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Radiation from radioactive materials

There are three main types of radiation which come from radioactive materials, plus two others you need to be aware of. In this activity, you will learn the properties of these different types of radiation, and how to tell the three main ones apart.

'Radiation from radioactive materials' worksheet

Key stage:  KS 4

Curriculum topic:  Physics: Atomic Structure

Curriculum subtopic:  Radioactive Nuclei

Difficulty level:  

down

Worksheet Overview

QUESTION 1 of 10

Some materials give off different types of invisible radiation; these materials are called radioactive. We now know that radioactive materials give off radiation because of changes which happen in the nuclei of the atoms the material is made of. Because we understand how radioactivity works, we are also able to use it in medical and engineering applications.

How radioactivity was discovered

The first experiment which showed that some materials are radioactive was done by Henri Becquerel. In 1896, he placed some lumps of a salt containing uranium on a photographic plate (used in the cameras of the time), and left them in a dark place. You can see one of the photographs he took by clicking on this link. (Right-click, and open in a new window). The dark patches are where the lumps of salt were, which showed that the salt was giving off radiation, even though nothing could be seen. The cross in the lower patch was where a metal cross had got trapped between the radioactive lumps and the photographic film.

From this, Becquerel worked out three things:

1. The photographic plate was detecting radiation coming from the lumps of salt. (We now know that this was due to the uranium.)

2. The radiation was invisible to human eyes.

3. The radiation given off by the lumps of salt could be absorbed by a thin sheet of metal.

Other scientists (including Marie Curie and Ernest Rutherford) joined Becquerel in doing experiments like this, and found that a lot of other materials were radioactive.

Telling alpha, beta and gamma radiation apart

The experiments showed that there were three types of radiation which could be distinguished by how easy or hard it was to stop the radiation. They were called alpha, beta and gamma radiation.

Alpha radiation (α) is the easiest to stop. A few centimetres or air, or a very thin piece of paper, are able absorb it.

Beta radiation (β) is harder to stop. A sheet of aluminium about 3 milimetres thick is needed to absorb it. Beta radiation can travel through a few metres of air before it is reliably absorbed.

Gamma radiation (γ) is most able to penetrate through objects. To absorb a beam of gamma radiation needs a sheet of lead about 300 mm thick, or several metres of concrete.

These results are often shown in a diagram: 

Alpha radiation is stopped easity (by a thin sheet of paper), beta radiation is stopped by 3 mm aluminium, gamma radiation is stopped by 300 mm lead.

You might have to draw this diagram from memory in an exam, or complete an incomplete version of the diagram. Be careful to do this accurately; alpha radiation stops at the sheet of paper, not before or after, and beta radiation stops in the aluminium sheet.

Many applications of radioactivity depend on the way that different radiations are absorbed or transmitted. For any radiation and absorber, a thicker layer of the absorber absorbs more of the radiation than a thinner one. You could be asked a question like this:

In a paper factory, radiation from a radioactive source is used to check that the paper doesn't get too thick or too thin. If the paper is too thin, too much radiation will pass through. If the paper is too thick, too little radiation will pass through. Which type of radiation (alpha, beta or gamma) must be used?

Answer: Beta radiation needs to be used: alpha radiation cannot penetrate even very thin paper, and gamma radiation will penetrate through any thickness of paper.

Other properties and other radiations

As scientists found out more about radioactivity, they found other properties of the different radiations (mass, charge and how easily they ionise other materials), and also some other types of radiation. The properties you need to remember are listed in this table.

Radiation Mass Charge Penetrating power Ionising 
power
What the radiation is
Alpha 4 +2 low high 2 protons + 2 neutrons, ejected from the nucleus
Beta (or beta minus) 1/2000 -1 moderate moderate 1 electron, made in the nucleus and then ejected
Gamma 0 0 high low A pulse of energy, ejected from the nucleus
Positron (or beta plus) 1/2000 +1 moderate moderate A positively charged version of an electron, made in the nucleus and then ejected
Neutron 1 0 very high not directly ionising 1 neutron, ejected from the nucleus

The mass is on the atomic mass scale (so a proton or a neutron = 1 on this scale).

The charge in on the electron scale (so a proton = +1 and an electron = -1).

Penetrating power describes how easily the radiation passes through other materials.

Ionising power describes how strongly the radiation can ionise other materials; in other words, how easily it can remove electrons from other materials and change their properties.

Which of these three radiations is the most penetrating?

Alpha

Beta

Gamma

Which type of radiation has the most mass?

Alpha particle

Beta particle

Gamma ray

Match up these radiations with what is needed to absorb them.

Column A

Column B

Alpha
3 mm thick sheet of aluminium
Beta
300 mm thick sheet of lead
Gamma
A thin sheet of paper

Which type of radiation is the most ionising?

Alpha

Beta

Gamma

Complete this pattern:

As the ionising power of radiation increases, its penetrating power...

increases

stays constant

decreases

does not show any pattern

In Becquerel's original experiment, the radiation given off by the uranium compound was not able to pass through a piece of metal a few milimetres thick. Which type of radiation could this have been? Tick any which are possible.

Alpha

Beta

Gamma

Engineers can study cracks in underground pipes by putting a radioactive substance in the pipe, and checking where they can detect radiation at ground level. If the pipe has a crack, the radioactive substance will leak out of the pipe into the soil. This saves them having to dig up the entire pipe. Which type (or types) of radiation can be used for this?

Alpha

Beta

Gamma

What thickness of aluminium is needed to stop beta radiation?

0.03 cm

0.3 cm

3 cm

30 cm

A physics lab has some radioactive samples. Some of them give off alpha radiation, and some give off beta radiation. Which of these containers could safely store all the samples together, and prevent almost all radiation escaping? Tick all the correct possibilities.

A 2 mm thick paper/cardboard box

A metal box, made of 1 mm thick aluminium

A metal box, made of 5 mm thick aluminium

A metal box, made of 10 mm thick lead

This paragraph contains 3 mistakes. Underline the sentences which are incorrect.

The three commonest types of radiation are alpha, beta and gamma. Beta radiation is made of electrons from the shells around the atomic nucleus. Beta radiation is the most ionising radiation. When radiation passes through materials, the radiation can be absorbed. The thicker the absorber, the more radiation is absorbed. A 1 mm thick sheet of aluminium absorbs no beta radiation. However, a 5 mm thick sheet of aluminium will absorb nearly all the particles in a beam of beta radiation.
  • Question 1

Which of these three radiations is the most penetrating?

CORRECT ANSWER
Gamma
EDDIE SAYS
The diagram shows that gamma radiation can pass through a 3 mm thick layer of aluminium, but alpha and beta radiation cannot. This means that gamma radiation is the most penetrating.
  • Question 2

Which type of radiation has the most mass?

CORRECT ANSWER
Alpha particle
EDDIE SAYS
The table shows that the mass of an alpha particle is 4 atomic mass units, which is more than any of the others.
  • Question 3

Match up these radiations with what is needed to absorb them.

CORRECT ANSWER

Column A

Column B

Alpha
A thin sheet of paper
Beta
3 mm thick sheet of aluminium
Gamma
300 mm thick sheet of lead
EDDIE SAYS
This information is in the table of different radiations.
  • Question 4

Which type of radiation is the most ionising?

CORRECT ANSWER
Alpha
EDDIE SAYS
According to the table of properties, alpha radiation is the most ionising. This is because it has a higher mass than the other types of radiation.
  • Question 5

Complete this pattern:

As the ionising power of radiation increases, its penetrating power...

CORRECT ANSWER
decreases
EDDIE SAYS
The table shows that alpha radiation has strong ionisation and weak penetration, and that gamma radiation has strong penetration and weak ionisation. That makes sense, because radiation needs to be absorbed for ionisation to happen.
  • Question 6

In Becquerel's original experiment, the radiation given off by the uranium compound was not able to pass through a piece of metal a few milimetres thick. Which type of radiation could this have been? Tick any which are possible.

CORRECT ANSWER
Alpha
Beta
EDDIE SAYS
The radiation cannot have been gamma radiation, because that needs a very thick layer of lead to be absorbed. A 3 mm thick layer of alumimium is able to absorb beta radiation, so that is possible. Alpha radiation can be stopped by a very thin layer of paper, so a thin layer of metal will be more than enough to absorb alpha radiation.
  • Question 7

Engineers can study cracks in underground pipes by putting a radioactive substance in the pipe, and checking where they can detect radiation at ground level. If the pipe has a crack, the radioactive substance will leak out of the pipe into the soil. This saves them having to dig up the entire pipe. Which type (or types) of radiation can be used for this?

CORRECT ANSWER
Gamma
EDDIE SAYS
Only gamma radiation will work for this, because alpha and beta radiation would be absorbed in the soil before they reached the detector.
  • Question 8

What thickness of aluminium is needed to stop beta radiation?

CORRECT ANSWER
0.3 cm
EDDIE SAYS
In physics, you always have to be careful about the units. The table and the diagram tell you that it takes 3 mm of aluminium to stop beta radiation, which is the same as 0.3 cm, because 10 mm = 1 cm.
  • Question 9

A physics lab has some radioactive samples. Some of them give off alpha radiation, and some give off beta radiation. Which of these containers could safely store all the samples together, and prevent almost all radiation escaping? Tick all the correct possibilities.

CORRECT ANSWER
A metal box, made of 5 mm thick aluminium
A metal box, made of 10 mm thick lead
EDDIE SAYS
The first two possibilities (2 mm thick paper/card, and 1 mm thick aluminium) would stop alpha radiation, but not beta. The final two possibilities (5 mm aluminium and 10 mm lead) would stop both, though neither would stop gamma radiation. In real science labs, the rules for storing radioactive materials safely are much stricter than this.
  • Question 10

This paragraph contains 3 mistakes. Underline the sentences which are incorrect.

CORRECT ANSWER
The three commonest types of radiation are alpha, beta and gamma. Beta radiation is made of electrons from the shells around the atomic nucleus. Beta radiation is the most ionising radiation. When radiation passes through materials, the radiation can be absorbed. The thicker the absorber, the more radiation is absorbed. A 1 mm thick sheet of aluminium absorbs no beta radiation. However, a 5 mm thick sheet of aluminium will absorb nearly all the particles in a beam of beta radiation.
EDDIE SAYS
Beta radiation comes from the nucleus of an atom. A beta particle is made when a neutron breaks apart into a proton and an electron. Alpha radiation is more ionising than beta radiation. Although a 1 mm thick sheet of aluminium will not absorb all the particles in a beam of beta radiation, it will absorb a significant number.
---- OR ----

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