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Alpha particles can be detected by measuring the radioluminescence light which they induce when absorbed in air. The light is emitted in the near ultraviolet region by nitrogen molecules excited by secondary electrons. The accurate knowledge of the radioluminescence yield is of utmost importance for novel radiation detection applications utilizing this secondary effect. Here, the radioluminescence yield of an alpha particle is investigated as a function of energy loss in air for the first time. Also, the total radioluminescence yield of the particle is measured with a carefully calibrated 239 Pu emitter used in the experiments. The obtained results consistently indicate that alpha particles generate ± 19 3 photons per one MeV of energy released in air at normal pressure (temperature°2 2 C, relative humidity 43%) and the dependence is found to be linear in the studied energy range from 0.3 MeV to 5.1 MeV. The determined radioluminescence yield is higher than previously reported for alpha particles and similar to the radioluminescence yield of electrons at comparable energies. This strengthens the evidence that the luminescence induced by charged particles is mostly proportional to the energy loss in the media and not very sensitive to the type of primary particle.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. New J. Phys. 16 (2014) 053022 J Sand et al New J. Phys. 16 (2014) 053022 J Sand et al 3 New J. Phys. 16 (2014) 053022 J Sand et al 4 New J. Phys. 16 (2014) 053022 J Sand et al 5 New J. Phys. 16 (2014) 053022 J Sand et al 6 New J. Phys. 16 (2014) 053022 J Sand et al 7 New J. Phys. 16 (2014) 053022 J Sand et al 8 New J. Phys. 16 (2014) 053022 J Sand et al 9 New J. Phys. 16 (2014) 053022 J Sand et al 10

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A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in an optical multipass configuration. A detection limit of 22 ppb (10−9) was achieved for flowing NO2 in N2 at normal pressure by using the maximum of 70 laser beams between the resonator plates. The corresponding minimum detectable absorption and the normalized noise-equivalent absorption coefficients were 2.2 × 10−7 cm−1 and 3.2 × 10−9 cm−1WHz−1/2, respectively.