Radioactivity ☢ Flashcards
Rutherford Scattering lore
Demonstrated the existence of the nucleus
Successor of Plum Pudding model which stated that the atom was made up of a sphere positive charge with small areas of negative charge evenly distributed throughout
Led to the production of a new model
Rutherford scattering apparatus
Rutherfords apparatus included an alpha source and gold foil in an evacuated chamber which was covered in fluorescent coating, which meant you could see the alpha particles hit the inside of the chamber
To observe the path of the alpha particles there was a microscope which could be moved around the outside of the chamber
Rutherford scattering observations
• Most alpha particles passed through the foil with no deflection which implies that the atom is mostly empty space
• Small amount of particles were deflected by a large angle which implies centre of the atom is positively charged
• Very few particles were deflected back by more than 90° which implies that the centre of the atom was very dense as it could deflect fast moving alpha particles
Radiation
Unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable
Alpha radiation
2-10 cm range in air
Highly ionising
Deflected by magnetic fields
Absorbed by paper
Beta radiation
Around 1m range in air
Weakly ionising
Deflected by electric fields
Absorbed by aluminium foil
Gamma radiation
Infinite range : follows inverse square law
Very weakly ionising
Not deflected by electric fields
Absorbed by several metres of concrete or several inches of lead
What can radiation monitor
All three of these types of radiation can be used to monitor the thickness of certain materials while they are being produced, for example 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
Gamma in medicine
• As a detector - a radioactive source with a short half life, 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
• Sterilisation of equipment
• Radiation therapy - kill cancerous cells in targeted region
Inverse square law (gamma)
As gamma moves through the air it spreads out in all directions equally, therefore the intensity follows an ISL
I = k/x^2
Handling radioactive substances safely
• Using long handed 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 people
Background radiation
Corrected count = Total count rate - background count
Sources of background radiation
• Radon gas - released from rocks
• Artificial sources - nuclear weapon testing
• Cosmic rays - enters Earths atmosphere from space
• Rocks containing naturally occurring radioactive isotopes
Radioactive decay
• Random process
• Radioactive nucleus will have a constant decay probability
• Probability of a nucleus decaying per unit time
• △N/△t = -λN
(Change in number of nuclei of a sample over time over the initial number of nuclei
Radioactive decay described as exponential decay
N = Noe^-λt
