Radioactivity

Radioactivity

1. ATOMIC STRUCTURE

   • 3 sub-atomic particles: protons,neutrons and electrons
     • PROTON - relative mass of 1 - relative charge of 1
     • NEUTRON- relative mass of 1 - relative charge of 0
     • ELECTRON- relative mass of 0 - relative charge of -1
   • protons and neutrons are found in the nucleus, whereas electrons are found in the outer shells
     • protons=neutrons so atoms are electrically neutral overall
   • When atoms lose or gain electrons they form particles called IONS:
     • if an atom loses one or more electrons, it becomes a positively charged ion
     • if an atom gains one or more electrons, it becomes a negatively charged ion
   • ISOTOPES
     • Isotopes - atoms of an element with different numbers of neutrons, they have the same proton number, but different mass numbers

2. PROPERTIES OF RADIATION

   • There are three main types of ionising radiation emitted from the unstable nuclei of radioactive atoms - these are alpha, beta and gamma radiation.
     • Alpha radiation consists of alpha particles. An alpha particle is identical to the nucleus of a helium atom --> two protons and two neutrons.
     • Beta radiation - high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed, leaving the new proton behind in the nucleus.
     • Beta radiation - high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed, leaving the new proton behind in the nucleus.
     • Gamma radiation is very short wavelength, high frequency electromagnetic radiation. This is similar to other types of electromagnetic radiation, such as visible light and X-rays, which can travel long distances.
   • Radiation can be absorbed by substances in its path.
     • For example, alpha radiation travels only a few centimetres in air, beta radiation travels tens of centimetres in air, and gamma radiation travels very large distances.
     • All types of radiation become less intense as they travel further away from the radioactive material this is because the particles or rays become more spread out.
       • The thicker the substance, the more the radiation is absorbed. The three types of radiation penetrate materials in different ways.
         • Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a human hand.
         • Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.
           • the 3 types are given off by rocks, food, building materials, air and cosmic rays around us --> background radiation
         • Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead or many metres of concrete.
       • IONISATION
         • when radiation collides with neutral atoms or molecules it alters their structure by knocking off electrons - this will leave bbehind ions
         • USES OF RADIOACTIVITY
           • MEDICAL USES - gamma rays can be used to destroy cancerous cells or to sterilise medical equipment
           • TRACERS - a tracer is a small amount of radioactive material used to detect things eg. leak in pipe
           • NUCLEAR FISSION
             • Each fission releases energy in the form of heat. In a nuclear power plant this heat is used to boil water, which is used to drive turbines etc. The energy from each reaction is very small, but there are billion of reactions every second. The waste products from these reactions are radioactive, which is why nuclear power plants are controversial.
   • HALF LIFE
     • The decay of radioisotopes can be used to measure the material's age. The HALF LIFE of an atom is the time taken for half of the radioisotopes in a sample to decay
       • It is not possible to predict when an individual atom might decay. But it is possible to measure how long it takes for half the nuclei of a piece of radioactive material to decay. This is called the half-life of the radioactive isotope.

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