Radioactive Decay

Question 1

What is the atomic number of the nucleus shown below?

Answer 1

3 (this lower number is also known as the ‘proton number’)

Question 2

What is the mass number of the nucleus shown below?

Answer 2

7 (this upper number is also known as the ‘nucleon number’)

Question 3

What is the nucleon number of the atom shown below?

Answer 3

7 (this upper number is also known as the ‘mass number’)

Question 4

What is the proton number of the atom shown below?

Answer 4

3 (this lower number is also known as the ‘atomic number’)

Question 5

How many protons does the nucleus shown below have?

Answer 5

3

Question 6

How many neutrons does the nucleus shown below have?

Answer 6

4 (it’s the difference between the mass number and the proton number)

Question 7

Lithium-6 and Lithium-7 are isotopes. What does the word ‘isotopes’ mean here?

Answer 7

It means they have the same number of protons but different numbers of neutrons

Question 8

What is the mass number of Lithium-7?

Answer 8

7

Question 9

Sometimes a large, unstable nucleus will change into a new element, emitting an energetic particle as it does so. What is the name for this process?

Answer 9

Radioactive decay

Question 10

During alpha decay, an unstable nucleus emits an alpha particle. What is an alpha particle?

Answer 10

A highly energetic particle made of two protons and two neutrons

Question 11

During beta decay, an unstable nucleus emits an alpha particle. What is a beta particle?

Answer 11

A very high energy electron

Question 12

What is a gamma ray?

Answer 12

A very high frequency electromagnetic wave

Question 13

We refer to alpha particles, beta particles and gamma rays as ‘ionising radiation’. What does this mean?

Answer 13

They can knock electrons off atoms (when they collide with them)

Question 14

Which kind of ionising radiation can be stopped by a sheet of card?

Answer 14

Alpha particles

Question 15

Which kind of ionising radiation can be stopped by a few cm of air?

Answer 15

Alpha particles

Question 16

Which kind of ionising radiation will pass through card, but can by stopped by a few mm of aluminium?

Answer 16

Beta particles

Question 17

Which kind of ionising radiation will pass through a few mm of aluminium, but will be stopped by a few metres of lead?

Answer 17

Gamma rays

Question 18

Name two things you could use to detect ionising radiation.

Answer 18

A Geiger counter
Photographic film

Question 19

Name two health risks posed by exposure to ionising radiation.

Answer 19

Cell damage
Genetic mutation (including a risk of cancer)

Question 20

What is the name for the energetic particle made up of two protons and two neutrons, sometimes released when an unstable nucleus decays?

Answer 20

An alpha particle

Question 21

What is the name for a highly energetic electron, sometimes released when an unstable nucleus decays?

Answer 21

A beta particle

Question 22

What is the name of the high frequency e-m wave emitted when an unstable nucleus decays?

Answer 22

A gamma ray

Question 23

What is the mass number of an alpha particle?

Answer 23

4

Question 24

What is the proton number of an alpha particle?

Answer 24

2

Question 25

What is the mass number of a beta particle?

Answer 25

0

Question 26

What is the proton number of a beta particle?

Answer 26

-1

Question 27

What number should replace the question mark in the nuclear decay equation shown below?

Answer 27

206 (the nucleon numbers to the left of the arrow must add to equal the nucleon numbers to the right of the arrow)

Question 28

What number should replace the question mark in the nuclear decay equation shown below?

Answer 28

85 (the proton numbers to the left of the arrow must add to equal the proton numbers to the right of the arrow)

Question 29

What number should replace the question mark in the nuclear decay equation shown below?

Answer 29

7 (the proton numbers to the left of the arrow must add to equal the proton numbers to the right of the arrow)

Question 30

What number should replace the question mark in the nuclear decay equation shown below?

Answer 30

14 (the mass numbers to the left of the arrow must add to equal the mass numbers to the right of the arrow)

Question 31

What is the name for the radiation all around us, that we are exposed to as a result of everyday life?

Answer 31

Background radiation

Question 32

Name three natural sources of background radiation.

Answer 32

Cosmic rays
Radon gas from rocks
Food and drink

Question 33

Name two artificial sources of background radiation

Answer 33

Medical x-rays
Nuclear power stations

Question 34

A nuclear reactor contains ‘fuel rods.’ What are ‘fuel rods’?

Answer 34

They are where the nuclear fission occurs. They contain the nuclear fuel.

Question 35

A nuclear reactor contains ‘control rods.’ What is the function of the ‘control rods’?

Answer 35

Control rods are made of boron and absorb neutrons. They can be raised and lowered between the fuel rods to increase or decrease the rate of the fission reaction.

Question 36

A nuclear reactor contains a ‘moderator.’ What is the role of the ‘moderator’?

Answer 36

A moderator is a chemical that slows down neutrons, making them more efficient at causing nuclear fission.

Question 37

“Nuclear fission can occur when a ……….. collides with an unstable nucleus.” What is the missing word?

Answer 37

neutron

Question 38

“A neutron can cause an unstable nucleus to undergo nuclear fission. The products of this reaction are a daughter nucleus, heat energy, and three or more ………….” What is the missing word?

Answer 38

neutrons

Question 39

“A neutron can cause an unstable nucleus to undergo nuclear fission. The products of this reaction are ……………., heat energy, and three or more neutrons.” What is the missing phrase?

Answer 39

a daughter nucleus

Question 40

What units is activity measured in?

Answer 40

Becquerels (Bq)

Question 41

What does an activity of 600 Bq mean?

Answer 41

600 unstable nuclei decay every second

Question 42

You measure the activity of a source. After 3 seconds your geiger counter has detected 600 decays. What is the activity of the source?

Answer 42

200 Bq (because there must be 200 decays every second)

Question 43

Explain what is meant by ‘the half-life of a radioactive sample’

Answer 43

The half life is the time taken for half of the atoms in a radioactive sample to decay
OR
The half life is the time taken for the activity of a radioactive sample to halve

Question 44

Sodium-24 has a half-life of 15 hours. What fraction of a sample of sodium-24 will remain after 45 hours?

Answer 44

An eighth. (In this case, 45 hours is three half-lives. So the sample will have halved three times. Half of a half of a half is an eighth)

Question 45

A sample of Iodine has an activity 1200 Bq and a half-life of 8 days. What will the activity of the source be after 16 days?

Answer 45

300 Bq. (In this case, 16 days is two half-lives. So the activity will have halved two times. Halve 1200 and then halve it again to get your answer)

Question 46

Bismuth-212 has a half-life of 60 seconds. A sample containing 800 atoms of Bismuth-212 is left for 4 minutes. How many atoms remain after this time?

Answer 46

50 atoms. (4 minutes = 4 half lives, in this case. So halve 800 four times to get your answer)

Question 47

Name four uses of radioactive sources

Answer 47

Smoke detectors
Medical tracers
Monitoring the thickness of paper in a paper mill
Carbon dating

Question 48

Which kind of source is used in smoke detectors (alpha, beta or gamma) and why?

Answer 48

Alpha.
Only alpha would be strongly absorbed by the smoke. Beta and gamma are too penetrating to be strongly absorbed by the smoke.

Question 49

Which kind of source (alpha, beta or gamma) is used to measure the thickness of paper in a paper mill and why?

Answer 49

Beta.
Alpha is not penetrating enough and would almost all be absorbed by the paper. Gamma is too penetrating and would hardly be absorbed at all.

Question 50

Isotope A has a half-life of 5 minutes. Isotope B has a half-life of 3 hours. Isotope C has a half-life of 16 years. Which isotope could a doctor use as a medical tracer, and why?

Answer 50

Only isotope B has a suitable half-life. The half-life of A is too short: little activity will remain by the time it is administered to the patient. The half-life of C is too long: it will continue to expose the patient to radiation long after they have left the hospital.