Hatano Y., Katsumura Y., Mozumder A. (Eds.) Charged Particle and Photon Interactions with Matter - Recent Advances, Applications, and Interfaces

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Introduction

Yoshihiko Hatano

Japan Atomic Energy Agency

Tokai,

Japan

Yosuke Katsumura

The University of Tokyo

Tokyo,

Japan

and

Japan

Atomic Energy Agency

Tokai, Japan

Asokendu Mozumder

University of Notre Dame

Notre

Dame, Indiana

Chapter 1 of Charged Particle and Photon Interactions with Matter: Chemical, Physicochemical,

and Biological Consequences with Applications (Mozumder and Hatano, 2004), early investigations

were briey described with respect to photochemistry and radiation chemistry. The Bethe theory was

also discussed briey in terms of the quantitative similarity of the excitation and ionization processes of

a molecule by photon and charged particle impacts, with emphasis on the importance of optical oscil-

lator strength. It was further pointed out that the applications in the eld of charged particle and photon

interactions with matter have a relatively short history, except for some medical applications. However,

their importance has gradually increased in science and technology since the 1960s.

The chapter briey discussed the timescale of charged particle and photon interactions with

matter, for example, in liquid water. Fundamental processes in the physical, physicochemical, and

chemical

stages of these interactions were delineated.

The

2004 book was organized into 26 chapters, and a list of chapters along with their contribu-

tors

follows:

1. Introduction

(A. Mozumder and Y. Hatano)

2. Interaction

of Fast Charged Particles with Matter (A. Mozumder)

3. Ionization

and Secondary Electron Production by Fast Charged Particles (L. H. Toburen)

Contents

1.1 Theoretical Studies as New Approaches to Primary Processes

ThatMotivateNewExperiments..............................................................................................3

1.2 Advances

in the Theoretical and Experimental Studies

ofthePhysicochemical,Chemical,

and Biological Stages.......................................................6

References..........................................................................................................................................7

2 Charged Particle and Photon Interactions with Matter

4. Modeling of Physicochemical and Chemical Processes in the Interactions of Fast Charged

Particles

with Matter (S. M. Pimblott and A. Mozumder)

5. Interaction of Photonswith Molecules: Photoabsorption,Photoionization,and Photodissocia-

tion Cross Sections (N. Kouchi and Y. Hatano)

6. Reactions of Low-Energy Electrons, Ions, Excited Atoms and Molecules, and Free Radicals

in the Gas Phase as Studied by Pulse Radiolysis Methods (M. Ukai and Y. Hatano)

7. Studies

of Solvation Using Electrons and Anions in Alcohol Solutions (C. D. Jonah)

8. Electrons

in Nonpolar Liquids (R. A. Holroyd)

9. Interactions of Low-Energy Electrons with Atomic and Molecular Solids (A. D. Bass

andL.

Sanche)

10. Electron−Ion Recombination in Condensed Matter: Geminate and Bulk Recombination

Processes

(M. Wojcik, M. Tachiya, S. Tagawa, and Y. Hatano)

11. Radical

Ions in Liquids (I. A. Shkrob and M. C. Sauer, Jr.)

12. The

Radiation Chemistry of Liquid Water: Principles and Applications (G. V. Buxton)

13. Photochemistry and Radiation Chemistry of Liquid Alkanes: Formation and Decay of

Low-Energy Excited States (L. Wojnarovits)

14. Radiation

Chemical Effects of Heavy Ions (J. A. LaVerne)

15. DNA Damage Dictates the Biological Consequences of Ionizing Irradiation: The Chemical

Pathways

(W. A. Bernhard and D. M. Close)

16. Photon-Induced

Biological Consequences (K. Kobayashi)

17. Track Structure Studies of Biological Systems (H. Nikjoo and S. Uehara)

18. Microdosimetry

and Its Medical Applications (M. Zaider and J. F. Dicello)

19. Charged Particle and Photon-Induced Reactions in Polymers (S. Tagawa, S. Seki, and

T.Kozawa)

20. Charged Particle and Photon Interactions in Metal Clusters and Photographic System

Studies (J. Belloni and M. Mostafavi)

21. Applications of Radiation Chemical Reactions to the Molecular Design of Functional

Organic

Materials (T. Ichikawa)

22. Applications

to Reaction Mechanism Studies of Organic Systems (T. Majima)

23. Applications

of Radiation Chemistry to Nuclear Technology (Y. Katsumura)

24. Electron Beam Applications to Flue Gas Treatment (H. Namba)

25. Ion-Beam Therapy: Rationale, Achievements, and Expectations (A. Wambersie, J.Gueulette,

D. T. L. Jones, and R. Gahbauer)

26. Food

Irradiation (J. Farkas)

27. New Applications of Ion Beams to Material, Space, and Biological Science and Engineering

(M. Fukuda, H. Itoh, T. Ohshima, M. Saidoh, and A. Tanaka)

The 2004 book was motivated by two projects. One was a long-term IAEA international

project, from 1985 to 1995, that surveyed the accomplishments in basic radiation research over

the past 100 years following the discovery of ionizing radiation by Curie and Roentgen in the

late nineteenth century (Inokuti, 1995). The other was a textbook of radiation chemistry pub-

lished in 1999 (Mozumder, 1999). Since the activities of the former project, summarized in an

IAEA report, were unfortunately not well known among the international science and technol-

ogy communities, the participants of the IAEA project agreed that the scientic results of the

activities should be published elsewhere, in a book with wider circulation. Furthermore, the

IAEA project focused mainly on primary interactions, that is, the physical stage of the fun-

damental processes of radiation chemistry. Therefore, Mozumder and Hatano collaborated to

edit a new book that would include the physicochemical and chemical stages, in addition to the

physical stage, of the fundamental processes of radiation chemistry, and, consequently, those

of radiation biology.

Introduction 3

The fundamental processes of radiation chemistry are shown in Table 1.1 (Mozumder and

Hatano, 2004), in which the rst three constitute the physical stage or the primary process of the

charged particle and photon interactions with matter (Hatano, 2003). Here “primary” means the

earliest stage that is conceivable either theoretically or experimentally. Sometimes “initial” is used

for measured yields at the shortest time that is possible in a given experimental setup. The primary

stage is followed by the physicochemical and chemical stages. These are followed by the biological

stages.

See also Chapter 1 of the 2004 book.

The

2004 book succeeded in surveying critically and in detail the comprehensive features of

the physical, physicochemical, chemical, and biological stages. Further, the applications of charged

particle and photon interactions with matter were treated briey. Most of the papers referred in the

2004 book were published before 2000.

1.1 theoretiCal studies as new approaChes to primary

proCesses

hat

otivate

xperiments

From the late nineteenth century to the rst half of the twentieth century, studies of the interac-

tion of ionizing radiation with matter were mainly phenomenological in character. A new theoreti-

cal approach, particularly for the primary process, that is, the physical stage, was initiated during

1955–1965 by Platzman, Fano, and Inokuti. They considered the interaction to be the collision of

table 1.1

Fundamental

rocesses

of r

adiation

Chemistry

+ e

−

Direct ionization

AB**

Superexcitation (direct excitation)

AB*

Excitation (direct excitation)

AB**

→

+ e

−

Autoionization

→ A

+ B

Dissociation

→ A

+ B

Ion dissociation

+ AB or S → Products

Ion–molecule reaction

+ e

−

→ AB*

Electron–ion recombination

+ S

−

→ Products

Ion–ion recombination

−

+ S → S

−

Electron attachment

−

+ nAB → e

−

Solvation

AB*

→

+ B

Dissociation

→ AB

Internal conversion and intersystemcrossing

→

Isomerization

→ AB

+ hν

Fluorescence

AB* + S

→ AB

+ S*

Energy transfer

AB*

→ (AB)

Excimer formation

2A → A

Radical recombination

→

C + D

Disproportionation

→

Addition

→ A

+ B

Abstraction

Source: Mozumder, A. and Hatano, Y. (eds.), Charged Particle and Photon

Interactions with Matter: Chemical, Physicochemical, and Biological

Consequences with Applications, Marcel Dekker, NewYork, 2004.

4 Charged Particle and Photon Interactions with Matter

high-energy particles with matter, that is, basically molecules. The important ndings of their stud-

ies are summarized as follows (Platzman, 1962a,b; Hatano, 1999, 2003; Mozumder and Hatano,

2004,

Chapters 1 and 5; and Chapter2):

1. Ionizing radiation is generally classied according to high-energy (a) photons; (b) electrons;

Although the initial interaction of each of these particles with a molecule depends largely

on the kind and energy of the particle, common features among the initial interactions and

further the following electron−molecule collisions should be the formation of electrons in

a wide energy range. These are called “secondary electrons.” The secondary electrons are

classied according to their energy in the middle- and high-energy ranges, and those in

the subexcitation energy region. It was concluded that the essential features of the inter-

action of ionizing radiation with molecules in the primary process is electron−molecule

collisions in a wide range of collision energies, which are followed by cascades of multiple

electron−molecule collisions in matter (Spencer and Fano, 1954; Mozumder and Hatano,

2004,

Chapters 3, 6, and 9; and Chapter 3).

2. Secondary electron collisions with molecules in the middle- and high-energy ranges may

be treated approximately by the Bethe theory (Inokuti, 1971), resulting in the important

conclusion that the generalized oscillator strength and, further, the optical oscillator

strength are of great importance in interpreting the primary result of the interaction of

ionizing radiation with matter. Thus, G-values have been estimated theoretically from the

optical oscillator strength by “the optical approximation” (Platzman, 1962a,b). That is,

the energy deposition spectra in the interaction of ionizing radiation with molecules can

be estimated from the optical oscillator strength (Hatano, 2003, 2009; Mozumder and

Hatano,

2004, Chapter 5; and Chapter 2).

3. Since the optical oscillator strength, which is of the great importance in basic sciences, had

not yet been calculated either theoretically or experimentally, Platzman and Fano realized

and pointed out for the rst time in the late 1950s that synchrotron radiation should be a

powerful photon source in a wide span of photon energies from UV-visible to hard x-rays

(Hatano,

1995).

4. After a scientically careful and intuitive analysis of the primary interaction of ionizing

radiation with molecules, as obtained from the Bethe theory and optical approximation,

Platzman realized that for most molecules there is a big difference between the ionization

threshold energy and the energy region where the major part of the oscillator strength dis-

tribution is located, as deduced from optical data and sum rules. He presented his idea of

“superexcited states,” which are neutral excited states located in the energy region above

the ionization threshold (Platzman, 1962a,b; Hatano, 2003; Mozumder and Hatano, 2004,

Chapter

5; and Chapter 2).

The

theoretical studies, summarized above in (1) through (4), have motivated much new experimen-

tal research since the late 1960s as described below (Hatano, 1999; Mozumder and Hatano, 2004,

Chapter

5; and Chapter 2):

1. Experimental evidence was rst obtained, independent of these theoretical studies, for the

reaction of hot hydrogen atoms formed from the dissociation of highly excited states, pro-

duced by direct excitation during the radiolysis of liquid olens (Hatano and Shida, 1967).

The experimental results were analyzed in terms of the theoretical studies to compare the

experimental G-values with the theoretical ones for the superexcited states estimated by

the optical approximation, giving the rst experimental evidence for the important role of

superexcited states in radiolysis (Hatano et al., 1968).

Introduction 5

2. To obtain experimentally the electronic states of superexcited molecules and their dis-

sociation dynamics to form hot hydrogen atoms, which could be electronically and/or

translationally excited, Doppler spectroscopy combined with an electron−molecule colli-

sion apparatus was developed (Ito et al., 1976, 1977; Hatano, 1983; Kouchi et al., 1997).

In this experiment using molecular hydrogen, the doubly excited and singly excited (with

vibrational/rotational excitation) high Rydberg states converging individually to each of

the ionized states were observed as superexcited states for the rst time. For other mol-

ecules such as HF, H

O, NH

, and CH

, the doubly and inner-core excited states were also

observed.

3. To obtain more detailed information with state selectivity and higher-energy resolution,

synchrotron radiation (SR) has been used as an excitation source for this kind of investiga-

tion (Hatano, 1999). The measurements in these SR experiments are classied into two

types: One is the absolute measurements of photoabsorption cross sections (optical oscil-

lator strengths), photoionization cross sections, photodissociation cross sections, and pho-

toionization quantum yields. The other is the measurement, with high-energy resolution,

of state-specied dissociation fragments formed from state-specied superexcited states.

It was concluded that the electronic states and the dissociation dynamics of molecular

superexcited states were experimentally evidenced for the rst time in these investigations

(Hatano, 1999). Accordingly, an important role of the superexcited states in the primary

process of the interaction of ionizing radiation with matter has been well substantiated

(Hatano, 2003). The results obtained are summarized as follows. Further, these investiga-

tions

have made great progress recently, which are described in Chapter 2.

a. Superexcited states are (i) vibrationally/rotationally excited high Rydberg states, (ii)

doubly excited states, or (iii) inner-core excited states, giving conclusive experimental

evidence

for Platzman’s idea.

b. They dissociate into neutral fragments, with excess electronic or translational energies,

competition with autoionization.

c. Their dissociation dynamics, as well as the dissociation products, are quite different

from

those for the lower excited states below ionization thresholds.

d. Molecules

are not easily ionized, which is an unexpected phenomenon.

e. New information obtained has motivated fresh investigations of quantum theo-

ries applied to the spectroscopy and dynamics of such highly excited molecules

(seeChapter2), as well as explaining the oscillator strengths (see Chapter 4).

f. The new information obtained has also substantiated, to a great extent, the superexcited

states considered as a collision complex in some important processes such as Penning

ionization,

electron−ion recombination, and electron attachment to molecules.

g. The new information has greatly motivated the reanalysis of various other kinds of

phenomena, besides radiolysis, for the ionization and excitation of molecules, such as

reactive

plasmas, plasmas in the upper atmosphere and space, and so on.

h. The new information was previously almost limited to molecules in the gas phase. The

oscillator strengths in the condensed phase were discussed briey (Hatano and Inokuti,

1995) and have recently been measured using a newly developed method (see Chapter 5).

4. Measurements of optical oscillator strengths (photoabsorption cross sections and photo-

ionization cross sections) as deduced from electron−molecule collision experiments have

been made in which the optimum conditions were selected using the Bethe theory. This

method has been called the “poor man’s synchrotron experiments” or “imaginary-photon

experiments” as opposed to “real-photon experiments” using synchrotron radiation,

which requires the construction of big-scale facilities. These two types of experiments

were compared in detail in Chapter 5 of the 2004 book. The data obtained by these meth-

ods have been critically evaluated and compiled elsewhere as recommended ones (Kameta

etal., 2003).

6 Charged Particle and Photon Interactions with Matter

An important part of the new theories of the primary processes was obtained from W-value stud-

ies (Platzman, 1961). New directions in these studies have been made possible by using synchrotron

radiation

and are reviewed in Chapter 6.

Remarkable

progress has recently been made of the interaction of positrons and muons with

matter,

which are surveyed in Chapters 7 and 8, respectively.

With

regard to the information summarized above, future perspectives and future research pro-

grams that need more work on the theoretical and experimental aspects of the primary processes

have

recently been discussed elsewhere (Hatano, 2009).

1.2 advanCes in the theoretiCal and experimental studies

Fthe p

hysiCoChemiCal,

Chemi

Cal,

and b

iologiCal

tages

Virtually all important studies published in or before 2000 of the physical, physicochemical, chemi-

cal, and biological stages of the charged particle and photon interactions with matter were surveyed

critically and in detail, both theoretically and experimentally, in the 2004 book. Some of these are

detailed

in the next paragraph.

The

theoretical studies were surveyed in Chapters 2, 4, 10, and 17. Reactions of electrons, ions,

excited atoms and molecules, and also of free radicals in the gas phase, as studied by pulse radioly-

sis methods, were surveyed in Chapter 6, while those in the condensed phase in Chapters 7, 8, 10,

and 11. The radiation chemistry of liquid water, liquid alkanes, polymers, and metal clusters/photo-

graphic systems was surveyed in Chapters 12, 13, 19, and 20, respectively. Radiation chemistry at

high-LET was reviewed in Chapter 14. Biological consequences were followed up in Chapters 15

and 16. Applications in medical microdosimetry, molecular designing, organic chemistry, nuclear

technology, ue gas treatment, ion-beam therapy, food irradiation, and other new material, space,

and

biological science and engineering were surveyed in Chapters 18, 21 through 27, respectively.

New

advances in the studies of these stages, which were not covered in the 2004 book, have been

remarkable since 2000. This has been pointed out in the preface. Furthermore, great progress has

recently been made in the applications and interface formation.

The outline of recent advances in the studies of primary processes (the physical stage) is

described briey in Section 1.2 (also refer Chapters 2 through 8). Those of the physicochemical,

chemical, and biological stages, as well as of the applications and the interface formation, are

briey described below.

New theoretical studies of the physicochemical and chemical stages are introduced in

Chapters9and 14, respectively; these studies describe the behavior of electrons in liquid hydro-

carbons and for the high-LET radiolysis of liquid water. In Chapter 9, the authors make the rst

application of the Anderson localization concept for electron mobility in liquid hydrocarbons. New

experimental research in the physicochemical and chemical stages are described in Chapters10

through 13, 15 through 18 for each of the specic characteristics of matter to be studied or under

their specic experimental conditions. New experimental studies of the biological stage are intro-

duced in Chapters 19 through 22. The applications in health physics and cancer therapy are found

in Chapters 23 and 24, respectively. Applications to polymers are discussed in Chapters 25 through

27. The applications and the interface formation in space science and technology are introduced

in Chapters 28 through 30. Applications for the research and development of radiation detec-

tors, environmental conservation, plant breeding, and nuclear engineering are further available in

Chapters

31 through 34, respectively.

With

regard to the information summarized above, future perspectives and research programs

that need more theoretical and experimental work on the physicochemical and chemical stages of

the fundamental processes have recently been discussed elsewhere (Hatano, 2009).

Introduction 7

reFerenCes

Hatano, Y. 1983. Electron impact dissociation of simple molecules. Comments Atom. Mol. Phys. 13: 259–273.

Hatano, Y. 1995. Applications of synchrotron radiation to radiation research. In Radiation Research (Congress

Lecture, the 10th International Congress of Radiation Research, Wurzburg, Germany), U. Hagen,

D.Harder, H. Jung, and C. Streffer (eds.), Vol. II, pp. 86–92. Wurzburg, Germany: Universitatsdrukerei,

Strutz

AG.

Hatano,Y. 1999. Interaction of vacuum ultraviolet photons with molecules. Formation and dissociation dynam-

ics

of molecular superexcited states. Phys. Rep. 313: 109–169.

Hatano,

Y. 2003. Spectroscopy and dynamics of molecular superexcited states. Aspects of primary processes of

radiation

chemistry. Radiat. Phys. Chem. 67: 187–198.

Hatano,

2009. Future perspectives of radiation chemistry. Radiat. Phys. Chem. 78: 1021–1025.

Hatano,

Y. and Inokuti, M. 1995. Photoabsorption, photoionization, and photodissociation cross sections. In

Atomic and Molecular Data for Radiotherapy and Radiation Research, IAEA-TECDOC-799, M. Inokuti

(ed.),

Chapter 5.

Vienna, Austria:

IAEA.

Hatano,

Y. and Shida, S. 1967. Hydrogen formation in the radiolyses of liquid butene-1 and trans-butene-2.

J.Chem. Phys.

46: 4784–4788.

Hatano,

Y., Shida, S., and Inokuti, M. 1968. Hydrogen formation and superexcited states in the radiolysis of

liquid

olens. J. Chem. Phys. 48: 940–941.

Inokuti,

M. 1971. Inelastic collisions of fast charged particles with atoms and molecules. The Bethe theory

revisited.

Rev. Mod. Phys. 43: 297–347.

Inokuti,

M. (ed.). 1995. Atomic and Molecular Data for Radiotherapy and Radiation Research, IAEA-

TECDOC-799. Vienna, Austria:

IAEA.

Ito,

K., Oda, N., Hatano,Y., and Tsuboi, T. 1976. Doppler prole measurements of Balmer-α radiation by elec-

tron

impact on H

. Chem. Phys. 17: 35–43.

Ito, K., Oda, N., Hatano, Y., and Tsuboi, T. 1977. The electron energy dependence of the Doppler proles of

Balmer-α emission from H

, D

, CH

and other simple hydrocarbons by electron impact. Chem. Phys.

21:

203–210.

Kameta,

K., Kouchi, N., and Hatano, Y. 2003. Cross sections for photoabsorption, photoionization, and pho-

todissociation of molecules. In Landolt-Boernstein, Y. Itikawa (ed.), New Series, Vol. I/17C. Berlin,

Germany:

Springer.

Kouchi,

N., Ukai, M., and Hatano, Y. 1997. Dissociation dynamics of superexcited molecular hydrogen.

J.Phys. B: Atom. Mol. Opt. Phys.

30: 2319–2344.

Mozumder,

1999. Fundamentals of Radiation Chemistry. San Diego, CA:

Academic

Press.

Mozumder,

A. and Hatano, Y. (eds.). 2004. Charged Particle and Photon Interactions with Matter: Chemical,

Physicochemical, and Biological Consequences with Applications.

New

York:

Marcel Dekker.

Platzman,

R. L. 1961. Total ionization in gases by high energy particles: An appraisal of our understanding. Int.

J. Appl. Radiat. Isot.

10: 116–127.

Platzman,

R. L. 1962a. Superexcited states of molecules, and the primary action of ionizing radiation. Vortex

23:

372–385.

Platzman,

R. L. 1962b. Superexcited states of molecules. Radiat. Res. 17: 419–425.

Spencer,

L. V. and Fano, U. 1954. Energy spectrum resulting from electron slowing down. Phys. Rev. 93:

1172–1181.

Oscillator Strength

Distribution

of Molecules

the Gas Phase in the

Vacuum

Ultraviolet Range

and

Dynamics of Singly

Inner-Valence

Excited and

Multiply

Excited States

Superexcited States

Takeshi Odagiri

Tokyo Institute of Technology

Tokyo,

Japan

Noriyuki Kouchi

Tokyo Institute of Technology

Tokyo,

Japan

2.1 introduCtion

The interaction of light with an atom or molecule is classied into absorption, scattering, and pair

production (Hatano, 1999: 109). In this chapter, the trivial interaction of light of moderate photon

energy, in particular, the interaction of vacuum ultraviolet light, is discussed, and therefore, only the

absorption process is considered. We follow the denition of the vacuum ultraviolet light by Samson

(Samson, 1980: 1–3), that is, the light of wavelength ranging from 200 to 0.2nm. The photon energy

of the vacuum ultraviolet light thus ranges from approximately 6eV to 6keV. The reason why we

Contents

2.1 Introduction ..............................................................................................................................9

2.2 Superexcited

States of Molecules ........................................................................................... 13

2.3

Observing

the Singly Inner-Valence Excited and Multiply Excited States ............................ 17

2.4

Oscillator Strength Distribution for the Emission of Fluorescence

fromNeutralFragments .....................................................................................................18

2.5 Conclusion ..............................................................................................................................25

Acknowledgments............................................................................................................................25

References........................................................................................................................................25