Beta-plus decay and antimatter
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 practice questions, 5 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 hospital scan that uses antimatter
- Beta-plus decay
Read the transcript of the teaching part
Last time
Before we start: last time, in The nuclear atom and alpha scattering, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
A hospital scan that uses antimatter
In a PET scan, a patient is given a radioactive sugar. The atoms inside emit positrons, which are antimatter, and each positron meets an electron within millimetres. Both vanish in a flash of gamma rays, which the scanner detects. The positron comes from beta-plus decay.
Beta-plus decay
In beta-plus decay, a proton in the nucleus changes into a neutron, emitting a positron and an electron neutrino. The nucleon number is unchanged and the proton number falls by one. Nitrogen-12, with seven protons, decays to carbon-12, with six, plus a positron and a neutrino. The positron is the antiparticle of the electron. The neutrino here is an ordinary electron neutrino, not an antineutrino.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: β⁺ decay.
The whole chapter: Particle Physics, Particle Physics.
Chapter 11.4: Beta decay
- Beta-minus decay and the neutrino 5 min
- Beta-plus decay and antimatter 6 min
- Beta-plus decay, hadrons and quarks 5 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.