Radioactivity Atomic number/proton number – Number of protons in the nucleus Atomic mass/mass number – Number of protons and neutrons in the nucleus 7
6
3
3
Li
Li
Isotopes of an element have the same number of protons but different numbers of neutrons
The nuclei of some atoms are unstable. To become stable they emit particles (we say that the nucleus has “decayed” and the emission of a particle is called radioactive decay). This is a completely random process, we cannot say when it will happen, and it is unaffected by temperature and other physical processes. Types of particle Type of particle
Symbol
What is it?
Charge
Penetrating power
Ionizatio n
Alpha
α
+2
β
Gamma
γ
A photon of high frequency electromagnetic radiation
None
Stopped by paper or several cm of air Stopped by 3 mm of Aluminium Stopped by several cm of lead
Strongly
Beta
A helium nucleus (2 protons and 2 neutrons) A fast moving electron
-1
Deflection by elec and mag fields Small deflection
Weakly
Large deflection
Weakly
No deflection
Other The most dangerous INSIDE the body
Detection - Radioactive particles can be detected by a Geiger –Muller tube (GM tube) attached to a counter, or by photographic film. Background radioactivity - This is the small amount of radioactivity that surrounds us all the time. It comes from radioactive rocks in the ground, space and from the remains of nuclear tests and accidents (Chernobyl) Handling and Storage - Radioactive materials have to be handled carefully as the radioactive particles emitted can cause illness. They are normally stored in lead boxes and should be handled at a distance (using tongs or some other devices). The time exposed to the material should also be kept as short as possible. Hazards - radiation burns, hair loss (temporary or permanent), cancer, reproductive sterility, mutations in offspring Alpha decay – The proton number goes down by two and the mass number goes down by 4. Beta decay – The proton number goes up by one and the mass number stays the same. Half-life – The time it takes for the radioactivity/count rate/number of undecayed atoms to halve. Uses – Sterilising medical instruments and irradiating food to kill microbes, as a medical tracer, detecting leaks in pipes, measuring thicknesses of manufactured materials, radiocarbon dating.
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