Lecture 4: Nuclear Energy and Elementary Particles

Vocabulary flashcards covering key terms from the lecture notes on nuclear energy and elementary particles.

Fission

A nuclear reaction in which a heavy nucleus splits into two lighter nuclei, releasing energy.

Fusion

A reaction where two light nuclei combine to form a heavier nucleus, releasing energy.

Fission fragments

The two lighter nuclei produced when a heavy nucleus fissions.

235U

An isotope of uranium (U-235) that is fissile and used as reactor fuel.

236U*

An intermediate, short-lived excited state formed when 235U captures a neutron.

Neutron

A neutral subatomic particle that participates in fission and chain reactions.

Chain reaction

A self-sustaining sequence of fission events in which emitted neutrons trigger further fissions.

Critical

A state where the chain reaction is self-sustaining with K = 1.

Subcritical

A condition where K < 1; the chain reaction dies out.

Supercritical

A condition where K > 1; the chain reaction grows uncontrollably.

Moderator

Material that slows neutrons to increase fission probability (e.g., heavy water).

Heavy water

Water where hydrogen is deuterium (D2O); used as a neutron moderator.

Control rod

Neutron-absorbing rods used to control the rate of fission in a reactor.

Neutron capture

A process by which a nucleus absorbs a neutron, becoming a heavier isotope.

Neutron leakage

Loss of neutrons from the reactor core, reducing fission events.

Primary system

The reactor’s closed loop where fission heat is produced and carried by water.

Secondary system

The system where heat is transferred to generate steam and drive the turbine.

Containment

A structure designed to contain radiation and fission products.

China Syndrome

Hypothetical meltdown scenario where molten core breaches containment and melts into ground water.

Binding energy per nucleon

Approximately 7.2 MeV for heavy nuclei and 8.2 MeV for intermediate nuclei.

1 MeV per nucleon (approximate)

Estimated energy release per nucleon in fission (~1 MeV per nucleon times ~240 nucleons).

Fission products

The nuclei produced from fission besides neutrons (the fragments X and Y).

Thermal neutron

A slow-moving neutron that efficiently causes fission in certain nuclei.

90 different daughter nuclei

A typical variety of fission fragments that can be produced from 235U fission.

Prompt neutrons

Neutrons released immediately during the fission event.

235U captures a thermal neutron

Process leading to the formation of 236U* and fission.

PWR (Pressurized Water Reactor)

A light-water reactor with a primary high-pressure loop and a secondary steam cycle.

Nuclear reactor

A device designed to sustain a self-sustained chain reaction for power generation.

D+D fusion reaction

Fusion of two deuterium nuclei producing helium and/or neutrons.

D+T fusion reaction

Fusion of deuterium and tritium producing helium and a neutron.

Lawson’s criterion

Condition for net power in a fusion reactor: nτ must exceed a threshold.

nτ

Plasma density multiplied by confinement time; a key fusion performance metric.

Tokamak

A doughnut-shaped magnetic confinement device for plasma in fusion research.

NSTX

National Spherical Torus Experiment, a tokamak-based fusion experiment.

JET

Joint European Torus, a major international tokamak fusion device.

TFTR

Tokamak Fusion Test Reactor at Princeton; achieved high ion temperatures.

ITER

International Thermonuclear Experimental Reactor, large global fusion project.

Inertial confinement

A fusion approach where fuel is compressed by powerful lasers.

Inertial electrostatic confinement

A fusion approach using electrostatic fields to accelerate ions for fusion.

Proton-proton cycle

Fusion sequence in stars where hydrogen nuclei fuse to form helium.

Pion (π)

Light meson involved in strong interactions; types include π+, π−, π0.

Muon

Heavier lepton (μ) that decays via weak interactions.

Electron

Light negatively charged lepton; fundamental constituent of atoms.

Neutrino

Neutral, very light lepton that interacts only weakly.

Electron neutrino

Neutrino associated with the electron in lepton family.

Leptons

Fundamental particles that do not participate in strong interactions.

Baryons

Hadrons composed of three quarks (e.g., proton, neutron).

Mesons

Hadrons composed of a quark and an antiquark pair.

Quarks

Fundamental constituents of hadrons: up, down, strange, charm, top, bottom.

Up quark (u)

+2/3 elementary charge; one of the light quark flavors.

Down quark (d)

−1/3 elementary charge; one of the light quark flavors.

Strange quark (s)

Quark flavor associated with strangeness; −1/3 charge.

Charm quark (c)

Heavy quark flavor; central to charm family; forms J/ψ.

Top quark (t)

Heaviest quark flavor; discovered in 1995.

Bottom quark (b)

Quark flavor; discovery in 1977.

Antiquark

The antiparticle of a quark with opposite charge, baryon number, and strangeness.

Hadrons

Particles made of quarks bound by the strong force.

Leptons

Fundamental particles not bound by the strong force.

Color charge

Property of quarks in QCD; red, blue, green as colors.

Red

One of the three color charges of quarks.

Green

One of the three color charges of quarks.

Blue

One of the three color charges of quarks.

Antired

Anticolor corresponding to red in antiquarks.

Antigreen

Anticolor corresponding to green in antiquarks.

Antiblue

Anticolor corresponding to blue in antiquarks.

Colorless

A state with no net color charge; required for observable hadrons.

Color confinement

Quarks cannot exist freely; they are confined in color-neutral hadrons.

QCD (Quantum Chromodynamics)

Theory describing strong interactions via color charge and gluons.

Gluon

Massless mediator of the strong force carrying color charge.

Photon

Massless mediator of the electromagnetic force.

W and Z bosons

Massive mediators of the weak force; enable beta decay.

Graviton

Hypothetical mediator of gravity not yet observed.

Higgs boson

Particle associated with mass generation in gauge theories; proposed in the Standard Model.

Standard Model

The theory describing electromagnetic, weak, and strong interactions of fundamental particles.

Electroweak theory

Unified description of electromagnetic and weak interactions.

Gell-Mann

Physicist who proposed the Eightfold Way and contributed to the quark model.

Ne’eman

Physicist who contributed to the Eightfold Way classification.

Eightfold Way

Pattern organizing hadrons into multiplets by spin, strangeness, etc.

Baryon number

Conserved quantity: B=+1 for baryons, B=−1 for antibaryons, 0 otherwise.

Lepton number

Conserved quantity for each lepton family (electron, muon, tau).

Conservation of Baryon Number

In reactions/decays, total baryon number is preserved.

Conservation of Lepton Number

In reactions/decays, total lepton number in each family is preserved.

Strangeness

Quantum number for strange particles; conserved in strong/electromagnetic, not in weak interactions.

Bubble chamber

Detector showing particle tracks in a liquid to study decays.

Pion decay

Example: π− → μ− + ν̄μ with a short lifetime (~2.6×10−8 s).

Antiparticle

Particle with equal mass and opposite charge to its partner.

Dirac

Physicist who unified quantum mechanics and relativity; predicted antimatter.

George Gamow

Physicist who helped predict early universe abundances and CBR features.

Cosmic Background Radiation (CBR)

Remnant radiation from the Big Bang, observed as a 3 K blackbody spectrum.

Big Bang

Cosmological model in which all four fundamental forces were once unified.

Pion masses

π± ~139.6 MeV/c^2; π0 ~135.0 MeV/c^2.

J/ψ

Charm-anticharm bound state discovered in 1974; evidence for charm quark.

Charmonium

Bound state of a charm quark and its antiquark (e.g., J/ψ).