Radioactive Decay

Question 1

State four types of nuclear radiation.

Answer 1

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

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 is 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

Afew centimetres (normally in the range
of 2-10cm).

Question 9

What will block beta radiation?

Answer 9

● Athin sheet of aluminium

● Several metres of air

Question 10

What will block gamma radiation?

Answer 10

● Several centimetres of lead

● Afew metres of concrete

Question 11

Which type of radiation is most ionising?

Answer 11

Alpha radiation.

Question 12

Which type of radiation is 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
(< 90º)
● Afew particles were deflected by large angles
(> 90º)

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 of 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
● Anew 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 a 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.