Presence Of Secondary Electrons Research Articles

Alfvénic reacceleration of relativistic particles in galaxy clusters in the presence of secondary electrons and positrons

In a previous paper we presented the first self-consistent calculations of the time-dependent coupled equations for electrons, hadrons and Alfvén waves in the intracluster medium, which describe the stochastic acceleration of the charged particles and the corresponding spectral modification of the waves. Under viable assumptions, this system of mutually interacting components was shown to accurately describe several observational findings related to the radio haloes in clusters of galaxies. In this paper, we add to the self-consistency of the calculations by including the generation and re-energization of secondary electrons and positrons, produced by the inelastic interactions of cosmic rays with the thermal gas in the intracluster medium. The bulk of cosmic rays are expected to be confined within the cluster volume for cosmological times, so that the rate of production of secondary electrons, as well as gamma-rays, may become correspondingly enhanced. If magnetohydrodynamic waves are present, as may be expected in the case of a recent merger event, then the reacceleration of secondary electrons and positrons can significantly affect the phenomenology of the non-thermal processes in clusters. We investigate these effects here for the first time.

Influence of an internal electric field in a sample on the secondary electron emission phenomenon

The influence of an internal electric field generated in a sample on the value of the secondary electron emission coefficient and energy distributions of secondary electrons were studied. Microscopic glasses covered on both sides with thin conducting films were used as samples. The dependences of the secondary electron emission coefficient on the bias voltage of the sample for primary electron energies ranging from 25 eV to 200 eV were determined. The diagrams obtained are characterized by high non-monotonic behaviour. Some specific effects of the internal field, such as the presence of secondary electrons with energy greater than incident energy, were found.

Angular and energy distributions of low energy electrons in backscattered-Mössbauer spectroscopy

The angular and energy distributions of resonant and nonresonant electrons below 50 eV have been investigated during backscattered conversion electron Mössbauer spectroscopy (CEMS). Reasonable consistency is achieved between theoretical predictions and experimental studies. Relatively few resonant or nonresonant electrons are observed/predicted between 600 eV and 50 eV, while a significant fraction of the total electron signal emerges below 50 eV. The low energy signal is shown to result from low energy Auger cascades, low energy shake-off electrons and secondary electrons attributed to higher energy events. Despite the presence of secondary electrons, the signal arising from low energy Auger and shake-off electrons can be used to discriminate those resonant electrons (i.e., resonant spectra) arising from the topmost 1.0 nm of the absorber. The relatively large number of low energy electrons permits relatively short acquisition times (ca. 1 h) and enhanced surface sensitivities. They may be especially useful in future depth-deconvolution efforts.

An investigation into the presence of secondary electrons in megavoltage photon beams (radiotherapy application)

The presence of secondary electrons in photon beams of 60Co and 4, 8, 10 15 and 25 MV X-rays has been studied by measuring surface charge using thin window ionisation chambers. Measurements have been made for square fields from 4*4 cm2 to 35*35 cm2 for locations from the collimator head to a distance of 4 m from the target. In addition, measurements have been made from rectangular fields at 10 MV and 25 MV for fields of equivalent area from 5*5 cm2 to 25*25 cm2. By eliminating the inverse square effect, the presence of contaminants from the head and the effect of build-up in air are clearly seen and well separated. Comparison between the curves at different energies indicates an increasing effect of contamination from the head with energy and a decreasing effect of electron production in air with increasing energy.

The measurement of the ratio of radial diffusion coefficient to mobility and the amplification coefficient for electrons at high E/p

A generalized method is given for the measurement of the amplification coefficient g and the ratio of radial diffusion coefficient to experimental mobility, Der/μexp, for electron swarms moving through uniform electric fields in the presence of secondary electrons. The technique requires the experimental measurement of both the current amplification and the radial distribution of anode current. Measurements are reported for swarms in hydrogen for 30<or=E/p0<or=350 V cm−1 Torr−1 (at 0°C).