2.5 Radioactive Substances

Question 1

What’s the mass number?

Answer 1

The total number of protons + the total number of neutrons

Question 2

What’s the atomic number?

Answer 2

The total number of protons

The total number of electrons

Question 3

What’s an isotope?

Answer 3

An atom that has a different number of neutrons

Question 4

What’s a radioactive substance?

Answer 4

A substance that gives out radiation from the nuclei of its atoms all the time

Question 5

What was the plum pudding model?

Answer 5

Question 6

What did Rutherford and Marsden’s experiment show?

Answer 6

What happened?

1. Most alpha particles went straight through gold foil
2. Some alpha particles were deflected by the gold foil

What did it show?

1. Most of an atom is just nothing
2. There’s a positively charged nucleus (the positively charged alpha particle was repelled by the nucleus)

Question 7

Where does background radiation come from?

Answer 7

• Naturally occuring radioactive isotopes (air, food, rocks)
• Space (mainly the sun)
• Man-made sources (nuclear weapon tests, nuclear accidents, nuclear waste)

Question 8

What are the properties of alpha radiation?

Answer 8

• 2 neutrons and 2 protons (a helium nucleus)
• Big, heavy and slow
• Don’t penetrate very far, stopped by air
• Strongly ionising

Question 9

What are the properties of beta radiation?

Answer 9

• An electron
• Quite fast and quite small
• Moderately penetrating
• Moderately ionising
• When a beta particle is emitted, a neutron turns into a proton

Question 10

What are the properties of gamma radiation?

Answer 10

• Short wavelength electromagnetic waves
• Very penetrating
• Weakly ionising

Question 11

What happens in terms of mass number and atomic number when an alpha particle is emitted?

Answer 11

Atomic number = Down 2

Mass number = Down 4

Question 12

What happens in terms of mass number and atomic number when a beta particle is emitted?

Answer 12

Mass number = Stays the same

Atomic number = Up 1

Question 13

What happens to alpha and beta particles in a magnetic field?

Answer 13

They are reflected in different directions due to their different charges. The alpha particles are deflected with a greater force as they have a greater charge

Question 14

What is half life?

Answer 14

The average time it takes for the number of nuclei in a radioactive isotope sample to halve

Question 15

Give some uses of radiation? (4)

Answer 15

• Smoke detectors - alpha
• Tracers in medicine - beta or gamma
• Radiotherapy
• Sterilisation of food and surgical equipment - gamma

Question 16

What is the most dangerous type of radiation inside the body?

Answer 16

Alpha

Question 17

What is the most dangerous type of radiation outside the body?

Answer 17

Beta and gamma

Question 18

Give some safety precautions when using radiation (4)

Answer 18

• Use radioactive substances for as short of a time as possible
• Don’t touch the radioactive substance, hold it at arm’s length with tongs
• Keep the source pointing away from you and don’t look at it directly
• Store it in a lead box, wear lead aprons, stand behind lead screens