Beta-minus decay and the neutrino
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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
- The missing energy
- Beta-minus decay
Read the transcript of the teaching part
Last time
Before we start: last time, in Beta-plus decay, hadrons and quarks, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
The missing energy
In the 1920s, physicists measured the energy of electrons from beta decay and found something worrying. Every decay of the same nucleus released the same energy, yet the electrons came out with different energies, and some seemed to vanish. Wolfgang Pauli suggested a hidden particle carrying the missing energy: the neutrino.
Beta-minus decay
In beta-minus decay, a neutron in the nucleus changes into a proton, emitting an electron and an electron antineutrino. The nucleon number is unchanged, and the proton number rises by one. Potassium-40, with 19 protons, decays to calcium-40, with 20 protons. The electron and the antineutrino are both leptons. They are fundamental particles.
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.