Electrons Positrons Research Articles

Total cross sections in electron- and positron-helium scattering

The eikonal-Born series method is used to study the imaginary part of the forward elastic-scattering amplitude for the scattering of electrons (positrons) by helium. Total cross sections are obtained by use of the optical theorem, and these cross sections are compared with recent experimental results and with optical-model predictions. This comparison shows clearly the very different convergence rates of perturbation theory in the electron and positron cases.

Screening Corrections to the Fermi Function for AllowedβDecay

The influence of electron screening on the Fermi function $F(W,Z)$ for allowed $\ensuremath{\beta}$ decay is reconsidered. Numerical values for $F(W,Z)$ are obtained by integrating the radial Dirac equations for the decay electrons (positrons) in a self-consistent atomic potential. Relativistic Hartree-Fock-Slater equations are used to construct the atomic potential. The Fermi function is tabulated for various nuclei and energies, and comparisons are made with $F(W,Z)$ for a pure Coulomb field. Detailed comparisons are also made with the WKB screening formula of Rose as well as with the previous numerical results of Reitz and of B\uhring. It is found that the Rose formula provides an accurate approximation to $F(W,Z)$ over the dominant portion of the $\ensuremath{\beta}$ spectrum provided the endpoint energy is sufficiently high and provided further that an appropriate value of the potential at the nucleus ${V}_{0}$ is used. An empirical formula for ${V}_{0}$ from the Hartree-Fock-Slater calculations is provided. The numerical results of Reitz appear to be badly in error, especially for large electron momenta. The predictions of B\uhring for a screened-potential model are in good agreement with the present work. Corrections to the $\mathrm{ft}$ value of several superallowed Fermi transitions are recomputed and found to be negligibly different from the predictions made using the Rose approximation.

Galactic cosmic-ray electrons

The production and equilibrium spectra of secondary electrons (negatrons and positrons) resulting from cosmic-ray interactions in the galaxy are calculated. These electrons arise from the decay of secondary pions and neutrons produced by nuclear interactions of cosmic-ray protons and alpha particles with the interstellar gas. The equilibrium flux is determined by escape of electrons from the galaxy and by ionization, inverse Compton, and synchrotron energy losses. A comparison of the calculated secondary electron equilibrium spectrum with the measured electron intensity, positron-negatron ratio, and nonthermal radio emission from the galactic halo suggests that an additional primary electron source of roughly the same magnitude is required.

Measurement of absorbed dose by the third space satellite vehicle

GAMMA-400 is an international project of a high apogee orbital astrophysical observatory for studying the characteristics of high-energy gamma-emission, electrons/positrons and light nuclei fluxes. The energy range for γ-rays and electrons/positrons registration in the main aperture is from ∼0.1 GeV to ∼3.0 TeV. Also, this aperture allows high energy light nuclei fluxes characteristics investigation. Moreover, special aperture configuration allows registering of gamma-quanta, electrons (positrons) and light nuclei from the lateral directions too.The spacecraft GAMMA-400 orbit will be located in the Earth's magnetosphere and will pass front shock wave from magnetosphere interaction with the solar wind, turbulent-transition region, magnetopause and so on. During the satellite's movement through various Earth's magnetosphere regions its anticoincidence detectors will register high intensity fluxes of low energy charged particles captured by the magnetic field. The working area sections of GAMMA-400 detector systems used as anticoincidence shield are about 1 m2 each. The high intensity low energy charged particles flux influence on anticoincidence detectors should be taken into account during particle identification.This article presents a comparison between Earth's magnetosphere theoretical model according to SPENVIIS package and real data measured by detectors onboard THEMIS series satellites. The differences between these two datasets indicate that the calculated data are not sufficient to make short time predictions of variations of magnetic induction in the outer magnetosphere. A special trigger marker flag will be produced by GAMMA-400 counting and triggers signals formation system accordingly to the data of two onboard magnetometers. This flag's presence leads to special algorithms execution start, putting the plastic detectors into a dedicated working mode taking into account possible high count rates of external detector layers.

I. Cyclotron-produced Isotopes in Clinical and Experimental Medicine

Before the discovery of the nuclear chain reaction, the cyclotron was the only important source of radioactive isotopes for medical purposes. The development of the nuclear reactor made large scale isotope production possible and a wide range of radioactive isotopes is now readily available at a reasonably low cost. In consequence the demand for cyclotron-produced isotopes has decreased. However, there is now an increasing requirement for isotopes which are not available from the reactor for one reason or the other but which can be produced in a cyclotron. The true magnitude of this requirement is as yet unknown and can only be properly assessed by making such isotopes more freely available. Isotopes are produced in the reactor by neutron capture, by fission, or when the thresholds are suitable, by (n, p) or (n, α) reactions. It can be seen from Fig. 1 that (n, γ), (n, p) or (n, α) reactions tend to produce nuclides with a surplus of neutrons. Such isotopes decay towards the stability line by emission of negative electrons. Most fission products and their daughters also decay in this manner. It is in consequence rarely possible to obtain from the nuclear reactor an isotope which is neutron-deficient and which therefore decays either by emission of positive electrons (positrons) or by orbital electron capture followed by emission of characteristic X rays. Such isotopes can only be prepared in a cyclotron (Moeken, 1957) or a high-energy (20 to 30 MeV) linear accelerator (MacGregor, 1958), but often have desirable properties.

Interaction of Heavy Nuclear Particles

SOME time ago, it was suggested that the interaction between neutrons and protons goes on via particles of small mass—electrons (positrons) and neutrinos—somewhat in the same way as electromagnetic interaction (compare Coulomb's law) is transferred by photons1. After a recent discussion of the problem by Heisenberg2, who pointed out the necessity for changing the r5 law to one involving r1 or r9, it seems desirable to perform the calculations for the magnitude of interaction in the most simple manner.