Chapter 7 - Radioactivity

Question 1

How does a radioactive substance stabilize unstable nuclei?

Answer 1

• It emits radiation.

Question 2

State the names of the 3 types of radiation.

Answer 2

• Alpha
• Beta
• Gamma

Question 3

What was the name of the correct model of an atom and who discovered it?

Answer 3

• The Bohr model by Niels Bohr.

Question 4

State the definition of an isotope.

Answer 4

• Atoms of the same element with same number of protons but different number of neutrons.

Question 5

How many protons and neutrons are in an isotope of Uranium which has a mass number of 235 and an atomic number of 92?

Answer 5

• Protons = 235
• Neutrons = 143

Question 6

Describe the characteristics of alpha emission.

Answer 6

• 2 protons and 2 neutrons
• 2+ relative charge

Question 7

Describe the characteristics of Beta emission.

Answer 7

• It has a charge of -1
• When an unstable nucleus emits beta emission, the atomic number decreases by 1.

Question 8

Describe the characteristics of gamma emission.

Answer 8

• Electromagnetic radiation
• Uncharged and no mass
• Mass and charge stay the same

Question 9

Give the 3 materials which can stop the three types of radiation.

Answer 9

Alpha - Paper
Beta - Thin aluminium sheet
Gamma - Thick lead sheet

Question 10

Identify how far each type of radiation can travel.

Answer 10

Alpha - 5cm
Beta - 1m
Gamma - Unlimited

Question 11

Why are all radiation types dangerous?

Answer 11

• They can ionise substances they pass through, killing them.

Question 12

State the definition of the activity of a radioactive source.

Answer 12

• Number of unstable atoms that decay per second.

Question 13

State the definition of the count rate of a sample.

Answer 13

• Number of counts per second.

Question 14

What is the half-life of a radioactive isotope?

Answer 14

• Average time taken for the number of nuclei to half.

Question 15

How do you calculate the count rate after ‘n’ half-lives?

Answer 15

• initial count rate / 2(n)
• n = number of half-lifes

Question 16

A radioactive isotope has a half-life of 15 hours. A tube has 48 grams of the isotope.

Calculate the mass of the tube after:
- 22.5 hours
- 30 hours

Answer 16

• 18 grams
• 12 grams

Question 17

What are the 2 factors which decide how effective a radioactive isotope is?

Answer 17

• It’s half-life
• Type of radiation emitted (a,b,y)

Question 18

Give 2 uses of radioactive isotopes in medicines.

Answer 18

• Medical imaging
• Treatment of cancer

Question 19

What is nuclear fission?

Answer 19

• Splitting of an atom’s nucleus into 2 smaller nuclei.

Question 20

How does a chain reaction occur?

Answer 20

• When a fission event causes further fission events.

Question 21

What is nuclear fusion?

Answer 21

• Forcing 2 nuclei together to form 1 larger nucleus.

Question 22

What is released when 2 light nuclei collide?

Answer 22

• Lots of energy

Question 23

Why does a fusion reactor need to be a high temperature?

Answer 23

• This is because the nuclei involved in fusion is difficult to store otherwise.

Question 24

Give 2 examples where nuclear accidents have occured.

Answer 24

• Chernobyl
• Fukushima

Question 25

Why is nuclear waste dangerous?

Answer 25

• It contains many radioactive isotopes that emit nuclear radiation for a long time, which can cause cancer.