7b Radioactivity

Question 1

What is the mass of a proton, neutron and electron?

Answer 1

Proton - 1
Neutron - 1
Electron - Almost 0 (1/2000)

Question 2

What is the charge of a proton, neutron and electron?

Answer 2

Proton - +1
Neutron - 0
Electron - -1

Question 3

What is an isotope?

Answer 3

Isotopes have the same atomic number but different mass number or the same number of protons but different amount of neutrons

Question 4

What is an ion?

Answer 4

If an electron is added or removed then this creates an ion

Question 5

Do atoms have a neutral charge?

Answer 5

Atoms are neutral (they have not charge) so the number of protons and electrons must be the same

Question 6

What is radioactive decay?

Answer 6

Some nuclei are unstable - they decay into other nuclei and emit ionising radiation

Question 7

What are the 3 main types of decay?

Answer 7

Alpha, Beta and Gamma

Question 8

What is alpha decay?

Answer 8

A nucleus emits an alpha particle (made up of 2 protons + 2 neutrons)

Question 9

What is beta decay?

Answer 9

A neutron in the nucleus changes into a proton and emits a beta particle (fast moving electron)

Question 10

What is gamma decay?

Answer 10

A nucleus emits a wave (a type of electromagnetic wave)

Question 11

What is the atomic number of the 3 types of decay?

Answer 11

Alpha - 2
Beta - - 1/0
Gamma - 0

Question 12

What is the mass number of the 3 types of decay?

Answer 12

Alpha - 4
Beta - 0
Gamma - 0

Question 13

What is the charge of the 3 types of decay?

Answer 13

Alpha - +2
Beta - -1
Gamma - 0

Question 14

What is the ionising power of the 3 types of decay?

Answer 14

Alpha - high
Beta - Medium
Gamma - Low

Question 15

What is the penetrating power of the 3 types of decay?

Answer 15

Alpha - Low
Beta - Medium
Gamma - high

Question 16

What objects do each of the 3 types of decay go through?

Answer 16

Alpha - 5cm - stopped by paper
Beta - 50cm - stopped by Aluminium
Gamma - Doesn’t really stop - but lead almost stops it

Question 17

How can radioactivity be detected?

Answer 17

Geiger-Muller tube or photographic film

Question 18

How can radioactive decays be counted?

Answer 18

Radioactive decays are counted with a counter

Question 19

What is radioactive activity?

Answer 19

The activity of a radioactive source is equal to number of decays per second

Question 20

What is radioactive activity measured in?

Answer 20

Becquerels (Bq)
1Bq = 1 decay per second

Question 21

What happens when the nuclei decay?

Answer 21

As the nuclei decay, the number of nuclei decreases, so there are fewer unstable nuclei left to decay

Question 22

What is half life?

Answer 22

• The half life of a radioactive isotope is the average time it takes for half of the nuclei of the isotope to decay (into some other isotope)

OR

• The half life of a radioactive source is the average time taken for the activity to half

Question 23

What are the units of half life?

Answer 23

Units of time eg. seconds

Question 24

What happens to 110 nuclei of X with a half life of 2hours?

Answer 24

Start - 100
2h - 50
4h - 25

Question 25

What is background radiation?

Answer 25

Background radiation is ionising radiation that is always present around us

Question 26

What are some sources of background radiation?

Answer 26

There are several sources of it:
1) Radon gas (alpha) in the air -> about 50% of natural background radiation
2) Cosmic rays (gamma) (from Space)
3) Carbon-14 eg. in food
4) Artificial sources eg. nuclear weapons testing, medical uses

Question 27

How to measure the activity of a source without background radiation?

Answer 27

• First used the Geiger-Muller tube to measure the count without the source present. This is the background count
• Then measure the count with the source
• Now, subtract the background count from the count with the source to get the activity of the source.