04 september 2015 today’s title: cw: ionising radiation learning question: what makes some...

19 April 2023

Today’s Title: CW: Ionising radiation

Learning Question: What makes some isotopes radioactive?

Starter – Name the two parts that make up the nucleus of an atom

Key words…

•Radiation

•Ion•Radioactive

•Penetration distance

•Alpha and beta particles

•Gama rays

Atoms

• Atoms are made up of two main parts, the nucleus and orbiting electrons.

• Electrons can be lost or gained and this forms charged particles - ions.

• The nucleus contains two types of particles called neutrons and protons.

• As protons, neutrons and electrons are the building blocks of atoms they're called sub-atomic particles.

Electron (e-)

proton (p+)

Neutron (n+)

Ions

Particle Relative mass

Relative charge

Proton 1 +1

Neutron 1 0

Electron Almost zero

-1

• Since the number of electrons and protons in an atom are equal, there is no overall charge.

• If an atom gains or loses an electron, its charge will change and it becomes an ion

Ionising radiation• Ionising radiation has enough energy to cause atoms to

lose electrons and become ions

• A radioactive substance has an unstable nucleus.

• The unstable nucleus decays to become more stable by losing energy when certain types of ionising radiation are emitted from the nucleus.

• The types of radiation t hat can do this are:– Alpha particles– Beta particles and – Gamma radiation

You cannot predict when a nucleus will decay – it is a

random process!

Ionising radiation – alpha particles• Alpha particles contain 2 protons and 2 neutrons, just

like the nucleus of He.

• Alpha particles have NO electrons, so have an overall charge of +2.

• Alpha particles travel at high speeds, so lose energy quickly.

• This means that they only travel short distances and have a short penetration distance. They can be stopped by a sheet of paper.

Alpha particle summary

Alpha particle

equivalent to the nucleus of a helium atom – contains 2 protons and 2 neutrons

charge of +2

stopped by a few cm of air or a few sheets of paper

most ionising type of radiation

Ionising radiation – beta particles

• Beta particles are electrons that are given out from an unstable nucleus

• These particles are much less ionising than alpha particles, so can travel further into an object.

• Beta particles can be stopped by a thin layer of aluminium or by an even smaller layer of lead

Beta particle summary

Beta particleelectron emitted from nucleus

charge of –1

stopped by a few mm of aluminium

moderately ionising

Ionising radiation – gamma rays• Gamma rays are high frequency electromagnetic waves

that are given out by some unstable nuclei and so travel at the speed of light.

• Gamma rays do not have an electrical charge.

• Gamma rays are x10 less ionising that beta particles. This means they can travel further and penetrate matter very easily.

• Gamma rays can be stopped by a few centimetres of lead and absorbed by many meters of concrete.

Gamma ray summary

Gamma ray

electromagnetic wave

not charged

stopped by a few cm of lead or many metres of concrete

least ionising form of radiation

http://www.bbc.co.uk/learningzone/clips/alpha-beta-and-gamma-radiation-pt-1-2/4561.html



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17

1 What is an ion?

A: An atom with an electrical charge.


18

2 A fluorine atom has seven electrons. It gains an electron when it becomes an ion. What charge does a fluoride ion have?

A: –1.


19

3 What is the mass number of an alpha particle?

A: 4


20

4 What materials will absorb and stop beta particles?

A: A few millimetres of aluminium or a smaller thickness of lead .


21

5 The reactor in a nuclear power station is surrounded by large amounts of concrete. Why is this necessary?

A: To stop gamma rays.

6 Draw up a table to summarise the form, charge, penetration and ionisation properties of the three types of radiation.

A: Alpha particle Beta particle Gamma ray

equivalent to the nucleus of a helium atom – contains 2 protons and 2 neutrons

electron emitted from nucleus

electromagnetic wave

charge of +2 charge of –1 not charged

stopped by a few cm of air or a few sheets of paper

stopped by a few mm of aluminium

stopped by a few cm of lead or many metres of concrete

most ionising type of radiation

moderately ionising least ionising form of radiation


23

7 What changes take place in a nucleus when it emits an alpha particle?

A: Its mass number goes down by 4 and its atomic number goes down by 2 – it becomes a different element.


24

8 Explain how an oxygen molecule in the air might become an ion by being near a radioactive source.


25

A: Radioactive source emits ionising radiation (e.g. alpha particles, beta particles or gamma rays).Ionising radiation collides with oxygen atom.Collision knocks an electron out of the oxygen atom. Charge in the nucleus is now not balanced by the charge on the electrons. The atom has a net charge and so is an ion.

04 september 2015 today’s title: cw: ionising radiation learning question: what makes some...

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