P7: Radioactivity

What is the structure of an atom?

• Positively charged nucleus made of protons and neutrons located at the center.

• Negatively charged electrons orbiting the nucleus at specific energy levels or shells.

What was the plum pudding model of the atom?

Suggested the atom was a sphere of positive charge with negative electrons embedded throughout it.

What did the Rutherford alpha scattering experiment discover?

• Most alpha particles passed straight through thin gold foil, proving atoms are mostly empty space.

• Some alpha particles deflected at large angles, proving a small, dense, positively charged nucleus exists at the center.

How did Niels Bohr improve the nuclear model?

Suggested that electrons orbit the nucleus at specific fixed distances called energy levels.

How can electron energy levels change within an atom?

• Absorbing electromagnetic radiation causes an electron to move higher to a further energy level.

• Emitting electromagnetic radiation causes an electron to drop to a lower energy level closer to the nucleus.

What are isotopes?

Atoms of the same element with the same number of protons but different numbers of neutrons.

What is radioactive decay?

A completely random process where an unstable atomic nucleus emits nuclear radiation to become more stable.

What is an alpha particle and its properties?

• Composed of two protons and two neutrons, identical to a helium nucleus.

• Highly ionising, short range of a few centimeters in air, and absorbed by a thin sheet of paper.

What is a beta particle and its properties?

• High-speed electron emitted from the nucleus when a neutron turns into a proton.

• Moderately ionising, range of about one meter in air, and absorbed by a thin sheet of aluminium.

What is a gamma ray and its properties?

• High-energy electromagnetic radiation emitted from the nucleus.

• Weakly ionising, infinite range in air, and absorbed by thick lead or several meters of concrete.

How do alpha and beta decay affect nuclear mass and atomic numbers?

• Alpha decay decreases atomic mass number by four and atomic number by two.

• Beta decay keeps atomic mass number unchanged and increases atomic number by one.

What is half-life?

• Time taken for the number of radioactive nuclei in a sample to halve.

• Time taken for the count rate or activity of a sample to drop to half its initial value.

What is the difference between irradiation and radioactive contamination?

• Irradiation is exposing an object to nuclear radiation without making the object radioactive.

• Contamination is the unwanted presence of radioactive atoms on or inside a material, causing ongoing radiation exposure.

How can workers reduce exposure to radioactive hazards?

• Minimising exposure time near radioactive sources.

• Increasing distance using long tongs.

• Standing behind shielding such as lead barriers or lead aprons.

What is nuclear fission?

• Splitting of a large, unstable nucleus into two smaller daughter nuclei after absorbing a slow neutron.

• Releases two or three neutrons, gamma rays, and kinetic energy, which can trigger a controlled chain reaction.

What is nuclear fusion?

• Joining of two light nuclei to form a heavier nucleus, releasing massive amounts of energy.

• Primary energy source powering stars like the Sun, requiring extremely high temperatures and pressures to overcome electrostatic repulsio