Radioactivity & Detection Lecture

Vocabulary flashcards summarizing key terms and definitions from the lecture on nuclear stability, decay processes, detection methods, and decay kinetics.

Neutron-to-Proton Ratio (N/Z)

The number of neutrons divided by the number of protons; its value helps predict nuclear stability and possible decay.

Band of Stability

Region on an N vs. Z plot where nuclei have stable neutron-to-proton ratios; nuclei outside this band tend to undergo radioactive decay.

Magic Numbers

Specific numbers of nucleons (2, 8, 20, 28, 50, 82, 126) that confer exceptional nuclear stability.

Lead-208 (²⁰⁸Pb)

A particularly stable isotope with Z = 82 and N = 126, matching two magic numbers.

Parent Isotope

The original radioactive nucleus that undergoes decay in a decay series.

Daughter Isotope

The product nucleus formed after a radioactive decay step; may be stable or continue to decay.

Radioactive Decay Series

A chain of successive decays that transforms a parent isotope into a final stable daughter isotope.

Uranium-238 Decay Series

Sequence of decays beginning with ²³⁸U and ending with stable ²⁰⁶Pb, involving a mass decrease of 32 units.

Uranium-235

Isotope (~1 % of natural uranium) crucial for nuclear energy and weapons; decays to ²⁰⁷Pb.

Uranium-232

Isotope that undergoes a decay series terminating at stable ²⁰⁸Pb.

Alpha Decay (α)

Emission of a ⁴He nucleus; lowers mass number by 4 and atomic number by 2.

Beta Decay (β)

Conversion of a neutron to a proton (β⁻) or vice versa (β⁺), accompanied by electron/positron emission.

Gamma Emission (γ)

Release of high-energy photons that lowers nuclear energy without changing mass or atomic numbers.

Geiger–Müller Counter

Radiation detector filled with inert gas that becomes ionized by alpha, beta, or gamma rays, producing an electrical pulse but not distinguishing ray types.

Scintillation Detector

Device using a phosphorescent material that emits light flashes when struck by radiation; more sensitive than a Geiger counter.

Cloud Chamber

Sealed chamber with supersaturated alcohol vapor where alpha or beta particles ionize the vapor, leaving visible condensation trails.

Dosimeter

Personal device that measures accumulated radiation exposure over time, used by medical and nuclear workers.

Bubble Chamber

Super-cooled liquid detector historically used in physics; forms bubbles along the paths of charged particles.

First-Order Radioactive Decay

Kinetic behavior where decay rate is directly proportional to the amount of radioactive substance present.

Decay Constant (λ)

First-order rate constant that quantifies the probability of decay per unit time.

First-Order Decay Law

N(t) = N₀ e^(–λt); describes the amount of radioisotope remaining after time t.

Half-Life (t½)

Time required for half of a radioactive sample to decay; for first-order decay, t½ = 0.693 / λ.

Rate–Amount Relationship

In first-order decay, a larger quantity of radioactive nuclei produces a proportionally faster decay rate.

Ionization in Geiger Counter

Radiation entering the tube ionizes helium or argon gas, generating a detectable current pulse.