Isotopes
Atoms of the same element with the same atomic number (and same number of protons) can have different numbers of neutrons. Different types of the same element are called isotopes.
Atoms up to atomic number 82 have one or more stable isotopes, for example, oxygen-16 and oxygen-18. Atoms of unstable isotopes can break apart and emit radioactivity from the nucleus, including alpha, beta and gamma radiation.
Some isotopes (such as Uranium-235) can be made unstable when they ‘capture’ a neutron.
Fundamental forces
The four fundamental forces are gravitational, electromagnetic, strong nuclear and weak nuclear force.
Alpha, beta and gamma radiation
Alpha radiation is particles made of two neutrons and two protons that have a charge of +2 and a mass of 4.
Beta radiation is fast moving electrons with a charge of -1 and a mass of 0.0005. They are not emitted from electron shells but by the nucleus when a neutron decays into a proton and an electron.
Gamma radiation is high energy electromagnetic waves emitted by the nucleus.
Gamma radiation has the lowest ionizing effect and highest penetrating ability. Alpha particles have the lowest penetrating ability and the highest ionizing effect.
Alpha particles will be absorbed by a sheet of paper or skin. Beta particles are absorbed by a sheet of aluminium. Thick sheets of lead or concrete walls are needed to absorb gamma rays.
Radioactive deacy
Radioactive emissions occur randomly with a certain probability.
Nuclear equations to represent the decay process for alpha and beta decay.
For example:
22688Ra + 22286Ra + 42α (α is another way to write 42He2+ )
Neutrons can be written as 10n and protons can be written as 11p.
The larger number is always the mass number.
Half life is the time for the activity of a sample to fall by a half. The half lives of some important radionuclides are I-131 8days, Cs-134 2 years, Cs-137 30 years, C-14 5700 years, U-238 700million years.
Activity and half life
The activity of a sample of radioactive material is measured in Becquerels where 1 Bq = 1 decay/s
The half life of an isotope is the time for the activity of a sample of a radioactive isotope to fall by ½.
Detection of radioactivity
Alpha-particles, beta-particles and gamma rays can be detected using a Geiger-Müller (GM) tube which gives an electric pulse when ionizing radiation passes through.
Background radioactivity is the natural radioactivity from the lithosphere, biosphere and atmosphere.
Using Radioactivity
Radioactive isotopes are used for medical imaging, treating cancer, dating archaeological objects, and for nuclear power and nuclear weapons.
Precautions must be taking when handling, using and storing radioactive material including protective clothing, dosimeters, shielding.
Nuclear Fission
A Uranium-235 nucleus can capture a neutron and become unstable uranium-236.
Uranium-236 undergoes fission, where the nucleus breaks up into two pieces, and also emits neutrons. The pieces are new nuclei which are often radioactive, including I-131, Cs-134 and Cs-137. Energy is also released as heat.
Natural uranium contains only 0.7% U-235, with 99.3% U-238 which does not capture neutrons. Enriching uranium increases the proportion of U-235.
Nuclear Fusion
When two light nuclei join together to make a heavier atom, energy can be released in nuclear fusion.
Energy and nuclear reactions
Energy and matter can be interchanged with the amount of energy calculated from E=mc2 where c is the speed of light in a vacuum c = 3×108ms-1
Generating electricity
Methods for generating electricity include solar, wind, geothermal, nuclear, fossil fuel and hydroelectric. Each has advantages and disadvantages.
Isotopes
Atoms of the same element with the same atomic number (and same number of protons) can have different numbers of neutrons. Different types of the same element are called isotopes.
Atoms up to atomic number 82 have one or more stable isotopes, for example, oxygen-16 and oxygen-18. Atoms of unstable isotopes can break apart and emit radioactivity from the nucleus, including alpha, beta and gamma radiation.
Some isotopes (such as Uranium-235) can be made unstable when they ‘capture’ a neutron.
Alpha, beta and gamma radiation
Alpha radiation is particles made of two neutrons and two protons that have a charge of +2 and a mass of 4.
Beta radiation is fast moving electrons with a charge of -1 and a mass of 0.0005. They are not emitted from electron shells but by the nucleus when a neutron decays into a proton and an electron.
Gamma radiation is high energy electromagnetic waves emitted by the nucleus.
Gamma radiation has the lowest ionizing effect and highest penetrating ability. Alpha particles have the lowest penetrating ability and the highest ionizing effect.
Alpha particles will be absorbed by a sheet of paper or skin. Beta particles are absorbed by a sheet of aluminium. Thick sheets of lead or concrete walls are needed to absorb gamma rays.
Radioactive deacy
Radioactive emissions occur randomly with a certain probability.
Nuclear equations to represent the decay process for alpha and beta decay. For example:
22688Ra à 22286Ra + 42α (α is another way to write 42He2+ )
13153I à 13154Xe + 0-1 β (β is another way to write 0-1e– )
Neutrons can be written as 10n and protons can be written as 11p.
The larger number is always the mass number.
Half life is the time for the activity of a sample to fall by a half. The half lives of some important radionuclides are I-131 8days, Cs-134 2 years, Cs-137 30 years, C-14 5700 years, U-238 700million years
Detection of radioactivity
Alpha-particles, beta-particles and gamma rays can be detected using a Geiger-Müller (GM) tube which gives an electric pulse when ionizing radiation passes through.
Background radioactivity is the natural radioactivity from the lithosphere, biosphere and atmosphere.
Using Radioactivity
Radioactive isotopes are used for medical imaging, treating cancer, dating archaeological objects, and for nuclear power and nuclear weapons.
Precautions must be taking when handling, using and storing radioactive material including protective clothing, dosimeters, shielding.
Nuclear Fission
A Uranium-235 nucleus can capture a neutron and become unstable uranium-236.
Uranium-236 undergoes fission, where the nucleus breaks up into two pieces, and also emits neutrons. The pieces are new nuclei which are often radioactive, including I-131, Cs-134 and Cs-137. Energy is also released as heat.
Natural uranium contains only 0.7% U-235, with 99.3% U-238 which does not capture neutrons. Enriching uranium increases the proportion of U-235.
Energy
Energy can take different forms including kinetic, potential (chemical, nuclear, electrical, gravitational, elastic), thermal, and radiant (including light and sound).
Energy can be transferred (from one object to another) or transformed (to a different type).
Energy transfer diagrams show the transfer and transformation of energy.
The total amount of energy in a closed system is constant. (law of conservation of energy).
The unit of energy is Joules (J). Energy is calculated in different ways for each form of energy.
Power
Power is the rate of energy transfer and is the energy transferred in one second.
Power = Energy change ÷ time, P = E/t
The unit of power is Watts 
Nuclear power stations
A nuclear power station are thermal power stations and typically generate around 1GW (1 x 109W). In Sweden nuclear power produces around 40% of its electricity.
Nuclear power stations use enriched uranium or plutonium fuel in fuel rods for a controlled chain reaction.
A chain reaction occurs in a nuclear power plant when neutrons from one fission reaction start other fission reactions.
A nuclear reactor contains control rods which absorb neutrons and these are used to speed up or slow down the reaction.
Nuclear power stations are designed with a number of safety features to prevent the release of radioactive material, including a containment vessel, an isolated coolant and control rods which automatically drop in if there is a problem.
Nuclear power stations can also be used to produce radioactive material for medicine and plutonium for nuclear bombs.
Nuclear Fusion
In the sun and other stars, light atoms (such as hydrogen and helium) fuse together to make larger atoms and release energy in a process called nuclear fusion. This is how all elements are made.
Humans have achieved nuclear fusion in bombs (‘H-bombs’), but have not yet built a fusion reactor that produces more electricity than is needed to start the fusion reaction.
Effect of Radioactivity on Living Organisms
The Sievert (Sv) is the unit of radioactivity used to measure the effect on living organisms whatever the type of radiation. An X-ray exposes a person to around 1mSv.
Radioactive particles damage living cells by ionizing atoms as they pass through. This can cause cancer if DNA in cells is damaged by radioactivity.
Radioactive iodine (Iodine-131) can build up in the thyroid gland and cause thyroid cancer, the most significant cause of deaths from the Chernobyl nuclear disaster. This can be prevented by taking potassium iodide tablets.
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