In Pairs....

…write down all you can remember about radiation and radioactivity.

• What is radiation?• What is radioactivity?• What’s the difference?

Different types of radiation

Alpha – α He nucleus emitted

Nucleus gets smaller

Beta – β (strictly β-) Neutron decays in to a proton, an electron

and an anti-neutrino Gamma – Energy released as the nucleus rearranges EM Photon

Alpha Decay

α decay (α is a helium nuclei, 2 protons and 2 neutrons)

4242

YX AZ

AZ

4223490

23892 ThU

4222488

22890 RaTh

i.e.

Complete this example:

Beta Minus Decayβ- decay (β- is a high energy electron)

e-

νe

n

p

Before

After

W-

eepn 1000

1001

0011

0010

eA

ZAZ YX

011

The standard formula:

Beta Plus Decayβ+ decay (β+ is a high energy positron)

e+

νe

n

p Before

After

W+

eenp 1

0

0

0

1

0

0

1

0

0

1

0

0

0

1

1

eA

ZAZ YX

011

The standard formula:

Gamma Emission

No change occurs in the number of protons or neutrons in the nucleus

The energy released in gamma ray (γ) emission comes from reordering the nucleus to a more stable arrangement

It usually occurs after the emission of an α particle or a β- particle

Electron CaptureA new one for you!

This occurs in proton rich nuclei, where the nucleus captures an inner shell electron, causing a proton to turn in to a neutron emitting a neutrino.

The inner shell vacancy is filled by an outer shell electron causing the emission of an X-ray photon

eA

ZAZ YeX 1

01

The standard formula:

So that’s radiation, what’s radioactivity?

Radioactivity is the decay of unstable isotopes of an element, which results in the emission of ionising radiation.

Discuss - Why is something unstable?

Consider a nucleus with 14 nucleons...We can arrange the protons and neutrons in

different ways...

P N PN P

NP

NP NP

NP N

P N PN P

NP

NN

PN

P N

N147 C146 O148

NP N P

N PN

P

NP

PN

P N P

This is stable. There are the same number of protons and neutrons, they are packed in their lowest energy state

These are possible but unstable. There are either too many neutrons or too many protons, so they not in their lowest energy state.

NNN

N

N

PN

He142

This is impossible, far too unstable to exist!

N

NN

NP NN

The process of radioactive decay

Radioactive decay is dangerous because of the ionising radiation emitted.

In addition for a single atom of an isotope, the process is random and uncontrollable.

They could decay at any moment...

Please listen very carefully!

Dice Analogue

Draw a table like the one shown.

Count you initial number of blocks; enter this as your zero ‘ Dice Remaining’ reading. Roll your blocks, if they land colour side up then they have decayed, put them to one side. Count the number decayed and calculate the number of remaining blocks. Repeat this process making sure you do not lose any blocks.

Once you have all your data, enter it on the class spread sheet.

Throw Number

Dice Decayed Dice Remaining

0 -----------------

1

2

…

19

20

Review the Dice Analogue Experiment

1. Why is this experiment a good analogue for radioactive decay?

2. Will the values ever really reach zero if they were radioactive isotopes?

3. If you replaced the dice with coins how would your results be affected?

4. If radioactive isotopes A decayed faster than radioactive isotope B, which would be more dangerous and why?

Radioactivity• The decay of any single nucleus is completely

random• You cannot predict when any one nucleus will

decay• If there are enough nuclei you can accurately

estimate how many nuclei will decay every time period.