Beta Decay and Neutrinos
At nucleon level, beta-minus is n -> p + e- + anti-nu and beta-plus is p -> n + e+ + nu. Nuclear A stays fixed while Z changes by +1 or -1. Electron capture is another proton-to-neutron channel.
Why this shows up in the exam
Balancing beta-decay equations · Tracking decay chains · Explaining continuous beta spectra
Learn the idea
Beta decay changes neutron-proton balance while conserving A, charge, energy, momentum, and lepton number. In beta-minus decay a neutron converts to a proton and emits an electron plus antineutrino. In beta-plus decay a proton converts to a neutron and emits a positron plus neutrino; the neutrino carries variable energy and momentum.
🧠 Memory hook: Beta minus raises Z; beta plus lowers Z; A stays.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- n -> p + e- + anti-nu_e — beta-minus decay at nucleon level
- p -> n + e+ + nu_e — beta-plus decay at nucleon level
- Delta A = 0; Delta Z = +1 for beta- and -1 for beta+ — daughter-nuclide bookkeeping
How to approach it
- 1Identify the beta sign
- 2Keep A unchanged and update Z
- 3Check lepton and charge conservation
Common slip-ups that cost marks
- •Calling the beta electron an orbital electron
- •Omitting the neutrino or antineutrino
- •Changing mass number during beta decay
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
In hydrogen, an electron transitions from n = 2 to n = 1. Using E_n = -13.6/n^2 eV, find the emitted photon energy.
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