Electric charging of aerosol particles taking into account track fluctuations of the ion density

Abstract

Aerosols can acquire a significant electric charge when the atmosphere is ionized (or particles are ionized) by irradiation, heating, chemical reactions, and so on. Charging of aerosols in an ionized atmosphere (even under the conditions of a spatially uniform ion distribution) is of a statistical character [1][2][3], and the statistics are determined from the dynamic equilibrium of a charged particle and the embedded gas.Under the conditions of irradiation additional factors resulting in a statistical spread of the charges of the particles appear: emission of charge by an active particle during radioactive decay and fluctuations of the ion concentration in the tracks of ionizing radiation which appear in the gas. The nonuniformity of the distribution of the radioactive matter over the particles (even for the same particle size) that is associated with the genesis of particles can play a definite role. The contribution of this factor to the statistical distribution of the charges can be easily taken into account.Pronounced tracks with large changes in the ion density are formed in the normal atmosphere during the passage of s-particles and fission fragments; for B-electrons such fluctuations are smaller. An aerodispersed system can be found in conditions of external irradiation when the particles may be inactive or self-irradiated, when some particles are radioactive or the embedded gas is radioactive. We confine our attention to the case of inactive particles in an irradiation field with a uniform dose rate (i.e., the case of radiation fluxes which are equal at all points in space). This means that the track concentration (after averaging over a corresponding time interval) is the same for all points in the gas.*The tracks are statistical objects, which have a different size and ion distribution. Fluctuations of the density of ions having charges of opposite sign are different at different points of the track, and for this reason in the general case they are independent random quantities. The spatial correlations of the ion density fluctuations are not of interest, since we are concerned with the charging of separate particles which are small compared to the cross sections of the tracks. The objective of this work is to calculate the effect of fluctuations of the ion density in tracks on the statistics of charging of aerosols.The introduction of the distribution function f~P(R, k) of the transformation of the charge accompanying capture in the track of an aerosol particle of size R and charge k. i.e.. the probability that a particle with an initial charge k acquires a charge (k + p) when it is captured in a track (this probability being averaged over the volume of the track), is fundamental for the further description. For each R the function ,.OP(R, k) is different from zero only for the bounded number p [-Po. Po], and P0 increases with R. Evidently, flP(R, k) depends on the type of radiation producing the track. For example. for R = 1 /zm for tracks of B-particles P0 = 1 and for tracks of s-particles P0 = 10. ...