PHY 1020 – Chapter 5: Chain Reactions, Nuclear Reactors, and Atomic Bombs

Vocabulary flashcards covering major terms from Chapter 5: chain reactions, fission and fusion physics, nuclear weapons, reactor technology, accidents, and related phenomena.

Chain Reaction

A self-sustaining sequence of events in which one reaction triggers additional reactions.

Fission

Nuclear process where a heavy nucleus splits into smaller nuclei, releasing energy and neutrons.

Exponential Growth

Increase at a rate proportional to current value; in chain reactions often illustrated as 1→2→4→8, etc.

Law of Doubling

Rule stating that with each step in a binary chain reaction the quantity doubles (2^N).

Critical Mass

Smallest amount of fissile material needed to maintain a sustained chain reaction.

Uranium-235

Fissile isotope of uranium used in reactors and bombs; critical mass ≈ 15 kg.

Plutonium-239

Fissile isotope produced in reactors; critical mass ≈ 5 kg and used in ‘Fat Man’ bomb.

Little Boy

Uranium gun-type fission bomb dropped on Hiroshima (~15 kilotons).

Fat Man

Plutonium implosion-type fission bomb dropped on Nagasaki (~20 kilotons).

Thermonuclear (Hydrogen) Bomb

Weapon using a fission trigger to start fusion, producing megaton-scale explosions.

Nuclear Enrichment

Process of increasing the concentration of fissile U-235, often via UF₆ gas separation.

Uranium Hexafluoride (UF₆)

Gaseous compound used to separate uranium isotopes during enrichment.

Slow (Thermal) Neutrons

Low-energy neutrons required to sustain reactions in most power reactors.

Moderator

Material (e.g., water, heavy water, graphite) that slows neutrons in a reactor.

Cherenkov Radiation

Blue glow produced when charged particles travel faster than light’s speed in water.

Dirty Bomb

Conventional explosion that spreads radioactive material; not a nuclear detonation.

Three Mile Island

1979 U.S. reactor accident caused by loss of cooling, leading to partial core meltdown.

Chernobyl

1986 Soviet reactor disaster triggered by unsafe test; graphite-moderated core exploded.

Fukushima

2011 Japanese reactor crisis where tsunami disabled cooling, causing hydrogen explosions.

Breeder Reactor

Reactor that produces more fissile fuel than it consumes by converting fertile material.

Generation IV Reactor

Advanced reactor designs (e.g., lead-cooled) aimed at higher safety and efficiency.

Nuclear Waste

Radioactive by-products of fission that remain hazardous for thousands of years.

Yucca Mountain

Proposed deep-geologic U.S. repository for long-term storage of nuclear waste.

Fusion

Combining light nuclei (e.g., hydrogen) into heavier ones, releasing vast energy; powers stars.

Tokamak

Doughnut-shaped magnetic confinement device for controlled fusion plasma.

Inertial Confinement (Laser) Fusion

Fusion approach using powerful lasers to compress and heat a tiny fuel pellet.

Cold Fusion

Hypothesized low-temperature fusion; conventional science has not confirmed practical success.

Muon-Catalyzed Fusion

Cold fusion concept where muons replace electrons, bringing nuclei close enough to fuse.

Lightning Electron Avalanche

Runaway chain of electron acceleration in thunderstorms, analogous to a chain reaction.

Cancer

Uncontrolled cell growth due to failure of mechanisms that remove damaged cells.

Population Growth

Rapid increase in human numbers that can stress environmental resources.

Breeder Fuel Generation

Creation of new fissile isotopes (e.g., Pu-239) from fertile material (e.g., U-238) within a reactor.