CHAPTER 1 RADIATION AND RADIOACTIVITY

Transcription

1 CHAPTER 1 RADIATION AND RADIOACTIVITY 1 Atomic Model Atomic Structure Atomic Number Mass Number Isotope [Mass Number][HKCEE] If the nucleus of an atom is represented by the symbol X, it means that this atom has (1) 131 protons in its nucleus. (2) 83 electrons outside its nucleus. (3) 214 neutrons in its nucleus A. (1) only B. (2) only C. (3) only D. (1) and (2) only E. (2) and (3) only Page 1

2 2 Types of Radiation Radiation Radioactivity / Nuclear Decay Page 2

3 3 α, β, γradiations Nature α radiation β radiation γ radiation Range Penetrating Power Ionizing Power Blocking Equation Detection In Electric Field In Magnetic Field Page 3

4 [Radiations][HKCEE] In a factory producing aluminium sheets of 1 mm thickness, a thickness gauge is used to monitor the thickness of aluminium sheets. Which of the following states the correct radioactive source to be used in the thickness gauge and the reason behind? Source Reason A. α α particles have strong ionizing power and can be easily detected. B. α The amount of α particles passing through aluminium depends on its thickness. C. β The amount of β particles passing through aluminium depends on its thickness. D. β β particles are less harmful to human beings. E. γ γ radiation has the greatest penetrating power. [Count Rate][HKCEE] Different absorbers are placed in turn between a radioactive source and a Geiger-Muller tube. Three readingsare taken for each absorber. The following data are obtained: What type(s) of radiation does the source emit? A. β only B. γ only C. β and γ only D. α, β and γ [Equation][HKCEE] U decays by emitting two α particles and two β particles. Which of the following represents the resulting nuclide? A Th B. U C Ra D. 90Th E. Rn 86 Page 4

5 Geiger-Muller Counter Cloud Chamber Page 5

6 4 Decay Process Randomness of Decay Process Principle of Decay Process Mathematical Law of Decay Process Page 6

7 Half-life and decay constant [Half-life and discounted rate][hkcee] In an experiment to measure the half-life of a radioactive isotope in a place where the background count rateis 20 counts per minute, the following results are recorded : The half-life is about A. 4 minutes B. 6 minutes C. 8 minutes D. 10 minutes E. 12 minutes [Half-life][HKCEE] The activity of a radioactive source drops from 640 disintegration per second to 40 disintegration per secondin 2 hours. Find the half-life of the source. A. 7.5 minutes B. 15 minutes C. 24 minutes D. 30 minutes E. 60 minutes Page 7

8 5 X Ray Nature of X Ray Origin of X Ray Uses Page 8

9 6 Radiation Application and Safety Application of Radioactivity Radiation Equivalent Dose Potential Hazards of Ionizing Radiation Precautions in Handling Radioactive Sources Page 9

10 7 Nuclear Energy Binding Energy Nuclear Fission Chain Reaction Page 10

11 Nuclear Fusion Mass-Energy Relation Atomic Mass Unit Page 11

12 [Example] [Nuclear Fusion] Find the energy released in the fusion reaction in the sun: H+ 1H 2 He+ 0n. Given the following data: Particle Mass (Atomic Mass Unit) 2 H H He FINAL REMARKS αβγ,, radiations are the main theme of the topic of radioactivity. Students are required to understand their properties, especially on ionization power, range and behavior in electric/magnetic field. Students should also note that radioactivity is a purely random process that does not affected by environmental condition. On the other hand, X ray is also a kind of ionizing radiation but not usually emitted through radioactive nuclei. Page 12