PHY 1020 – Chapter 4: Nuclei and Radioactivity

Vocabulary flashcards summarizing the essential terms from the lecture on nuclei, radioactivity, radiation, and their applications.

Heat

The random motion and vibration of atoms and molecules; sensed as temperature and measured in Kelvin, Celsius, or Fahrenheit.

Kelvin (K)

An absolute temperature scale whose zero point (0 K) is absolute zero, where all molecular motion stops.

Element

A substance whose atoms all contain the same number of protons (atomic number).

Atom

The basic unit of matter, consisting of a nucleus of protons and neutrons surrounded by electrons.

Proton

A positively charged particle in the atomic nucleus; its count defines the element.

Neutron

An electrically neutral particle in the nucleus; variations in neutron number create isotopes. Free neutrons live ~15 min before beta decay.

Electron

A negatively charged particle orbiting the nucleus; emitted as the beta-minus particle in radioactive decay.

Isotope

Atoms of the same element that contain different numbers of neutrons (e.g., ¹H, ²H, ³H).

Fusion

A nuclear reaction in which two light nuclei combine to form a heavier nucleus, releasing energy (powers the Sun).

Radioactivity (Radioactive Decay)

The spontaneous transformation of an unstable nucleus into a more stable one, accompanied by emission of particles or radiation.

Alpha (α) Decay

Radioactive process in which a heavy nucleus emits a helium-4 nucleus (2 p, 2 n), reducing its mass and charge.

Alpha Particle

The helium-4 nucleus released during alpha decay; low penetration (stopped by paper or skin).

Beta-minus (β⁻) Decay

A neutron converts to a proton, emitting an electron and an antineutrino.

Beta-plus (β⁺) Decay

A proton converts to a neutron, emitting a positron and a neutrino.

Gamma Ray

Very high-energy photon emitted by excited nuclei; highly penetrating and biologically hazardous.

Cosmic Radiation

High-energy charged particles (mainly protons and electrons) from the Sun and other stars that continually strike Earth.

Radiation Penetration Depth

Relative ability to pass through matter: α stopped by paper, β by thin metal, γ requires dense concrete, neutrons slowed by water/concrete.

Rem (roentgen equivalent man)

A unit of radiation dose that reflects biological effect; 1 rem = 1,000 mrem = 0.01 Sv.

Sievert (Sv)

The SI unit of dose equivalent; 1 Sv = 100 rem. Annual exposure guideline ≈ 50 mSv (5,000 mrem).

Linear Hypothesis (Radiation Risk)

Model stating that cancer probability increases linearly with dose, with no safe threshold (≈1 extra cancer per 2.5 rem per 1,000 people).

Half-life

The time required for half of a radioactive sample to decay (e.g., ¹⁴C half-life = 5,730 years).

Fission

The splitting of a heavy nucleus into two lighter nuclei plus neutrons and energy; can produce a chain reaction.

Radioisotope Thermoelectric Generator (RTG)

Device that converts heat from radioactive decay (e.g., Pu-238) into electricity via thermocouples; powers spacecraft like the Mars rover and New Horizons.

Ionization Smoke Detector

Household alarm that uses an alpha-emitting source to ionize air; smoke disrupts the ion current and triggers the alarm.

Carbon-14 Dating

Age-determination method measuring residual ¹⁴C activity (half-life 5,730 y) to date formerly living materials up to ~60,000 years.

Potassium-40 Dating

Geologic dating technique using ⁴⁰K decay (half-life 1.25 × 10⁹ y) to ⁴⁰Ca and ⁴⁰Ar to determine rock ages.

Ionizing Radiation

Radiation energetic enough to remove electrons from atoms (α, β, γ, X-rays, cosmic rays); can damage biological tissue.

Non-ionizing Radiation

Radiation lacking sufficient energy to ionize atoms (visible light, microwaves, radio waves); generally less biologically damaging.