CHAPTER XV 



ELECTRONS, NEUTRONS, AND ALPHA 



PARTICLES 



L. II. Gray, Badiotherapeulic Research Unit of the Medical Research Council, 



London 



A . Place of Ionizing Radiations in Nature and llesearcii 492 



1 . Ionizing Radiations 492 



2 . Effects of Ionizing Radiations on Living Cells 493 



3 . Ionizing Radiations as Part of the Environment of Living 



Organisms 494 



4. Ionizing Radiations as a Health Hazard 496 



5 . Ionizing Radiations as Carcinogenic Agents 497 



6. Ionizing Radiations as Mutagenic Agents 498 



B . Physical Characteristics of Different Ionizing Radiations and 



Their Relation to Effects Produced in Living Cells 500 



1 . Available Sources of Ionizing Radiation 500 



2. Classification of Ionizing Radiations According to Mean 



Spacing of Ions along Tracks of Ionizing Particles 501 



3. Irregularities in Ion Spacing and Their Biological Signifi- 



cance 509 



4. Low Velocity Secondary Electrons, or Delta Rays 513 



5. Relative Positions Occupied by Positive and Negative 



Ions at Moment of Formation and Their Subsequent 



Movement 514 



C. Sources of Ionizing Radiation for Research 519 



1 . Electrons 519 



2. Protons 526 



3. Fast Neutrons 528 



4. Slow and Thermal Neutrons 532 



5. Alpha Particles 535 



D . Measurement of Ionizing Radiation 537 



1 . Units of Dose 538 



2. Measurement of Ionization 540 



3. Energy Equivalent of One Electrostatic Unit of Ions 



Formed in Air 542 



4. Design of Ionization Chambers and the Choice of Condi- 



tions of Irradiation for Experiments with Particular 



Sources 543 



5. Ionization in Tissue 556 



References 557 



491 



