SP6 Radioactivity Flashcards
What would happen to an electron in an atom if it absorbed electromagnetic radiation?
An inner electron could move up to a higher energy level (higher electron shell) if it absorbed the right amount of energy from EM radiation.
When it moves up, it is said to be excited.
The elctron would quickly fall back to its original energy level, and will therefore emit the same amount of energy it gained, and this is energy is carried away by EM radiation.
What is the type of EM radiation emitted from the atom dependant on?
The energy levels the electron moves between.
If the electron falls from the 3rd to 2nd shell it would release less energy than if it fell from 2nd to 1st.
This is because as you move further away from the nucleus, the energy levels gets closer together, so the difference in energy between 2 levels gets smaller. The frequncy of generated radiation decreases as you get further from the nucleus.
So a higher energy = a higher frequency of EM radiation.
What can be released when electrons move between energy levels?
Visible light.
What is ionising radiation?
What are examples of ionising radiation?
If an outer electron absorbs radiation with enough energy, it can move so far that it leaves the atom. Now that it is a free electron, the atom is said to be ionised as a positive ion as it has lost an electron.
Ionising radiation is any radiation that causes and electron to escape.
Examples: alpha, beta, positron, gamma
What are alpha particles and how penetrating and ionising are they?
Alpha particles are helium nuclei (they are 2 protons and 2 neutrons)
They don’t penetrate very far into materials and are stopped quickly.
They can only travel a few cm in air and are absorbed by a thin sheet of paper.
Because of their size, they are strongly ionising.
What can beta particles be?
Electrons or positrons
What are beta-minus particles and how penetrating and ionising are they?
Fast moving electrons released by the nucleus.
Have virtually no mass, and a relative charge of -1.
Have a range in air of a few cm and are absorbed by a sheet of aluminium (approx 5mm thick).
Moderately ionising.
What are beta-plus particles and how penetrating and ionising are they?
A fast moving positron.
A positron is the antiparticle of the electron - meaning it has exactly the same mass as the electron but a positive +1 charge.
Have a small range, because when they hit and electron the 2 destroy each other and produce gamma rays - this is known as annihilation (it’s used in PET scanning)
Moderately ionising
What are gamma rays and how penetrating and ionising are they?
EM waves with a short wavelength
Penetrate far into materials without being stopped and will travel a long distance through air
This means they are weakly ionising because they tend to pass through rather than collide with atoms
Eventually they hit something and do damage
They can be absorbed by thick sheets of lead or metres of concrete.
What are nuclear equations?
A way of showing radioactive decay by using element symbols.
Atom before decay —> atom after decay + radiation emitted
The total mass and atomic numbers must be equal on both sides
How does alpha decay affect the nucleus of an atom?
When a nucleus emits an alpha particle, it loses 2 protons and 2 neutrons so:
Mass number = -4
Atomic number = -2
How does beta-minus decay affect the nucleus of an atom?
In beta-minus decay, a neutron changes into a proton and an electron, so:
Mass number = no change
Atomic number = +1
How does positron emission affect the nucleus of an atom?
In beta-plus decay, a proton changes into a neutron and a positron, so:
Mass number = no change
Atomic number = -1
How does neutron emission affect the nucleus of an atom?
The nucelus is losing a neutron, so:
Mass number = no change
Atomic number = -1
How do gamma rays affect the nucleus of an atom?
Gamma rays are a way of getting rid of excess energy from an atom. The nucleus goes from an excited state to a mroe stable state by emitting a gamma ray, so:
Mass number = no change
Atomic number = no change
