Radioactivity

1. Radioactivity Unit 8 – Part A

2. Radioactivity • Radioactive: When an element emits any form of radiation. • Radiation: The transfer of energy by the means of electromagnetic waves or particles. • Types of emitted radiation: • Alpha • Beta • Gamma

3. Radioactivity • Alpha Particle: • Radiation consisting of fast-flying, positively charged subatomic particles. • Combination of 2 protons and 2 neutrons.

4. Radioactivity • Beta Particle: • Consists of a fast-flying, negatively charged subatomic particle. • Occurs as a neutron transforms into a proton and an electron, and this electron is ejected by theatomic nucleus.

5. Radioactivity • Gamma Radiation: • Extremely energetic form of electromagnetic radiation. • Possesses much more energy than visible light. • Carries no electric charge and has no mass.

6. Alpha Radiation • Their large size causes particles to be trapped by solid materials, and has a positive charge of 2+. • Can cause significant damage to the surface of materials, especially living tissue. • Uses: Most often found in smoke detectors.

7. Beta Radiation • Normally faster than alpha particles and not as easy to stop. • Able to penetrate light materials and can penetrate deeply into skin. • Unable to penetrate denser materials like aluminum. • Once stopped they become part of the material they are in. • Uses: Most often found in industrial production of goods to reduce the static charge.

8. Gamma Radiation • Pure energy but much greater than the amount of energy in visible light. • Can penetrate most materials, except dense materials such as lead. • Much more harmful to us than alpha or beta particles. • Uses: • Food sterilization • Medical instrument sterilization • Medical Treatments (cancer)

11. Radioactivity = Decay • Remember that radiation is the process of a nucleus undergoing a change by emitting energy in the form of particles or rays. • Alpha / Beta / Gamma • Original nucleus is designated as the parent nucleus and the resulting nuclei are called daughter nuclei.

12. Ways to determine stability of a Nucleus • Transuranic elements: • Unstable elements above the atomic number of 92 • The nucleus has fewer neutrons than protons. • The nucleus is odd-odd • Proton and neutron numbers are odd.

13. Nuclear Transmutation • When a radioactive nucleus emits an alpha or beta particle, the atomic number of the nucleus is changed. • The identity of the element also changes. • Consider an 238Uranium nucleus (p=92, n=146). When an alpha particle is ejected, the nucleus loses 2 protons and 2 neutrons. • The remaining nucleus (p=90, n=144) has a different identity. • 234Thorium.

14. Nuclear Transmutation • 234Thorium is radioactive, and when it decays, it emits a beta particle. • Beta particle = lose an electron and gain a proton as a neutron transforms. • The remaining nucleus (p=91, n=143) has a different identity. • 234Protactium.

15. Nuclear Half-Life • The rate of decay of a given nucleus is described as the term half-life. • The time it takes for half of the nuclei of a given radioactive sample to decay.

16. Nuclear Half-Life • What fraction and mass of a 40-mg sample of iodine-131 (half-life = 8 days) will remain after 24 days?

17. Nuclear Half-Life • Strontium-90 (half-life = 29 years) is one of the worst components of fallout from atmospheric testing of nuclear bombs because it concentrates in your bones. The last such bomb was tested in 1963. In the year 2021, how many half-lives will have gone by for the strontium-90 produced in the blast? What fraction of the strontium-90 will remain in the year?

18. Nuclear Half-Life • How long would it take a sample of 14Carbon to decay to one-fourth of its original activity? The half-life of 14Carbon is 5,730 years.