Atoms are made up of protons, neutrons and electrons.
Protons and neutrons are in the nucleus, electrons are in the shells
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Atomic (proton) number is the number of protons in the nucleus of an atom. Mass (nucleon) number is the total number of protons and neutrons in the nucleus of an atom. An isotope is an atom of the same element, i.e. it has the same number of protons/same atomic number, but has a different number of neutrons/different mass number. Two atoms with the same atomic number but different mass numbers are isotopes see 7.02 for example |
There are three types of ionising radiation:
Alpha (α), Beta (β) and Gamma (γ)
One radioactive source can release different types of radiation.
Ionisation is when an atom loses or gains an electron, causing it to become an ion (an atom which is positively or negatively charged).
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Detect using a Geiger Müller Tube. Try the three different materials in order, paper then aluminium then lead. Count rate will significantly decrease if radiation is stopped. |
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Alpha decay: · 2 protons and 2 neutrons are lost. · Mass number decreases by 4 · Atomic number decreases by 2 Beta decay · 1 neutron is converted to an electron (lost from the atom) and proton · Mass number is unchanged · Atomic number increases by 1 Gamma decay · Energy is lost from an atom in the form of an electromagnetic wave · Mass number is unchanged · Atomic number is unchanged |
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Particle |
Symbol |
Mass |
Charge |
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Alpha |
α |
4 |
+2 |
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Beta |
β |
0 |
-1 |
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Gamma |
γ |
0 |
0 |
Geiger Müller detector:
When connected to a counter, the detector will be able to measure radioactivity.
Photographic film:
Radiation will cause photographic film to darken.
The activity of a radioactive source decreases over a period of time and is
measured in becquerels.
The Half-life is the time taken for the radioactivity of a specific isotope to fall to half its original value.
Numerical:
A radioactive source has a half-life of 2 hours. If the mass starts at 40mg, what will the mass be after 4 hours?
Graphical:
Several different times for the half-life can be calculated and averaged.
Gamma radiography:
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Medical tracer: – Radioactive tracer put in body (swallowed/injected) – Detector put around body – Computer generates an image |
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Gauging: – Coal absorbs a lot of radiation – If only a small amount of radiation is detected back after it is reflected by what you are trying to gauge, lots of coal is present. |
Radiotherapy
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Pipe tracers: – A radioactive material which emits gamma radiation with a short half-life is put in the water – A detector is placed above the pipe – A spike in detected radioactivity suggests a leak in the pipe |
Sterilisation:
Carbon dating:
Occurs when material that contains radioactive atoms is deposited on materials, skin, clothing, or any place where it is not desired.
The process by which an object is exposed to radiation.
