ADVANCES IN RADIATION RESEARCH

J.F. DUPLAN and A. CHAPIRO, E d i t o r s

BIOLOGY AND MEDICINE Volume I Volume I I Volume I I I

PHYSICS AND CHEMISTRY Volume I Volume I I

Advances in Radiation Research •

PHYSICS AND CHEMISTRY

E d i t o r s J.F. DUPLAN and A. CHAPIRO

Labovatoire Pasteur de l 'Institut du Radium

VOLUME 1

GORDON AND BREACH SCIENCE PUBLISHERS New York London P a r i s

CONTENTS

VOLUME I

CHAPTER 1

Preface A. CHAPIRO x i

The I n t e r n a t i o n a l Commission on Radiation Units & Measurements (ICRU) and i t s r e l a t i o n to r a d i a t i o n research H.H. ROSSI . 1

Energy t r a n s f e r from charged p a r t i c l e s J.W. BOAG 9

Role of radiation-produced intermediates i n u t i l i z a t i o n of energy J.L. MAGEE and A. MOZUMDER 15

Energy d e p o s i t i o n by f a s t electrons i n small regions of matter D. HARDER 25

Track s t r u c t u r e i n photographic emulsion P.H. FOWLER 39

C r i t i c a l l e v e l s of energy degradation A. KELLERER . 53

Comparison of photoabsorption and resonance energy t r a n s f e r processes C.E. KLOTS 61

Energy t r a n s f e r e f f e c t s i n aromatic l i q u i d s R.B. CUNDALL and G.B. EVANS 69

E x c i t a t i o n energy t r a n s f e r i n Dye-polyanion complexes R.B. CUNDALL, C. LEWIS, P.J. LLEWELLYN and G.O. PHILLIPS . . . 79

R a d i o l y t i c energy t r a n s f e r induced by r a r e gases L. KEVAN 89

Energy t r a n s p o r t and p r o t e c t i o n i n carbohydrate systems f o l l o w i n g γ-irradiation G.O. PHILLIPS, J.S. MOORE and D. RHYS 123

ν

CHAPTER 2

I n t e r a c t i o n of low-energy electrons w i t h molecules A. KUPPERMANN 133

Long-lived parent negative ions formed by capture of low-energy electrons (0 t o 3 eV) i n the f i e l d of the ground and excited e l e c t r o n i c s t a t e s of organic molecules L.G. CHRISTOPHOROU, J.C. CARTER, E.L. CHANEY and P.M. COLLINS 145

I r r a d i a t i o n d'hydrocarbures gazeux par des electr o n s de f a i b l e s energie J. DANON, R. DERAI and J. MILHAUD 159

Free r a d i c a l s formed i n gaseous phase by low energy e l e c t r o n s : Neopentane, Isobutane, Isobutene R. MARX, G. MAUCLAIRE and M. WALLART 173

Slow electrons and negative ions i n organic l i q u i d s A. HUMMEL 183

El e c t r o n t r a n s p o r t i n i r r a d i a t e d model chemical and b i o l o g i c a l systems G.E. ADAMS and R.L. WILLSON 199

I n t e r v e n t i o n d l'oxygene m o l e c u l a i r e s i n g u l e r dans l e s processus photobiologiques e t radiobiologiques P. DOUZOU 217

Some c o n t r i b u t i o n s of pulse r a d i o l y s i s to general chemistry J.H. BAXENDALE * 229

Pulse r a d i o l y s i s M.S. MATHESON 247

Mathematical a n a l y s i s of f l a s h p h o t o l y s i s and pulse r a d i o l y s i s data L . I . GROSSWEINER and 261

A Stroboscopic pulse r a d i o l y s i s system capable of 20 picosecond time r e s o l u t i o n J.W. HUNT, M.J. BRONSKILL and R.K. WOLFF 271

v i

EPR d e t e c t i o n of s h o r t - l i v e d f r e e r a d i c a l s produced by pulsed r a d i o l y s i s B. SMALLER, J.R. REMKO and E.C. AVERY 279

E l e c t r i c a l c o n d u c t i v i t y i n the pulse r a d i o l y s i s of aqueous s o l u t i o n s K. SCHMIDT 285

Special UV techniques i n pulse r a d i o l y s i s . The absorption spectra of D and OD

S.O. NIELSEN, P. PAGSBERG, Η. CHRISTENSEN and G. NILSSON . . 297

Laser p h o t o l y s i s J.K. THOMAS 303 Ion-molecule r e a c t i o n s J.H. FUTRELL 311

Fast r e a c t i o n methods i n chemistry and bi o l o g y J-M. LHOSTE and J-Ph. RIVET 327

Use of photosynthesis f l o w i n g methods A.-L. ETIENNE 339

VOLUME I I

CHAPTER 1

Comparison between the r a d i o l y s i s of gases and t h a t of the condensed phases G.R. FREEMAN 351

New i n s i g h t s i n t o primary mechanisms of gas phase r a d i o l y s i s by y i e l d measurements at high dose rates C. WILLIS and A.W. BOYD 361

Pulse r a d i o l y s i s : f o r m a t i o n of the N 3 - r a d i c a l i n gaseous n i t r o g e n mixtures

D. PERNER, M.W. BOSNALI, J.W. DREYER and L. SUTTERLIN . . . . 369

A comparison of r a d i o l y t i c and p h o t o l y t i c systems P. AUSLOOS 377

v i i

Etude des ions metastables dans l e spectre de masse des ethylenes deuteres I . BAUMEL, R. HAGEMMAN and R. BOTTER 393

Unimolecular decomposition of ex c i t e d ions Ch. OTTINGER 405

El e c t r o n - i o n n e u t r a l i z a t i o n i n the r a d i o l y s i s of gases L.P. THEARD 419

CHAPTER 2

Nonhomogeneous k i n e t i c s of i o n i c r e a c t i o n s i n organic l i q u i d s G.R. FREEMAN 431

Solvated electrons and ions i n organic systems L.B. MAGNUSSON, J.T. RICHARDS and J.K. THOMAS 441

Pulse o p t i c a l and e l e c t r i c a l methods i n i n v e s t i g a t i n g c e r t a i n r a d i a t i o n - i n d u c e d i o n i c r e a c t i o n s N. BACH, A. REVINA and A. VANNIKOV 449

I o n i c r e a c t i o n s i n γ-irradiated cyclohexane J. KROH, S. KAROLCZAK and H. ZEGOTA 459

Spectroscopic studies of an i o n - r a d i c a l s i n γ-irradiated fr o z e n s o l u t i o n s T. SHIDA 469

A p p l i c a t i o n de l a methode de thermoluminescence ä l 1 e t u d e d'especes ioniques dans l e s s o l i d e s organiques i r r a d i e s A. DEROULEDE, F. KIEFFER, C. MEYER and J. RIGAUT 483

Charge n e u t r a l i z a t i o n and scavenging i n i r r a d i a t e d condensed media A. MOZUMDER 493

K i n e t i c s of ex c i t o n i n t e r a c t i o n s i n molecular c r y s t a l s M. POPE 501

Free r a d i c a l s i n i r r a d i a t e d naphthalene s i n g l e c r y s t a l s N. ITOH, T. CHONG and T. OKUBO 507

v i i i

A di s c u s s i o n of charge c a r r i e r generation and s c i n t i l l a t i o n y i e l d s i n anthracene c r y s t a l s under e l e c t r o n or p a r t i c l e bombardment M. SCHOTT 515

E x c i t a t i o n of fluorescence of anthracene by low-energy e l e c t r o n s E.L. FRANKE VI CH and I . KULES 525

Radiothermoluminescence k i n e t i c s f o r amorphous organic s o l i d s V.G. NIKOL'SKII and V.A. TOCHIN 535

S c i n t i l l a t i o n e f f i c i e n c y assessment of r a d i a t i o n damage i n p l a s t i c media R. HARDWICK and V. SCHWARTZENBACH 547

I o n i c processes i n i r r a d i a t e d organic glasses

H. YOSHIDA, M. IRIE and K. HAYASHI 555

CHAPTER 3

I n t r o d u c t i o n to i n d u s t r i a l a p p l i c a t i o n s C. ROSSI 567 Tri-dimensional network format i o n i n elastomers under i r r a d i a t i o n A.S. KUZMINSKII 571

Ennoblissement des t e x t i l e s par l e g r e f f a g e radiochimique G.Y. GAUSSENS - . . . 589

Perm-selective membranes obtained by r a d i a t i o n g r a f t i n g : a promising t o o l f o r i n d u s t r i a l a p p l i c a t i o n S. MUNARI 599

Cost analysis and economics of e l e c t r o n r a d i a t i o n i n i n d u s t r i a l chemical processes P.J.C.A. SIMONIS 623

Progress and prospects i n Physics and Chemistry J.W. BOAG 633

i x

CRITICAL LEVELS OF ENERGY DEGRADATION

ALBRECHT KELLERER

Radiological Research Laboratories, Columbia University, Ν.Υ.Λ Ν.Υ.Λ U.S.A.

The term i o n i z a t i o n i s so r e a d i l y employed i n theo­r e t i c a l r a d i o b i o l o g y t h a t i t has o c c a s i o n a l l y become a synonym f o r c r i t i c a l event i n the primary stage of r a ­d i a t i o n a c t i o n . I n p r a c t i c a l dosimetry and i n i t s r e ­cent branch microdosimetry i o n i z a t i o n i s the basis of most measurements. Yet one must be aware t h a t the no­t i o n of an i o n i z a t i o n a pplied t o a condensed medium i s vague as there are no sharp c r i t e r i a separating atomic, molecular, and unbound s t a t e s of the e l e c t r o n s .

I t i s paradoxical t h a t one of the most widely used terms i n r a d i o b i o l o g y should also be one of the most i l l - d e f i n e d , and i t seems t h e r e f o r e appropriate to ask how f a r the nature of the c r i t i c a l primary events i n ­fluences the proper d e f i n i t i o n s of r a d i a t i o n q u a n t i ­t i e s , and how f a r i t determines the d i r e c t i o n which microdosimetric research has to take i n the f u t u r e .

I t w i l l be pointed out here t h a t the e x i s t i n g looseness i n the fundamental d e f i n i t i o n s , s p e c i f i c a l l y i n t h a t of absorbed dose, represents no p r a c t i c a l d i s ­advantage. On the other hand i t w i l l be noted t h a t the c r i t i c a l l e v e l s of energy degradation have to be w e l l d efined i f one deals w i t h s p a t i a l d i s t r i b u t i o n s of energy d e p o s i t i o n i n volumes smaller than 100 Ä. Present techniques based on i o n i z a t i o n measurements are severely l i m i t e d by t h i s f a c t . There i s , however, reason t o assume t h a t the microdosimetry data most r e ­levant to r a d i o b i o l o g i c a l studies are those f o r regions

53

54 KELLERER

of the order of magnitude of 1 μ. These data are v a l i d regardless of the nature of the c r i t i c a l events.

1. THE AMBIGUITY IN THE DEFINITION OF ABSORBED DOSE

I n t e r a c t i o n of r a d i a t i o n and matter i s a suc­cession of steps of energy t r a n s f o r m a t i o n and degradation. I n a rough s i m p l i f i c a t i o n one may d i s t i n g u i s h three pools of energy:

1 Rest mass 2 K i n e t i c energy of i o n i z i n g p a r t i c l e s (charged

and uncharged) 3 Energy of chemical bonds and thermal energy

ICRU [1] defines absorbed dose as the f l o w from 1 and 2 t o 3 per u n i t mass. The d e f i n i t i o n i s somewhat loose i n so f a r as the term ' i o n i z i n g * i s not s p e c i f i e d . Electrons w i t h k i n e t i c energy between 1 eV and 100 eV c o n t r i b u t e a p p r e c i a b l y t o the f l u e n c e , Φ, and even t o the energy f l u e n c e , Ψ, of any degradation spectrum of i o n i z i n g r a d i a t i o n . Yet i t i s not s t a t e d , down t o e x a c t l y what energy t h i s f l u e n c e has t o be included i n 2. One must t h e r e f o r e ask how t h i s u n c e r t a i n t y a f f e c t s the d e f i n i t i o n of absorbed dose.

For such a co n s i d e r a t i o n i t i s u s e f u l t o formulate the d e f i n i t i o n of absorbed dose i n the rig o r o u s manner proposed by Rossi and Roesch [ 5 ] :

D - ^ ^ (1)

where the v e c t o r i a l energy f l u e n c e , Ψ, i s the v e c t o r i a l i n t e g r a l oyer the angular d i s t r i b u t i o n ,

of energy f l u e n c e :

Ψ = / Ψ Ω Ω dß, (2)

and Q i s the net energy transformed per u n i t volume from r e s t mass i n t o other forms of energy.

CRITICAL LEVELS OF ENERGY DEGRADATION 55

equation (1) d e f i n e s a q u a n t i t y which i n many p r a c t i c a l cases i s equal t o Kerma.

Though the sum remains equal and the mean value of D over a c e r t a i n volume remains unchanged, exclusion of a c e r t a i n p a r t of the fluence spectrum can lead t o d i s ­t o r t i o n s of the dose p r o f i l e i n a s t r o n g l y inhomogenous f i e l d . The e f f e c t i s s i g n i f i c a n t only i f the fluence v a r i e s appreciably over distances comparable t o the ränge of the p a r t i c l e s which are excluded. I f t h i s i s the case choice of a hig h e r c u t - o f f always leads t o somewhat steep­er dose p r o f i l e s . This corresponds to the f a c t t h a t Kerma inhomogeneities exceed those of absorbed dose.

2. SPATIAL DISTRIBUTION OF DEGRADATION EVENTS

I f one i s concerned w i t h regions l a r g e enough t h a t each t r a v e r s i n g p a r t i c l e produces numerous c o l l i s i o n s i n t h i s r e g i o n then i t matters l i t t l e which events of energy degradation are considered as c r i t i c a l . I n a f i r s t approximation the y i e l d s , k, of various r a d i a t i o n products per rad i n the region of i n t e r e s t can be assumed to be independent of the energy of the primary p a r t i c l e . I f one knows the microdosimetric p r o b a b i l i t y d i s t r i b u t i o n , f ( z ) , of s p e c i f i c energy, z, i n a c e r t a i n region one can the r e f o r e compute the p r o b a b i l i t y d i s t r i b u t i o n , p ( v ) , of the number of c r i t i c a l events according t o the k value i n question:

oo \)

P(v) = / e ~ k z -Ö2i- f ( z ) dz (3) ο

The r e l a t i v e variance of ζ u s u a l l y exceeds t h a t of the Poissonian terms by f a r whenever V > 1. D i r e c t e q u a l i t y of the two d i s t r i b u t i o n s i s then a good approximation:

p(v) = f ( z ) / k , V = kz (4)

Eqs. (3) and (4) are important because i t i s o f t e n er­roneously assumed t h a t the a p p l i c a b i l i t y of microdosimetric d i s t r i b u t i o n s depends on the c o n d i t i o n t h a t i o n i z a t i o n s are the r e l e v a n t ' a c t i v a t i o n events'.

56 KELLERER

From t h i s r e l a t i o n one can r e a d i l y see t h a t D i s very i n s e n s i t i v e t o the choice of the l i m i t of k i n e t i c energy below which p a r t i c l e s are not counted i n Ψ. The low-energy p a r t of the degradation spectrum i s always the most i s o t r o p i c one, because low energy d e l t a - r a y s are emitted n e a r l y i s o t r o p i c l y and because p a r t i c l e s near the end of t h e i r t r a c k become i s o t r o p i c due to repeated angular s c a t t e r i n g . I f a f i e l d i s i s o t r o p i c Ψ i s zero even i f Ψ i s l a r g e . Thus t h e ^ c o n t r i b u t i o n of the low energy p a r t of the spectrum to ν·Ψ i s n e g l i g i b l e even i f the c o n d i t i o n f o r e q u i l i b r i u m (ν*ΨΕ = 0) i s not f u l f i l l e d . One can there­f o r e s t a t e t h a t i n equation (1) one may choose any a r b i ­t r a r y c u t - o f f energy i n the order of magnitude of the bind­i n g energies of the o u t e r - s h e l l e l e c t r o n s .

This answers the question as f a r as absorbed dose i s concerned. A somewhat more d e t a i l e d c o n s i d e r a t i o n i s , however, u s e f u l because i t w i l l show t h a t i n the d e f i ­n i t i o n of microdosimetric f u n c t i o n s a c l a s s i f i c a t i o n of the u l t i m a t e steps of energy degradation can be c r u c i a l .

Consider a proton t r a c k as schematized i n F i g . l a . The proton i s released through the impact of a neutron (broken l i n e ) . The branches along the proton t r a c k are de l t a - r a y s . Each dot on the proton t r a c k and on the elec­t r o n t r a c k s i s an energy degradation step i n an e l e c t r o n i c c o l l i s i o n . Branching p o i n t s represent ' i o n i z a t i o n s ' , the other p o i n t s e x c i t a t i o n s i n which no secondary charged p a r t ­i c l e i s l i b e r a t e d . The term ν·Ψ/ρ i s made up of the d i f ­ferences, ε, of the k i n e t i c energy of the p a r t i c l e e n t e r ­ing and the p a r t i c l e ( s ) l e a v i n g each p o i n t , ε represents t h a t p o r t i o n of the energy which flows from pool 2 i n t o 3 i n i n e l a s t i c c o l l i s i o n s .

I f one excludes p a r t i c l e s below a c e r t a i n energy, the diagram i s modified as i n d i c a t e d i n F i g . l b and c. The two cases represent exclusion of el e c t r o n s below 100 eV and complete exclusi o n of e l e c t r o n s . The sum of a l l d i f ­ferences, ε, i s not changed because the values ε are i n ­creased i n those p o i n t s which are marked by a c i r c l e . I f one goes a step f u r t h e r and excludes a l l charged p a r t i c l e s ,

C R I T I C A L L E V E L S O F ENERGY DEGRADATION

F i g . 1. Schematic representation of a segment of a proton track <>2MeV) and the contibution to the term V ψ/ρ.

58 KELLERER

The equivalence i s , however, l i m i t e d to regions l a r g e as compared t o the distances spanned i n the de­g r a d a t i o n process from energies of the order of magni-of o u t e r - s h e l l b i n d i n g energies down to thermal energies. This i m p l i e s a much more s e r i o s l i m i t a t i o n of the use of p r o p o r t i o n a l counters than the f a c t t h a t such counters respond only to i o n i z a t i o n s . From experiments w i t h UV l i g h t i t i s apparent t h a t e x c i t a t i o n s are much l e s s e f f i c i e n t than i o n i z a t i o n s , and i o n i z a t i o n i n gas i s i n so f a r a sound basis of microdosimetric measurements. The s p a t i a l s h i f t i n the degradation process i s , however, a serious obstacle i n d e a l i n g w i t h very small regions. F i g . 2 i l l u s t r a t e s the p o i n t ; the example of a proton t r a c k i s used again. E x c i t a t i o n s are not con­sidered. I n scheme a) p o s i t i v e ions are marked as dots. One may assume t h a t i n many cases, s p e c i f i c a l l y i n dry systems, the p o s i t i v e ions are the f o c a l p o i n t s of the r e a c t i o n chain which leads to the primary l e s i o n s . A p r o p o r t i o n a l counter, or any other e l e c t r o n - c o l l e c t i n g device, does, however, not respond to the p a t t e r n rep­resented i n F i g . 2a. Instead i t c o l l e c t s the e l e c t r o n s a f t e r they are thermalized. The t y p i c a l t h e r m a l i z a t i o n distances f o r e l e c t r o n s are of the order of magnitude of 100 A. This means t h a t the counter responds to the p a t t e r n of thermalized or n e a r l y thermalized e l e c t r o n s schematically represented i n F i g . 2b. The p a t t e r n i s c l e a r l y d i s t i n c t from t h a t of the p o s i t i v e ions. The main e f f e c t i s one of decreased l o c a l c oncentrations. I f , f o r example, one determines 'associated volumes 1

(see Lea [ 2 ] ) f o r r a d i i below 100 A, the values derived w i t h e l e c t r o n c o l l e c t i n g devices must s i g n i f i c a n t l y exceed those derived w i t h a device which c o l l e c t s p o s i ­t i v e ions. I t i s important to note t h a t t h i s i s not a discrepancy due t o d i f f u s i o n of the e l e c t r o n s i n the c o l ­l e c t i n g process. The c r i t i c a l step i s the t h e r m a l i z a t i o n process. One must conclude t h a t microdosimetric ex­periments on extremely small volumes have to be based on the counting of p o s i t i v e i o ns.

I t should, however, be mentioned t h a t a recent a n a l y s i s of various RBE data on the basis of ideas

C R I T I C A L L E V E L S OF ENERGY DEGRADATION 59

(a)

(b)

Fig. 2. Schematic representation of the s p a t i a l pattern of p o s i t i v e ions (a) and of thermalized electrons (b) around a proton track.

60 KELLERER

expressed by Rossi [4] r e a f f i r m s the usefulness of e x i s t i n g microdosimetric data f o r l a r g e r volumes. I n agreement w i t h conclusion reached e a r l i e r [3,6] i t ap­pears t h a t the c r i t i c a l primary lesions i n the c e l l are due t o two events, each induced by a s i n g l e e l e c t r o n i c c o l l i s i o n ; these events i n t e r a c t over a distance of about one micrometer [ 7 ] .

SUMMARY

Radiation q u a n t i t i e s , as f o r example absorbed dose, and microdosimetric f u n c t i o n s f o r regions of the order of magnitude of 1 μ are meaningful w i t h o u t s p e c i f i c a t i o n of the c r i t i c a l steps of energy degradation. This i s not t r u e f o r microdosimetric q u a n t i t i e s r e l a t e d t o regions w i t h l i n e a r dimensions near or below 100 Ä ; the usual techniques of i o n i z a t i o n c o l l e c t i o n are not ap­p l i c a b l e i n t h i s case and measurements have t o be based on the c o l l e c t i o n of p o s i t i v e ions.

REFERENCES

1. ICRU Report, Radiation Quantities and Units.

2. LEA, D.E., Action of Radiations on Living Cells, Cambridge U n i v e r s i t y Press (1946)

3. NEARY, G.J., Int. J. Rad. Biol. , 9, hll (1965)

4. ROSSI, H.H., Physics in Med. and Biol. , IS, 255 (1970)

5. ROSSI, H.H. and W.C. Roesch, Rad. Res., 16, 783 (1962)

6. WOLFF, S., Radiat. Res., 1, 453, 1959.

7. KELLERER, A.M. and ROSSI, H.H., Radiat. Res., 47, 15, 1971.