Section 7 - Radioactivity and Particles

Question 1

Describe the structure of an atom

Answer 1

There is a proton (+) and neutrons in the nucleus of an atom. Electrons (-) orbit on shells (or orbitals) around the nucleus

Question 2

What does atomic number mean?

Answer 2

The number of protons in the nucleus

Question 3

What does mass number mean?

Answer 3

The total number of protons and neutrons in the nucleus

Question 4

What is an isotope?

Answer 4

Isotopes are atoms with the same atomic number, but different mass number

Question 5

Describe the characteristics of an alpha particle

Answer 5

They are made up of 2 protons and 2 neutrons - helium nucleus and are highly ionising

They don’t penetrate far into materials (can’t penetrate paper)

They decrease the atomic number by 2 and mass number by 4

Question 6

Describe the characteristics of a beta particle

Answer 6

A beta particle is an electron which has been emitted from the nucleus of an atom when a neutron turns into a proton and an electron.

They penetrate moderately (won’t penetrate aluminium) and ionise moderately

They increase the atomic number by 1

Question 7

Describe the characteristics of a gamma ray

Answer 7

They can penetrate a long way into materials (won’t penetrate lead)

They are weakly ionising.

They have no charge and no effect on the atomic or mass number

It occurs after beta or alpha decay

Question 8

How can a Geiger-Muller detector be used to detect ionising radiations?

Answer 8

Geiger-Muller detectors beep when ionising radiation is detected. The faster the beep, the more ionising it is.

Question 9

How can photographic film be used to detect ionising radiation?

Answer 9

Photographic film is white and absorbs radiations. When it does, it will turn black

Question 10

What are some sources of background radiation?

Answer 10

1. Substances on Earth - air, food, building materials, soil, rocks …
2. Radiation from space (mostly from the Sun)
3. Living things - there is a little bit of radioactive material in all living things

Question 11

What happens to the activity of a radioactive source over a period of time?

Answer 11

It decreases. Each time decay happens, a little bit more of the radioactive nucleus has disappeared. As the unstable nuclei disappear, the activity as a whole will decrease.

The amount of radiation given out is measured in becquerels

Question 12

What is half-life?

Answer 12

Half-life is the time taken for half of the radioactive atoms now present to decay

Question 13

How is radioactivity used in non-medical tracers?

Answer 13

A radioactive source is put into a system (like a piping network). It will build up where there is a blockage and this can be detected.

Question 14

How is radioactivity used in medical tracers?

Answer 14

A radioactive source is put into a body and will build up at a blockage so the area of the problem can be detected

Question 15

How is radioactivity used in radiotherapy?

Answer 15

Radiation is used to destroy unwanted cells (cancerous cells)

Question 16

How is radioactivity used in radioactive dating / carbon dating?

Answer 16

The amount of radiation from an object is measured. the half life of the carbon is then used to see how old the object is.

Archaeologists use this to tell the age of an object

Question 17

What are the dangers of ionising radiation?

Answer 17

• It can cause mutations in living organisms
• It can damage cells and tissues
• The problems arising in the disposal of radioactive products

Question 18

How does ionising radiation cause mutations in living organisms?

Answer 18

Radiation can damage the structure of a cells DNA. When the cells replicate, the changes will be passed on. this can be how cancer is caused

Question 19

How does ionising radiation cause damage to cells and tissues?

Answer 19

Atoms can be changed by radiation. This prohibits them functioning properly. This can mean cells and tissues are damaged

Question 20

How does ionising radiation cause problems arising the disposal of radioactive waste?

Answer 20

The waste emits radiation that can be dangerous.
If the waste is put into water, it can poison ecosystems.
Radioactive waste tends to be buried underground with the thinking that it would be less harmful.

Question 21

What precautions can be made to make an individual safer from ionising radiation?

Answer 21

Minimise your exposure:

• never allow skin contact (use tongs)
• store radioactive sources in a sealed lead box

For those working with radioactive materials:

• use lead aprons and stand behind lead screens
• industrial nuclear workers wear full protective suits
• workers can also use remote-controlled robot arms to carry out tasks

Question 22

Describe the results of Geiger and Marsden’s experiments with gold foil and alpha particles

Answer 22

Alpha radiation was beamed at a sheet of gold foil. A sheet of zinc sulphide surrounding the foil showed where the alpha particles ended up.

A few went straight through, but many were deflected at angles.

Question 23

Describe Rutherford’s nuclear model of the atom

Answer 23

A central nucleus with positive protons and neutral neutrons surrounds by orbiting negative electrons

Question 24

Explain the results of Geiger and Marsden’s experiments with gold foil and alpha particles

Answer 24

Previously, the plum pudding model was used (a positive sphere contained with negative electrons dotted inside). However, if this was true, then the alpha particles would have gone straight through the gold foil

Instead, there are positive alpha particles being repelled by a positive charge and others were going through the spaces between the charged areas.. The faster the they hit the positive charge, the faster they were repelled.

Question 25

What is nuclear fission and what does it produce?

Answer 25

Nuclear fission is the splitting of a nucleus of Uranium-235 by collision with a neutron, which releases kinetic energy.

It produces two daughter nuclei and a small number of neutrons

Question 26

How can a chain reaction be set up during the fission of U-235?

Answer 26

If the neutrons (a product of a fission reaction) strikes another U-235 nuclei to cause another fission reaction

Question 27

What role do the control rods and moderators play during the fission reaction of U-235?

Answer 27

Control Rods (boron) - limit the rate of fission by absorbing excess neutrons

Moderator (graphite or water) - slows neutrons so that they can successfully collide with uranium nuclei and sustain the chain reaction