Glossary of terms found in GCSE exam papers Absorption Radiation is “absorbed” when it stops passing through a material. For an alpha or beta particle, we say it is absorbed when it is stopped. Gamma radiation is attenuated – i.e. its strength is progressively reduced by increased thickness of absorber. Alpha Radiation particle consisting of two protons and two neutrons. Positively charged, large mass, relatively slowly moving, alpha particles are very highly ionising and penetrate matter weakly. Alpha emitters tend to be large nuclei. By losing two neutrons and two protons, the atomic mass falls, making the nucleus (slightly) more stable. Americium Am-241 is artificially produced in (nuclear power stations). It is an alpha emitter. It is the alpha source commonly used in schools and the source present in domestic smoke alarms. Atom Smallest part of matter that has chemical properties of an element. Atomic mass The total number of protons and neutrons in the nucleus. Atomic number The number of protons in the nucleus. Symbol Z. Background The number of background radiations detected (in a certain period of count time). Background Radiation that is always present, even when no (particular) radioactive radiation source is present. This radiation comes from natural sources and results from human activities – radioactive rocks (such as granite), radon in the air and cosmic rays are natural sources of background radiation; fallout from nuclear tests is an artificial source of background radiation. Becquerel The unit of measurement of activity of a source. One becquerel is one disintegration (decay) per second. Older sources in schools have activities shown in curie (or microcurie); 1 curie = 3.7 x 1010 Bq. Beta Radiation particle consisting of an electron. Negatively charged, (almost) no mass, relatively fast moving, beta particles are less ionising than alphas and correspondingly penetrate matter more. A neutron (charge 0, mass 1) can split into a proton (charge +1, mass 1) and an electron (charge -1, mass 0). This is how beta decay occurs. Boron Radioactive isotope B-12 has a halflife of 0.02s and is a beta emitter. It is a nice small nucleus to draw! Cancer When animal cells reproduce much too quickly, a lump called a tumour or cancer is the result. Radiation can damage the DNA of animal cells causing them to reproduce in this way. Chain reaction In a nuclear (fission) reactor, one nucleus is broken by a neutron hitting it. As it breaks, it releases more neutrons. These in turn hit more nuclei splitting them. This is referred to as a chain reaction. Charge Alpha and beta radiations are charged particles. Charges are often compared to the charge of one electron. So an alpha has a charge of +2 (electron’s worth) and a beta has a charge of -1 (the same as an electron). Charge is conserved: this means the total charge before a nuclear reaction is the same as the total charge after the reaction. Cobalt Co-60 is a common gamma source in schools. It has a halflife of 5.3 years. A school source that is 20 or 30 years old thus has an activity about 1/16 to 1/64 of its initial activity. Co-60 is also used in some hospitals for gamma therapy, and in some thickness measuring applications. Glossary of terms found in GCSE exam papers Composition Used to mean the same as structure or nature. What a nuclear radiation particle is made up of: e.g. an alpha’s composition / structure / nature is two neutrons plus two protons. Cosmic rays High energy rays from Space. Much of the cosmic ray radiation is absorbed by the Earth’s atmosphere, but some reaches ground level where it contributes to the natural background count. Pilots, aircrew, and frequent flyers are exposed to significantly higher doses of cosmic rays than others are. Counter A counter is attached to a detector to record the count or activity. The detector can produce a click that can be counted by someone; we have to use a counter when the radiation arrives too frequently to be counted. Decay When a radioactive nucleus changes, we say it decays. One decay per second is one becquerel. When the activity of a radioactive sample decreases over time we say it decays. Detector There are many ways to detect ionising radiation: Geiger-Muller tube, spark counter, film badge, solid state detector. In schools, generally a GM tube is used. Electron Negatively charged particle that (generally) orbits the nucleus of an atom. Emitter A source can be referred to as an emitter of radiation. For example, “an alpha emitter is placed 2cm from a GM tube…” Fission The splitting of large nuclei into two smaller nuclei. This process often releases neutrons. Gamma An electromagnetic wave. Gamma radiation is not a particle, so has no mass. It travels at the speed of light, and is very weakly ionising, but very highly penetrating. GM tube Geiger-Muller tube. A detector for ionising radiation. Halflife The time taken for the activity of a radioactive sample to halve. The time taken for the number of undecayed atoms in a radioactive sample to halve. Iodine Iodine isotopes (I-131 and more commonly now I-123) are used in thyroid gland diagnostic tests and treatments. Ionisation The process of knocking an electron from an atom, leaving it charged. The atom is then called an ion. Ionising Knocking electrons from an atom, leaving it charged. An atom (or molecule) that’s missing an electron is called an ion, and we say it is ionised. Isotope Two atoms that have the same number of protons, but a different number of neutrons are called isotopes of the same element. We sometimes use the word isotope to indicate that we are particularly concerned with what isotope it is. Mass The nucleus of an atom is where the atom’s mass is concentrated. Neutrons and protons have the same mass as each other. Electrons have (almost) no mass. Mass is conserved: this means the total mass before a nuclear reaction is the same as the total mass after the reaction – for example when beta decay occurs, a neutron (mass 1) changes into a proton (mass 1) and an electron (no mass). Glossary of terms found in GCSE exam papers Mass number The total number of protons and neutrons in the nucleus. The same as the nucleon number of an isotope. Mutation When a cell’s DNA is changed, but the cell is not killed, we say the cell has mutated. The information carried in the DNA is different. This mutation can be the cause of a cancer. Nature Used to mean the same as structure or composition. What a nuclear radiation particle is made up of: e.g. an alpha’s composition / structure / nature is two neutrons plus two protons. Neutron Uncharged particle in the nucleus. It has the same mass as a proton. A neutron (charge 0, mass 1) can split into a proton (charge +1, mass 1) and an electron (charge -1, mass 0). This is how beta decay occurs. The neutron number is the number of neutrons in an isotope. Neutron number has symbol N. (N = A – Z) Nuclear An equation showing the proton (atomic) number and mass (nucleon) equation number for each isotope and particle of radiation. Nuclear The way of showing proton (atomic) number and mass (nucleon) number notation for an isotope e.g. 241 Am is nuclear notation telling us that americium has 95 95 protons and 241-95=146 neutrons. Nucleon The total number of protons and neutrons in the nucleus. The same as the number atomic mass of an isotope. Symbol A. Nucleus Central part of an atom. It contains protons and neutrons. The nucleus is positively charged and accounts for nearly all the mass of an atom. Penetrating This describes how far a radiation can pass through matter such as air, power aluminium, lead, concrete. Alphas are weakly penetrating (being stopped by a few cm of air or by a sheet of paper), betas are more penetrating (being stopped by 20-30cm of air, or thin aluminium), and gamma is highly penetrating radiation (being reduced only by thick lead or very thick concrete). Proton Particle in the nucleus of an atom. Has mass 1 (compared with a proton), the same as a neutron. It has a positive charge (the same amount as an electron, but the opposite sign). Proton number The number of protons in a nucleus is the proton (or atomic) number for the element. The proton number tells us what element it is – a proton number of 1 is always hydrogen; proton number 8 is always oxygen. Radiation A particle or wave that is emitted and that travels away from its source in a straight path. Ionising radiation includes alpha, beta, gamma, X-ray, cosmic rays. Often (at GCSE) we are dealing with ionising nuclear radiation (radiation that causes ionisation and that comes from the nucleus of an atom). Alpha, beta and gamma are the three ionising nuclear radiations. Radiocarbon A way of finding out how long ago something died. Radiocarbon dating dating (or carbon dating) finds out how many years have gone by since a plant or animal died. It is often used to date fabric, wood, or other objects made from once living material. Radon Radon gas seeps out of granite rock. It is an alpha emitter. Its radiation contributes to the natural background radiation. Glossary of terms found in GCSE exam papers Source Often this means a sample of radioactive material that is sealed into a small container. In general, it means a radioactive material. Stable When a nucleus has given out a particle of radiation (and will not give out another one) it is stable. Stable isotopes are not radioactive; radioactive isotopes are unstable. Strontium Sr-90 is a beta emitter. School beta sources are Sr-90. It is commonly used in industrial applications such as measuring thickness of paper or aluminium foil. Structure Used to mean the same as nature or composition. What a nuclear radiation particle is made up of: e.g. an alpha’s composition / structure / nature is two neutrons plus two protons. Tracer A chemical that is injected into the (human) body to monitor how a part of the body is working. A tracer has two parts: it is a chemical that should be dealt with in a particular way (so doctors know where it should go) and it emits gamma rays (so a gamma camera can detect where it actually goes). Technetium-99 (Tc-99) is a very common isotope that can be attached to a many different chemicals, to investigate different organs and systems. Unstable Any nucleus that is radioactive is unstable. Uranium All isotopes of uranium are radioactive, although U-238 has a halflife of four and a half billion years. U-235 is an isotope that undergoes fission in (some) nuclear power stations.