P6 - Radioactive Materials Flashcards
What is ionisation?
When ionising radiation transfers enough energy to break an atom or molecule into bits called ions.
Describe alpha radiation and what happens during alpha decay
An alpha particle is a helium nucleus – made up of two protons and two neutrons. Alpha particles are relatively big and heavy and fairly slow–moving. Alpha decay always changes the element of the atom that decaying, since it loses protons.
Describe beta radiation and what happens during beta decay
A beta particle is identical to electron, with virtually no mass and a charge of -1. Beta particles move quite fast and they are quite small. During beta decay, a neutron in the nucleus turns into a proton, so the element changes and a beta particle is emitted.
Describe gamma radiation
Gamma radiation is an electromagnetic wave. They have no mass. They can penetrate a long way into materials without being stopped. Since a gamma ray is just energy, it doesn’t change the element of the nucleus that emits it.
What blocks alpha particles?
Skin and paper
What blocks beta particles?
A thin sheet of any metal (e.g aluminium)
What blocks gamma rays?
Thick lead or thick concrete
What is half-life?
The time taken for half of the radioactive nuclei now present to decay.
What happens when an unstable atom decays?
It spits out one or more three types of ionising radiation – alpha, beta and gamma. In the process, the atom often changes into a new element.
How did the Rutherford scattering show that atoms have a positive nucleus?
He fired alpha particles - which are positively charged -‘at thin gold foil. Most of them went straight through but the occasional one came back. This meant that most of the mass of the gold atom was concentrated at the centre in a tiny nucleus, which had to have a positive charge to repel the alpha particles. The rest of the atom must be mainly empty space as most of the alpha particles went straight through.
How is the nucleus held together?
The nucleus contains positively charged protons particles which repel each other. The nucleus doesn’t fly part because it is held together by an attractive force much greater than the repulsive electrostatic force between protons. This is called a strong force. The strong force only has a very short range.
What is nuclear fusion? Give an example
Well it to nuclei combined to create a larger nucleus, releasing energy when they do. For example hydrogen nuclei fuse together to make helium nuclei.
How do nuclei fuse?
They overcome the repulsive electrostatic force and get close enough for the strong force to hold them together. This takes a lots of energy – which means a high temperature.
What happens to nuclei when they undergo nuclear fusion or station? How can you calculate this?
They lose mass and energy is released . You can calculate how much energy is released using the equation
energy = mass x [speed]^2
What is nuclear fission?
When neutrons are fired nuclear fuel, causing some of its large, unstable nuclei to split into two smaller nuclei of roughly equal size. Each split nucleus also releases two or three more neutrons and lots of energy.
