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Flip to reveal answersWhat two quantities are conserved in a nuclear decay equation?
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All 16 Flashcards — Decay equations and conservation laws
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Question
What two quantities are conserved in a nuclear decay equation?
Answer
The **nucleon number A** (top numbers balance) and the **proton number Z** (bottom numbers balance).
Question
What is the alpha particle, in nuclide notation?
Answer
${}^{4}_{2}\alpha$ — a **helium-4 nucleus** (2 protons + 2 neutrons).
Question
What is the beta-minus particle, in nuclide notation?
Answer
${}^{\;\;0}_{-1}e$ — an **electron** (created when a neutron turns into a proton). An antineutrino is emitted with it.
Question
In ALPHA decay, how do A and Z change?
Answer
A **falls by 4** and Z **falls by 2** (A → A − 4, Z → Z − 2).
Question
In BETA-MINUS decay, how do A and Z change?
Answer
A is **unchanged**; Z **rises by 1** (A → A, Z → Z + 1).
Question
Why does the proton number RISE in beta-minus decay?
Answer
A **neutron becomes a proton**, so there is one more proton. The emitted electron's −1 charge forces the daughter's Z up by 1 to balance.
Question
Write the general ALPHA decay equation.
Answer
${}^{A}_{Z}X \to {}^{A-4}_{Z-2}Y + {}^{4}_{2}\alpha$.
Question
Write the general BETA-MINUS decay equation.
Answer
${}^{A}_{Z}X \to {}^{\;\;A}_{Z+1}Y + {}^{\;\;0}_{-1}e + \bar{\nu}$.
Question
Bismuth-212 (Z = 83) decays by beta-minus. What is the daughter's proton number?
Answer
Z + 1 = 83 + 1 = **84** (polonium). A is unchanged.
Question
Radium-226 (A = 226, Z = 88) decays by alpha. What is the daughter nuclide's A and Z?
Answer
A = 226 − 4 = **222**, Z = 88 − 2 = **86** (radon-222).
Question
How do you handle a decay CHAIN (two emissions in a row)?
Answer
Apply the changes **one emission at a time**, updating A and Z after each step.
Question
How do you find the daughter's neutron number?
Answer
Find the daughter's A and Z first, then use **N = A − Z** (nucleon number − proton number).
Question
How do A and Z change in beta-plus decay?
Answer
A is **unchanged**, Z **falls by 1**: a proton becomes a neutron, emitting a positron and a neutrino.
Question
How do A and Z change in gamma decay?
Answer
**Neither changes**: the nucleus only drops from an excited energy level to a lower one.
Question
Which extra particle comes out in beta-minus decay, and which in beta-plus?
Answer
Beta-minus: an **antineutrino**. Beta-plus: a **neutrino**.
Question
Why does the continuous energy spectrum of beta particles show that neutrinos exist?
Answer
With only two products the beta energy would be fixed; a **range** of energies means a third particle shares the energy.
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Radioactive decay
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