What is an alpha particle?
Describe Alpha emission.
- Alpha particles are Helium nuclei, so they have two protons and two neutrons.
- Mass number decreases by four. Atomic number decreases by two.
What is a beta particle?
Describe beta emission.
- An electron that has been emitted from the nucleus of an atom when a neutron turns into a proton and electron
- The mass number stays the same
- Atomic number increases by one
What is a gamma ray?
Describe gamma emission and gamma/alpha emission.
- They are very short EM waves. They have no mass, they are just energy.
- gamma emission: nothing happens. Mass and atomic number stays the same.
- Gamma/alpha emission: mass number decreases by, atomic number by two - basically just alpha emission.
Give two uses of gamma radiation.
- Medical tracers
- Industrial tracers
Describe how gamma radiation is used in medical tracers.
- Gamma source put in body
- Radiation penetrates body tissues and can be detected externally
- On-screen display is created to show where radiation is coming from and so doctors can use this method to check if organs are working as they should.
Why would an alpha source be a bad choice for medical tracers?
- Because it does not have much penetrating power (so would be stopped by body tissues) and couldn’t be detected externally.
- It is strongly ionising so if it gets inside you it’s really harmful.
Describe how gamma radiation is used in industrial tracers.
Why must the radiation be gamma?
- A gamma source is put into a pipe and allowed to flow along.
- If there’s a crack in the pipe the gamma radiation will build up in that area and so a detector will read extra higher radiation in that same area.
- Gamma radiation has a very high penetrating power so it can be detected through rocks and earth surrounding the pipes - alpha and beta would be too easily blocked.
Describe how radioactive dating works.
- It allows scientists to accurately work out the age of rocks, fossils and archaeological experiments.
- It works on the principle of half-life. By measuring the amount of radioactive isotope left in a sample, and knowing its half-life, you can work out how long the thing has been left around.
Define half-life.
The time taken for half of the radioactive atoms now present to decay.
Define radioactive decay.
- The nuclei of unstable atoms break down at random, unaffected by physical conditions or any sort of chemical bonding.
- When the nucleus does decay, it releases one or more of the three types of radiation (alpha, beta or gamma)
- In the process, the nucleus often changes into a new element.
Briefly describe how radiation can be used to treat cancer.
Once cancer has started, patients can be given radiotherapy to kill cancer cells and stop them dividing.
This involves high doses of gamma rays, carefully directed to zap cells in the tumour while minimising the dose to the rest of the body.
Because it is a high dose of radiation it kills cells completely without mutating them and causing more cancer.
Describe how to use a graph to measure half-life.
- Take several readings from a radioactive source using a Geiger-Muller detector.
- Plot the time interval on the x-axis and the activity in becquerels on the y-axis.
- The half-life is found from finding the time interval that corresponds on the graph to a halving of activity on the vertical axis.
- Background radiation that has nothing to do with the source affects the results so you have to measure the level of background radiation first, and then subtract it from your activity readings to get an accurate value.
Which sources of radiation are harmful outside the body? Why?
- Beta and Gamma
- They can penetrate soft tissues to reach delicate organs and do damage.
- If they get inside the body their radiation passes out without doing too much damage.
Which source of radiation is harmful inside the body?
- Alpha
- It can’t penetrate the skin but if it gets inside the body it’s very dangerous because it will not pass quickly out again.
- Their damage is done in a very localised area.
What is ionisation?
Why is it dangerous?
- When radiation enters your body it will collide with molecules in your body.
- These collisions cause ionisation. This means electrons are knocked from your molecules giving them a charge and making them ions.
- Ionisation damages or detroys molecules.
How is ionisation related to cancer?
- Lower doses of ionising radiation tend to cause minor damage without killing the cell.
- This can lead to mutations in cells which then divide uncontrollably.
- This is cancer.
Why is high-level radioactive waste difficult to dispose of safely?
- It has an extremely long half-life so it stays radioactive for tens of thousands of years. This means it has to be treated very carefully.
- It is often sealed in glass blocks which it then sealed in metal cannisters and buried deep underground.
- The site where it is buried MUST be geologically stable (no earthquakes) otherwise there is risk of a leak of radioactive material.
Give some percautions to take when working with radioactive materials. (3)
- Never allow skin contact, hold it at arms length using tongs
- Keep source pointed away from you
- Store radioactive sources in sealed containers
What are the extra percautions taken if you work regularly with? (3)
- Wear lead aprons and stand behind lead screens
- Industrial nuclear workers use full protective suits that prevent radioactive particles being inhaled or lodged in the skin
- They can use remote-control robot arms to carry highly radioactive sources.
What is nuclear fission?
What is it used for?
- Nuclear fission is the splitting of the nucleus of an atom which results in the a small number of neutrons being released. This process releases a lot of kinetic energy.
- In a nuclear reactor nuclear fission is carried out in controlled chain reactions, releasing lots of energy.
Give some sources of background radiation.
- substances on eath: air, food, soil e.c.t.
- radiation from space (cosmic rays)
- living things
- human activity, i.e. fallout from nuclear explosions or radioactive waste.
What are the differences between rutherford’s nuclear model and the plum pudding model?
Plum pudding:
- Atoms were spheres of positive charge with tiny negative electrons stuck inside them.
Rutherford:
- Most of the mass is concentrated at the centre, and most of the atom is empty space
- The nucleus must be very small and positively charged
What is a chain reaction?
When neutrons released from a split nucleus are absorbed by other atoms which then in turn release morre neutrons as their nuclei split. The process continues.
What is the purpose of the moderator in nuclear reactors?
What could a moderator be made of?
- The moderator slows down neutrons so that they can succesfully collide with uranium nuclei and sustain a chain reaction
- They are normally made from graphite but sometimes take the form of a coolant (e.g. water)
