Radioactive Decay

Question 1

State four types of nuclear radiation.

Answer 1

1. Alpha particles
2. Beta particles
3. Gamma rays
4. Neutrons

Question 2

What is meant by background radiation?

Answer 2

• Radiation that is always present
• It is in very small amounts and so not harmful

Question 3

Give 4 sources of background radiation.

Answer 3

1. Rocks
2. Cosmic rays from space
3. Nuclear weapon testing
4. Nuclear accidents

Question 4

How do you measure and detect background radiation?

Answer 4

1. Photographic film
2. Geiger-Muller counter

Question 5

How is photographic film used to measure radiation?

Answer 5

A photographic film turns dark when it absorbs radiation. This is useful for people who work on radiation as the more radiation they are exposed to, the darker the film becomes. Therefore the workers know when they have been exposed to too much radiation.

Question 6

How are Geiger-Muller tubes used to measure radiation?

Answer 6

When the Geiger-Muller tube absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation. The frequency of the pulse depends on how much radiation is present. A high frequency would mean the tube is absorbing a large amount of radiation

Question 7

What constitutes of an alpha particle?

Answer 7

• Two protons and two neutrons
• It is the same as a helium nucleus

Question 8

What is the range of an alpha particle through air?

Answer 8

A few centimetres (normally in the range of 2-10cm)

Question 9

What will block beta radiation?

Answer 9

• A thin sheet of aluminium
• Several metres of air

Question 10

What will block gamma radiation?

Answer 10

• Several centimetres of lead
• A few metres of concrete

Question 11

What type of radiation is most ionising?

Answer 11

Alpha radiation

Question 12

Which type of radiation it least ionising?

Answer 12

Gamma radiation

Question 13

How does gamma emission affect the mass/charge of an atom?

Answer 13

Both mass and charge remain unchanged

Question 14

Describe the plum-pudding model of the atom.

Answer 14

A sphere of positive charge, with the negatively charged electrons distributed evenly throughout it

Question 15

Prior to the discovery of the electron, what was believed about the atom?

Answer 15

The atom was believed to be indivisible

Question 16

Which experiment led to the plum-pudding model being discarded?

Answer 16

Rutherford’s alpha-Scattering experiment

Question 17

What is the name given to the currently accepted model of the atom?

Answer 17

The Bohr model

Question 18

Describe Rutherford’s experiment.

Answer 18

• Alpha particles (charge +2) were fired at a thin sheet of gold foil
• Most particles went straight through
• Some particles were deflected by small angles (<90°)
• A few particles were deflected by large angles (>90°)

Question 19

What are the conclusions of Rutherford’s experiment?

Answer 19

• Most of an atom is empty space
• The nucleus has a positive charge
• Most if the mass is concentrated in the nucleus

Question 20

What happens in the process of beta plus decay?

Answer 20

A proton turns into a neutron and a positron (in order to conserve charge)

Question 21

What is the process called when a neutron changes into a proton and an electron?

Answer 21

Beta minus decay

Question 22

When alpha decay occurs, what happens to the atomic number and the mass number of the atom?

Answer 22

• The atomic number decreases by 2
• The mass number decreases by 4
• A new element is made since the atomic number has changed

Question 23

What effect does beta minus decay have on the mass number and atomic number of an atom?

Answer 23

• The mass number stays the same as the total number of neutrons and protons hasn’t changed (one has just turned in the other)
• The atomic number increases since there is one more proton