Radiation Physics

Emico Okuno , Elisabeth Mateus Yoshimura

Since the discovery of radioactivity and x-ray at the end of the nineteenth century radiation has become more and more important in everyday life, with significant applications in industries and especially in medicine. There are countless uses of radiation in the detection and treatment of diseases through radiology, radiotherapy and nuclear medicine.

This book addresses the main topics in the study of Radiation Physics, from chemical elements and radioisotopes, nuclear decay and radiation interaction with matter, to the applications of radiation and its biological effects, besides detection and radiological protection.

Radiation Physics presents the subject didactically, offering solved exercises and even broadens the reader horizons with the biographies of renowned scientists, historical curiosities and lists of exercises. It is a fundamental work for undergraduates and postgraduates Physics, Medical Physics and Clinical Engineering students, as well as a reference for all professionals involved in Radiology.

Original title
Física das radiações
Year of publication

About the authors

Emico Okuno

Emico Okuno has a doctorate in Physics from University of São Paulo (USP) and a post-doctorate from University of Parma (Italy). She was professor at the Institute of Physics of USP from 1960 to 2006.

Author's CV (in portuguese).

Elizabeth Yoshimura

Elizabeth Yoshimura is professor in the Nuclear Physics department of the Physics Institute of the University of São Paulo since 1986. Conducts research and orients students in the area of Radiation Physics and Interaction of Light with Tissues.

Author's CV (in portuguese).

1. Radiation
Electromagnetic radiation and the human body
Atoms, molecules, and ions
The atomic structure
Atomic models
The Bohr model of the hydrogen atom


2. X-rays
X-ray production
X-ray attenuation


3. Radioisotopes
Isotopes and radioisotopes
A little bit of history
Artificial production of radioisotopes

Physical half-life, biological half-life, and effective half-life
Radioisotopes environmental contamination


4. Nuclear disintegration
Atomic masses
Reasons for nuclear disintegration
Nuclear decay
Activity of a radioactive sample
Successive decays


5. Types of decay
State of the art in physics from 1900 to 1940
Alpha decay
Beta decay
Auger electron emission
Gamma Decay
Radioisotopes instability


6. Interaction of radiation
Directly Ionizing radiation: fast heavy charged particles
Directly Ionizing radiation: fast light charged particles
Indirectly ionizing radiation: photons
Indirectly ionizing radiation: neutrons
Radiation energy deposition: absorbed dose


7. Interaction of fast charged particles with matter
Characterization of interactions
Stopping power
Heavy charged particles
Light charged particles: electrons and positrons
Energy deposition in matter by charged particles


8. Interaction of X and gamma rays with matter
Photon beam attenuation
Rayleigh coherent scattering
The Compton Effect
Photoelectric effect
Electron-positron pair production
Attenuation coefficient
Energy transferred to the medium in the interactions of X and gamma rays


9. Quantities and units
Quantities and units
Physical quantities
Protection quantities
Operational quantities


10. Radiation biological effects on living beings
The stages of action
Radiation action mechanisms
Nature of biological effects
Induction of other diseases resulting from exposure to ionizing radiation
Biological effects recent results
Summary of the difference between high dose and low dose effects


11. Radiation detectors
Gas detectors and the Geiger-Müller counter
Scintillator detectors
Dosimetric Detectors: calorimeters and luminescent detectors


12. Ionizing radiation applications
Industrial applications
Medical Applications


13. Radiation protection
Evolution in the values ​​of dose limit
Model of the relationship between dose and effect
Risk Calculation
Radiological protection system base and structure
Occupational exposure
Basic rules of radiation protection





We both are proud to be teachers. We like to teach and interact with students. For us teaching is an art form and we draw great pleasure from it, especially because through teaching we are able to keep on learning. In such days as these, when education is not receiving the merit it deserves we are striving to make our contribution. It's the least we can do to repay the education given us for free during our lives as student; furthermore, we believe that education is the cornerstone upon where the future of any nation is built. Simultaneously, we are full time researchers – even while giving classes or writing a book. We know we have made- and still are making – a difference for many students who have come to meet us.

We started teaching classes in Radiation Physics back in 1987, in the Institute of Physics at the University of Sao Paulo, when we were asked by the students about titles in Portuguese on the subject. From that point on we strived to meet such need with brochures and handouts. The decision to compile all the material we´d gathered along the years into a single textbook came because of the absence of anything similar in Portuguese, the increase in the number of courses in Medical Physics in Brazil and by reaching an agreement with Oficina de Textos Publishing house. Such decision has brought us great satisfaction and enthusiasm, alongside with hard work and great responsibility. This is a project that has been cultured over the last 20 years; therefore, we believe it is a mature work piece, for much of its text and exercises content have been tested out with our students, who were our “lab rats”, in the good sense, of course.

The book consists of 13 chapters. The first chapter is an introduction to the theory of atomic and nuclear physics. The second chapter discusses X-rays and their attenuation. Chapter 3 discusses chemical elements and isotopes. Nuclear decay in general is discussed in Chapter 4 and types of decay, in Chapter 5. The sixth chapter is an introduction on the interaction of radiation with matter. More specifically to the subject, chapters 7 and 8 deal with the interaction of charged particles and photons. Chapter 9 presents the quantities and units of Radiation Physics, and Chapter 10 its biological effects. The radiation detectors are in Chapter 11, and radiation applications in Chapter 12. Finally, Chapter 13 is an introduction to radiological protection. Throughout the book, and intended for better learning and students understanding, resolved exercises weaver the texts. Yet, there is a list of exercises in nearly every chapter, and interesting stories on each topic. At the end of each chapter, the reader finds bibliographic data and a short biography we´ve collected on scientists who contributed to the most significant researches and teaching in the area. Not all chapters dig equally deep in each subject, that allows the reader to explore the book at no particular order and according to everyone´s needs. This book does not address the physics of non-ionizing radiation.

This book can be used in undergraduate courses in Physics, Medical Physics, Clinical Engineering, in advancements courses to physics in the medical field and, in graduate courses with applied subjects in their areas of research. It can be used as a textbook, as a reference for consultation or to deepen one´s knowledge on a given topic.

High school teachers may also take advantage of this book to sort out doubts and gain knowledge in the area; for despite its importance in the modern world, radiation physics is seldom included in undergraduate physics subjects.

Our deepest desire is that this book is indeed a useful resource for the learning of Ionizing Radiation Physics to those professionally involved with the subject.

In the several years we´ve dedicated to the making of this book, there´s been many colleagues and friends who´ve helped us in many ways – providing us with material, bibliographic suggestions, discussions, motivation and friendly words - we are not able to name and thank everyone. However, we´ve chosen a friend, our first reader Almy A. R. da Silva to embody them all and who we thank for his comments, dedication, and quickly giving us feedback. We also thank our former students in the Physics Institute at USP for helping in the assembly of texts for this book and for keeping in us the fire for teaching burning high. We are also grateful to our families, who were the backbone that kept us standing during this intense endeavor, especially through the final stretch.