don’t forget you have a test on thursday!

Do now! Don’t forget you have a test on Thursday!

Can you write the title

Radioactivityin your books?

Radioactivity

Today’s lesson

• describe the structure of an atom in terms of protons, neutrons and electrons and use symbols to describe particular nuclei

• understand the terms atomic (proton) number, mass (nucleon) number and isotope

• understand that ionising radiations can be detected using a photographic film or a Geiger-Muller detector

• recall the sources of background radiation

The atomorbiting electrons

Nucleus (protons and neutrons)

Nuclide notation

Li3

7

Atomic number (proton number) = number of protons

Atomic mass (mass number) = number of protons and neutrons

Isotopes

Li3

7

It is possible for the nuclei of the same element to have different numbers of neutrons in the nucleus (but it must have the same number of protons)

Li3

6

Isotopes

Li3

7

For example, Lithium atoms occur in two forms, Lithium-6 and Lithium-7

Li3

6

4 neutrons3 neutrons

Relative atomic massOn average, lithium atoms have a mass of 6.941 (relative to Carbon 12)

Li3

6.941

Isotopes of Hydrogen

H1

1

The three isotopes of Hydrogen even have their own names!

H1

2

H1

3

Hi! I’m hydrogen

They call me

deuterium

Hola! Mi nombre es tritium y yo

soy de Madrid!

Questions!Element Chemical

symbolAtomic number

Hydrogen H 1

Helium He 2

Lithium Li 3

Beryllium Be 4

Boron B 5

Carbon C 6

Nitrogen N 7

Oxygen O 8

Radium Ra 88

Thorium Th 90

Uranium U 92

Plutonium Pu 94

Unstable nuclei

Some nuclei are unstable, for example Uranium 235

Hi! I’m uranium-235 and I’m unstable. I really need to

lose some particles from my nucleus to become more

stable.

Unstable nuclei

To become stable, an unstable nuclei emits a particle

Weeeeeeeeeeeeee!

Unstable nuclei

We say the atom has decayed

Weeeeeeeeeeeeee!

Unstable nucleiThe decay of an unstable nucleus is random. We know it’s

going to happen, but we can’t say when! It cannot be affected by temperature/pressure etc.

Weeeeeeeeeeeeee!

Becquerels (Bq)

• The amount of radioactivity given out by a substance is measured in Becquerels. One becquerel is one particle emitted per second.

Detection

• Particles can be detected by photographic film

• Particles can also be detected (and counted) by a Geiger-Müller tube (GM tube) connected to a counter

Background radiation

There are small amounts radioactive particles around us all the time. This is called background radioactivity. The amount varies depending on location.

Background radiation

Background radiation comes from

• Cosmic rays from space

• Radioactive rocks in the ground

• Nuclear tests• Nuclear bombs• Nuclear accidents

Radiation Safety

Radiation Safety

• Run away!

Mr Porter

Radiation Safety

• Run away!• In other words keep the distance between

you and a radioactive source as big as possible!

Mr Porter

Radiation Safety

• Don’t waste time!

Radiation Safety

• Don’t waste time!• In other words limit the time you are exposed

to radiation.

Radiation Safety

• If you can’t run away, hide behind something!

Radiation Safety

• If you can’t run away, hide behind something!• Put a barrier between you and the radiation

source that can absorb the radioactive particles

Let’s try some questions.

Let’s try some questions.