lane and Robson. The model treats the center of mass correctly and includes noncentral components in the nucleon–nucleon interaction via the Sussex interaction. The 4He(γ,p)3H and 4He(γ,n)3He cross sections are sensitive to the 4He level spectrum, but are in reasonable agreement with the photonuclear data for level schemes which agree with the spectrum suggested by Fiarman and Meyerhof (FM). Other spectra which bracket the FM levels lead to poorer photonuclear cross sections. R-matrix model results also lead to a (γ,p)/(γ,n) cross section ratio which is about unity.

STOPPING CROSS SECTIONS IN CARBON FOR LOW-ENERGY ATOMS WITH

1963 ◽  
Vol 41 (9) ◽  
pp. 1424-1442 ◽  
Author(s):  
J. H. Ormrod ◽  
H. E. Duckworth
Keyword(s):  
Monte Carlo ◽  
Cross Section ◽  
Atomic Number ◽  
Cross Sections ◽  
Monte Carlo Calculation ◽  
Low Energy ◽  
Energy Interval ◽  
Nuclear Scattering

The electronic stopping cross sections in carbon for atomic projectiles with [Formula: see text] have been determined in the energy interval from 10 to 140 kev. In doing so a Monte Carlo calculation was used to subtract from each experimentally observed cross section the contribution which arises from nuclear scattering. The trend of the results thus obtained agrees well with theory. In addition, however, a periodic dependence of Sε on the atomic number of the projectile is observed.

Calculation of Photoabsorption Cross Section of an Extended Thomas-Fermi Atom

1981 ◽  
Vol 50 (3) ◽  
pp. 941-948 ◽  
Author(s):  
Yasuo Tomishima ◽  
Ryozo Akamatsu ◽  
Tetsuo Horita
Keyword(s):  
Cross Section ◽  
Photoabsorption Cross Section ◽  
Thomas Fermi

K*(892)0Λ & K+Σ*(1385)- PHOTOPRODUCTION ON THE DEUTERON

2014 ◽  
Vol 26 ◽  
pp. 1460101 ◽  
Author(s):  
◽  
PAUL MATTIONE
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Differential Cross ◽  
Experimental Cross Section ◽  
Differential Cross Sections ◽  
Cross Section Data ◽  
Jefferson Lab ◽  
Section Data ◽  
Experimental Cross ◽  
Using Data

Preliminary measurements of the differential cross sections of the γn → K*(892)0Λ and γn → K+Σ*(1385)- reactions are shown using data from the Jefferson Lab Hall B CLAS g13 experiment. No experimental cross section data have yet been published on the γn → K*(892)0Λ reaction, and the only published cross section data on the γn → K+Σ*(1385)- reaction are at forward angles, where t-channel K+ and K*+ exchanges are predicted to dominate. These data can be used to contribute to the search for the "missing" N* resonances, some of which are predicted to have non-negligible couplings to the excited strangeness channels.

Photoneutron cross sections in 7Li

1977 ◽  
Vol 55 (5) ◽  
pp. 428-433 ◽  
Author(s):  
H. Ferdinande ◽  
N. K. Sherman ◽  
K. H. Lokan ◽  
C. K. Ross
Keyword(s):  
Fine Structure ◽  
Excited State ◽  
Cross Section ◽  
Cross Sections ◽  
Ground State ◽  
Reasonable Agreement ◽  
Branching Ratio ◽  
Energy Spectra ◽  
Average Value ◽  
First Excited State

Photoneutron energy spectra from 7Li have been measured by time-of-flight methods, for bremsstrahlung end-point energies increasing in 2 MeV steps from 13 to 25 MeV. The ground-state and approximate first-excited-state differential cross sections at 90° have been obtained from 8.5 to 23 MeV. No pronounced fine structure has been observed. The measured branching ratio to the first excited state falls from an average value of 0.70 between 10.3 and 14.5 MeV to an average of 0.29 between 14.5 and 18 MeV, and rises again to an average of 0.38 between 18 and 23 MeV. This behaviour can be explained by a crude theoretical model in which 1p → 2s and 1p → 1d single particle transitions dominate below 18 MeV. The calculation predicts a branching ratio of 0.50 near threshold, falling to 0.23 at higher energies, in reasonable agreement with the experiment. The integrated value of the ground-state cross section up to 23 MeV is about (38.7 ± 3.9) MeV mb, while that for the first excited state is about (17.2 ± 3.4) MeV mb. Together they account for 39% of the exchange-augmented dipole sum of 7Li.

Remarks on the scattering of electrons by atomic fields

1930 ◽  
Vol 26 (4) ◽  
pp. 556-563 ◽  
Author(s):  
E. C. Bullard ◽  
H. S. W. Massey
Keyword(s):  
Angular Distribution ◽  
Atomic Number ◽  
Cross Sections ◽  
Approximate Expression ◽  
Thomas Fermi ◽  
Scattering Cross ◽  
Single Curve ◽  
Scattering Cross Sections

It is shown that, by use of the Thomas-Fermi atom, effective scattering cross-sections may be obtained from a single curve for all atoms (provided that the atomic number is not too small). This curve is calculated. The range of validity of such values has been obtained and Born's formula shown to be inaccurate for representing the scattering of electrons with velocities less than 400 volts except by atoms of very low atomic number. For the case of high velocities an approximate expression is obtained for the angular distribution allowing for screening by the extra-nuclear electrons.

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