1

RADIATION CHEMISTRY

RADIATION CHEMISTRY

Absorption of ionizing radiation From Physics to Chemistry

2

WHEN IS RADIATION CHEMISTRY OFIMPORTANCE?

Nuclear reactors Nuclear materials (in general) Biological effects of ionizing radiation Atmospheric chemistry Tool for studying radical chemistry Synthesis of novel materials (e.g. nanoparticles)

IONIZING RADIATION

Radiation with energy > 100 eV

Ionization < 15 eV Chemical bonds 1-5 eV

3

DECAY ENERGIES

α: 4-9 MeV

β: 0.02-4 MeV

γ: 0.1-2 MeV

Ca. 100 000 ionizations per decay!

RADIATION TYPES

Protons and heavy ions (e.g. α-particles)

Electrons (β+ and β-)

Photons (γ)

Neutrons

4

ABSORPTION OF IONIZING RADIATION

Interactions with the electrons of the absorber

(Neutrons): Interactions with nuclei resulting in radioactive decay

RELATIVE TRANSMISSION

5

LINEAR ENERGY TRANSFERLET

LET=-dE/dx

LET depends on the electron density of the absorber (usually proportional to the

physical density)

Radiation (3 MeV) LET (keV/μm) cm in air

Electron 0.20 1400

Proton 21 14

Deuteron 34 8.8

α 180 1.7

ABSORPTION

6

PROTONS AND HEAVY IONS

The Bethe equation

charge particle

masselectron

potential ionization

velocity

eunit volumper atoms absorbing of no.

no. atomic part.

no atomic abs.

2ln

4

2

2

2

2

42

==

==

===

∝−

=−

e

m

I

v

N

z

Z

v

z

dx

dE

I

mvNZ

mv

ez

dx

dE π

THE BRAGG CURVE(HEAVY CHARGED PARTICLES)

2/3 :General ER ∝

7

ELECTRONS(THE BETHE EQUATION)

GAMMA RADIATION

photons of No.==

=−−

N

eNN

Ndxdnxμ

μ

8

GAMMA RADIATION

RADIATION SHIELDING

Radiation Rel. Penetration depth Shielding

α 1 Paper, skin

β 100 3 mm Al

γ 10 000 Concrete, lead

Keep the distance: r-2!

9

ABSORBED DOSE

Unit: 1 Gy (Gray) = 1 J/kg

1 Gy = 100 rad

outinabs

abs

EEE

dm

dED

−=

=

RADIATION CHEMISTRY

From Physics to Chemistry

Chemical Effects (G-values)

Chemical Systems

10

RADIATION EFFECTS ON GASES, LIQUIDS AND SOLIDS

Gas: Low density, high mobility

Liquid: High density, intermediate mobility

Solid: High density, low mobility

ABSORPTION OF IONIZING RADIATION

LET = dEabs/dx(Depends on charge and velocity of the particle and

on the density of the absorber)

Dose = dEabs/dm

11

DOSE RATE

Proportional to activity/current and LET

Unit: Gy/s

RADIATION CHEMICAL YIELD

G-value: GX=d[X]/dEabs

Unit (SI): mol/J(older unit: number of molecules / 100 eV)

12

SOLIDS

Metals: Displacements (heavy particles)

Inorganic nonmetallic compounds:-ExcitationFluorescence-Crystal defects (heavy particles)-Decomposition

ORGANIC COMPOUNDS

13

ORGANIC COMPOUNDS

TRACK

14

RADIOLYSIS OF WATER

H2O

H2O+ + e-

HO· + H3O+

HO· + H-

HO· + H2+OH -

H2O*

e-aq

H2O

H2O H2O

H2O*

H · + ·OH

H2 + O(1D)

H2 + 2HO·

H2O

HO· (0.28), H· (0.062), e-aq (0.28)

Ionizing radiation Time (s) 0

10-15

10-12

10-6 (G values, μmol/J)

Physical stage ionization excitation

Physico-chemical stage

Chemical stage

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Black : e-

aq

Red : H3O+

Green : OHBlue : HCyan : H

2

Magenta : OH-

Yellow : H2O

2

Dark yellow : O(3P)

Z A

xis

(nm

)

Y Axis (nm)

X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Z A

xis

(nm

)

Y Axis (nm)

X Axis (nm)

DIFFERENCES IN 10 KEV TRACK SEGMENTS AT 1 PS

10 MeV 1H

5 MeV 4He

Modern codes give “realistic” track structures.

15

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

100 ps

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

1 ns

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

10 ns

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

100 ns

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

1 ps

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

1 μs

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Primary track

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Secondary tracks

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Low energy electrons

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

Development of a 10 keV Section of a 5 MeV 4He2+ Ion Track in Water

eaq-

H+

OH H H2

OH-

H2O2

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Primary track

Z A

xis

(nm

)

Y Axis (nm)

X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Secondary tracks

Z A

xis

(nm

)

Y Axis (nm)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

Low energy electrons

Z A

xis

(nm

)

Y Axis (nm)

X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

1 ps

Z A

xis

(nm

)

Y Axis (nm)

X Axis (nm)

16

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

100 ps

Z A

xis

(nm

)

Y Axis (nm)X Axis (nm)

0

50

0

50

100

0

50

1 ns

Z A

xis

(nm

)

Y Axis (n

m)X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

10 ns

Z A

xis

(nm

)

Y Axis (nm)

X Axis (nm)

-100-50

0

50

100

-50

0

50

100

150

-50

0

50

100150

100 ns

Z A

xis

(nm

)

Y Axis (nm)

X Axis (nm)

LET AND G-VALUES FOR RADIOLYSISOF WATER

Radiation LET G(H2O) G(H2) G(H2O2) G(e-aq) G(H•) G(HO•) G(HO2

•)

γ, e- 0.24 -0.43 0.047 0.073 0.28 0.062 0.28 0.0027

α(12 MeV)

92 -0.294 0.115 0.112 0.0044 0.028 0.056 0.007

17

G-VALUES AT HIGH SCAVENGERCONCENTRATIONS

G(H2O2) decreases with increasing hydroxylradical scavenger concentration.

G-VALUE AS A FUNCTION OF LET

18

G-VALUE AS A FUNCTION OF T

PROPERTIES OF THE RADIOLYSISPRODUCTS

H2O2: Oxidant

H2: Reductant (slow)

HO•: Strong oxidant (very reactive)(HO• O•- + H+; pKa=11.9)e-

aq: Strong reductant

H•: Reductant (H•H+ + e-; pKa=9.6)

19

RADIOLYSIS OF AQUEOUSSOLUTIONS CONTAINING OXYGEN

H• + O2 HO2•

e-aq + O2 O2

•-

RADIATION CHEMICAL EFFECTS INNUCLEAR REACTORS

Oxidation of metals

Brittleness (H2)

Explosion (H2 + O2)

20

INTERFACIAL PHOTO AND RADIATIONCHEMISTRY

Surface reactions Radiation Chemistry in Heterogeneous systems Photochemistry in Heterogeneous systems

THE MAXIMUM RATE CONSTANT

[ ] [ ]V

NSolutee

k

RR

RTk

dt

Soluted SolidMolRT

E

PSolute

SolidMolBa

−=

−

max

2

3

2

πη

ca 10-3 m s-1 (μm-sized particles)ca 10-6 m s-1 (mm-sized particles)

Radiation induced processes at solid-liquid interfaces.Mats Jonsson, in Recent Trends in Radiation Chemistry, Eds. J. F. Wishart and B. S. M. Rao, World Scientific, in press

21

THE G-VALUE DEPENDS ON THESCAVENGING CAPACITY

B. Pastina, J. A. LaVerne, J. Phys. Chem. A, 1999, 103, 1592-1597

G-VALUE

B. Pastina, J. A. LaVerne, J. Phys. Chem. A, 1999, 103, 1592-1597

22

G(H2O2)

Will be reduced in concentrated solutions (e.g., brines)

INTERFACIAL G-VALUES

G(H2) increases with increasing solid surface area to solution volume ratio. This is not the case for H2O2.

23

SIO2 SLURRIES

J. A. LaVerne, S. E. Tonnies, J. Phys. Chem. B, 2003, 107, 7277-7280

UO2

J. A. LaVerne, L. Tandon, J. Phys. Chem. B, 2003, 107, 13623-13628

24

WHEN ARE INTERFACIAL G-VALUESIMPORTANT?

Surface area to solution volume ratio > 1.6 x 107

Water layer < 60 nm

Radiation induced processes at solid-liquid interfaces.Mats Jonsson, in Recent Trends in Radiation Chemistry, Eds. J. F. Wishart and B. S. M. Rao, World Scientific, in press

RADIATION INDUCED DISSOLUTION OF SPENTNUCLEAR FUEL UNDER DEEP REPOSITORYCONDITIONS

25

DEEP GEOLOGICAL REPOSITORY

We want to be able to accurately predict the rate of radionuclide release from spent nuclear fuel in contact with groundwater!

OTHER RELEVANT RADIATION INDUCEDPROCESSES

Radiation induced corrosion of copper

Radiation induced changes in Bentonite

26

RADIONUCLIDE RELEASE

Instant release

Matrix dissolution (dissolution of the UO2 matrix)

OXIDATIVE (MATRIX) DISSOLUTION

Ox + UO2 UO22+ UO2

2+(aq)

27

KEY PROCESSES

Groundwater radiolysis

Surface reactions (redox processes, catalysis and dissolution)

γ

e-aq

H•

H2

OH•

H2O2

H2O

Spent Nuclear Fuel

Fission products

Actinides

2 e-

2 H+

H2

α

β

Oxidizing species

Reduced speciesU(IV)

UO22+ (aq)

Fission productsActinides

HCO3-

U(VI)

ε

28

γ

e-aq

H•

H2

OH•

H2O2

H2O

Spent Nuclear Fuel

Fission products

Actinides

2 e-

2 H+

H2

α

β

Oxidizing species

Reduced speciesU(IV)

UO22+ (aq)

Fission productsActinides

HCO3-

U(VI)

ε

UO2 OXIDATION KINETICS

The rate constant for oxidation is a function of reduction potential.

-25

-20

-15

-10

-5

0

-0,5 0,5 1,5 2,5

E0 (V)

ln k

1

2

8

43

56

7

Ella Ekeroth and Mats Jonsson, Journal of Nuclear Materials, 2003, 322, 242-248

29

RATE CONSTANTS

Oxidant k (m s-1)

H2O2 7.3 x 10-8

O2 3.6 x 10-10

OH● 10-6

CO3●- 10-6

Olivia Roth and Mats Jonsson, Cent. Eur. J. Chem. 2008, 6, 1-14

ARE THE RATE CONSTANTS CONSISTENTWITH EXPERIMENTAL DATA?

Olivia Roth and Mats Jonsson, Cent. Eur. J. Chem. 2008, 6, 1-14

30

HOW TO USE THE RATE CONSTANTS FORRADIATION INDUCED UO2 DISSOLUTION

Total rate of oxidation:

[ ]=

−==

n

ox

eoxUO

VIU nOxkA

dt

dnrate

1

)(

22

Ella Ekeroth, Olivia Roth and Mats Jonsson Journal of Nuclear Materials, 2006, 355, 38-46

Γ-RADIOLYSIS OF UO2-SUSPENSIONS

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

0 50 100 150 200 250 300

Irradiation time (min)

nU

(VI) (μm

ol)

Calculated

Experimental

Ella Ekeroth, Olivia Roth and Mats Jonsson Journal of Nuclear Materials, 2006, 355, 38-46

γ-radiolysis

31

RELATIVE IMPACT OF (Α-) RADIOLYSISPRODUCTS

H2O2 O2 O2•- HO2

• CO3•- OH•

No additives 100.0 % 0.01 % 0 % 0.03 % 0 % 0 %

H2 (40 bar) 99.9 % 0 % 0 % 0.02 % 0 % 0.03 %

H2 (40 bar)HCO3

- (10 mM) 100.0 % 0 % 0 % 0 % 0.02% 0 %

HCO3- (10 mM) 99.9 % 0.09 % 0 % 0 % 0 % 0 %

[ ]2

Oxrate e

1oxUO

U(VI)

2

−=

==n

kAdt

dn n

ox

E. Ekeroth, O. Roth, M. Jonsson, J. Nucl. Mater. 355 (2006) 38-46.

H2O2 is the major oxidant!

RATE OF H2O2 PRODUCTION

dxOHGxDrx

xOH

=

××=max

22

022 )()( ρ

Mats Jonsson, Fredrik Nielsen, Olivia Roth, Ella Ekeroth, Sara Nilsson, Mohammad Mohsin Hossain,Environ Sci. Technol. 2007, 41, 7087-7093

Can this be simplified?

32

SURFACE CONCENTRATIONS(SIMPLE NUMERICAL SIMULATIONS)

0,00E+00

1,00E-10

2,00E-10

3,00E-10

4,00E-10

5,00E-10

6,00E-10

7,00E-10

8,00E-10

9,00E-10

0 20 40 60 80 100 120 140 160 180 200

Distance/µm

[H2O

2]/M

1 s3 s

10 s

41 s

Steady-state

J. Nucl. Mater. 2008, 372, 32-35 and J. Nucl. Mater. 2008, 374, 286-289

STEADY-STATE

90% of the steady-state (surface) concentration is reached in a very shorttime (Seconds-Minutes)

33

DOES THE STEADY-STATE APPROACHWORK?

Material (Dose rate)

p(H2) [HCO3

-](mol dm-3)

Time (days)

Calc. final conc

(mol dm-3)

Calc. diss rate(mol dm-3 d-1)

Experimental final conc. (mol dm-3)

10 % U-233 (99 Gy/h)

(Ar) 1.68×10-3 47 7.05×10-8 1.50×10-9 6.40×10-8

10 % U-233 (99 Gy/h)

(1,2 % O2) 1.07×10-3 126 1.96×10-6 1.56×10-8 5.69×10-7

SF (α = 828 Gy/h β = 31 Gy/h)

(Ar) 10×10-3 40 1.42×10-4 3.54×10-6 5,96×10-5

SF (α = 828 Gy/h β = 31 Gy/h)

5 bar 10×10-3 376 0 0 1.70 x 10-10

FACTORS AFFECTING (LOWERING) THESTEADY-STATE CONCENTRATION OF H2O2

Surface reaction (UO2 oxidation, Catalytic decomposition, H2 and ε-particles, surface area, radiation enhanced reactivity1)

Homogeneous reactions (e.g. H2O2 + Fe2+)2

β- and γ-radiolysis

1. Olivia Roth, Sara Nilsson and Mats Jonsson Journal of Nuclear Materials, 2006, 354, 131-136 2. O. Roth, M. Jonsson, J. Nucl. Mater. 2009, 385, 595-600

34

H2O2 INDUCED OXIDATIVEDISSOLUTION (DOPED UO2 PELLETS)

0

5E-10

1E-09

1.5E-09

2E-09

2.5E-09

3E-09

Y2O3 Y2O3 /Pd

Pd UO2

r_d

iss(

U(V

I))

/ mo

l L

-1 s

-11 % Pd, 0.3 % Y2O3

N2

RADIATION (Γ) INDUCED DISSOLUTION

0

10

20

30

40

50

60

70

80

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

c(U

ran

yl)

/ µM

time / min

N2 experiments

UO2

Y2O3

Y2O3/Pd

Pd

35

H2O2 CONSUMPTION SIMFUEL/UO2

0

0.5

1

1.5

2

2.5

0 50 100 150 200 250 300 350

H2O

2 co

nce

ntr

ati

on

(m

M)

reaction time (min)

Rate as expected from k(H2O2)*

*M. M. Hossain, E. Ekeroth, M. Jonsson. J. Nucl. Mater. 2006, 358, 202-208

H2O2 INDUCED U(VI) DISSOLUTIONSIMFUEL/UO2

-10

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600

con

cen

tra

tio

n U

(VI)

μM

reaction time (min)

UO2

SIMFUEL

36

RADIATION (Γ) INDUCED DISSOLUTION OFSIMFUEL/UO2

-1

0

1

2

3

4

5

6

7

8

0 1000 2000 3000 4000 5000 6000 7000

U(V

I) c

on

cen

tra

tio

n μ

M

irraditation time (min)

UO2

SIMFUEL

WHAT HAPPENS TO H2O2?

H2O2 + UO2

UO22+ + 2 OH- (Dissolution)

H2O + ½ O2 + UO2

catox

ox

kk

kYield

+=

37

CATALYTIC DECOMPOSITION OF H2O2

H2O2 2HO• (surface catalyzed)

HO• + H2O2 H2O + HO2•

HO2• + HO2

• O2 + H2O2

Σ 2H2O2 O2 + 2H2O

(ZrO2) Cláudio Lousada and Mats Jonsson, J. Phys. Chem. C, 2010, 114 (25)

UO2 POWDER

00.050.10.150.20.250.30.350.40.450.5

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 1000 2000 3000 4000 5000

[OH

] mM

[H2O

2] m

M

time (s)

38

UO2 PELLET

0

2

4

6

8

10

12

14

16

18

20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 20000 40000 60000 80000 100000 120000

[U] m

icroM

[HO

] m

M

time (s)

SIMFUEL PELLET

0

2

4

6

8

10

12

14

16

18

20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 20000 40000 60000 80000 100000 120000

[U] m

icroM

[HO

] m

M

time (s)

39

DISSOLUTION YIELDS BASED ON OH/U(VI)

UO2 powder: 83 % (80 % [U(VI)/[H2O2])

UO2 pellet: 2 % (14 %)

SIMFUEL pellet: 0 % (0.2 %)

Catalytic decomposition is the main reaction path for H2O2 on pellets!

OXIDATION OF UO2 BY MNO4-

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 100 200 300 400

UO2(Westinghouse)

SIMFUEL

40

OXIDATION OF UO2 BY MNO4-

Reactivity (doped UO2):

Y2O3/Pd<Y2O3<UO2<Pd

ACTIVATION ENERGIES (MNO4-)

UO2 (Westinghouse): 7.4 kJ mol-1

SIMFUEL: 12.9 kJ mol-1

41

THE REDOX REACTIVITY OF DOPED UO2

Pure one-electron oxidants are more reactivetowards UO2 than SIMFUEL.

The difference decreases with increasingreduction potential of the oxidant.

The main effect of doping is reduced redoxreactivity.

LINEAR ENERGY TRANSFER(HEAVY IONS)

velocity

no. atomic

2

2

==

∝−

v

z

v

z

dx

dE

42

NOBLE METAL CATALYZED REDUCTION BYH2

INHIBITION OF H2O2 INDUCEDDISSOLUTION

-0,1

0,1

0,3

0,5

0,7

0,9

1,1

1,3

-10 10 30 50 70 90 110 130

ε x pH 2 (bar)

0%

0.1 %

1%

3%

k = 10-6 m s-1 (diff. limited)

Martin Trummer, Sara Nilsson and Mats Jonsson, J. Nucl. Mater. 2008, 378, 55-59

43

ACCOUNTING FOR SOLID PHASEREACTIVITY

Surface k/m s-1

O2 H2O2 H2

UO2 3.9 x 10-10 7.3 x 10-8 --

UO2/UO22+(Pd) 10-7 10-6 1 x 10-6

UO2 (irrad.) 5.1 x 10-10 9.5 x 10-8 --

Olivia Roth, Martin Trummer and Mats Jonsson, Research on Chemical Intermediates, In press

ACCOUNTING FOR SOLID PHASEREACTIVITY

Solid Dissolution rate / mol m-2 s-1

Max H2 (40 bar) H2 (40 bar) 10-2 M HCO3

-GW GW

H2 (40 bar)

UO2 8.7 x 10-11 2.7 x 10-12 2.9 x 10-11 1.4 x 10-13

(5.6 x 10-13)1.4 x 10-13

(3.5 x 10-13)

UO2 + ε-part 8.7 x 10-11 0 0 1.4 x 10-13

(5.6 x 10-13)0

Olivia Roth, Martin Trummer and Mats Jonsson, Research on Chemical Intermediates, In press

44

SPENT FUEL LEACHING (CLOSED SYSTEM)

Radiation induced processes at solid-liquid interfaces.Mats Jonsson, in Recent Trends in Radiation Chemistry, Eds. J. F. Wishart and B. S. M. Rao, World Scientific, in press

RADIATION INDUCED CORROSION OFCOPPER

Upon irradiation (in solution) the copper conc. increases with dose.

The oxide layer grows to ca 100 nm

Exposure to H2O2 does not have this effect.

The copper concentrations in solution are higherthan the oxide solubility and do not match the amount of oxidant produced from radiolysis.

45

RADIATION INDUCED CORROSION OF CU

RADIATION INDUCED CORROSION OF CU

46

PHOTOCATALYSIS

TiO2

Kinetics (Adsorption)

Mechanism (Production of hydroxyl radicals)

QUANTUM YIELD

0

10

20

30

40

50

60

0 100 200 300 400 500 600

QY

(%

)

Conc. (mM)

O2

Air (gamla resultat)

Air (nya resultat)

N2