It is a helium nucleus that is slow and heavy. Alpha is strongly ionising and weakly penetrative
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What is beta?
It is an electron that is light and fast. It is moderately ionising and moderately penetrative.
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What is gamma?
Electromagnetic radiation that has no mass and is very fast. It is weakly ionising and strongly penetrative.
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What is a positron?
This is an antiparticle of an electron. They have a mass of 1/2000 but their charge is +1 instead of -1. They're light and fast moving and are moderately ionising/penetrating.
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Positron radiation is...
positively charged beta radiation.
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What is neutron radiation?
Neutrons are more penetrative than alpha or beta and sometimes more than gamma. Neutrons however aren't directly ionising but they can be absorbed by a nucleus. Absorbing a neutron can make a nucleus radioactive.
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What happens to these radioactive nuclei?
They emit ionising radiation, so neutrons are called 'indirectly ionising'
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What materials are used to shield from neutron radiation and why?
Neutrons are absorbed best by light nuclei and a hydrogen nucleus is lightest of all, so materials like water, concrete and polythene are used to make shielding.
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Why can thick lead also be used?
Because neutron absorption often makes nuclei emit gamma radiation so lead is used to stop gamma rays too.
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What can make a nucleus unstable?
If it has... too many neutrons/too few neutrons, too many protons and neutrons, or too much energy.
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What does an NZ graph show?
N represents the number of neutrons and Z the number of protons. An NZ graph shows a curve of stability for stable isotopes.
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What if an isotope is not on the curve?
This means that it is unstable.
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What does it mean when an isotope is above the curve?
This means it has too many neutrons to be stable.
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What does it mean when an isotope is below the curve?
This means it has too few neutrons to be stable.
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What is B- decay?
It is the emission of an electron from a nucleus.
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When does B- decay happen?
It happens in isotopes that are neutron rich (so have more neutrons than protons)
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What happens in B- decay when a nucleus emits an electron?
One of the neutrons in the nucleus turns into a proton, changing the atomic number by 1. The mass number stays the same.
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What is B+ decay?
This is the emission of a positron from a nucleus.
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What happens when a positron is emitted from a nucleus?
A proton gets changed into a neutron when a positron is emitted. The atomic number decreases by 1 and the mass number stays the same.
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What is alpha decay?
It only happens in very heavy atoms that have lots of protons when the nuclei of these atoms are too massive to be stable
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What happens when an alpha particle is emitted?
The atomic number increases by 2 and the mass number decreases by 4
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What happens in gamma radiation?
When alpha and beta decay, the nucleus often has excess energy which it loses by emitting gamma rays.
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When does gamma radiation occur?
It only ever occurs with beta or alpha decay, it never happens on its own.
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