Chapter 17 Radioactivity - Practice Flashcards

A comprehensive set of practice questions covering the core concepts of radioactivity, decay processes, dosimetry, interaction of radiation with matter, radiation protection, and medical applications presented in the notes.

What is radioactivity?

Emission of energy in the form of electromagnetic waves or subatomic particles by unstable nuclei to reach a more stable state.

What is 1 eV?

The energy gained by an electron when accelerated through a potential difference of 1 V; 1 eV = 1.6 × 10^-19 J.

Which nucleus has the highest nuclear binding energy per nucleon?

Iron-56 (Fe-56); it has the greatest binding energy per nucleon, ~8.8 MeV per nucleon.

How is an isotope notation written and what do A and Z represent?

A is the mass number, Z is the proton (atomic) number; N = A − Z; isotopes differ by the number of neutrons N.

What are isotopes?

Nuclei with the same proton number Z but different numbers of neutrons N.

Can an element lack a stable isotope?

Yes; some elements have no stable isotopes, e.g., technetium; others have one or more stable isotopes (e.g., tin has several).

Name the three classical radioactive decay modes.

Alpha decay (emission of a helium-4 nucleus), beta decay (β− or β+ emission with electrons/positrons and neutrinos/antineutrinos), and gamma decay (emission of a high-energy photon).

What is alpha decay?

Emission of a helium-4 nucleus; the parent nucleus loses 4 mass units and 2 protons, producing a lighter nucleus and releasing energy.

Beta minus decay equation?

A ZX → A(Z+1)Y + e− + ν̄e (neutron transforms to proton with emission of an electron and an electron antineutrino).

What accompanies β− decay besides the daughter nucleus?

An emitted electron (β−) and an electron antineutrino to conserve lepton number.

Beta plus decay equation?

A ZX → A(Z−1)Y + e+ + νe (proton transforms to neutron with emission of a positron and a neutrino).

Electron capture?

A nuclear process where a proton-rich nucleus captures an orbital electron (usually K-shell) to convert a proton into a neutron, emitting a neutrino: e− + AX → νe + A−1X.

Gamma decay and metastable states?

Emission of a gamma photon from an excited/metastable nuclear state; example: 99mTc (metastable) → 99Tc + γ (140 keV).

What does the superscript m indicate in isomer notation like 99mTc?

A metastable (excited) nuclear state that decays to a lower energy level via gamma emission.

What is a continuous beta spectrum and why does it occur?

Beta decay often emits a spectrum of electron energies because the decay energy can be shared between the electron and the (anti)neutrino, not fixed.

What conserved quantities accompany beta decay besides energy and charge?

Baryon number and lepton number (via the accompanying neutrino or antineutrino) are conserved.

Beta plus decay and PET relevance?

β+ emission produces positrons; annihilation with electrons yields 511 keV photons used in PET imaging.

Positron annihilation energy and PET?

Positrons annihilate with electrons to produce two 511 keV photons detected in PET imaging.

Photonuclear reaction?

Photon interacts with a nucleus to emit neutrons (e.g., γ + AZX → A−1 ZX + n); requires high photon energy.

Emission of neutrons from nuclei?

Some isotopes with excess neutrons can emit neutrons: A ZX → A−1 Z X + n; the element stays the same but the mass number decreases.

What is activity A and its unit?

A(t) = −dN/dt = λN(t); unit is the becquerel (Bq), defined as 1 disintegration per second.

Mean lifetime and half-life relationship?

Mean lifetime τ0 = 1/λ; half-life t1/2 = τ0 ln(2). N(t) = N0 e^(−λt) = N0 e^(−t/τ0).

What is committed dose?

The dose delivered while the radioactive source remains in the body; typically evaluated over 50 years for adults or 70 years for children.

ALARA/ALARP principle?

As Low As Reasonably Achievable (or Practicable) in radiation protection, aiming to minimize dose via distance, time, and shielding.

Shielding for alpha particles?

Very short range; usually stopped by a sheet of paper, skin, or a small amount of air—ingestion is the main risk.

Shielding for neutrons?

Depends on energy: slow neutrons absorbed by boron-10; fast neutrons slowed by materials such as water or concrete; shielding often borated materials.

Shielding for photons (X- and γ-rays)?

Dense high-Z materials (e.g., lead, tungsten) are used; attenuation is exponential with thickness; shielding is designed via half-value layers.

Principle of X-ray radiography?

X-rays cross the body with minimal deviation; detectors measure transmitted intensity to form a 2D image of attenuation differences.

What are Hounsfield units?

HU = 1000(μ − μwater)/(μwater − μair); water = 0 HU, air = −1000 HU, bone can be around 1800–1900 HU; used in CT imaging to map attenuation.

Difference between PET and CT imaging?

CT provides anatomical structure via x-ray attenuation; PET provides functional/metabolic information via radiotracers; often combined as PET/CT.

What devices generate high-energy photons or particles for therapy?

X-ray tubes, linear accelerators (linacs), cyclotrons, and synchrotrons; they accelerate electrons or protons to produce photons or particle beams for radiotherapy.

Bragg peak in proton therapy?

Protons deposit most of their energy at a specific depth (Bragg peak), allowing maximal dose to the tumor with reduced exit dose in surrounding tissue.

Key EM interactions with matter for photons?

Photoelectric effect, Rayleigh scattering, Compton scattering, pair production, and photonuclear interactions.