Molecular bremsstrahlung radiation at GHz frequencies in air

Abstract

A detection technique for ultra-high energy cosmic rays, complementary to the fluorescence technique, would be the use of the molecular Bremsstrahlung radiation emitted by low-energy ionization electrons left after the passage of the showers in the atmosphere. In this article, a detailed estimate of the spectral intensity of photons at ground level originating from this radiation is presented. The spectral intensity expected from the passage of the high-energy electrons of the cascade is also estimated. The absorption of the photons in the plasma of electrons/neutral molecules is shown to be negligible. The obtained spectral intensity is shown to be 2 × 10 −21 W cm −2 GHz −1 at 10 km from the shower core for a vertical shower induced by a proton of 10 17.5 eV. In addition, a recent measurement of Bremsstrahlung radiation in air at gigahertz frequencies from a beam of electrons produced at 95 keV by an electron gun is also discussed and reasonably reproduced by the model.

Revealing neutral bremsstrahlung in two-phase argon electroluminescence

“…This phenomenon could in principle explain the weak primary scintillations in liquid Ar in the visible and NIR range, observed earlier by a number of groups [67,72,73], Indeed, if the secondary scintillation in the VUV in gaseous Ar (S2 signal) is associated with the primary scintillation in the VUV in liquid Ar (S1 signal), why does this not happen with the NBrS scintillation? Following [28], such primary scintillations in liquid Ar in the visible and NIR range might be explained by neutral bremsstrahlung of the primary ionization electrons.…”

“…It is also worth mention the application of NBrS radiation which is already used in practice to develop a detection technique for ultra-high-energy cosmic rays [28]. Here the NBrS radiation in the radio-frequency range (to be recored with antennas on the Earth surface) is emitted by primary ionization electrons left after the passage of the showers in the atmosphere.…”

Neutral bremsstrahlung in two-phase argon electroluminescence: further studies and possible applications

“…It is worth mention the possible application of NBrS radiation to develop a detection technique for ultra-high-energy cosmic rays [16]. Here the NBrS radiation in the radio-frequency range (to be recored with antennas on the Earth surface) is emitted by primary ionization electrons left after the passage of the showers in the atmosphere.…”

GIGAS: A set of microwave sensor arrays to detect molecular bremsstrahlung radiation from extensive air shower

“…However, such detection occurred only for air showers at distances less than around 200 m from the GIGAS61 antenna and could be also explained by other emission processes than the MBR. Furthermore, new estimations of the expected MBR intensity [18,19] led to the development of two new versions of EASIER, called GIGADuck-C (installed in March 2015) and GIGADuck-L (installed in December 2016), with an enhanced sensitivity to search for signal from larger distances hence fainter.…”

“…The very low flux of Ultra High Energy Cosmic Rays (UHECRs), less than one particle per year per square kilometers above 10 19 eV, requires a very large detection surface at ground level to measure the primary particle properties via the Extensive Air Showers (EAS) they produce in the atmosphere. Such an indirect measurement is a very difficult technical challenge and the search for efficient but low cost techniques is an ongoing process.…”