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Radioactivity - Atoms and Radiation

This GCSE Physics radioactivity quiz will challenge you on atoms and radiation. Radioactive substances emit radiation from the nuclei of their atoms all the time, this is called radioactive decay. These nuclear radiations can be very useful but may also be very dangerous. At the surface of the Earth, there is a constant background radiation which comes from a variety of sources, including gases in the air, radioactive substances in the rocks, fallout from nuclear explosions and accidents at nuclear power stations, and also from space (cosmic radiation and radiation from the Sun).

To understand what happens to radioactive substances when they decay we need to understand the structure of the atoms from which they are made.

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The model of an atom that we use at GCSE was developed in the early part of the twentieth century. At the centre of the atom is the nucleus; this occupies only a very tiny volume of the whole atom. The nucleus is made up from protons and neutrons that are bound together by nuclear forces. The protons are said to have a mass of 1 atomic mass unit and a small electrostatic charge of +1. Neutrons are electrically neutral and also have a mass of 1 atomic mass unit. The nucleus therefore has an overall positive electrical charge and an atomic mass equal to the number of particles present. Surrounding the nucleus are 'shells' of electrons. These shells are also referred to as 'energy levels'. Electrons have a mass of just 1/1860th of an atomic mass unit so effectively, they do not contribute much to the mass of an atom. They have a charge of -1 and were the first of the subatomic particles to be discovered. An atom has the same number of electrons as protons so the electrical charges cancel out - atoms are neutral. An atom that is not neutral is not an atom, it is an ion.

In order to harness the power of radioactivity safely, it is important to understand the properties of different types of nuclear radiation. The three types of radiation are named using the first three letters of the Greek alphabet - alpha, beta and gamma. Alpha radiation is in fact a particle containing two protons and two neutrons, you should recognise this as being the same as a helium nucleus. It is the heaviest and slowest-moving type of radiation and can be easily stopped by paper or cloth. Beta radiation is also a particle, it is a fast-moving electron. This is harder to stop; it passes easily through paper and cloth but is stopped by thin sheets of metal such as aluminium. The third type of radiation (gamma radiation) is not a particle, it is a high frequency, short wavelength, high energy electromagnetic wave. It is the most penetrating form of radiation and is very difficult to stop. Alpha and beta radiation can both be deflected by magnetic and electric fields as they are charged particles. Beta particles are deflected more than alpha particles. All three types of radiation are ionising and can therefore damage living tissue. Gamma is the least ionising whilst alpha is highly ionising.

The dangers and uses that we make of radioactive sources depends on their penetrating power and half-life. The half-life is a measure of how long it takes for the radiation level to fall by a half, more strongly radioactive materials have shorter half lives.

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  1. What is background radiation due to?
    Cosmic rays account for most of the background radiation that we experience, however the other types can be major factors in specific areas
  2. What is an alpha particle?
    It is the nucleus of a helium atom
  3. What is a beta particle?
    Higher tier candidates may be asked to balance the atomic numbers and mass numbers in an equation showing what happens to an atom when it undergoes radioactive decay to produce an alpha or beta particle
  4. What is gamma radiation?
    It is the highest energy radiation of the electromagnetic spectrum
  5. Which type of radiation would be blocked by a thin sheet of paper?
    Alpha radiation also struggles to penetrate more than a few centimetres through the air
  6. Which type of radiation would be blocked by a thin sheet of aluminium - but not by paper?
    These fast-moving electrons are much smaller than alpha particles
  7. Which type of radiation would be blocked by several inches of lead - but not by a thin sheet of aluminium or paper?
    In nuclear reactors at nuclear power stations, gamma radiation is blocked from escaping by several metres of concrete
  8. What types of radiation can be deflected by electric and magnetic fields?
    Gamma radiation has no electrostatic charge
  9. What is the half-life of a radioactive isotope?
    This is why the count rate falls by half during one half life. It can be used to calculate how long it will take for the radiation from a particular sample of radioactive substance to drop to a safe level
  10. Which radiation is deflected more by electric and magnetic fields?
    Alpha particles are deflected less, despite having a greater charge, due to having a much greater mass than beta particles. They are deflected in opposite directions as they have opposite charges

Author: Martin Moore

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