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

Vocabulary flashcards covering key terms related to chain reactions, nuclear bombs, reactors, fusion technologies, accidents, and waste management discussed in Chapter 5.

Chain Reaction

A sequence of reactions in which one event triggers subsequent events, leading to self-sustained growth.

Nuclear Fission

Splitting of a heavy nucleus (e.g., U-235 or Pu-239) into lighter nuclei with the release of neutrons and energy.

Uranium-235

Fissile isotope of uranium that undergoes fission with slow neutrons and is used in nuclear bombs and reactors.

Exponential Growth

Increase proportional to current value; in chain reactions each step doubles the number of events (2ⁿ).

Law of Doubling

Rule stating that each fission produces two neutrons, so the number of reactions doubles each generation (2ⁿ).

Cellular Division

Biological chain reaction where one cell splits into two; ~37 doublings produce ≈10¹¹ human cells.

Cancer

Uncontrolled cell growth resulting from loss of the body’s ability to eliminate damaged or unwanted cells.

Critical Mass

Smallest amount of fissile material needed to sustain a nuclear chain reaction (≈15 kg U-235; ≈5 kg Pu-239).

Fast Neutrons

High-energy neutrons required for rapid chain reactions in nuclear weapons.

Slow (Thermal) Neutrons

Low-energy neutrons that sustain controlled reactions in nuclear reactors.

Moderator

Material (e.g., water, heavy water, graphite) that slows neutrons through collisions inside a reactor.

Cherenkov Radiation

Blue glow produced when charged particles exceed the speed of light in water.

Uranium Bomb – “Little Boy”

Hiroshima weapon (≈15 kT) made by firing a hollow U-235 projectile into a U-235 target to reach critical mass.

Plutonium Bomb – “Fat Man”

Nagasaki weapon (≈20 kT) using explosive lenses to compress Pu-239 into a supercritical mass.

Thermonuclear Weapon (Hydrogen Bomb)

Bomb that uses a fission trigger to ignite fusion of light nuclei, yielding vastly greater energy.

Tsar Bomba

Largest thermonuclear test (50 Mt, USSR) demonstrating fusion weapon power far beyond fission bombs.

Uranium Enrichment

Process of increasing the concentration of U-235 (often via UF₆ gas) for reactors or weapons.

Uranium Hexafluoride (UF₆)

Volatile compound used to separate U-235 from U-238 in enrichment facilities like Oak Ridge’s K-25.

Nuclear Reactor

Device that maintains a controlled, sustained fission chain reaction to produce heat for electricity.

Dirty Bomb

Conventional explosion that disperses radioactive material; a runaway reactor resembles this, not a nuke.

Three Mile Island

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

Chernobyl

1986 Soviet reactor disaster triggered by a flawed safety test and graphite-tipped control rods.

Fukushima Daiichi

2011 Japanese nuclear crisis where earthquake-tsunami destroyed power and cooling, causing hydrogen explosions.

Breeder Reactor

Reactor type that produces more fissile fuel (e.g., Pu-239) than it consumes.

Generation IV Reactor

Advanced design (e.g., lead-cooled) aiming for higher efficiency, safety, and minimal waste.

Nuclear Waste

Radioactive by-products of fission that remain hazardous for thousands of years and require secure storage.

Yucca Mountain

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

Fusion

Process of combining light nuclei (e.g., hydrogen) into heavier ones, releasing vast energy (powers stars).

Tokamak

Toroidal magnetic confinement device researched for controlled thermonuclear fusion.

Inertial Confinement Fusion

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

Muon-Catalyzed (Cold) Fusion

Fusion method where muons replace electrons in hydrogen isotopes, bringing nuclei close enough to fuse at low temperatures.