Physics 2 Flashcards
Rutherford scattering.
Most alpha particles went straight through the gold foil but a few were deflected. This is because…
Most of the atom is empty space as they passed through the foil.
Nucleus must have large positive charge as positively charged alpha part lies were deflected at a large angle.
Nucleus must be small as few particles were deflected back.
What did Rutherford and Marsden come up with?
Nuclear model.
What are radioactive substances?
Give out radiation from their nucleus of atoms all the time. This is known as radioactive decay.
Is radioactive decay random?
Yes.
What happens to unstable isotopes of elements during radioactive decay?
They turn into stable ones.
Alpha decay.
Two neutrons, two protons, same as helium nucleus. When an atom decays by emitting an alpha particle, two protons and two neutrons are lost from the nucleus. They are slow and big so the don’t penetrate far into materials. But as they are large, they are ionising as they knock into atoms and cause electrons to go off, this creates many ions.
Beta decay.
Has no mass and a charge of -1. In beta decay a neutron turns into a proton in the nucleus, this releases a beta particle. They are small and fast so the penetrate a bit and are a little ionising.
Gamma decay.
Short wavelength electromagnetic waves. No mass and no charge. Penetrate far but weakly ionising as they don’t collide with atoms.
What happens to alpha and beta particles when traveling through a magnetic field?
They are deflected as they are charged. Alpha are deflected less as they have a larger mass. They also have a greater charge so feel more force in a magnetic field.
What is a half-life?
Average time in which it takes for the number of nuclei of a radioactive isotope to halve.
Where does background radiation come from?
Space, nuclear waste, rocks, air.
What are the safety precautions to reduce exposure to radiation?
Keep exposure to minimum. Don't point towards body. Don't make contact with source. Keep it far from the body. Lead absorbs the radiation, so keep in lead box, wear lead aprons, stand behind lead screens, only expose the part of the body that needs to be
Smoke detectors.
Use alpha radiation. A weak source is positioned in the detector, close to two electrodes. A current can flow between the two electrodes as the alpha causes ionisation of the molecules in the air by knocking electrons. If there is a fire, smoke absorbs the radiation and the current stops.
Medical tracers.
Beta or gamma used. They are placed into people and their progress around the body is followed by an external detector.
Radiotherapy.
The treatment of cancer. This uses ionising radiation. The radiation such as gamma is aimed at the right area with the correct dosage. This ensures that cancer cells are killed but other cells aren’t however, they will get slightly damaged.
Sterilisation.
High doses of gamma rays kill microbes.
What is nuclear fission?
When an atomic nucleus splits up. This creates two nuclei which are smaller.
Nuclear fission releases a lot of energy.
Uranium 235 and Plutonium 239 are used in nuclear power stations.
In order for nuclear fission to occur, a neutron which a moving slowly must be absorbed into the nucleus. This makes the nucleus unstable so it splits to form to smaller nuclei which are radioactive as they don’t have the right amount of neutrons.
Nuclear power stations.
Use nuclear reactors. Inside this, there is chain reaction which is controlled. Uranium 235 or Plutonium 239 nuclei split up and release energy as heat. This can be used to heat a coolant which is then pumped into a boiler. The heat is then transferred to water to produce steam which drives a turbine which is connected to a generator. The coolant can then be pumped into the reactor and the process proceeds.
What are the disadvantages of nuclear power?
Difficult and costly so dispose radioactive waste.
Expensive to build and decommission.
What are the advantages of nuclear power?
Cheap.
