b) Radioactivity

Describe the structure of an atom?

Incredibly small.

Have a tiny, dense nucleus at their centre with electrons orbiting it.

Where are the particles found in an atom?

Protons - in nucleus, positively charged, one mass

Neutrons, in nucleus, neutral charge, one mass

Electrons - Electrons shells, negative charge, zero mass

What is an atomic (proton) number?

The number of protons in an atom.

What is a mass(nucleon) number?

The total number of particles in the nucleus of an atom.

Define isotope?

An atom, or atoms, of the same element that have an equal number of protons but a different number of neutrons.

What happens when an unstable nuclei decays?

It emits Alpha and Beta particles, Gamma rays.

Properties of Alpha particles?

Nature: Helium nucleus(2protons, 2 neutrons)

Penetrating power: Low, stopped by thin sheet of paper.

Ionising ability: High

Properties of Beta particles?

Nature: High-energy electron.

Penetrating power: moderate, stopped by few mm of aluminium foil.

Ionising ability: moderate.

Properties of Gamma rays?

Nature: Electromagnetic wave.

Penetrating power: High, reduced by few cm of lead.

Ionising ability: Low.

How to investigate the penetration powers of different types of radiation using radioactive sources or simulations?

1. Connect Geiger-Müller tube to the counter.

2. Without any sources present, measure background radiation over 1 minute.

3. Repeat this 3 times and take an average.

4. Subtract this value from all the subsequent readings.

5. Place a radioactive source a fixed distance away from the tube and take another reading of count rate over 1 minute.

6. Take a set of absorbers( paper, different thickness of aluminium and lead)

7. One at a time, place these absorbers between source and tube and take another reading of count rate over 1 minute.

8. Repeat experiment above for other radioactive sources.

What are the effects on mass and atomic number when alpha particles are emitted?

Mass number: decreases by 4

Atomic number: decreases by 2

What are the effects of atomic and mass number when beta particles are emitted?

Atomic number: increases by 1

Mass number: stays same

What are the effects on atomic and mass number when gamma ray is emitted?

Atomic number: stays same

Mass number: stays same

What are the effects on atomic and mass number when neutrons are emitted?

Atomic number: stays same

Mass number: decreases by 1

How to balance nuclear equations in terms of mass and charge?

mass and charge has to be same after reaction as they were before.

What are two ways you can detect ionising radiation?

Photographic film

Geiger-müller tube

Explain the sources of background radiation?

Rocks

Cosmic rays from space

Foods

Define activity of a radioactive source and units?

The rate at which the unstable nuclei decay.

Becquerels (Bq)

State what happens to the activity over time?

It decreases

Define half-life?

The time it takes for the number of nuclei of a sample to decrease by half.

Do different isotopes have different half-lives?

Yes

Describe the uses of radioactivity in the industry?

Smoke detectors:

Alpha particles used in smoke detectors.

Alpha radiation will ionise the air within detector, creating a current.

Alpha emitter is blocked when smoke enters the detector.

Alarm is triggered by a microchip when sensor detects no alpha.

Describe the uses of radioactivity in medicine?

Sterilising medical equipment:

Gamma radiation is used because:

Most penetrating

Penetrating enough to irradiate all sides of instrument

Instrument can be sterilised without removing package.

Define contamination?

The accidental transfer of a radioactive substance onto or into a material.

Define irradiation?

The process of exposing a material to ionising radiation.

Differences between contamination and irradiation?

Source: contamination, exposure on or within the object. Irradiation, exposure to radiation outside the object.

Prevention: contamination, can’t be blocked once contaminated but can be prevented by handling source safely. Irradiation, blocked by using shielding such as lead.

Causes: contamination, accidental transfer of radioactive material. Irradiation, deliberate exposure to radiation.

Dangers of ionising radiations?

Can cause mutation in living organisms.

Can damage cells and tissues.

Radioactive waste is difficult to dispose safely.

How can the dangers of ionising radiation waste be reduced?

Waste with long half-life be buried.

Waste mist be stored in strong containers, able to resist rust and corrosion.

Disposal site must have high security.