Radioactivity and Atomic Physics

Flashcards covering atomic structure, subatomic particles, isotopes, radioactive decay equations, properties of radiation, Rutherford scattering conclusions, radiation hazards, safety precautions, and half-life calculations.

What are the mass, charge, and location of a proton?

Mass: $1$, Charge: $+1$, Location: Nucleus.

What are the mass, charge, and location of a neutron?

Mass: $1$, Charge: $0$, Location: Nucleus.

What are the mass, charge, and location of an electron?

Mass: $\frac{1}{1800}$, Charge: $-1$, Location: Outershell.

How are isotopes defined?

Atoms of the same element that have the same number of protons but different number of neutrons.

How do isotopes compare in terms of their physical and chemical properties?

They have the same chemical properties, but different physical properties.

What nuclear concept is illustrated by these three hydrogen nuclei ($^1\text{H}$, $^2\text{H}$, and $^3\text{H}$)?

Isotopes, which are atoms of the same element containing equal numbers of protons but different numbers of neutrons.

What is the definition of radioactive decay?

Random and spontaneous emission of alpha, beta, and gamma radiation from unstable nuclei.

What is the general nuclear equation for alpha decay?

$$^A_Z X \rightarrow ^{A-4}_{Z-2} Y + ^4_2 \alpha$$

What is the equation for the alpha decay of Uranium-238 ($^{238}_{92}\text{U}$)?

$$^{238}_{92}\text{U} \rightarrow ^{234}_{90}\text{Th} + ^4_2 \alpha$$

What is the general nuclear equation for beta decay?

$$^A_Z X \rightarrow ^A_{Z+1} Y + ^0_{-1} \beta$$

Why is there variation in measured radioactive decay counts over time?

Due to the random nature of the decay.

What is ionization in the context of radioactivity?

Separation of electrons from molecules so that matter conducts electricity.

What three sources of background radioactivity are listed in the notes?

Cosmic rays from the sun, radio gases in atoms, and rocks and fossils.

What application of radioactive isotopes is shown in this diagram?

Thickness control of an aluminium sheet using a radiation source, rollers, and a detector.

How do alpha, beta, and gamma emissions behave when passed through an electric field as shown?

Positively charged alpha particles and negatively charged beta particles deflect toward oppositely charged plates, whereas uncharged gamma radiation passes straight through.

Why do charged particles follow a curved path in an electric or magnetic field?

Because the force acting on the particle is perpendicular to its motion.

What are the composition, mass, charge, ionization power, and absorption characteristics of alpha ($ \alpha$) radiation?

Composition: $2$ protons and $2$ neutrons; Mass: $4$; Charge: $+1$; Ionization: Very strong; Absorption/Range: $5\text{--}10\,\text{cm}$, stopped by paper.

What are the composition, mass, charge, ionization power, and absorption characteristics of beta ($\beta$) radiation?

Composition: $1$ electron; Mass: $\sim \frac{1}{2000}$; Charge: $-1$; Ionization: Weak; Absorption/Range: $5\text{--}10\,\text{m}$, stopped by an aluminium sheet.

What are the composition, mass, charge, ionization power, and absorption characteristics of gamma ($\gamma$) radiation?

Composition: Electromagnetic with high frequency; Mass: $0$; Charge: $0$; Ionization: Very weak; Absorption/Range: $5\text{--}10\,\text{km}$, stopped by concrete or lead.

What structural feature of atoms is concluded from the observation that most alpha particles are not deflected?

Atoms are mainly empty space.

What nuclear feature is concluded from observing that some alpha particles are deflected?

The nucleus is positively charged.

What conclusion is drawn from observing that very few alpha particles are deflected back?

Mass is concentrated in a tiny nucleus.

What safety precautions must be taken when handling radioactive sources?

Use lead-lined precautions, store the source in a lead-labeled box, handle sources with long forceps, and keep exposure time to a minimum.

What health hazards are caused by exposure to radioactive sources?

Hair loss, skin burns, cancer, and death.

Thorium-232 has a half-life of $1.4 \times 10^{10}\,\text{years}$. How long does it take for the activity of a sample to fall from $120\,\text{Bq}$ to $15\,\text{Bq}$?

$4.2 \times 10^{10}\,\text{years}$ (the sample undergoes $3$ half-lives: $120 \rightarrow 60 \rightarrow 30 \rightarrow 15\,\text{Bq}$, so $3 \times 1.4 \times 10^{10} = 4.2 \times 10^{10}\,\text{years}$).

When the activity of a Thorium-232 sample drops to $15\,\text{Bq}$, why is much of the sample no longer Thorium-232?

Because the proton number changed, so the element changed.

Why can the activity of Thorium-232 be regarded as constant during a laboratory experiment?

Because its half-life ($1.4 \times 10^{10}\,\text{years}$) is too long.

What three readings must a student record to determine the percentage of beta particles absorbed by an aluminium sheet?

$1.$ Background reading, $2.$ Initial reading, and $3.$ Final reading.