Section 3 - Radioactivity and Astronomy
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Where is the majority of an atom’s mass located?
In the nucleus.
What size is the nucleus compared to the whole of the atom?
About 10,000 times smaller.
What is the rough size of an atom?
1 x 10⁻¹⁰
What happens if an electron is excited?
It shifts from one energy level to a higher one.
What happens when an electron drops to a lower energy level?
It will emit an EM wave with the same amount of energy as was used to raise the electron’s energy level.
What happens with energy levels the further from the nucleus they get?
The distances between energy levels shrink.
What is ionising radiation?
Any radiation that can knock electrons off of an atom.
What are Isotopes?
Different forms of the same atom.
How can isotopes be written?
(Element name)-(Relative mass of atom)
What are the types of nuclear radiation?
Alpha, beta-minus, beta-plus, gamma and neutron.
What are alpha particles?
Helium nuclei.
What does it take to stop alpha particles?
A few cm of air or a thin sheet of paper.
What does it take to stop beta-minus particles?
A few metres of air or a sheet of 5mm aluminium.
What does it take to stop beta-plus particles?
Anything with electrons.
What are beta-minus particles?
Fast moving electrons.
What are beta-plus particles?
Fast moving positrons.
What are positrons?
Antimatter, with virtually no mass and a positive relative charge of +1
What is nuclear radiation?
Any radiation that comes from an atom’s nucleus.
What happens when a positron meets an electron?
They annihilate and produce gamma rays.
What are gamma rays?
A form of short wavelength EM radiation.
How does ionisation happen?
An atom looses or gains an electron.
What does it take to stop gamma rays?
Thick lead or metres of concrete.
How are nuclear equations written?
Atom before decay → atom after decay + radiation
How is an alpha particle written in an equation?
⁴₊₂α