Radioactivity C17 Worksheet Notes

5105 Science (Physics) Chapter 17 | Radioactivity 1 Name: _________________________________________TG: ______ Date: ___________ Chapter 17: Radioactivity Content: • The composition of the atom • Radioactive decay • Dangers and uses of radioactivity Learning Outcomes: Candidates should be able to: (a) describe the composition of an atom in terms of a positively charged nucleus (with protons and neutrons) and negatively charged electrons (b) use the terms proton (atomic) number Z, nucleon (mass) number A and isotope (c) use and interpret the term nuclide and use the nuclide notation 𝑋𝑍 𝐴 (d) show an understanding that nuclear decay is a random and spontaneous process whereby an unstable nucleus loses energy by emitting radiation (e) show an understanding of the nature of alpha (α), beta (β), and gamma (γ) radiation (including ionising effect and penetrating power) [β - particles are assumed to be β– particles only] (f) show an understanding of background radiation (g) use the term half -life in simple calculations, which might involve information in tables or decay curves (h) state the applications (e.g. medical and industrial uses) and hazards of radioactivity.

5105 Science (Physics) Chapter 17 | Radioactivity 2 17.1 What is the composition of an atom? • Subatomic particles: protons, neutrons and electrons • Are held together by: strong attractive forces • Positively charged nucleus and negatively charged electrons. • Nuclide Notation: Example 1 (17A): (a) No. of protons = 92 (b) No. of neutrons = 235 – 92 = 143 Nucleon (mass) number : Total number of neutrons and protons in the nucleus of an atom Proton (atomic) number : Number of protons or Number of electrons in an atom Chemical symbol of the nuclide To find number of neutrons N, N = Nucleon Number A – Proton Number Z in a nucleus Electron : negatively charged Neutron : does not carry any charge. Proton : positively charged -1 +1 0

5105 Science (Physics) Chapter 17 | Radioactivity 3 Example 2 (Let’s Practise 17.1) (d) What is the nuclide notation of the atom? (a) 84 protons (b) 84 electrons (atom is neutral) (c) No. of neutrons = 209 - 84 = 125 (d) 209 X 84 Isotopes Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. • Isotopes of the same element have identical chemical properties. 17.2 What is radioactivity? Nuclear Decay Nuclear decay is a random process by which an unstable atomic nucleus loses its energy by emission of electromagnetic radiation or particle(s) Nuclear decay is also known as radioactive decay or radioactivity. The instability of the atomic nuclei is because the nuclear forces within the nuclei are not enough to bind the nucleons together. • A material is radioactive when: it contains unstable nuclei • Radiation emitted is spontaneous and random in direction.

5105 Science (Physics) Chapter 17 | Radioactivity 4 Three types of nuclear emission Nuclear emission Nature Relative Ionising Effect Relative Penetrating Power • Consists of • Identical to helium nucleus • • • Easily absorbed by • • • • Absorbed by • An electromagnetic radiation emitted by • • • Pass through most materials easily. • Absorbed by Example 3 1. Three radioactive sources are available. Source A emit alpha particles. Source B emit beta particles. Source C emit gamma radiation. a. State what is an alpha particle. b. State the nuclide notation of an alpha, beta and gamma radiation. c. State and explain the materials that can be used to contain source C.

5105 Science (Physics) Chapter 17 | Radioactivity 5 Background Radiation and GM counter • Ionising radiation: _________________________________________________ • Background radiation: ______________________________________________ • Geiger-Muller Counter (GM Counter) measures number of times a radioactive atoms decay (count). • SI unit: _________________________ • One __________________ = _______________________________________ To measure background radiation: Step 1: Step 2 Step 3: Step 4: Example 4 (17B)

5105 Science (Physics) Chapter 17 | Radioactivity 6 Half-life The half-life of a radioactive nuclide is _________________________________ _________________________________________________________________. Example 5 (17C) Example 6 (17D)

5105 Science (Physics) Chapter 17 | Radioactivity 7 Example 7 (Let’s Practise 17.2) 17.3 What are the uses and hazards of radioactivity? (Self-Study) • Uses related to damages to the cells. Radiation Use Medical γ-rays • • Isotope has short half -life (6 hours) so it does not remain in body for too long. β-particles • • Destroy the thyroid cells including cancer cells. • Short half-life (8 days) so does not remain in body for too long. γ-rays • Gamma knife radiosurgery, γ-rays are directed at brain to destroy brain tumours. •

5105 Science (Physics) Chapter 17 | Radioactivity 8 Safety γ-rays • γ-rays used to kill microbes so that food is safe of consumption and last longer. • γ-rays • • Isotope has long half-life (a few years). It takes long time for it to decay so only small quantity is needed over a long time. • Uses related to radioactive decay and half-life. Radiation Use Geology α-rays • • Isotope decays to stable isotope, lead-206. Age of rock can be known by determining relative amounts of uranium-238 and lead-206 in a sample. • • Uses related to penetrating abilities and ionising effects. Radiation Use Safety α-particles • • . • Flow of current is disrupted and triggers detector’s alarm. Industrial β-particles or γ-rays • Measure the thickness of materials and ensure material is of uniform thickness. • • • Geology is the study of physical structure of Earth.

5105 Science (Physics) Chapter 17 | Radioactivity 9 • • Hazards of Radioactivity • Energy carried by ionising radiation can kill cells, cause mutation and cancer. Protecting ourselves from Radioactive Materials Limit Contamination • Leave immediate area quickly. • Remove outer layer of clothing. • Wash all exposed parts with soap and lukewarm water. Reduce Exposure • Carry out experiment with radioactive materials in designated locations. Example 8 (Let’s Practise 17.3)

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