Radioactivity ch 22

• Number of neutrons = nucleon number - proton number in a nucleus
• Isotopes are atom of the same element that have the same number of protons but different numbers of neutrons
• Nuclear decay is a random process by which an unstable atomic nucleus loses its energy by emission of electromagnetic radiation of particles
• Nuclear decay is known as radioactive decay or radioactivity
• three types of nuclear emission

  1. alpha particles (a-particles)
  2. beta particles
  3. gamma ray ( Y-ray)
• a-particle have the highest relative ionising effect, the least relative penetrating ability
• B-particles has medium relative ionising effect, medium relative penetrating ability
• Y-ray has the lowest relative ionising effect, highest relative penetrating ability
• nature of a-particle:

  An a-particle consists of two protons and two neutrons tightly bound together. It is identical to a helium nucleus
• nature of b-particle:

  an b-particle is a fast-moving electron ejected from the radioactive nucleus
• nature of Y-ray:

  A Y-ray is electromagnetic radiation emitted by a radioactive nucleus with excess energy
• when a nucleus undergoes alpha-decay, it emits an a-particle and the nucleon number decreases by four and the proton number decreases by 2
• The total charge before and after a nuclear emission should be the same
• when a nucleus undergo beta-decay, it emits a b-particle ( an electron) and the nucleon number remains the same and the proton number increases by one
• when nuclei undergo alpha-decay or beta-decay, gamma radiation is emitted
• Ionising radiation is radiation with high energies that can knock off electrons from atom to form ions
• background radiation refers to nuclear radiation in environment where no radioactive source has been deliberately introduced.
• 3 Artificial sources of radiation

  1. Medical X-rays
  2. building materials
  3. waste products from nuclear power station
• 3 natural sources of radiation

  1. Rocks
  2. radon gas in the air
  3. food and drinks eg. food high in potassium (banana, carrots and salt)
• Geiger-Muller is used to measure radioactivity
• SI unit for radioactivity is Becquerel ( Bq)
• 1 becquerel is equals to 1 disintegration per seconds
• disintegration refers to the amount of ionising radiation when a ( to be continued )
• measure of radiation is the rate of count per unit time, known as count rate
• unit for count rate = counts per seconds ( counts/s)
• every nuclide has a fix rate of decay, because most has a fixed half-life
• the half-life of a radioactive nuclide is the time taken for half of the nuclei of the nuclide in any sample to decay
• decay curve is the graph of the number of atoms or count rate against time
• the number of atoms ( maybe count rate ) will never go to zero in a decay curve
• radioactivity is a random process in which an unstable atomic nucleus loses energy through emission of electromagnetic radiation of particles