Radioactive Decay Flashcards
What is the atomic number of the nucleus shown below?
3 (this lower number is also known as the ‘proton number’)
What is the mass number of the nucleus shown below?
7 (this upper number is also known as the ‘nucleon number’)
What is the nucleon number of the atom shown below?
7 (this upper number is also known as the ‘mass number’)
What is the proton number of the atom shown below?
3 (this lower number is also known as the ‘atomic number’)
How many protons does the nucleus shown below have?
3
How many neutrons does the nucleus shown below have?
4 (it’s the difference between the mass number and the proton number)
Lithium-6 and Lithium-7 are isotopes. What does the word ‘isotopes’ mean here?
It means they have the same number of protons but different numbers of neutrons
What is the mass number of Lithium-7?
7
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?
Radioactive decay
During alpha decay, an unstable nucleus emits an alpha particle. What is an alpha particle?
A highly energetic particle made of two protons and two neutrons
During beta decay, an unstable nucleus emits an alpha particle. What is a beta particle?
A very high energy electron
What is a gamma ray?
A very high frequency electromagnetic wave
We refer to alpha particles, beta particles and gamma rays as ‘ionising radiation’. What does this mean?
They can knock electrons off atoms (when they collide with them)
Which kind of ionising radiation can be stopped by a sheet of card?
Alpha particles
Which kind of ionising radiation can be stopped by a few cm of air?
Alpha particles
Which kind of ionising radiation will pass through card, but can by stopped by a few mm of aluminium?
Beta particles
Which kind of ionising radiation will pass through a few mm of aluminium, but will be stopped by a few metres of lead?
Gamma rays
Name two things you could use to detect ionising radiation.
A Geiger counter
Photographic film
Name two health risks posed by exposure to ionising radiation.
Cell damage Genetic mutation (including a risk of cancer)
What is the name for the energetic particle made up of two protons and two neutrons, sometimes released when an unstable nucleus decays?
An alpha particle
What is the name for a highly energetic electron, sometimes released when an unstable nucleus decays?
A beta particle
What is the name of the high frequency e-m wave emitted when an unstable nucleus decays?
A gamma ray
What is the mass number of an alpha particle?
4
What is the proton number of an alpha particle?
2
What is the mass number of a beta particle?
0
What is the proton number of a beta particle?
-1
What number should replace the question mark in the nuclear decay equation shown below?
206 (the nucleon numbers to the left of the arrow must add to equal the nucleon numbers to the right of the arrow)
What number should replace the question mark in the nuclear decay equation shown below?
85 (the proton numbers to the left of the arrow must add to equal the proton numbers to the right of the arrow)
What number should replace the question mark in the nuclear decay equation shown below?
7 (the proton numbers to the left of the arrow must add to equal the proton numbers to the right of the arrow)
What number should replace the question mark in the nuclear decay equation shown below?
14 (the mass numbers to the left of the arrow must add to equal the mass numbers to the right of the arrow)
What is the name for the radiation all around us, that we are exposed to as a result of everyday life?
Background radiation
Name three natural sources of background radiation.
Cosmic rays
Radon gas from rocks
Food and drink
Name two artificial sources of background radiation
Medical x-rays
Nuclear power stations
A nuclear reactor contains ‘fuel rods.’ What are ‘fuel rods’?
They are where the nuclear fission occurs. They contain the nuclear fuel.
A nuclear reactor contains ‘control rods.’ What is the function of the ‘control rods’?
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.
A nuclear reactor contains a ‘moderator.’ What is the role of the ‘moderator’?
A moderator is a chemical that slows down neutrons, making them more efficient at causing nuclear fission.
“Nuclear fission can occur when a ……….. collides with an unstable nucleus.” What is the missing word?
neutron
“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?
neutrons
“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?
a daughter nucleus
What units is activity measured in?
Becquerels (Bq)
What does an activity of 600 Bq mean?
600 unstable nuclei decay every second
You measure the activity of a source. After 3 seconds your geiger counter has detected 600 decays. What is the activity of the source?
200 Bq (because there must be 200 decays every second)
Explain what is meant by ‘the half-life of a radioactive sample’
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
Sodium-24 has a half-life of 15 hours. What fraction of a sample of sodium-24 will remain after 45 hours?
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)
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?
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)
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?
50 atoms. (4 minutes = 4 half lives, in this case. So halve 800 four times to get your answer)
Name four uses of radioactive sources
Smoke detectors
Medical tracers
Monitoring the thickness of paper in a paper mill
Carbon dating
Which kind of source is used in smoke detectors (alpha, beta or gamma) and why?
Alpha.
Only alpha would be strongly absorbed by the smoke. Beta and gamma are too penetrating to be strongly absorbed by the smoke.
Which kind of source (alpha, beta or gamma) is used to measure the thickness of paper in a paper mill and why?
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.
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?
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.
