4PH1

Properties of Radiation

Radioactivity & Particles · 2 question types

Practise

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 8% of your exam marks.

stable
Low
Stable8%

Properties of alpha, beta and gamma radiation and nuclear equations tested consistently.

Definition

  • An isotope is a form of an element whose atoms have the same number of but a different number of
  • Because the atomic number is unchanged, isotopes of an element are chemically identical. They sit in the same place on the periodic table and form the same compounds. The difference shows up in their mass and in their nuclear stability
  • Most elements have several naturally occurring isotopes:
    • Hydrogen has three: ¹₁H (protium, no neutrons), ²₁H (deuterium, 1 neutron) and ³₁H (tritium, 2 neutrons). Of these, only tritium is radioactive
    • Carbon has three common isotopes: ¹²₆C, ¹³₆C, and the radioactive ¹⁴₆C used in radiocarbon dating
    • Uranium has two common isotopes: ²³⁵₉₂U (used in nuclear fuel) and ²³⁸₉₂U (the more abundant one)
Table comparing the three isotopes of hydrogen (hydrogen-1, hydrogen-2 and hydrogen-3), each with one proton and one electron but 0, 1 and 2 neutrons respectively, alongside their nuclear symbols
Source: Isotopes by Save My Exams

Why some isotopes are stable and others aren't

  • The nucleus is held together by the strong nuclear force, which acts only over very short distances. Protons repel each other electrically, so a stable nucleus needs the right ratio of neutrons to protons to balance these effects
  • Stable isotopes have a nucleon balance the nuclear forces can hold together indefinitely
  • Unstable isotopes have too many neutrons (or in some cases, too few) and the nucleus will eventually emit a particle or a burst of energy to settle into a more stable arrangement. We call this
  • A few examples:
    • ¹²₆C is stable. ¹⁴₆C is unstable (it has two extra neutrons) and decays by beta emission
    • Heavy nuclei like ²³⁸₉₂U are unstable simply because they are large. They shed mass and charge in a chain of alpha and beta decays until they reach lead