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Radioactivity

Direction of Radioactivity
  • Background Radiation: A small amount of radiation is around us all the time because of radioactive materials in the environment. It mainly comes from natural sources such as soil, rocks, air, building materials, foods and drink — and even space
Geiger-Müller (GM) Tube 
  • This detects α, β, and γ
  • The ‘window’ is thin enough for alpha particles to pass through
  • If an alpha particle enters the tube, it ionizes the gas inside
  • This sets off a high-voltage spark across the gas and a pulse of current in the circuit
  • A beta particle or gamma radiation has the same effect
  • It can be connected to a rate meter (tells the counts per seconds) or a scaler (tells the total number of particles or bursts of gamma radiation)
Characteristics of the 3 Kinds of Emissions
  • Radioactive emissions occur randomly over space and time
Radioactive Decay
  • Radioactive Decay: A radioisotope (unstable arrangement of neutrons and protons) is altered to make a more stab;e arrangement.
    • The parent nucleus becomes a daughter nucleus and a particle (decay products)
  • Alpha Decay:
    • An element with a proton number 2 lower than that of the parent and nucleon number 4 lower than that of the parent and an alpha particle are made
    • For example: Radium-226 nucleus → Radon-222 + helium-4 nucleus
  • Beta Decay:
    • A neutron changes into a proton, an electron and an antineutrino. So an element with the same nucleon number but with a proton number 1 higher.
    • For example: iodine-131 → xenon-131 + beta particle + antineutrino
  • Gamma Emission:
    • Gamma emission by itself causes no change in mass number or atomic number; they just emit energy
    • Some isotopes do not change in mass or atomic number, however they emit energy as their particles rearrange themselves to become more stable
Half Life
  • Half-life of a radioisotope is the time taken for half the nuclei present in any given sample to decay
  • Some nuclei are more stable than others
Safety Precautions
  • Radioactive material is stored in a lead container
  • It is picked up with tongs, not bare hands
  • It is kept away from the body and not pointed at people
  • It is left out of its container for as short a time as possible
Atomic Model
  • Atoms consist of:
    • Nucleus: The central part of the atom made of protons (positively charged) and neutrons. These two types of particles are nucleons. They are bound together by the strong nuclear force
    • Electrons: They are almost mass-less particles which orbit the nucleus in shells
Rutherford’s Experiment
  • A thin gold foil is bombarded with alpha particles, which are positively charged
  • Most pass straight through, but few are repelled so strongly that they bounced back or deflected at large angles
  • Rutherford concluded that the atom must be largely empty space, with its positive charge and most of its mass concentrated in a tiny nucleus.
Properties of Magnets

  • The nucleus is composed of protons and neutrons
  • Proton number is the number of protons in an atom
  • Nucleon number is the number of nucleons (protons + neutrons) in an atom
Isotopes
  • Isotopes are atoms of the same element that have different numbers of neutrons. E.g. Carbon-12 and Carbon-14
  • There are non-radioactive isotopes and radioisotopes
  • Radioisotopes are unstable atoms which break down, giving radiation
    • Medical use: Cancer treatment (radiotherapy) — rays kill cancerous cells using cobalt-60
    • Industrial use: To check for leaks — radioisotopes (tracers) added to oil/gas. At leaks, radiation is detected using a Geiger counter
    • Archaeological use: Carbon-14 is used for carbon dating
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