Topic 6 – Radioactivity

• What is an atom?

  a positively charged nucleus, consisting of protons and neutrons, surrounded by negatively charged electrons.
• The overall size of an atom is 1 * 10^-10 m.
• What are isotopes?

  Isotopes are atoms of the same element that have different numbers of neutrons. This affects the mass number of the element.
• What is the mass and charge of a proton?

  mass: 1

  charge: + 1
• What is the mass and charge of a neutron?

  mass: 1

  Charge: 0
• What is the mass and charge of an electron?

  Mass: 0.0005

  charge: -1.
• in an atom, the number of protons equals the number of electrons and is therefore neutral.
• in each atom its electrons orbit the nucleus at different set distances from the nucleus.
• An electron can move up to a higher energy level if it gains energy from absorbing electromagnetic radiation. (Higher electron shell).
• If an outer electron gains enough energy, it can move so far that it leaves the atom. This means that the atom it left became a positively charged ion.
• Alpha, Beta (B+ & B-), and Gamma are types of radiation emitted from an unstable nucleus. This happens in a random process. Beta and gamma radiation is ionizing.
• What is meant by background radiation?

  Radiation that is present in the environment from natural and man-made sources.
• Describe the origins of background radiation from Earth and space:

  Radiation comes from the sun, foods, cosmic rays, rocks, building materials and nuclear waste.
• A Geiger–Müller tube measures radiation by clicking every time it detects a particle. It is measured in decays per second (becquerels). a photographic film becomes darker the more it is exposed to radiation.
• What happens during alpha radiation?

  An alpha particle is equivalent to a helium nucleus. It emits 2 protons and 2 neutrons. They can only travel a few cm in the air and can get stopped by a sheet of paper because of their size.

  
• What happens during Gamma radiation?

  Gamma rays are a type of electromagnetic radiation so they do not affect the atom. This means that they are the least ionizing but can travel a few km and need to be stopped by a wall of lead.
• What happens during Beta minus and positive radiation?

  A Neutron turns into a proton and an electron. The atomic number increases as it gains a proton. For Beta positive, a proton turns into an electron and a neutron - therefore, the atomic number decreases. The radiation can travel a few meters and can be stopped by an aluminum sheet. It is moderately ionizing.

  
• What happens during neutron emission?

  A neutron is emitted from the nucleus of an atom. This just decreases the mass number.
• nuclei that have undergone radioactive decay often undergo nuclear rearrangement with a loss of energy as gamma radiation.
• Unstable atoms undergo radioactive decay, transforming into stable atoms over time.
• What is half-life?

  The average time taken for the number of radioactive nuclei in an isotope to halve.
• it cannot be predicted when a particular nucleus will decay but half-life enables the activity of a very large number of nuclei to be predicted during the decay process.
• How do you calculate the half-life of an isotope?

  keep dividing by 2 until you find your desired number. 1/2n (n is the amount of times you divide).

  
• Uses of Radioactivity:

  1. Household Fire (Smoke) Alarms2. Irradiating Food3. Sterilization of Equipment4. Tracing and Gauging Thicknesses5. Diagnosis and Treatment of Cancer
• Outside the body, beta, and gamma radiation are the most dangerous as they can penetrate inside the body and damage your vital organs. Inside the body, Alpha radiation is the most dangerous as it is the most ionising meaning that it could do the most damage inside the body. Where protective gear and stay out of the radiation zone.
• The lower the half-life of a radioactive isotope, the safer it is as it will decay less and there would be less chance for it to damage your body.
• What is the difference between contamination and irradiation?

  Contamination refers to the presence of harmful substances on a surface or in a material, while irradiation refers to the exposure of an object or substance to radiation. It is dangerous to consume a contaminated object and it is dangerous to stand near an irradiated object.
• Alpha emitters are usually injected near the tumor while Beta emitters are implanted next to the tumor. They both have a short half-life.
• How do PET scanners work?

  • Inject a radioactive tracer into the patient.
  • Tracer emits positrons.
  • Positrons collide with electrons, causing annihilation.
  • Gamma rays produced during annihilation are detected.
  • The computer processes gamma-ray data to create a detailed 3D image.
• Explain why isotopes used in PET scanners have to be produced nearby:

  To minimize decay during transport and to be cost-effective.
• What are the pros and cons of Nuclear energy?

  Pros: Clean, efficient, reliable, low greenhouse gas emissions. Cons: High cost, potential for accidents, long-term waste disposal.
• How does nuclear fission work?

  1. A slow-moving neutron is fired at an unstable, uranium nucleus causing it to split.
  2. A daughter nucleus is formed releasing lots of energy and 2-3 neutrons that cause a chain reaction - creating a lot of energy.
• How does nuclear fusion work?

  2 hydrogen nuclei collide with each other creating a lot of energy and a Helium nucleus. It needs 10,000,000 C and high pressure for it to work,
• How can nuclear fission be controlled?

  The uranium fuel rods are placed inside control rods that absorb all of the excess neutrons.

  
• thermal energy from the chain reaction of nuclear fission is used in the generation of electricity in a nuclear power station.
• Nuclear fusion does not happen due to the electrostatic repulsion of electrons at normal pressure.