PHY 1020 – Chapter 4: Nuclei and Radioactivity

Vocabulary flashcards covering key terms from Chapter 4: Nuclei and Radioactivity.

Atom

The basic unit of matter, composed of protons, neutrons, and electrons.

Element

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

Isotope

Atoms of the same element that contain different numbers of neutrons.

Proton

Positively charged particle found in an atomic nucleus; determines the element’s identity.

Neutron

Neutral particle in the nucleus; variations in number create isotopes.

Electron

Negatively charged particle orbiting the nucleus of an atom.

Fusion

Nuclear process in which two light nuclei combine to form a heavier nucleus, releasing energy (e.g., hydrogen to helium in the Sun).

Fission

Splitting of a heavy nucleus into lighter nuclei, often releasing energy and neutrons.

Radioactivity (Radioactive Decay)

Spontaneous transformation of an unstable nucleus that releases radiation to reach stability.

Alpha Decay

Radioactive process that emits a helium nucleus (2 protons, 2 neutrons) and forms a lighter element.

Alpha Particle

The helium-4 nucleus (₂⁴He) ejected during alpha decay.

Beta Decay

Radioactive process where a nucleus converts a neutron to a proton (β⁻) or a proton to a neutron (β⁺), emitting an electron or positron.

Beta Minus (β⁻)

Decay in which a neutron becomes a proton and an electron is emitted.

Beta Plus (β⁺)

Decay in which a proton becomes a neutron and a positron is emitted.

Gamma Ray

High-energy electromagnetic radiation emitted from excited nuclei; deeply penetrating and dangerous.

Cosmic Radiation

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

Free Neutron

Neutron not bound inside a nucleus; survives ~15 minutes before beta decay into a proton and electron.

Radiation Penetration Depth

Relative ability of radiation to pass through matter—alpha stopped by paper, beta by plastic/metal, gamma needs lead or concrete, neutrons by water/concrete.

Sievert (Sv)

SI unit for radiation dose that reflects biological effect; 1 Sv = 100 rem.

rem (Roentgen Equivalent Man)

Older unit of radiation dose; 1 rem = 0.01 Sv = 1000 mrem.

Ionizing Radiation

Radiation energetic enough to remove electrons from atoms, potentially causing biological damage.

Non-Ionizing Radiation

Radiation that lacks sufficient energy to ionize atoms (e.g., visible light, microwaves).

Linear Hypothesis

Model stating cancer risk increases linearly with radiation dose (e.g., 2.5 rem → 1/1000 extra cancer case).

Half-Life

Time required for half of the atoms in a radioactive sample to decay.

Chain Reaction

Self-sustaining series of nuclear fissions produced when emitted neutrons trigger further fissions.

Radioisotope Thermoelectric Generator (RTG)

Device that converts heat from radioactive decay (e.g., Pu-238) into electricity for spacecraft.

Carbon-14 Dating

Method of determining age (up to ~60,000 years) by measuring remaining C-14 activity in once-living material.

Potassium-40 Dating

Geologic dating technique using decay of ⁴⁰K (half-life 1.25 × 10⁹ y) to ⁴⁰Ca or ⁴⁰Ar.

Radiation Sickness

Acute illness caused by large radiation doses (~100 rem+), with potentially lethal effects at ~500 rem.

Chernobyl Disaster

1986 nuclear reactor accident releasing ~60 million rem globally; caused acute radiation sickness in workers and predicted long-term cancer cases.

Smoke Detector (Alpha Emitter)

Household device that uses alpha radiation to ionize air; smoke disrupts ionization, triggering the alarm.

Denver Radiation Paradox

Observation that Denver’s higher natural background (~0.1 rem/yr) does not correlate with higher cancer rates, highlighting uncertainties in radiation risk.