Thermalisation distances

Range parameters, b (nm), for solvated electrons in various hydrocarbon solvents at room temperature, assuming a gaussian initial distribution of distances from the ionisation site to the thermalisation point... 

Although ionic species are undoubtedly produced as a result of the initial act of absorption of ionising radiation, there is considerable variation in the lifetime of such species. An electron ejected from a parent molecule will travel through the medium against the coulombic attraction of the parent ion until it is thermalised. The distance travelled by the electron will depend on its energy and its rate of energy loss. There are considerable theoretical difficulties in the treatment of this rate of energy loss. 

Thus although ionic intermediates may be formed, their lifetime is too short for them to be chemically significant. Lea12 had previously suggested that the electron could escape from the field of the parent ion. Calculations by Platzman13 indicated that the electron might well travel a distance of 50 A before thermalisation. 

Furthermore, the relative permittivity (or dielectric constant) ofthe liquid is an important parameter. The probability P of an electron (ef) which is thermalised at a distance r metres from its geminate positive ion (M +) escaping recombination with it is exp(-r/r) where is the distance at which the Coulomb potential between e and M is equal to thermal energy kT and is given by the Onsager expression where e is the elementary... 

The total quantum yield rj = r] (hv,T,E) was treated within a modified Onsager model by Silinsh and Inokuchi [28]. With the approximations of an isotropic density g(r) of the distances r of thermalised electrons from the ionised molecules, no field dependence of Oo, an isotropic dielectric constant s and for small electric... 

In the classical picture, the movement of the thermalised positron is a near-isotropic random walk [91]. The mean free path of thermalised positrons (i.e., the mean distance between two scattering events) is... 

The mean diffusion length L+ of the positron is defined as the mean distance from the point of thermalisation that the positron reaches by diffusion movement. This quantity is related to the diffusion coefficient by the relation [72]... 

This means that a positron travels the furthest (on average hundreds of pm) in a metal during its thermalisation, which in turn ensures that PAS provides non-local information on the microstructure of the studied material. A thermalised positron in a defect-free material travels a distance of hundreds of nm, its mean free path is a few nm, and its wavelength is a few tenths of a nm. 

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