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CED objectives

Types of Radioactive Decay

▶︎  Watch it animatedinteractive step-through · ~3 min · optional ⚙︎  Open the appletDecay Balancer · pick a parent and a mode, then let the nucleon row and the charge row name the daughter instead of recalling it

Alpha decay lowers the mass number by four and the atomic number by two; beta-minus holds the mass number fixed and raises the atomic number by one as a neutron becomes a proton; beta-plus holds the mass number fixed and lowers the atomic number by one. Gamma decay carries no charge and no nucleons, so it leaves both numbers untouched and the nucleus simply drops to a lower nuclear energy level. Beta decay conserves lepton number as well, so beta-minus emits an electron and an antineutrino while beta-plus emits a positron and a neutrino, and that third particle is what makes the beta energy spectrum continuous.

Three errors dominate. Naming the daughter from a half-remembered rule instead of balancing both rows, which moves the mass number in a beta decay or balances the top row while leaving the bottom one inconsistent. Having a gamma emission move the nucleus to a different element or isotope, or arguing that nothing decayed because the element never changed. And writing beta decay with only the daughter and the electron or positron, which leaves no account of why emitted beta electrons come out with a spread of energies rather than one fixed value.

label the emitted particle and the bookkeeping does itself decay emitted, with its A and Z daughter alpha helium-4: A = 4, Z = 2 A − 4, Z − 2 beta− electron: A = 0, Z = −1 A unchanged, Z + 1 beta+ positron: A = 0, Z = +1 A unchanged, Z − 1 gamma photon: A = 0, Z = 0 BOTH unchanged C-14 beta−: A = 14 and Z = 6, minus an electron at (0, −1), gives (14, 7) = N-14, NOT N-13 beta decay never moves the mass number: the electron has essentially no nucleons
Nothing in this table has to be recalled once the emitted particle carries its own two numbers. The daughter is whatever makes both rows sum equally.
why the third particle has to be there count electron energy endpoint MEASURED: a continuous spread a TWO-body decay would give one sharp energy, fixed by conservation NOT observed a third particle taking a variable share is what smears the line into a spectrum
The neutrino was inferred from this graph decades before anything detected it. A two-body decay has nowhere for the missing energy to go.

The work

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Lesson
Types of Radioactive Decay ›

Balances both rows explicitly so the arithmetic names the daughter, keeps gamma decay on the same nuclide at a lower nuclear energy level, and puts the neutrino into every beta equation.

Skill check · 10 scenarios
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Diagnostic
10-item topic check ›

Ten items spanning the failure modes of this topic: guessing the daughter from a half-remembered rule, moving the mass number in a beta decay, changing the element with a gamma emission, and omitting the neutrino. Take it cold to find which one is yours, or after the lesson to confirm it is not.

Not started · 10 items · ~15 min
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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears it for now and moves you to the next. Two in a row is a checkpoint, not proof: if the error resurfaces later, the misconception comes back.

Take the diagnostic to identify your misconceptions
Diagnostic first