ATOMIC STRUCTURE AND RADIOACTIVITY

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Radioactive decay is when nuclear / ionising radiation is emitted by unstable atomic nuclei so that they become more stable.
Radioactive decay is a random process
The process by which radiation can knock electrons out of atoms is called ionisation
There are 3 main types of radiation: alpha, beta, and gamma
During alpha radiation, the nucleus loses two protons and two neutrons
Alpha radiation has the highest ionising power
Alpha radiation can travel a few cm in air
Alpha radiation is stopped by a sheet of paper
An alpha particle is two protons and two neutrons
A beta particle is a fast moving electron
During beta radiation, in the nucleus a neutron changes into a proton and an electron
Beta radiation has a high ionising power
Beta particles travel 1 meter in air
Beta radiation is stopped by a few mm of aluminium
Gamma radiation is a short-wavelength, high frequency EM radiation
During gamma radiation, some energy is transferred away from the nucleus
Gamma radiation has low ionising power
Gamma radiation has virtually unlimited range in air
Gamma radiation is stopped by several cm of thick lead or metres of concrete
The activity of a radioactive source is the rate of decay of an unstable nucleus
Activity is measured in becquerel (Bq)
1 Bq = 1 decay per second
Detectors (e.g. Geiger-Muller tubes) record a count rate (number of decays detected per second)
Count rate after n half-lives = initial count rate / 2 to the power of n
The half-life of a radioactive source is the time for half the number of unstable nuclei in a sample to decay or the time for the count rate or activity of a source to half
Net decline is the ratio of isotopes present now to the initial isotope
Living ells can be damaged or killed by ionising radiation. The risk depends on the half-life of the source and the type of radiation
Alpha radiation is very dangerous inside the body because it affects all the surrounding tissue. Outside the body it only affects the skin and eyes because it cannot penetrate any further
Beta and gamma radiation are dangerous outside and inside the body because they can penetrate into tissues
Radiation dose, measure in sievert (Sv), measures the health risk of exposure to radiation. It depends on the type and amount of radiation
Background radiation is radiation that is around us all the time. It comes from:
* natural sources like rocks and cosmic rays
* nuclear weapons and nuclear accidents
Nuclear fission is when a large unstable nucleus absorbs an extra neutron and splits into two smaller nuclei of roughly equal size
During nuclear fission:
* gamma radiation is emitted and energy is released
* two or three neutrons are emitted that can go on to cause a chain reaction
Nuclear explosions are uncontrolled chain reactions
The chain reaction in a power station is controlled by absorbing neutrons
On rare occasions an unstable nucleus splits apart without absorbing a neutron. This is called spontaneous fission
Nuclear fusion is when two light nuclei join to make a heavier one
Some of the mass in nuclear fusion is converted to energy and transferred as radiation
Stars are an example of nuclear fusion
Irradiation is when an object is exposed to nuclear radiation