Decay

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					                   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.

				
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Lingjuan Ma Lingjuan Ma MS
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