Nuclear physics

• The nuclei of lighter elements contain fewer protons. This means they have a lower charge. Each alpha particle will therefore experience a smaller electric force acting on it and so deflect by a smaller angle.
• The nucleon number is the total number of protons and neutrons in a nucleus.
• Two nuclides are isotopes if they have the same number of protons and different numbers of neutrons.
• Nuclear fission happens in a nuclear reactor. A neutron collides with a large nucleus and is absorbed, creating an unstable nucleus. This nucleus then splits into fragments, releasing large amounts of energy and more neutrons, which can then collide with other nuclei.
• Nuclear fusion fuses 2 smaller nuclei to create 1 larger nucleus. Creating this larger nucleus releases energy.
• Stars generate their energy from the fusion of hydrogen and hellium nuclei.
• Hydrogen bombs use nuclear fusion to create an explosion
• If nuclear fission is not controlled, then the rate of nuclear fission can become faster and faster. This starts a chain reaction where each stage of fission produces more and more energy. This could lead to an explosion
• An unstable nucleus can become more stable over time by randomly emitting ionising radiation. This process is called radioactive decay
• Substances that decay radioactively are “radioactive substances”.
• Alpha radiation is produced by alpha decay. It is a helium nucleus
• Beta radiation is produced by beta decay. It is made up of electrons
• Gamma radiation is an electromagnetic wave produced by gamma decay
• Beta radiation is made up of high-energy electrons. It is more ionizing than gamma radiation but less ionizing than alpha radiation. It can pass through paper but is stopped by aluminium foil
• Gamma radiation is weakly ionizing. It does less damage than beta or alpha radiation but is stopped only by centimeters of lead or concrete
• Alpha particles contain 2 protons and 2 neutrons and have a mass of 4. Since the particles are big and heavy, alpha radiation is strongly ionizing. It does a lot of damage but can be stopped easily by a small amount of matter
• Uses of gamma radiation

  1. If a gamma-emitting isotope is inserted into the body we can trace the blood flowing around a patient's body
  2. Gamma radiation can also be used to sterilise equipment in hospitals
• Uses of beta radiation

  1. We can fire beta particles through paper in a factory to make sure that the paper being produced is the right thickness.
• Uses of alpha radiation

  1. A radioactive material fires alpha particles at a smoke detector.
  2. If there is smoke between the radioactive material and the smoke detector, then fewer alpha particles will reach the detector.
  3. This will set off the smoke alarm.
• In a uniform electric field, alpha particles will be attracted to the negative plate.
• In a uniform electric field, beta-particles will be attracted to the positive plate.
• Alpha particles are deflected less because they have a heavier mass
• In alpha decay, a nucleus loses an alpha particle - made of 2 protons and 2 neutrons. Since 2 protons get lost, a new element is formed
• In beta decay, a neutron in the nucleus decays to form a proton and electron. The electron is then ejected from the nucleus.
• In gamma decay, the composition of the nucleus is unchanged.
• The half-life is the average time taken for the number of radioactive nuclei to halve. Activity of a radioactive substance is measured in Becquerels (Bq).