Nuclear Chemistry Concepts

A series of vocabulary flashcards based on key concepts in nuclear chemistry.

Nucleon

Any particle found in the nucleus — protons and neutrons are both nucleons. Mass number A = total nucleon count.

Mass number (A)

Total number of protons and neutrons in a nucleus, calculated as A = Z + N.

Nuclide

A specific nucleus characterized by its number of protons (Z) and neutrons (N). Written as AzX.

Atomic number (Z)

Number of protons in the nucleus, which defines the element.

Radioactivity

The spontaneous emission of particles or energy from an unstable nucleus as it seeks a more stable configuration.

Radioactive decay

The process by which an unstable nucleus loses energy by emitting radiation (alpha/beta/gamma) to reach a more stable state.

Band of stability

The region on a plot of N vs Z where stable nuclei are found. For small nuclei N/Z ff 1; for large nuclei N/Z > 1 (up to ~1.4).

Magic numbers

Nucleon counts (2, 8, 20, 28, 50, 82, 126) that give exceptional nuclear stability — analogous to noble gas electron configurations.

Mass defect (Δm)

The difference between the mass of separate nucleons and the actual mass of the nucleus. missing mass is converted to binding energy

Binding energy + Binding energy per nucleon

Energy required to completely separate a nucleus into its individual protons and neutrons. e=mc²

Total binding energy divided by mass number A. Used to compare stability across nuclei. Iron-56 has the highest value (~8.8 MeV/nucleon).

Half-life (t½)

The time for the concentration or activity of a radioactive species to decrease to half its original value. all nuclear decay is 1st order

Decay series (decay chain)

A sequence of successive radioactive decays until a stable nucleus is reached. Typically involves a combination of alpha and beta decays.

Transmutation

The conversion of one element into another via nuclear reaction (decay, fission, fusion, or bombardment)

Critical mass / supercritical

The minimum mass of fissile material needed to sustain a chain reaction. Supercritical means the reaction grows exponentially.

Chain reaction

Each fission event releases neutrons that trigger more fissions, causing exponential growth in the number of reactions.

Positron

The antiparticle of an electron — same mass, opposite charge (+1). Emitted in ffff decay when Z is too high relative to N.

Electron capture

Nucleus captures an inner orbital electron. Proton + electron → neutron. A unchanged; Z decreases by 1. Same net effect as ffff decay.

Radiotracer / radiolabel

A radioactive isotope incorporated into a compound to track its movement by emitted radiation.

Alpha decay

A radioactive decay type where a helium-4 nucleus is emitted, reducing both atomic and mass numbers.

Beta-minus decay

A decay type in which a neutron converts to a proton and an electron is emitted, increasing the atomic number. occurs when N/Z is too high

A stays the same; Z increases by 1. Net reaction: neutron → proton + electron.

Gamma decay

A decay type that emits a high-energy photon with no change in mass or atomic numbers.

Fission

Splitting of a heavy nucleus into smaller nuclei + neutrons + energy. Usually triggered by neutron bombardment. Releases enormous energy via mass defect.

Fusion

Joining of light nuclei into a heavier nucleus, releasing energy. Occurs in stars. Requires extremely high temperatures (~4×10ff K).

Binding energy per nucleon

Total binding energy divided by mass number A; used to compare stability across nuclei.

Electron mass cancellation trick

The cancellation of electron mass when calculating mass defect using atomic masses.

First-order kinetics for nuclear decay

Nuclear decay follows first-order kinetics, described by the relationship Rate ∝ [N].

artificial transmutation

Transmutation induced by bombarding a nucleus with particles (e.g. neutrons), leading to fission or other nuclear reactions.

why does fusion require such high temperatures

Nuclei are positively charged and repel each other (Coulomb repulsion). Temperatures of ~4×10ff K are needed to give nuclei enough kinetic energy to overcome repulsion so the strong nuclear force can take over.

why does nuclear fission release so much energy

Products have slightly less mass than reactants. This mass defect (Δm) converts to energy via E = mc². Even a tiny Δm yields enormous energy because c² is ~9×10¹ff.

nuclear fusion in stars

The sun fuses light nuclei (primarily hydrogen isotopes) into helium at ~4×10ff K. Believed to be the primary source of helium on Earth.

Radiotracer — how it is used

A radioactive isotope is incorporated into a molecule. Its path through a system is tracked by measuring radiation levels as a function of time or position.

scintillation counter

More sensitive than a Geiger counter. Based on ZnS phosphorescence — radiation causes flashes of light that are detected electronically.

geiger counter

detects high-level radiation. radiation ionizes argon gas: Ar (g) → Ar (g) + e. the resulting current pulse is counted

fission chain reaction

the math : 1 neutron in → 3 neutrons produced per event. Count grows as 3 after n generations → exponential, supercritical chain reaction.

Balancing a nuclear equation — key rule

Both mass number (A) and atomic number (Z) must be conserved. Sum of A on left = sum of A on right; same for Z

After 3 half-lives — how much remains?

(½)³ = 1/8 of the original amount. General rule: after n half-lives, (½)ff of the original remains.

Half-life formula

t½ = 0.693/ff where ff is the decay constant. After n half-lives, amount remaining = Nff × (½)ff

First-order kinetics for nuclear decay

Rate ff [N]. Integrated: N(t) = Nff × e^(−fft). Half-life: t½ = ln(2)/ff = 0.693/ff. ALL nuclear decays follow 1st-order kinetics

MeV to Joules conversion

1 MeV = 1.60×10ff¹³ J. Example from lecture: He-4 has a binding energy of 7.13 MeV/nucleon.

Steps to calculate binding energy per nucleon

1) Identify Z and N.

2) Calculate Δm using atomic masses (electrons cancel).

3) Convert amu to kg (1 amu = 1.66×10ff²ff kg).

4) E = Δm × c².

5) Divide E by A for per-nucleon value.

Electron mass cancellation trick

When using atomic masses in the mass defect formula, the electron terms cancel out — so you can use atomic masses directly without converting to nuclear masses.

How do you calculate mass defect?

Δm = (mass of separate nucleons) − (actual nuclear mass). Use Z × m(proton) + N × m(neutron) minus the nuclear mass. Atomic masses can be used because electron masses cancel.

E = mc² — what does each variable mean?

E = energy (J), m = mass (kg), c = speed of light (3×10ff m/s). A tiny mass change produces enormous energy because c² ff 9×10¹ff.

Which decay types change the element? Which do not?

ff, ffff, ffff, and electron capture all change Z → change the element. ff decay does NOT change Z or A → same element, just lower energy state.

gamma decay — what is emitted + how do A and Z change

A high-energy photon. No change in A or Z. The nucleus drops from an excited energy state to a lower energy state.

Neither A nor Z changes. Only the energy state of the nucleus changes, like an electron dropping energy levels but for nucleons.

Beta-plus (ffff) / positron emission — what is emitted?

A positron (ffffffe). A proton converts to a neutron. A stays the same; Z decreases by 1. Occurs when N/Z is too low.

What decay is typical for very heavy nuclei (Z > 84)?

Alpha (ff) decay — ejection of a helium-4 nucleus reduces both Z and N, lowering the nuclide toward the band of stability.

If N/Z is too HIGH — which decay occurs?

decay — a neutron converts to a proton, emitting an electron. This lowers N/Z toward the band of stability.

If N/Z is too LOW — which decay occurs?

decay (positron emission) or electron capture — a proton converts to a neutron, raising N/Z.

What does (A−Z)/Z represent?

The neutron-to-proton ratio (N/Z). A = mass number, Z = protons, so A−Z = neutrons. Used to predict stability and decay type

Stability rule for large nuclei

For heavy nuclei (large Z), more neutrons are needed; stable N/Z ratio is in the range 1.2–1.4

Stability rule for small nuclei

For light nuclei (small Z), the neutron-to-proton ratio N/Z should be approximately 1 for stability