Electrical charging of radioactive aerosols—comparison of the Clement–Harrison models with new experiments
Introduction
Nowadays, it is well known that radioactive aerosols have an electric charging process that is different from that of non-radioactive aerosols. In fact, the electrical charge of a radioactive aerosol depends on its self-charge, resulting from the emission of charged particles (α, β and e−) during a decay. Several experimental studies carried out at the end of the 1960s by a Russian team (Ivanov, Kirichenko, & Petryanov, 1969; Ivanov & Kirichenko, 1970) and in the 1970s by an American team (Yeh, Newton, Raabe, & Boor, 1976; Yeh, Newton, & Teague, 1978) enabled the effect of the (alpha or beta) radioactivity of an aerosol on its electrical charge state to be clearly demonstrated. These studies showed that radioactive aerosols acquire a positive electrical charge by the emission of an electron during a beta decay, and by the emission of many secondary electrons which are removed from the particle by the He2+ nucleus during an alpha decay. These phenomena are shown in Fig. 1. Several successive theories have been developed to calculate, on the one hand the mean charge (Yeh, 1976; Reed, Jordan, & Gieseke, 1977) and on the other hand the distribution of the electrical charges of a radioactive aerosol (Clement & Harrison, 1992; Emets, Kascheev, & Poluektov, 1993). The various developments of these theories were summarised by Harrison (1992), and more recently by Gensdarmes (2000). In view of the risks represented by radioactive aerosols, and having regard to the significant effects of their electrical charge on their evolution, Clement and Harrison have done a great deal of theoretical work on this subject in the last ten years (Clement & Harrison, 1992; Clement, Calderbank, & Harrison, 1994; Clement, Clement, & Harrison, 1995; Clement & Harrison, 2000). In this way, they have successively demonstrated the effect of the low concentration of a radioactive aerosol on its electrical charge, the effect of the electrical charge of a radioactive aerosol on its coagulation and then the influence of local effects, both geometric and electrostatic.
Artificial radioactive aerosols are present in many applications, for example in the nuclear fuels facilities and in nuclear medicine, particularly in inhalation studies. Such aerosols are also present in the hypothesis of a serious accident inside a nuclear power plant.
Melandri et al. (1983) showed experimentally that the deposit of an aerosol in the respiratory tract may be increased by the image force due to the electrical charge of the particles. In addition, in a recent study, Clement and Harrison (2000) have shown that the electrical charge of a radioactive aerosol may increase noticeably in special situations such as dilution in the atmosphere, entry into a confined space or in the presence of an electrical field.
Although the situations in which radioactive aerosols involved are many, the validity of the various theories is difficult to assess because of the very limited amount of experimental data on the electrical charge of radioactive aerosols. In practice, the experimental work of Yeh, Newton, Raabe, Boor 1976, Yeh, Newton, Teague 1978 showed that the mean electrical charge of the aerosol increases with its specific activity, and that the various theories (Yeh, 1976; Reed et al., 1977; Clement & Harrison, 1992) are in qualitative agreement with this result. However, although the theory of Clement and Harrison (1992) is currently the most complete, the few experimental results available in the literature do not enable it to be fully and finally validated, because of uncertainties about the experimental parameters and the resulting uncertainties on the entry parameters of the theoretical model.
Under these conditions, it seemed to us that further experiments on the electrical charge of radioactive aerosols need to be carried out in order to assess the validity of the theoretical model of Clement and Harrison (1992), in particular for the calculation of the distribution of electrical charges as a function of the parameters of the radioactive aerosol and the parameters of the small positive and negative ions produced in the environment. Moreover, the numerous developments in the metrology of aerosols since the 1970s enable us nowadays to check in an accurate manner a larger number of experimental parameters.
In this article, we present a detailed experimental study of the charge distribution of a beta emitting radioactive aerosol containing caesium 137. In Section 2 we give a brief theoretical summary of the equations established by Clement and Harrison 1992, Clement and Harrison 2000 which enable the electrical charge distribution of a radioactive aerosol in the stationary state to be determined. In Section 3 we present in detail the experimental system that we designed and built for this study. Finally, in 4 Experimental results, 5 Discussion, we present the experimental results obtained and their interpretation.
Section snippets
Theoretical elements
In the stationary state, the electrical charge of a radioactive aerosol is the result of the equilibrium between a self-charging process and a process of neutralisation of the particles. The positive self-charging of an aerosol is due to the emission of beta electrons or to the emission of secondary electrons removed by alpha particles (Ivanov et al., 1969). The term of neutralisation is a function of the global flux of negative charges on the surface of the particle. This depends on the ratio
The experimental apparatus
To measure the charge distribution of a radioactive aerosol, we designed an experimental apparatus which included the following three distinct systems:
- •
a system for the production of standard monodispersed radioactive aerosols,
- •
a system for sampling the aerosol between production and measurement,
- •
a system for measuring the distribution of the electrical charges.
In Fig. 2, we show the experimental apparatus that we developed specifically for this work. Let us present the various systems used and
Measurement of the properties of the small ions and the initial charge distribution of aerosols
As we have stated in the presentation of the experimental apparatus, it is important to know on the one hand the properties of the small ions produced by the beta irradiation and on the other hand the initial charge distribution of the radioactive aerosol.
We determined the properties of the small ions produced by the 85Kr source of the neutraliser during the inactive qualification of the experimental apparatus, using a cylindrical capacitor (Tammet, 1967). The air flow through the neutraliser
Results obtained in the tank volume (i.e. maximum ionisation rate)
We note in Fig. 4, Fig. 6 that the charge distributions of the radioactive aerosol are not significantly different from the initial distributions represented by the inactive model of Clement and Harrison. These distributions were obtained for ageing times of t>150τC for and t>30τC for . In these cases, we consider that the evolution time of a charging process is sufficient to be in the stationary state, in view of the theoretical elements expressed previously.
Conclusion
In this article, we have presented a rapid summary of the theoretical and experimental work carried out on the electrical properties of radioactive aerosols, and we also recall the various expressions established by Clement and Harrison 1992, Clement and Harrison 2000. We also stress the difficulty of the experimental study of the electrical charge of radioactive aerosols due to the many parameters to be taken into account and the safety considerations for experiments relating to the handling
References (41)
- et al.
Study of a sedimentation battery
Journal of Aerosol Science
(1983) The behaviour and detection of radioactive aerosols in NATACHA
Journal of Aerosol Science
(1998)- et al.
Radioactive aerosol charging with spatially varying ion concentrations
Journal of Aerosol Science
(1994) - et al.
Charge distribution and coagulation of radioactive aerosols
Journal of Aerosol Science
(1995) - et al.
The charging of radioactive aerosols
Journal of Aerosol Science
(1992) - et al.
Enhanced localized charging of radioactive aerosols
Journal of Aerosol Science
(2000) - et al.
Statistics of aerosol electric charging
Journal of Aerosol Science
(1993) - et al.
Aerosol charging under gamma irradiation
Journal of Aerosol Science
(1998) - et al.
The electric charging of aerosols in high ionized atmosphere
Journal of Aerosol Science
(1999) The statistical electrification of aerosols by ionic diffusion
Journal of Colloid Science
(1955)
Equilibrium bipolar charge distribution of aerosols
Journal of Colloid and Interface Science
Electrical neutralization of aerosols
Journal of Aerosol Science
Deposition of charged particles in the human airways
Journal of Aerosol Science
Charging of radioactive aerosols
Journal of Aerosol Science
A theoretical study of electrical discharging of self-charging aerosols
Journal of Aerosol Science
Self-charging of 198Au labelled monodisperse gold aerosols studied with a miniature electrical spectrometer
Journal of Aerosol Science
Theory of diffusive deposition of decay products of inert gases in circular and flat channels
Translated from Atomnaya Energiya
Generation of monodisperse aerosol standards
Environmental Science and Technology
Etat de charge des aérosols ultra fins en milieu faiblement ionisé application aux gros ions atmosphériques
Journal de Physique Appliquée
Electric charge and radioactivity of naturally occurring aerosols
Cited by (33)
Charging of radioactive and environmental airborne particles
2022, Journal of Environmental RadioactivityCitation Excerpt :Triboelectric charging can occur even between particles composed of the same material if the particles are bipolarly charged. When compared with other airborne dust particles, particulates that contain radionuclides can, in addition to triboelectric charging, be self-charged through radioactive decay (Clement and Harrison, 1992; Gensdarmes et al., 2001). The rate of radioactive self-charging depends on the activity (i.e., decay incidents per unit of time) of the radioisotopes found in the aerosol and on the type of radioactive decay (i.e., α or β decay) that those isotopes undergo.
Charging and dynamics of polystyrene latex aerosols under bipolar and unipolar ion field–ELPI measurements and comparison with charging theories
2022, Journal of ElectrostaticsCitation Excerpt :The aerosols are radioactive, poly-disperse, multicomponent, having higher dielectric constants and different morphological properties [5–10]. The particulate contaminants suspended in the containment acquire charges by both self-charging (by radioactive disintegrations of the material itself) and diffusion charging (with bipolar ions created in suspended air medium by the radiation) [11,12]. At this juncture, the charged aerosol dynamics (coagulation and deposition) is influenced by additional electrostatic attraction, repulsion, and image forces among the charged particles and with deposition surfaces [1,13].
Studying the impact of radioactive charging on the microphysical evolution and transport of radioactive aerosols with the TOMAS-RC v1 framework
2018, Journal of Environmental RadioactivityIncorporating radioactive decay into charging and coagulation of multicomponent radioactive aerosols
2017, Journal of Aerosol ScienceCitation Excerpt :For example, the initial total radioactivity levels of 132Te-(NH4)2SO4 (fTe-132 = 0.05) and 131I-(NH4)2SO4 (fI-131 = 0.05) aerosols following the log-normal size distribution were 1.54 × 1013 and 6.15 × 1012 Bq m-3, respectively. These input values correspond to a range of the initial total aerosol concentrations (106 − 1013 m-3) and radioactivity levels (3 × 102 − 1.2 × 1019 Bq m-3) used in typical experimental and modeling investigations of the charging and coagulation of radioactive aerosols (Clement & Harrison, 1992; Clement et al., 1995; Clement, Clement et al., 1992; Gensdarmes et al., 2001; Greenfield, 1956; Kim et al., 2014, 2015, 2016; Rosinski et al., 1962; Subramanian, Kumar, Baskaran, Misra, & Venkatraman, 2012; Vasilakos et al., 2017; Yeh et al., 1976). Microphysical evolution of radioactive aerosols can be affected by other processes, such as aerosol diffusion (Anand & Mayya, 2009, 2011) and adsorption of gaseous radionuclides (Anand & Mayya, 2015).
Mobilization of tungsten dust by electric forces and its bearing on tritiated particles in the ITER tokamak
2017, Journal of ElectrostaticsCitation Excerpt :Because of the severe conditions expected in the chamber (particularly in the divertor), its walls will be exposed to erosion resulting in the production of high amount of tungsten dust, activated and tritiated [1]. Radioactive aerosols are known to naturally self-charge through the decay of the radionuclides they bear, making them sensitive to electrostatic interactions [2]. In case of a loss of vacuum (LOVA) accident scenario in ITER, airborne release of charged dust particles will be among the main sources of contamination.