Alpha decay, energy and beam current
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- A battery that runs for decades
- Counting nucleons
Read the transcript of the teaching part
Last time
Before we start: last time, in Quarks, antiquarks and hadron charges, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
A battery that runs for decades
Space probes far from the Sun carry a small lump of plutonium-238. It decays by emitting alpha particles, and the energy of those particles heats the lump. That heat is turned into electricity, and it keeps going for decades. Let us work out how many decays are needed for a given power.
Counting nucleons
In alpha decay, the daughter has four fewer nucleons and two fewer protons than the parent. Plutonium-238 has 94 protons. The daughter X has 92 protons and 234 nucleons, so 142 neutrons. A stationary nucleus X decays to neptunium-237, with 93 protons. So X has 95 protons and 241 nucleons, which is 146 neutrons.
Chapter 11.2: Radioactive decay
- Isotopes, alpha and beta particles 6 min
- Alpha decay, energy and beam current 7 min
- Decay chains and the N-Z graph 7 min
Also for A Level Physics 9702
Which topics come up most in A Level Physics 9702 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency.