.

Heavy ions, γ-photons, fast electrons – all of them produce

low-energy secondary electrons in the medium

(γ: photoeffect, Compton-effect, pair production).

The good part of the electron energy is imparted to the

atoms/molecules of the medium via Coulomb interaction

,~,

, 3

rErE

vrvr

rE

tFourier

tt

et

Optical approximation– as if the medium were illuminated with white light.Hence: energy absorption is connected with optical absorption spectra.

Types, sources of radiation

α 210Po (E=5,3 MeV)

β 90Sr (Emax=2,18 MeV, <E>=0,765 MeV)

Accelerators: van de Graaff, LINAC, etc.

γ 60Co (E=1,1; 1,3 MeV, <E>=1,25 MeV)

Energy loss of a charged fast particle:

E

nMz

dx

dE

MI

Emn

m

M

E

ze

dx

dE

e

n

ee

e

2

2

24 4ln

8LET

0

Bragg-curve:Number of ions as a function of depth

Bragg-Gray : γ dose, measured in a thimble chamber

gáz

fal

gáz

fal

dxdE

dxdE

D

D

1

1

Ideal case – poliethylene thimble filled with ethylene gas

Absolute dosimetry:

Dose D coming from a volume element of the source,

reaching a volume element of the irradiated space

One must know the activity

of the source, then

must be integrated over source and

irradiated space.

r

2r

eAD

r

elementary

elementaryD

This was written in 1907. Ramsay thought it was a question of total energy. Others compared water radiolysis with electrolysis

Radolysis of water

Does this type of reaction scheme explain more than it was

devised to?

Effect of LET on the yields of radiaton chemical processes .

Diffusion controlled kinetics

Heavy ion Fast electron

trajectories observed in a cloud chamber

Radiolysis products are not distributed homogeneously –

hence diffusion, recombination and chemical reaction proceed

simultaneously and in interaction.

Radical diffusion theory

Neutral radicals, hence no Coulomb interaction.

Number of equations = number of radical types.

Coupled equations

LET effect due to different initial geometries.

jjijiri

i cckckcDt

ci

22

Highland Park, USA, 1951

Some suspicion: two types of „H-atoms”?

Pulse radiolysis (a sister of flash photolysis)Accelerators, with short and shorter pulse lengths are needed.

A not-too-modern equipment: Pune (India) 2006

The first spectrun of the hydrated electron (Hart and Boag, 1962)

As it was expected.

The first kinetic trace of the hydrated electron (Keene, 1963)

Chemistry of the hydrated electron

- The ideal of the reducing agent: no oxidised product left

- the perfect nucleophyilic partner

- very selective, in certain cases diffusion controlled rates

- previously unknown products, e.g.Ag0, Cu0

A naive model

(polaron in a dielectric

medium)

Hydrated Electrons in Water Clusters: Inside or Outside, Cavity or Noncavity? László Turi Department of Physical Chemistry, Eötvös Loránd University, P.O. Box 32, Budapest 112, H-1518 HungaryJ. Chem. Theory Comput., 2015, 11 (4), pp 1745–1755

Detour – in parenthesis

(Simultaneous diffusion and migration:

Markov-process Master equation Fokker-Planck equation:

c = concentration ; P = probability. But, as we know…)

xx Eu 2

2),(

x

c D

x

c u

t

txc x

})({2

1})({

),(221 PaPa

t

tPy

yy

y y

22

1

a

a

Is electron formation a particular wonder?Onsager problem: simultaneous ion migration and diffusion – with the result: recombination.

Steady state approximation

R

Iki

Ibe

RkTq

ouin

outescape e

II

IW 2

e

e

+

If so, complete ion-electron recombination would proceed.

Solvated electrons discovered in a good number of

polar liquids: alcohols, amines, ethers

Electron spectra:

Electron yields in a series of polar liquids: the effect of energy

fluctuations

Hydrated electron yield in supercooled water

Excess electrons in a number of non-polar liquids

Electron mobilities

Hel, Xel, n-hexane, neo-pentane χ[10-3, 103] cm2/Vs

Energy of the localized state: Et ;

Bottom of the conductivity band: V0

Et < V0 lokalizáció (buborék)

Localization probability, P, defined by energy fluctuation:

vt

xt CkT

EVx dteP 2202/2

2

1

Pf 1

Radiaton chemistry of organic molecules

R-CH2-CH2-R’ R-CH2· ·CH2-R’

R-CH2· + R-CH2-CH2-R’RCH3 + R-C·H-CH2-R’

H· + R-CH2-CH2-R’ H2+ R-C·H-CH2-R’

Generally speaking: bond cleavage and bond formation.

Main product usually H2

The failure of the organic moderated reactors.

But: chemistry of the nuclear reactors!!

β irradiation of oxidized iron surfaces, after that electrode

Impedance in aquoeus SO32- solution (hole capture).

Equivalent circuit:

Result:

Faraday process gets

faster due to irradiation

γ irradiation of carbon steels (Daub (2011)

Irradiation in aqueous solutions at different pH values

Ecorr= -0.65 V Ecorr= 0 V

SCE; pH 10,6

γ-Fe2O3 is formed upon

the irradiated surface.

Raman spectra for comparison

Hydrogen economy

Hydrogen from water.

Catalytic cycle:  

2AB + 2H2O 2AH + 2BOH

2BOH 2B + ½O2 + H2O

2AH 2A + H2

2A + 2B 2AB

Low-temperature extotherm, and high-temperature endotherm

stages are desired.

High temperature is always needed!

Gas-cooled nuclear reactors?

 For example: UT-3 Process

CaBr2 + H2O CaO + 2HBr [700 0C] CaO + Br2 CaBr2 + ½O2 [550 0C]

Fe3O4 + 8HBr 3FeBr2 + 4H2O + Br2 [250 0C] 3FeBr2 + 4H2O Fe3O4 + 6HBr + H2 [600 0C]  

2C800

22 O2

36HCl3ClO3H

0

O9H6FeClO3Fe8HCl1 22C400C100

32

00

Another possibility:

243C600

22 2H12HClO2FeO8HFeCl60

32400

243 OFe3O2

1OFe2

0

C