7b Radioactivity Flashcards
What is the mass of a proton, neutron and electron?
Proton - 1
Neutron - 1
Electron - Almost 0 (1/2000)
What is the charge of a proton, neutron and electron?
Proton - +1
Neutron - 0
Electron - -1
What is an isotope?
Isotopes have the same atomic number but different mass number or the same number of protons but different amount of neutrons
What is an ion?
If an electron is added or removed then this creates an ion
Do atoms have a neutral charge?
Atoms are neutral (they have not charge) so the number of protons and electrons must be the same
What is radioactive decay?
Some nuclei are unstable - they decay into other nuclei and emit ionising radiation
What are the 3 main types of decay?
Alpha, Beta and Gamma
What is alpha decay?
A nucleus emits an alpha particle (made up of 2 protons + 2 neutrons)
What is beta decay?
A neutron in the nucleus changes into a proton and emits a beta particle (fast moving electron)
What is gamma decay?
A nucleus emits a wave (a type of electromagnetic wave)
What is the atomic number of the 3 types of decay?
Alpha - 2
Beta - - 1/0
Gamma - 0
What is the mass number of the 3 types of decay?
Alpha - 4
Beta - 0
Gamma - 0
What is the charge of the 3 types of decay?
Alpha - +2
Beta - -1
Gamma - 0
What is the ionising power of the 3 types of decay?
Alpha - high
Beta - Medium
Gamma - Low
What is the penetrating power of the 3 types of decay?
Alpha - Low
Beta - Medium
Gamma - high
What objects do each of the 3 types of decay go through?
Alpha - 5cm - stopped by paper
Beta - 50cm - stopped by Aluminium
Gamma - Doesn’t really stop - but lead almost stops it
How can radioactivity be detected?
Geiger-Muller tube or photographic film
How can radioactive decays be counted?
Radioactive decays are counted with a counter
What is radioactive activity?
The activity of a radioactive source is equal to number of decays per second
What is radioactive activity measured in?
Becquerels (Bq)
1Bq = 1 decay per second
What happens when the nuclei decay?
As the nuclei decay, the number of nuclei decreases, so there are fewer unstable nuclei left to decay
What is half life?
- The half life of a radioactive isotope is the average time it takes for half of the nuclei of the isotope to decay (into some other isotope)
OR
- The half life of a radioactive source is the average time taken for the activity to half
What are the units of half life?
Units of time eg. seconds
What happens to 100 nuclei of X with a half life of 2hours?
Start - 100
2h - 50
4h - 25
What is background radiation?
Background radiation is ionising radiation that is always present around us
What are some sources of background radiation?
There are several sources of it:
1) Radon gas (alpha) in the air -> about 50% of natural background radiation
2) Cosmic rays (gamma) (from Space)
3) Carbon-14 eg. in food
4) Artificial sources eg. nuclear weapons testing, medical uses
How to measure the activity of a source without background radiation?
- First used the Geiger-Muller tube to measure the count without the source present. This is the background count
- Then measure the count with the source
- Now, subtract the background count from the count with the source to get the activity of the source.
What are the dangers of ionising radiation?
Ionising radiation can:
- Kill cells
- Increase the risk of cancer (by causing mutations in DNA)
What does ionising mean?
‘ionising’ means removing (or adding) an electron from an atom
How can the risks be reduced?
- Wearing gloves (to prevent contamination)
- Wear shielding eg. lead apron
- Store the radioactive sources in a lead case
- Handle sources with tongs
- Reduce exposure time
- Wear radiation badge
What is irradiation?
- Irradiation of an object is when an object is exposed to ionising radiation
What is contamination?
- Contamination of an object is when a radioactive source is introduced onto it
What type of radiation is used in smoke alarms?
- Alpha
- The detector detects the alpha particles hitting it.
- When there is smoke in the a;arm, the smoke particles absorb/block the alpha particles, preventing them from reaching the detector which readings go down
What type of radiation is used in monitoring the thickness of paper or metal?
- Beta
- The thicker the paper is the fewer beta particles can go through the paper to reach the detector
What type of radiation is used for sterilising medical equipment and preserving food?
- Gamma (normally)
- The gamma rays irradicate equipment/food and kills any pathogens on them
What type of radiation is used for radiotherapy cancer treatment?
- Gamma
- The gamma rays irradicate cancer cells to kill them
- The gamma rays are arranged to focus on one specific area, and are strong enough to go through your skin
What type of radiation is used in radioactive dating (carbon dating)?
- Beta (if using carbon-14)
- Living things all contain carbon-14
- After they die, the activity of the carbon-14 decreases
- We can see how much activity has dropped and work out how long ago the organism died
What type of radiation is used in tracers?
- Gamma
- Medical tracers: person eats/breathes is injected with gamma source
- Gamma is detected outside the body
- This shows any regions where the tracer does not reach eg. because of blocked blood vessel
