Radioactivity and Particles Quiz

Radioactivity and Particles

• Atom Structure: Atoms consist of a positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons.
• Nucleus: The nucleus contains almost all the atom's mass. The radius of the nucleus is much smaller than the atom's overall radius.
• Particle Properties:
  • Protons: Relative mass 1, Relative charge +1
  • Neutrons: Relative mass 1, Relative charge 0
  • Electrons: Relative mass 0.0005, Relative charge -1
• Isotopes: Atoms of the same element can have different numbers of neutrons, these are called isotopes.
• Radioactive Decay: Unstable nuclei undergo spontaneous transformation into a more stable nucleus by releasing radiation. This process is random and unpredictable.
• Decay Processes:
  • Alpha Decay: A heavy nucleus emits an alpha particle (helium nucleus - 2 protons and 2 neutrons). These are highly ionizing and weakly penetrating, stopped by paper or a thin sheet of metal.
  • Beta Decay: The nucleus changes by converting a neutron into a proton and an electron (beta particle). This changes the atomic number and creates a different element. They are moderately ionizing and moderately penetrating, stopped by thin sheets of aluminum.
  • Gamma Radiation: A nucleus with excess energy emits a gamma ray. They are a form of electromagnetic radiation, are lowly ionizing, and highly penetrating, requiring several centimeters of lead for stopping.
  • Neutron Emission: In neutron rich nuclides, neutrons can be emitted.
• Detecting Radiation: Methods include photographic film badges, Geiger-Müller tubes.
• Background Radiation: Weak radiation from external sources.
• Sources of Background Radiation: Cosmic rays, radioactive rocks, food and drink (containing isotopes), industrial fallout, medical sources (X-rays, MRI), nuclear power.
• Activity: The number of decays per unit time, measured in becquerels (Bq).
• Half-Life: The time taken for half of the nuclei in a sample to decay (or for the activity to halve). A constant for a given isotope, independent of starting amount.
• Uses of Radioactivity:
  • Medicine: Sterilization of equipment, diagnosis and treatment using tracers (short half-life gamma emitters), destroying tumors (high dose gamma emitters)
  • Industry: Thickness monitoring of materials using beta radiation, smoke detectors (using alpha radiation).
• Contamination vs. Irradiation: Contamination is when a radioactive source is on or in an item, making it radioactive. Irradiation occurs when an item is near or exposed to a radioactive source, but the source isn't on/in the item therefore the object remains non-radioactive.
• Safety Measures: Minimizing exposure time, maximizing distance, using shielding.

Fission and Fusion

• Nuclear Fission: The splitting of a heavy nucleus (like Uranium-235) into lighter nuclei. This releases a large amount of energy. Used in nuclear power plants and weapons.
• Fission Process: The process often starts by a neutron hitting the nucleus, which splits into two or more fragments and releases further neutrons, causing further reactions and a chain reaction of splitting. Control rods and moderators are used to control the speed and number of these splits and to prevent the reactor from melting down.
• Nuclear Fusion: Combining light nuclei (like hydrogen) into a heavier nucleus. Also releasing a large amount of energy.
• Fusion Process: This process needs extremely high temperatures and pressures to overcome electrostatic repulsion between protons and occurs in stars, rather than being currently utilized on earth in a controlled manner.