The yield of air fluorescence induced by electrons

Abstract

The fluorescence yield for dry air and pure nitrogen excited by electrons is calculated using a combination of well-established molecular properties and experimental data of the involved cross sections. Particular attention has been paid to the role of secondary electrons from ionization processes. At high pressure and high energy, observed fluorescence turns out to be proportional to the ionization cross section which follows the Born-Bethe law. Predictions on fluorescence yields in a very wide interval of electron energies (eV -GeV) and pressures (1 and 1013 hPa) as expected from laboratory measurements are presented. Experimental results at energies over 1 MeV are in very good agreement with our calculations for pure nitrogen while discrepancies of about 20% are found for dry air, very likely associated to uncertainties in the available data on quenching cross sections. The relationship between fluorescence emission, stopping power and deposited energy is discussed.

Air fluorescence measurements in the spectral range 300–420nm using a 28.5GeV electron beam

“…Within the gas molecules the energy flow is very complicated because of the number of energy levels available, and the pressure-dependent competition between fluorescent emission and energy transfer in molecular collisions. Work towards the theoretical modeling and calculation of the fluorescent light yield is progressing [13,14,15,16].…”

Modelling of anomalous Doppler broadened lines, thermalization of electrons and the role of radicals in discharges at high E/N

“…Thus we propose that the high E/N experiments may be used to benchmark the codes for thermalization. While our results are directly applicable to compare with the results of papers [23,24] it is also important to note that the upper atmosphere lightning's also involve high energy runaway electrons [29,30]. In addition our results are relevant to other studies of thermalization of electrons [33] and positrons [34,35] that in addition to atmospheric phenomena may include biomedical applications and radiation damage.…”

“…Emission from the higher layer of the atmosphere has been proposed as a probe of the particles of cosmic origin with extremely high energies [22,23]. In their papers Blanco and Arqueros [23,24] have applied a Monte Carlo technique to calculate the emission due to thermalization of very high energy electrons in nitrogen at low pressures that correspond to the conditions in the upper atmosphere. These authors have initially assumed that the cross section may depend on the pressure if one needs to model the low pressure and the high pressure limits.…”

Air fluorescence relevant for cosmic-ray detection—Summary of the 5th fluorescence workshop, El Escorial 2007

“…The curve for the 2P system shows a sharp maximum at about 15 eV followed by a fast E −2 decrease, as expected from the optically forbidden nature of this transition. On the contrary, the excitation cross section for the 1N system shows a much softer maximum at about 100 eV followed by a much slower (log E)/E decrease which becomes a soft growing behavior at relativistic energies [33] [34].…”

“…The total number ε λ of fluorescence photons generated per unit path length in a very large medium can be expressed as a function of the optical cross section σ λ of the transition by [34] …”