Radiation

• Gamma radiation is a form of electromagnetic radiation that is highly penetrating and does not consist of particles.
• What are isotopes?

  Isotopes are atoms of the same element that have different numbers of neutrons but same number of protons.
• What are the 4 types of radiation?

  Alpha, Beta, Gamma, Neutron
• What are three types if ionising radiation?

  Alpha, beta, gamma
• Ionising radiation is radioactive particles that can ionise atoms they collide with. These alters the structure of the atoms by knocking off electrons which will leave behind ions.

  
• What are alpha particles?

  Alpha particles are positively charged particles consisting of two protons and two neutrons, emitted during radioactive decay.
• Characteristics of Alpha Particle:

  • Same as the nucleus of a helium atom
  • Move slowly - because of their size
  • Highly ionising
  • Move an inch in air
  • Stopped by paper/few cm of air
  • Deflected by electric fields and strong magnetic fields

  
• What are Beta Particles?

  High-energy or fast moving electrons.
• Characteristics of Beta Particles:

  • Weakly ionising
  • Travels one metre in the air
  • Stopped by 3MM of aluminium
  • Strongly deflected in an electric field and magnetic fields

  
• What are gamma rays?

  High-energy electromagnetic radiation.
• Characteristics of Gamma Rays:

  • Very weakly ionising
  • Stopped by several cm of lead/several metres of concrete
  • Not deflected in an electric or magnetic field (not affected)

  
• What is a non-ionising radiation?

  Non-ionising radiation is a type of electromagnetic radiation that does not have enough energy to ionize atoms or molecules.
• What is an unstable isotope?

  An unstable isotope is a type of atom that is radioactive and the nucleus is unstable, so it decays (breaks down) and emits radiation such as Carbon-14.
• When a nucleus decay happens it produces one or more types of radiation such as alpha, beta, gamma or neutrons. In this process the nucleus often changes into a new element.
• Where does background nuclear radiation come from?

  It is around us ALL the time

  • substances here on Earth - e.g: air, food, soil, rocks
  • living things
  • radiation from space (cosmic rays)
  • human activity - fallout
• The further the radiation can penetrate before hitting an atom and getting stopped, the less damage it will do along the way causing it to be less ionising
• Ionising radiation can be detected by: 1) Geiger-Muller detector - GM detector or photographic film
• Gamma emission always happens after beta or alpha decay.
• If a nucleus has excess energy, it loses this energy by emitting a gamma ray.
• What is neutron radiation?

  
  

  • Neutrons can be emitted from unstable nuclei which they are non-ionising but can cause other atoms to become radioactive. Stopped by materials such as concrete & water
• Neutrons can be absorbed by other atoms and cause them to become radioactive. These new radioactive atoms will decay by emitting ionising radiation.
• What happens when an atoms decay?

  Some nuclei are unstable and for it to become stable, they emit a particle which is called decaying.
• When an atom decays it is random and it cannot be affected by temperature/pressure, etc.
• What happens during alpha decay?

  During alpha decay, an atomic nucleus emits an alpha particle, which consists of two protons and two neutrons. This emission reduces the atomic number by 2 and the mass number by 4.
• During the alpha decay, the number of protons changed and the decayed atom changed into a new element.
• General equation for Alpha Decay?

  Atomic mass goes down by 4 and atomic number goes down by 2.

  
• What happens during beta decay?

  Neutron transforms into a proton, which stays in the nucleus, and a high energy electron, which is emitted. The decayed atom has gained a proton and it changed into a new element.
• During beta decay, the nucleus, a neutron changes into an electron (the beta particle which is ejected) and a proton (which stays in the nucleus)
• General equation for Beta Decay?

  
• What happens during gamma emission?

  It does not change the number of protons or neutrons in a nucleus. So, the mass and charge of the nucleus are unchanged.
• What happens during neutron decay?

  A neutron is ejected from the nucleus and the atomic number does not change. The mass of the nucleus has decreased because the total number of particles in the nucleus has decreased.

  
• The radioactivity of a sample always decreases over time
• What is the meaning of half-life?

  The time taken for half of the radioactive atoms now present to decay.
• Half-life is the time taken for the activity (or count rate) to fall by half.
• As the unstable nuclei all disappear, the activity which is the number of decays in a given time will decrease. So, the older a sample becomes, the less radiation it will emit.
• A short half-life means the activity falls quickly because lots of the nuclei decay quickly.
• Long half-life means the activity falls more slowly because most of the nuclei don't decay for a long time.
• Radioactivity is measured in becquerels (Bq). 1 Bq is 1 decay per second.
• The measuring of the half-life of a sample can be plotted as a graph.
• The half-life can be found on the graph by finding the time interval on the bottom (x-axis), corresponding to a halving of the activity on the vertical axis.