Radioactivity (Chapter P7)

Question 1

What is an isotope?

Answer 1

They are atoms of an element but with a different mass number

Question 2

Why do scientists look for new evidence?

Answer 2

New experimental evidence may lead to a scientific model being changed or replaced.

Question 3

How was our current model of the atom developed?

Answer 3

The discovery of the electron led to the plum pudding model of the atom (J.J. Thomson).

The results from Rutherford’s alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged (positively). This nuclear model replaced the plum pudding model.

Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.

James Chadwick provided the evidence to show the existence of neutrons within the nucleus.

Question 4

What are the 3 types of radiation

Answer 4

Alpha
Beta
Gamma

Question 5

What are the penetrative properties of nuclear radiation?

Answer 5

Alpha particles are strongly ionising. They have a short range in air (a few cm) and are stopped by a thin sheet of paper.

Beta particles are less ionising and have a greater range in air. They are stopped by a few mm of aluminium.

Gamma waves ionise weakly. They have an unlimited range in air. They can be stopped by thick concrete/lead.

Question 6

What are the common uses of alpha radiation

Answer 6

Alpha particles can be used in smoke detectors. They are very good at ionising the air so an electric current can flow. If smoke gets into the detector, not as much ionisation takes place and the current changes. This makes the alarm sound.

Question 7

What are the common uses of beta radiation

Answer 7

Beta particles can be used to check the thickness of paper/thin metals. A source of beta particles is directed towards the material. A detector on the other side counts the number of particles that get through. If more get through, the material is too thin and the rollers being used to thicken/thin the material are moved apart to allow the material to thicken. As it thickens the count on the detector will drop.

Question 8

What are the common uses of gamma radiation

Answer 8

Gamma rays have various uses, most of which involve the destroying of cells in the sterilisation of medical equipment or on food. They can be used to detect and treat cancer. They can be used to find leaks in pipes underground.

Question 9

What is the half-life of a substance?

Answer 9

The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve.
Or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.

Question 10

What is contamination

Answer 10

The unwanted presence of materials containing radioactive atoms on other materials. The hazard from contamination is due to the decay of the contaminating atoms.

Question 11

What is irradiation

Answer 11

The process of exposing an object to nuclear radiation. The irradiated object does not become radioactive.

Question 12

What is background radiation?

Answer 12

It is the radiation we all experience from many sources like radon gas

Question 13

What is a radiation dose measured in

Answer 13

sieverts (Sv)

Question 14

How is radiation used in medicine?

Answer 14

Radioactive tracers
To destroy cancerous tumours (radiotherapy)
Radioactive implants
Images

Question 15

How do radioactive tracers work

Answer 15

They are injected into a person’s bloodstream and it can be used to identify blockages/tumours as it works it way through the body
The tracers emit gamma radiation

Question 16

How is radiation used to destroy cancerous tumours

Answer 16

Gamma radiation in a narrow beam

Question 17

What is nuclear fission?

Answer 17

It is the splitting of a large and unstable nucleus into two smaller daughter nuclei. In the process energy is released in large amounts and excess neutrons (usually 2 or 3) are emitted (fission neutrons).
This causes a chain reaction

Question 18

How is fission controlled in a nuclear power station?

Answer 18

The chain reaction is controlled in a nuclear reactor with control rods that absorb some of the neutrons (so they cannot cause further fissions) to control the energy released.
A moderator is used in a nuclear reactor to ensure that fission neutrons slow down to be absorbed by further uranium nuclei.

Question 19

What is nuclear fusion?

Answer 19

Nuclear fusion is the joining of two small nuclei to form a heavier nucleus. Huge amounts of energy are released in the process.
High pressure and temperatures are needed to overcome electrostatic repulsion.

Question 20

How does nuclear fusion differ at the centre of the Sun?

Answer 20

High pressure and temperatures are still needed to overcome the electrostatic repulsion between protons and helium nuclei in the plasma. In stars these are achieved through gravitational collapse and the already hot core of the star which in the case of our Sun reaches 15 million Kelvin.