On the mechanism of formation of intratrack yields of water radiolysis products upon irradiation with fast electrons and positrons: 1. Model formulation

Abstract

A mathematical model is constructed for the formation of main transient ( , H, OH) and final ( H 2 , H 3 O + , OH -, Ps) radiolytic products formed in tracks of fast electrons and positrons in water and aqueous solutions. The model takes into account the occurrence of reactions of epithermal electrons, along with thermal and hydrated electrons, with a solute; the ambipolar character of diffusion of charged intratrack particles; and new pathways of the formation of hydrogen and positronium due to the appearance of weakly bound adducts of electrons with their scavengers, in addition to the traditional routes.e aq -132

Positronium formation in a liquid phase: Influence of intratrack reactions and temperature

“…A list of the most important primary reactions has been given in a number of previous publications [3,6,7]. The values of the diffusion coefficients D i and reaction rate coefficients, k ij , between species of i-and j-types are known at the nanosecond stage.…”

Ps formation in molecular media: low temperature hydrocarbons

“…J is the production rate of primary ionelectron pairs per unit volume 2 , f t is the probability of the track electron to survive in intratrack reactions and escape out of its track, κ = 1/(1+k re τ t C R ) is the probability that this electron escapes further capture 1 The end part of the e + (or e − ) track is usually called as blob. 2 In case of irradiation by the e + source J equals to the intensity of the source (0.15 MBq) multiplied by the average initial energy of the positrons (∼200 keV, for 22 Na), divided by the formation energy of one ion-electron pair (∼20 eV) and divided by the average volume, where positrons stop (∼0.1 cm 3 ). So J ∼ 1.5 · 10 10 pair/s/cm 3 = 2.3 · 10 −11 M/s.…”

On the Mechanism of Formation of Intratrack Yields of Water Radiolysis Products upon Irradiation with Fast Electrons and Positrons: 2. Concentration and Time Dependences of Yields

“…In the previous paper [1], we formulated the general model of chemical reactions in the tracks produced by fast electrons and positrons traveling in water and aqueous solutions. The model includes various processes involving primary, intermediate, and final radiolysis products and occurring over the wide span of time 10 − 13 -10 -6 s. The tracks of fast electrons and positrons are approximated by a set of single-type spherical clusters (spurs and blobs) that occur far from one another and are initially composed of the same number n 0 of short-lived radical cations H 2 O + and "hot" electrons e -* , which interact with one another and with water and dissolved solutes to form stable products ( Table 1).…”

“…The model includes various processes involving primary, intermediate, and final radiolysis products and occurring over the wide span of time 10 − 13 -10 -6 s. The tracks of fast electrons and positrons are approximated by a set of single-type spherical clusters (spurs and blobs) that occur far from one another and are initially composed of the same number n 0 of short-lived radical cations H 2 O + and "hot" electrons e -* , which interact with one another and with water and dissolved solutes to form stable products ( Table 1). The intratrack processes are quantitatively described by means of the following system of differential equations of inhomogeneous chemical kinetics: 1 Abstract-A mathematical model for the formation of main transient and final radiolysis products generated in tracks of fast electrons and positrons in water and aqueous solutions was constructed and described in terms of equations of inhomogeneous chemical kinetics in part 1 of this study. The model takes into account the reactions of a solute with epithermal electrons, thermal, and hydrated electrons; the ambipolar character of diffusion of charged intratrack particles; and new pathways of the formation of hydrogen and positronium due to the appearance of weakly bound states of electrons.…”

“…The charged presolvated species e -, H 2 O + , and S -, which further transform into , H 3 O + , S -, and OH -, first diffuse according to the law of ambipolar diffusion with identical diffusion coefficients 1 0 −2 cm 2 /s at t գ t th and D amb ~ 10 -4 cm 2 /s at t th գ t գ t amb . Then, at t տ t amb when the particles spread to distances at which interaction between them becomes negligible (տa bl ), their diffusion occurs with the coefficients characteristic of each individual sort of particles [1]. The time dependence of the diffusion coefficients was approximated by the expression D j (t) = D j + (D amb -…”