P2.5 Radioactive Decay

Question 1

Describe the ‘plum pudding’ structure

Answer 1

The theory that atoms were spheres of positive charge with tiny negative electrons stuck in them like plums in a plum pudding

Question 2

What experiments did Rutherford and Madsen carry out ?

Answer 2

• They fired alpha particles at a piece of gold foil
• Some passed through - the nucleus is actually very small and the rest of the atom is space
• Some deflected away slightly - the nucleus must have an overall positive charge as it repelled positive alpha particles
• Some reflected back - the nucleus is very dense

Question 3

Define ‘isotope’

Answer 3

The atoms of an element with a different neutron number

Question 4

Define ‘mass number’

Answer 4

The total number of protons and neutrons of an atom

Question 5

Define ‘atomic number’

Answer 5

The total number of protons/electrons of an atom

Question 6

What do radioactive substances do randomly?

Answer 6

Radioactive substances randomly give out radiation from their atom’s nuclei no matter what happens to them.

Question 7

What are two types of background radiation?

Answer 7

• Natural sources

- Manmade sources

Question 8

What are 5 examples of background radiation from natural sources?

Answer 8

• Air
• Rocks
• Food
• Building materials
• Cosmic rays from space

Question 9

What are 3 examples of background radiation from manmade ?

Answer 9

• Fallout from nuclear weapon tests
• Dumped nuclear waste
• Nuclear accidents

Question 10

What are the 3 types of radioactivity?

Answer 10

• Alpha particles
• Beta particles
• Gamma rays

Question 11

Describe the properties of an alpha particle (5)

Answer 11

• Helium nucleus (2 protons and 2 neutrons)
• Positive charge
• Big, heavy, slow moving
• Not penetrating, can only travel a few cm in air (can be a stopped by paper)
• Strongly ionising, because of their size they bash into atoms and knock electrons off them, creating ions.

Question 12

Describe the properties of a beta particle (5)

Answer 12

• An electron
• Negative charge
• They move quite fast and are quite small
• They can penetrate through air and paper, but stopped by aluminium
• Moderately ionising

Question 13

Describe the properties of a gamma ray (5)

Answer 13

• No mass
• No charge
• Least ionising - doesn’t collide
• E.M wave with very short wavelength
• Most penetrating, only stopped by thick lead

Question 14

Which types of radiation are affected by a magnetic field?

Answer 14

• Beta particles

- Alpha particles

Question 15

Why are alpha and beta particles deflected by a magnetic field?

Answer 15

• Because they have charge they are deflected by a magnetic field.
• They are both deflected in opposite directions as they have opposite charges.

Question 16

What are the two things that affect radiation dose?

Answer 16

• Location

- Occupation

Question 17

What are the four examples of situation that increase radiation dose?

Answer 17

• Living near/working at underground rocks (e.g mining) - higher levels at the surface, releasing radon gas.
• Nuclear industry workers and miners so they wear protective clothing.
• Radiographers and X-rayers work using ionising conditions, they wear lead aprons and lead screens
• At high altitudes there are more cosmic rays, increasing the dosage

Question 18

Name 3 uses of radiation

Answer 18

• Smoke detectors
• Tracers in medicine
• Radiotherapy in medicine

Question 19

How is radiation used in smoke detectors?

Answer 19

• There is alpha radiation between two electrodes, this causes ionisation
• A current flows between the two electrodes
• If there is smoke it will absorb the radiation, stopping the current and the alarm sounds

Question 20

How is radiation used in tracers and what should its properties be?

Answer 20

• Radioactive isotope is injected/swallowed by the patient
• Gives out radiation to be detected by an external detector
• It needs to be gamma/beta radiation so it can pass out of the body quickly (alpha isn’t penetrating enough)
• It needs to have a short half life so radioactivity in the patient quickly disappears

Question 21

How is radiation used in radiotherapy?

Answer 21

• High doses of gamma rays kill all living cells
• These rays are directed carefully and at the right dosage to cancer cells (although some of the normal cells are still killed off)

Question 22

How does radiation damage body cells?

Answer 22

By entering them and colliding with their molecules,

• In lower doses : minor damage to cell without destroying, causing mutant cells, causing cancer
• In higher doses: kill cells completely, causing radiation sickness if many are killed at once

Question 23

What 2 things does the extent of the harmful effects of radiation depend on?

Answer 23

• How much exposure you have to it

- The energy and penetration of it

Question 24

What 2 types of radiation are the most dangerous outside the body and why?

Answer 24

• Gamma
• Beta
• They are penetrating enough to get into delicate organs

Question 25

What type of radiation is the most dangerous inside the body and why?

Answer 25

• Alpha
• The most ionising in a localised area
• The least penetrating so doesn’t pass out the body

Question 26

Define ‘half life’

Answer 26

The average time it takes for the nuclei number in a radioactive isotope sample to halve

Question 27

Describe 5 ways of safety when dealing with radioactive sources

Answer 27

• Using radioactive sources for a minimum amount of time
  to keep exposure to a minimum
• Handle sources with tongs, never allow skin contact
• Hold sources at arms length, decreasing radiation amount that hits you especially as alpha can’t travel far in air.
• Store sources in a lead box, if X-raying use a lead apron and stand behind a lead screen