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. 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 Er, t e r vt 3 r vt ~ Fourier Er, t Er, 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: 4 Eme dE e4 z 2 M LET n e ln 2 dx 8 0 E me MI n Mz 2 ne dE dx E Bragg-curve: Number of ions as a function of depth Bragg-Gray : γ dose, measured in a thimble chamber D fal Dgáz dE dx dE dx 1 fal 1 gáz 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 e r Delementary A 2 r One must know the activity of the source, then Delementary must be integrated over source and irradiated space. r Radolysis of water This was written in 1907. Ramsay thought it was a question of total energy. Others compared water radiolysis with electrolysis 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 ci D 2 ci k r c i2 k jici c j t j Neutral radicals, hence no Coulomb interaction. Number of equations = number of radical types. Coupled equations LET effect due to different initial geometries. 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 Hungary J. Chem. Theory Comput., 2015, 11 (4), pp 1745–1755 Detour – in parenthesis (Simultaneous diffusion and migration: c ( x, t ) c 2c ux D t x x2 u x E x Markov-process Master equation Fokker-Planck equation: P ( y, t ) 1 {a1 ( y) P} {a2 ( y) P} 2 t y 2 y c = concentration ; P = probability. But, as we know… a1 a2 2 ) Is electron formation a particular wonder? Onsager problem: simultaneous ion migration and diffusion – with the result: recombination. Steady state approximation R + I out q 2 Wescape e I in I ou Ibe e Iki kTR 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: 1 P 2 x e t 2 / 2 dt x V0 Et 2 kT 2Cv f 1 P 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 CaO + Br2 CaBr2 + ½O2 Fe3O4 + 8HBr 3FeBr2 + 4H2O + Br2 3FeBr2 + 4H2O Fe3O4 + 6HBr + H2 [700 0C] [550 0C] [250 0C] [600 0C] Another possibility: 3 3H 2 O 3Cl 2 6HCl O 2 2 8000 C 1000 C 4000 C 18HCl 3Fe 2 O 3 6FeCl 2 9H 2 O 6000 C 6FeCl 2 8H 2 O 2Fe 3 O 4 12HCl 2H 2 1 4000 C 2Fe 3 O 4 O 2 3Fe 2 O 3 2