P7 - Radioactivity

• Before 1911, scientists believed in the plum pudding model of the atom (the atom consisted of positive matter with negative charges (electrons) dotted around)
• Rutherford fired positive alpha particles at thin gold foil in a vacuum
• Rutherford's experiment showed some alpha particles were deflected by something.
• Rutherford's experiment proved the existence of the nucleus.
• The mass number is the total number of protons and neutrons
• The atomic number is the number of protons/electrons
• Isotopes have the same number of protons but different number of neutrons.
• Isotopes are different types of an element.
• Isotopes of the same element have the same chemical properties, but different physical properties.
• An ion is an atom that has gained or lost an electron, making its charge positive/negative.
• Excitation is where electrons move to a higher energy level by absorbing electromagnetic radiation.
• De-excitation is where electrons move down to a lower energy level by giving out electromagnetic radiation.
• The main sources of background radiation include radon gas in the air, cosmic rays from the sun, rocks, and food and drink.
• Decaying: Where atoms with unstable nuclei change by emitting radiation.
• Alpha particles consist of 2 protons and 2 neutrons
• Beta particles are high speed electrons emitted from the nucleus.
• Beta radiation occurs when a neutron turns into a proton and emits a beta particle.
• Gamma radiation is an electromagnetic wave emitted by a nucleus which has too much energy following alpha/beta decay
• Ionising radiation can ionise atoms in the body, turning them into ions, causing mutations in DNA and leading to cancer
• Ionising radiation can kill cells
• You can reduce the risk of radiation by:

  • reducing time in contact with radiation
  • stay as far away from radioactive sources as possible
  • use shielding
• An unstable nucleus gives out radiation to become more stable. This is called radioactive decay.
• Radioactive decay is a random process
• Half life is the average amount of time it takes for the number of unstable nuclei to halve.
• Activity is the number of unstable atoms that decay per second.
• Activity is measured in Becquerels.
• Count rate is the number of decays per second recorded by a detector.
• Radioactive isotopes can be used to help doctors diagnose and treat medical disorders.
• Different radiation atoms have different radioactive power.
• Radioactive Tracer: where an isotope traces the flow of a substance through an organ
• A tracer is administered by drinking water containing the radioactive isotope/injecting the radioactive isotope into the patient.
• Tracers will pass through a kidney easily if it's healthy, and will be trapped in a blocked kidney, making it easy to spot which kidney is blocked.
• Radioactive iodine can be used as a tracer because:

  • It has a short enough half life to disappear in a few weeks, not doing damage to the patient
  • It has a long enough half life to get results
  • It decays into a stable product
  • It emits gamma radiation (detectable outside the body)
• Gamma cameras take images of internal organs that have taken up a radioactive isotope.
• Gamma-emitting isotopes are injected before a patient is placed under a gamma camera.
• Gamma cameras are designed with a collimating grid which only detect rays travelling parallel to the collimator.
• The radioactive isotope needs to emit gamma radiation, and have a half-life:

  • long enough for images to be formed
  • short enough that it decays shortly after images are formed
• A gamma knife produces a narrow beam of gamma radiation that destroys cancer cells precisely.
• Gamma knives use cobalt-60.
• Gamma is used in a gamma knife as it can penetrate further than alpha or beta