Section 8- Discovery Of Nucleus Flashcards
How big is a nucleus?
In the order of x10^-15m
How was the nucleus discovered?
Rutherford used a beam of alpha particles directed at a thin layer of gold atoms. Some bounced back, some were deflected and some passed straight through. He came to the conclusion there was a dense mass in the centre.
Why was the nucleus not discovered earlier?
They thought the positive charge was spread throughout the atom.
What is radiation?
It ionises air. Alpha is easily absorbed but beta is not. Gamma was more penetrating.
Alpha is the most dangerous because it is the most ionising.
What are the properties of alpha radiation?
2 protons and 2 neutrons Small range up to about 100mm Deflected by magnetic fields Stopped by paper Produces 10^4 ions per mm in air standard pressure
What are the properties of beta radiation?
Electron
Range of about 1m
Deflected opposite direction to alpha in magnetic field
Stopped by 5mm aluminium
Produces 100 ions per mm of air in standard pressure
What are the properties of gamma radiation?
Photons of energy Follows inverse square law for range in air Not deflected by magnetic fields Stopped/ reduced by several cm of lead Weak ionising effect
Describe what happens to the nucleus in a radioactive change.
A nucleus with too many protons emits a positron as a proton changes into a neutron.
How does the intensity of gamma radiation change as it spreads out?
Radiation energy per second/ total area = nhf/4(pi)r^2
Why is ionising radiation harmful?
It can destroy cell membranes which causes cells to die.
It can damage vital molecules directly or by ionising. Damaged DNA may cause a tumour or mutation for babies.
What should you think about when using radioactive materials?
Solid sources should be transferred using tongs.
Liquid or gas sources and powder should be in sealed containers.
You should not be exposed to sources for longer than necessary.
What is half life?
The time taken of the mass of a radioactive isotope to half.
What is exponential decrease?
The radioactivity will never completely disappear because it tends towards 0 but will never reach 0.
How do you do radioactive dating?
You can look at the materials half life and work out how long ago it began decaying.
Define radioactive tracers.
It follows a path of a substance through a system. The tracer should have a stable but short half life and emit beta or gamma radiation so it can be detected outside the body.
