ALPHA DECAY (α):
- Nucleus emits an alpha particle (2 protons + 2 neutrons)
- Mass number decreases by 4
- Atomic number decreases by 2
- Element CHANGES (2 fewer protons = different element)
Example: ²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂α
BETA DECAY (β):
- A neutron turns into a proton (and emits an electron)
- Mass number stays the SAME
- Atomic number increases by 1
- Element CHANGES (one more proton)
Example: ¹⁴₆C → ¹⁴₇N + ⁰₋₁β
GAMMA EMISSION (γ):
- Nucleus releases excess energy as gamma ray
- Mass number stays the SAME
- Atomic number stays the SAME
- Element does NOT change (just loses energy)
- Often follows alpha or beta decay
Quick Check: In beta decay, the mass number stays the same. Why?
In beta decay, a neutron converts into a proton. One nucleon (neutron) is replaced by another (proton), so the total number of nucleons — and therefore the mass number — stays the same.
This key facts covers What Happens in Each Decay within Radioactive Decay for GCSE Physics. Revise Radioactive Decay in Atomic Structure for GCSE Physics with 15 exam-style questions and 6 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 4 of 14 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Radioactive Decay
An alpha particle consists of which particles?
Explain why alpha radiation is described as highly ionising but weakly penetrating.