Alpha decayThe nucleus throws out an alpha particle. Its mass number falls by four and its atomic number by two. Alpha decay happens in heavy nuclei, far larger than this sketch.
Beta-minus decayA neutron becomes a proton. An electron leaves, the atomic number rises by one and the mass number stays the same.
Beta-plus decayA proton turns into a neutron. A positron leaves, the atomic number falls by one and the mass number stays the same.
Electron captureThe nucleus takes in an electron of its own atom. A proton turns into a neutron, so the atomic number falls by one and the mass number stays the same.
Gamma emissionThe nucleus gives off a gamma ray. The curved marks show it began with extra energy; no particle changes, so both numbers stay the same.
Nuclei and particles 7
Parent nucleusThe nucleus before it decays.
Daughter nucleusThe nucleus left after the decay.
Alpha particleTwo protons and two neutrons, bound together. It is the same as a helium-4 atom's nucleus.
Beta particle (electron)A fast electron that leaves the nucleus. It is made when a neutron becomes a proton.
PositronThe electron's antiparticle, with a positive charge. It is the beta particle of beta-plus decay.
Captured electronAn electron from the atom's inner shell. The nucleus takes it in, and a proton becomes a neutron.
Gamma rayA photon of very high energy. It is electromagnetic radiation, like light, with a much shorter wavelength.
How this list was compiled: Every name and every change of the atomic number and the mass number checked on 2026-10-03 in at least two of: Wikipedia, text only (Radioactive decay, Alpha decay, Beta decay, Positron emission, Electron capture, Gamma ray); Lawrence Berkeley National Laboratory, ABC's of Nuclear Science, https://www2.lbl.gov/abc/Basic.html ; Georgia State University, HyperPhysics, Radioactivity, http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/radact.html , beta.html and radact2.html ; two textbook passages read through archive.org full-text search (positron emission and electron capture: mass number unchanged, atomic number down by one). The Environmental Protection Agency page Radioactive Decay was read for the names alpha particle, beta particle, gamma ray and decay product. Licence: own work
The drawing: Drawn for this site on 2026-10-03 from plain circles and lines; nothing traced. Licence: own work
How it works
A radioactive nucleus changes by giving something off. Each panel shows a parent nucleus, an arrow and the daughter nucleus it leaves. A proton carries a plus mark; a neutron is plain.
Read the full guide
Name the kind of decay
Look at what leaves. A clump of four is alpha decay. A small particle with a minus mark is beta-minus decay, and one with a plus mark is beta-plus decay. An electron falling in from the dotted ring is electron capture. A wavy ray with no other change is gamma emission.
See what changed
The ringed particle is the one that changed. In beta-minus decay a neutron became a proton. In beta-plus decay and electron capture a proton became a neutron. The second view asks for the particles themselves.
Alpha decay is the only kind here that changes the mass number.
Count the plus marks in both nuclei to check the atomic number. The nuclei are small sketches: alpha decay happens in far heavier ones.
Questions and answers
What are the types of radioactive decay?
The three met first: alpha, beta, gamma decay. Beta decay comes as beta-minus, which gives off an electron, and beta-plus, which gives off a positron. Electron capture is a fifth kind: the nucleus takes in one of the atom's inner electrons.
How does each type of decay change the nucleus?
Alpha decay lowers the mass number by four and the atomic number by two. Beta-minus decay raises the atomic number by one. Beta-plus decay and electron capture lower it by one. Gamma emission changes neither number.
What is the difference between beta-minus and beta-plus decay?
In beta-minus decay a neutron turns into a proton, and an electron and an antineutrino leave. In beta-plus decay a proton turns into a neutron, and a positron and a neutrino leave. The neutrino and antineutrino are not drawn here.
Can I practice here for “label the figure according to the type of decay represented”?
Yes, for practice. That sentence is the instruction of a labeling exercise. These five pictures are our own drawing and not a copy of any course figure, so your figure may show different nuclei.