20 research outputs found
Fine structure of Vavilov-Cherenkov radiation near the Cherenkov threshold
We analyze the Vavilov-Cherenkov radiation (VCR) in a dispersive
nontransparent dielectric air-like medium both below and above the Cherenkov
threshold, in the framework of classical electrodynamics. It is shown that the
transition to the subthreshold energies leads to the destruction of
electromagnetic shock waves and to the sharp reduction of the frequency domain
where VCR is emitted. The fine wake-like structure of the Vavilov-Cherenkov
radiation survives and manifests the existence of the subthreshold radiation in
the domain of anomalous dispersion. These domains can approximately be defined
by the two phenomenological parameters of the medium, namely, the effective
frequency of oscillators and the damping describing an interaction with the
other degrees of freedom.Comment: 9 pages, 6 figure
Theoretical methods for the calculation of Bragg curves and 3D distributions of proton beams
The well-known Bragg-Kleeman rule RCSDA = A dot E0p has become a pioneer work
in radiation physics of charged particles and is still a useful tool to
estimate the range RCSDA of approximately monoenergetic protons with initial
energy E0 in a homogeneous medium. The rule is based on the
continuous-slowing-down-approximation (CSDA). It results from a generalized
(nonrelativistic) Langevin equation and a modification of the phenomenological
friction term. The complete integration of this equation provides information
about the residual energy E(z) and dE(z)/dz at each position z (0 <= z <=
RCSDA). A relativistic extension of the generalized Langevin equation yields
the formula RCSDA = A dot (E0 +E02/2M dot c2)p. The initial energy of
therapeutic protons satisfies E0 << 2M dot c2 (M dot c2 = 938.276 MeV), which
enables us to consider the relativistic contributions as correction terms.
Besides this phenomenological starting-point, a complete integration of the
Bethe-Bloch equation (BBE) is developed, which also provides the determination
of RCSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE
itself (i.e., without further empirical parameters like modification of
friction). The results obtained in the context of the aforementioned methods
are compared with Monte-Carlo calculations (GEANT4); this Monte-Carlo code is
also used with regard to further topics such as lateral scatter, nuclear
interactions, and buildup effects. In the framework of the CSDA, the energy
transfer from protons to environmental atomic electrons does not account for
local fluctuations.Comment: 97 pages review pape
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Energetic particle influence on the Earth's atmosphere
This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally
galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere
are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere
Modeling output factors of therapeutic proton beam formed by the passive double-scattering technique
Precise out-vacuum proton beam monitoring system based on vibrating wire
As an instrument for Korea Multi-purpose Accelerator Complex (KOMAC) facility proton beam profiling, a vibrating wire monitor (VWM) has been installed and tested at TR23 target room. Experiments were done at very low (100 nA) beam current conditions. At the number of particles about 10(11) proton/train and trains repetition rate of 0.1 Hz we have measured the beam profile by a few scanning steps. The experience accumulated in these experiments turned out to be useful for the VWM upgrades (e. g. understanding interactions of protons with wire materials and heat transfer processes) and will be particularly helpful for the KOMAC beam halo measurements in the future high-current operation