P7 - Radioactivity (PAPER 1)

Question 1

What is a radioactive substance

Answer 1

A substance that contains unstable nuclei that become stable by emitting radiation

Question 2

What are the three main forms of radiation

Answer 2

• Alpha
• Beta
• Gamma

Question 3

Why was the nuclear model of the atom made by Ernest Rutherford accepted

Answer 3

• It agreed with the measurements made by Geiger and Marsden
• explained how and why radioactivity happened
• predicted the existence of the neutron, which was then discovered at a later date

Question 4

Why was the plum pudding model rejected

Answer 4

It couldn’t explain why some alpha particles were scattered through large angles

Question 5

What is an isotope

Answer 5

An isotope of an element has the same amount of protons but a different amount of neutrons

Question 6

What changes in the nucleus during radioactive decay

Answer 6

Alpha - 2 protons and 2 neutrons are lost from the nucleus

Beta - One neutron from the nucleus changes into a proton

Question 7

What particles are emitted when radioactive decay occurs

Answer 7

Alpha - 2 protons and 2 neutrons are emitted as an alpha particle
Beta - An electron is created in the nucleus and is instantly emitted

Question 8

How far can alpha, beta and gamma particles travel in air

Answer 8

Alpha - a few centimetres
Beta - Around one metre
Gamma - an unlimited range

Question 9

What materials are able to stop alpha, beta and gamma particles

Answer 9

Alpha - a sheet of paper
Beta - a thin sheet of metal
Gamma - a thick layer of lead

Question 10

Which of the three types of radiation has the most ionising power

Answer 10

1. Alpha
2. Beta
3. Gamma

Question 11

What happens to atoms when they are ionised, and how can it affect a human cell

Answer 11

• The atoms begin to lose electrons, which make it charged

- This can kill or damage cells

Question 12

What is the half-life of a radioactive source

Answer 12

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

Question 13

what is the count-rate of a radioactive source

Answer 13

the number of counts per second on a Geiger counter

Question 14

what happens to the count rate from a radioactive isotope as it decays

Answer 14

the count rate is reduced

Question 15

what is the formula for calculating the count rate after a given number of half-lives

Answer 15

count rate after n half lives = initial count rate / 2^n