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Paper 5 Nuclear physics
A GM tube will detect background radiation even when there is no source pointed directly at it. It is detecting background radiation. It is created by the following sources:
Air: Radon gas released from rocks emits alpha radiation
Ground and buildings: All rocks will contain radioactive isotopes.
Cosmic radiation: High energy protons from space that collide with the upper atmosphere to form radioactive isotopes.
Living things: are made up of Carbon that may have traces or Carbon14.
Manmade radiation: Medical and industrial resources may emit radiation.
A nucleus will decay in order to become more stable. Unstable nuclei are caused by having too many neutrons, not enough neutrons, or too much energy in the nucleus. The nucleus continues to decay until it
reaches a stable isotope. Radioactivity is random.
A nucleus will release 2 neutrons and 2 protons. It has a +2 charge and mass of 4u.
A A-4 4
Z X = Z-2 Y + 2He
This moves a nucleus above the belt of stability down towards it. Occurs only in very heavy nuclei.
Beta minus decay
One neutron decays to form one proton and emits an electron. It has a 1 charge and negligible mass.
X = A
0 - 0
Z Z+1Y + -1 + 0e
This will move a nucleus to the left of the belt of stability towards it. It moves SE.
du + e-
12 - 3
-3 3 3
Beta plus decay
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One proton decays to form one neutron and emits a positron. It has a +1 charge and negligible mass.
Z X = A 0 + 0
Z-1Y + 1 + 0e
This will move a nucleus to the right of the belt of stability towards it. It move NW.
ud + e+
2 1 3
3 - 3 +3
Nuclei with too much energy will `reshuffle' and emit energy in the form of gamma radiation.…read more
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Rearranging this equation gives you the formula for half life. This is the average time it takes for the number of undecayed nucleus to halve.
t 1 = ln2
The mass of a nucleus is less than the mass of the individual nucleons added together. This is because the formation of a nucleus is in a lower energy state and energy will be given off when they join.…read more