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

Early history of particle physics

The discovery of cosmic rays is a standard example of ‘one man’s noise is another man’s signal’. From the apparently minor leakages of electricity from well-insulated detectors came a subject of great importance for modern science: the detection of a so-called ‘radiation’ coming from not just beyond the Earth’s atmosphere but from deep cosmic space. Furthermore, a radiation of energy density rivalling that of starlight. Our goal is to examine the history of the subject from the period of ‘pre-discovery’ in the years from 1900 to 1912, through the discovery itself up to the 1940’s when particle physics was continued with accelerators. The crucial role of ‘new techniques’, principally the Wulf electrometer and the Wilson cloud chamber and their use in precission studies by Hess, Kolhörster, Anderson and Blackett are described. The arguments about the veracity of Hess’s claim for an extra-terrestrial origin are included, as well as the developments leading to the inspired discovery of the positron and the muon. The question of ‘origin’ is also examined, from the contention by Hess that the Sun was not responsible, to the idea – still held – that supernovae are involved