Describe Thomson Plum Pudding Model
An atom was believed to be a sphere of positive charge, with small areas of negative charge evenly distributed throughout
Describe the Rutherford’s Scattering Experiment
- A beam of alpha particles was directed at a thin gold foil
- It occured in a vacumm so that no collisons between air particles and alpha particles occurred
- To observe the path of the alpha particles, there was a microscope which could be moved around the outside of the chamber
Why was a lead barrier used in the Rutherford Scattering Experiment
To keep the alpha source directed in one direction rather than randomly spreading out
What was inferred from the Rutherford Scattering Experiment
- Most alpha particles passed straight through the foil with no deflection - this suggested that the atom is mostly empty space
- A small amount of particles were deflected by a large angle - this suggested that the centre of the atom is positively charged, as positively charged alpha particles were repelled from the centre and deflected.
- Very few particles were deflected back by more than 90° - this suggested that the that the centre of the atom was very dense as it could deflect fast moving alpha particles, but also that is was very small as a very small amount of particles were deflected by this amount
- This evidence lead to a new model for the atom, known as the nuclear model
What is Radiation
Radiation is where an unstable nucleus emits energy in the form of electromganetic waves or subatomic particles in order to become more stable
Describe the Three Types of Radiation
Describe how you can identify the type of radiation emitted from a source
- Using a geiger-muller tube and counter, find the background count when the source is not present
- Place the source of radiation close to the GM tube and measure the count rate
- Place a sheet of paper between the source and GM tube and measure count rate again, if the count rate decreases significantly, then the source is emitting alpha radiation
- Repeat the above step using aluminium foil and several inches of lead. If there is a significant decrease in count rate for aluminium foil, then beta radiation is being emitted and if there is a significant decrease in count rate for the lead block, then gamma radiation is being emitted
Describe how radiation is used in the thickness measurements of aluminium foil, paper and steel
- In the production of aluminium foil a beta source is placed on one side of the material, while a detector is placed on the other
- If the material becomes too thick, less beta radiation will pass through the foil, therefore the reading on the detector decreases causing the rollers (which are flattening the foil) to move closer together
- Meanwhile if the material becomes too thin, the reading will increase causing the rollers to move apart
- Using the same method, alpha radiation can be used for the production of paper, while gamma radiation can be used for the production of steel sheets
Describe the uses of Gamma Radiation in Medicine
- As a detector - a radioactive source with a short half-life (to reduce exposure), which emits gamma radiation, can be injected into a patient and the gamma radiation can be detected using gamma cameras in order to help diagnose patients
- To sterilise surgical equipment - as gamma radiation will kill any bacteria present on the equipment
- In radiation therapy - gamma radiation can be used to kill cancerous cells in a targeted region of the body such as a tumour, however it will also kill any healthy cells in that region. Many safety measures are put in place to reduce this risk to medical staff and patients e.g. reduced exposure times, use of shielding
How are radioactive sources handled safely
- Using long handled tongs to move the source
- Storing the source in a lead-lined container when not in use
- Keeping the source as far away as possible from yourself and others
- Never pointing the source towards others
State some of the sources of background radiation
- Radon gas - which is released from rocks
- Artificial sources - caused by nuclear weapons testing and nuclear meltdowns
- Cosmic rays - enter the Earth’s atmosphere from space
- Rocks - some rocks contain naturally occurring radioactive isotopes
