P4 - Radioactivity

Question 1

Describe the structure of the atom.

Answer 1

In the centre - A small, positive nucleus containing protons and neurons
It is surrounded by electrons orbiting in different energy levels

If the electrons absorb energy they move up an energy level and get further from the nucleus.
If the electrons lose energy they move down an energy level and get closer to the nucleus.

Question 2

How big is an atom and how big is the nucleus?

Answer 2

Atoms are very small.
They have a radius of about 1×10^-10 metres

The nucleus is 1/10000th of the size

Question 3

Describe the differences and similarities between the plum pudding model of the atom and the nuclear model of the atom.

Answer 3

Similarities:
- Both spherical
- Both contain electeons
- Both have a positive charge

Differences:
- Electrons in the plum pudding model are inside the atom - Electrons in the nuclear model are on the outside
- Plum pudding model contains a cloud of positively charged matter evenly distributed - Nuclear model has protons in a nucleus

Question 4

What does it mean if an atom is radioactive?

Answer 4

It has an unstable nucleus

It will emit alpha, beta or gamma radiation from the nucleus to become stable

Question 5

What are alpha and beta particles made from?

Answer 5

An alpha particle is made from 2 protons and 2 neurons.
4 4
He OR α
2 2

A beta particle is an electron emitted from the nucleus.
0
β
-1

Question 6

What does the activity of a radioactive source mean and how is it measured?

Answer 6

It is the number of nuclei that decay every second

It is measured using a Geiger counter and the unit is the Bequerel (Bq)

Question 7

What is Gamma radiation?

Answer 7

It is an electromagnetic wave emitted from the nucleus of an unstable (radioactive) atom

Question 8

What are the penetraring properties of alpha, beta and gamma radiation?

Answer 8

Alpha travels 2-5cm in air (stopped by paper)

Beta travels up to 1m in air (stopped by aluminium)

Gamma is not stopped by air (stopped by lead)

Question 9

What is the definition of a half-life?

Answer 9

The half-life of a radioactive isotope is the time it takes for the number of nuclei, count rate or activity of the isotope in a sample to fall to half its initial level

Question 10

What is the difference between contamination and irradiation?

Answer 10

Contamination is when radioactive atoms get on or in other materials

Irradiation is being exposed to ionising radiation