Radioactivity (continued 1)
Visão Geral
Deep inside some atoms the nucleus is unstable, and at a moment that no one can predict it suddenly throws out a particle or a burst of radiation and changes into a different element. We cannot say when a single nucleus will decay, yet a large sample decays at a steady, measurable rate captured by its half-life.
In this topic you will learn the nature of alpha, beta and gamma emissions and how each changes the nucleus, write decay equations in nuclide notation, and define and calculate half-life from data and decay curves. You will also see how the choice of radioisotope for smoke alarms, sterilisation, thickness control and cancer treatment depends on its radiation type and half-life.
Objetivos
- Know that radioactive decay is a change in an unstable nucleus that can result in the emission of α-particles or β-particles and/or γ-radiation and know that these changes are spontaneous and random
- State that during α-decay or β-decay, the nucleus changes to that of a different element
- Define the half-life of a particular isotope as the time taken for half the nuclei of that isotope in any sample to decay; recall and use this definition in simple calculations, which might involve information in tables or decay curves (calculations will not include background radiation)
- [Supplement] Know that isotopes of an element may be radioactive due to an excess of neutrons in the nucleus and/or the nucleus being too heavy
- [Supplement] Describe the effect of α-decay, β-decay and γ-emissions on the nucleus, including an increase in stability and a reduction in the number of excess neutrons; the following change in the nucleus occurs during β-emission neutron → proton + electron
- [Supplement] Use decay equations, using nuclide notation, to show the emission of α-particles, β-particles and γ-radiation
- [Supplement] Calculate half-life from data or decay curves from which background radiation has not been subtracted
- [Supplement] Explain how the type of radiation emitted and the half-life of an isotope determine which isotope is used for applications including: (a) h ousehold fire (smoke) alarms (b) irradiating food to kill bacteria (c) sterilisation of equipment using gamma rays (d) measuring and controlling thicknesses of materials with the choice of radiations used linked to penetration and absorption (e) diagnosis and treatment of cancer using gamma rays
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- During alpha decay the nucleon number of a nucleus: A. increases by 4 B. decreases by 4 C. stays the same D. decreases by 2 Answer: B
- In beta decay the proton number of a nucleus: A. decreases by 1 B. increases by 1 C. stays the same D. decreases by 2 Answer: B
- The half-life of a source is the time for its activity to: A. double B. fall to zero C. fall to half D. stay constant Answer: C
- A source has a half-life of 4 hours. After 12 hours the fraction remaining is: A. 1/2 B. 1/4 C. 1/8 D. 1/12 Answer: C
- Which radiation is best for sterilising sealed medical equipment? A. alpha B. beta C. gamma D. infrared Answer: C
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Half Life and Radiometric Dating
Explain radioactive half-life and its role in radiometric dating
"Physics: Half Life and Radiometric Dating" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/physics/pages/22-3-half-life-and-radiometric-dating. Access for free at https://openstax.org/books/physics/pages/1-introduction
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