Physicists Observed Cherenkov Radiation In Beryllium For The First Time (Physics)

Uglov and Vukolov presented the new experimental results on the observation of X-ray Cherenkov radiation generated by 5.7 MeV electrons in the thin Beryllium (Be) and silicon (Si) foils. They observed Cherenkov effect from Beryllium for the first time. They also compared the experimental results with the calculations performed according to the theoretical model of transition radiation taking into account the oxide layer on the target output surface.

Figure 1. a) Scheme for XCR investigation using a multilayer mirror; b) top view of the vacuum chamber – Ch; T is a target, D is a channel-electron multiplier (CEM), M is a multilayer mirror, G is a goniometer, FC is a Faraday cup. © Uglov et al.

Currently, most of the Cherenkov phenomenon researches for the X-ray region are theoretical studies; there are only a few experiments in this area. These experiments presented convincing experimental evidence for the observation of the Cherenkov effect in the X-ray range. At the same time, not all experimental results show complete agreement with the theory.

Thus, after the first experimental observation of the Cherenkov effect in the ultra-soft X-ray range near the K-edge of carbon absorption, Dutch researchers obtained in their study an experimental confirmation of the Cherenkov effect existing near the absorption edges of elements such as titanium, vanadium, and silicon; at the same time, they failed to detect the Cherenkov effect for Ni and to confirm the Cherenkov effect in carbon. The carbon-related researches were carried out using various modifications of carbon such as diamond, amorphous carbon, graphite and carbon in organic compounds using a lower electron energy than Bazylev and colleagues considered in their study, but sufficient for the appearance of Cherenkov radiation according to the theory.

There are also disagreements between the calculations of the X-ray Cherenkov radiation (XCR) angular density and the experimental observation of the one during the sliding interaction of 75 MeV electron beam with targets. For example, the experimental Cherenkov angles for carbon and Si turned out to be the same, which does not agree with the theory.

Intensity of radiation reflected by a multilayer mirror [Mo/B4C]100 depending on 𝜃0 : a) for Be
and b) for Si targets. © Uglov et al.

But, Uglov and Vukolov’s calculations includes the effect of the oxide layer and pinholes which demonstrated an improvement in the agreement between the calculations and the experiment.

The fact of observing the Cherenkov radiation in Be may promote the development of a high-intensity, high-monochrome radiation source with the energy of emitted photons E∼ 111 eV. According to authors, the spectral-angular radiation density of such a source can be increased several times by using the sliding interaction of the electron beam with the target. Besides, the threshold nature of the XCR can be used for the development of threshold counters for the separation of the charged particles.

“These detectors are more promising for use with multiply charged ions since the XCR yield is proportional to the square of the particle charge.

— told Uglov, lead author of the study.

Reference: S. R. Uglov, A.V.Vukolov, “Observation of soft X-ray Cherenkov radiation in Be and Si foils”, ArXiv, pp. 1-13, 28 Feb 2021.

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