Radioactivity

Radioactivity

1. An introduction to radioactivity

   • The term radioactivity was given to uranium by Marie Curie who said that it gave out radiation all the time
     • We can use a Geiger counter to detect radioactivity, where the counter will click each time a particle from a radioactive substance enters the Geiger tube
       • Ernest Rutherford discovered two types of radiation:
         • - alpha radiation who’s symbol is α - beta radiation who’s symbol is β
           • Scientists later discovered a third type, gamma radiation, written γ
       • The nuclei of atoms of radioactive elements are unstable
         • An unstable nucleus becomes stable by emitting alpha, beta or gamma radiation – this is known also as decaying

2. Alpha, beta and gamma radiation

   • Alpha particles are helium nuclei, and cannot even penetrate a human hand or piece of paper
     • Beta particles are negative electron which can penetrate a thin aluminium sheet
       • Radiation from a radioactive substance can knock electrons out of atoms. These atoms become charged because they have lost electrons.
     • Gamma rays are electromagnetic waves which can penetrate some concrete
   • Beta’s range is about 1m in air
   • Gamma radiation’s range is approximately 10,000km – but we often say it is unlimited

3. Radioactive half-life

   • Atoms of elements can contain identical amounts of protons but different amounts of electrons – these are called isotopes
     • The activity of a radioactive substance is the number of atoms that decay per second
       • The number of clicks per minute that a Geiger tube detects from a radioactive substance is the count rate
     • The time taken for the count rate of a radioactive substance to half is its half-life
     • The half-life of a radioactive isotope is the time it takes:
       • - for the number of nuclei of the isotope in a sample to half
         • - for the count rare of the isotope to fall to half its initial value

4. Useful radiation

   • Radioactivity can be harmful to us and our skin, but it serves some uses
     • Automatic thickness monitoring
       • - if the thickness of the foil increases too much, the detector reading drops
       • - the detector sends a signal to the rollers to increase pressure on the metal sheet
     • Radioactive tracers can be used for medical purposes. Patients can drink a glass of water containing a small amount of a radioactive substance, if they want to test their kidneys. The substance would simply flow in and out of healthy kidney, but a blocked kidney would not allow the substance to exit for a lot longer
       • - This means that for a normal kidney the radioactive reading goes up then down
         • - …and for a blocked kidney, the reading goes up and stays up
           • Radioactive dating is a process where we can find out how old things are by using radioactivity. There are two types…
             • Carbon dating is used to find the age of ancient wood and trees
             • Uranium dating is used to find the age of igneous rocks