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HKDSE Science
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F4b • Unit 5
9 Concepts

Radioactivity and Nuclear Energy

放射性和核能

Unit Overview

In this topic, nuclear processes are examined. Ionizing radiation is very useful in industrial and medical fields but at the same time is hazardous to us. Nuclear radiation comes from natural and artificial sources. It is essential for students to understand the origin of radioactivity, the nature and the properties of radiation. Students should also learn simple methods to detect radiation and identify major sources of background radiation in our natural environment. Simple numerical problems involving half-lives are performed in order to understand the long-term effects of some radioactive sources. The potential hazards of ionizing radiation are studied scientifically and in a balanced way by bringing in the concept of dosage. In the atomic model, the basic structure of a nuclide is represented by a symbolic notation. Students learn the concepts of isotopes. They are also introduced to fission and fusion, nature’s most powerful energy sources.

Key Concepts

1

X-rays as Ionizing EM Radiation

X射線與電離電磁輻射

X-rays as short-wavelength ionizing electromagnetic waves with high penetrating power; how they are produced when fast electrons strike a heavy metal target; and common uses (and limits) of X-rays.

!
Common Pitfall“All electromagnetic waves are equally penetrating regardless of wavelength”
2

Alpha, Beta and Gamma Radiation

α、β、γ輻射的本質與性質

Origin and nature of α, β and γ emissions; comparing penetrating power, range, ionizing ability, behaviour in electric and magnetic fields, and typical cloud-chamber tracks.

!
Common Pitfall“γ must be charged because it comes from the nucleus”
3

Radioactive Decay, Half-life and the Exponential Law

放射性衰變、半衰期與指數定律

Unstable nuclides decay randomly; activity proportional to remaining nuclei; half-life from graphs or data; background radiation; exponential decay \(N = N_0 e^{-kt}\); linking decay constant \(k\) and half-life.

!
Common Pitfall“A nucleus ‘knows’ when its half-life is up and decays on schedule”

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Locked Topics
  • Detecting Radiation: Photographic Film and GM Counters
  • Radiation Dose (Sievert) and Safety
  • Atomic Structure and Nuclide Notation
  • Isotopes and Radioactive Transmutation Equations
  • + 2 more topics

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