topic 6

• ionising


  when radiation collides with electrons in the shells + knock them cut, so that atom loses an electron
• ionisation

  atom that loses an electron in ionising radiation causes ionisation
• penetration


  how far the atom can get through the material

  
  

  ALPHA: paper, skin, few cm of air

  BETA: thin metal

  GAMMA: thick lead

  
• electromagnetic radiation


  A form of energy transfer, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
• ionising radiation


  Radiation that can cause charged particles (ions) to be formed. It can cause tissue damage and DNA mutations.
• background radiation definition


  Ionising radiation that is around us all the time from a number of sources.
• background radiation comes from...

  → substances on earth (air, food, building materials, soil, rocks)

  → space (cosmic ray, rays from sun)

  → living things (radioactive material in all living things)

  → human activity (fall out from nuclear explosions, nuclear waste)

  → RADON GAS = 50%
• Geiger-Müller (GM) tube


  A device that can detect ionising radiation and is used to measure the activity of a radioactive source.
• alpha particle

  -made of two protons and two neutrons

  -emitted as ionising radiation from some radioactive isotopes

  -big, heavy, slow moving

  ↓∴ don't penetrate far into materials, stopped quickly

  ↓size: strongly ionising → collide with lots of atoms + knock electrons out of shells → creates many ions

  - electrically charged (positive charge) ∴ deflected by electric and magnetic fields

  - emitting alpha particle: decrease proton number of nucleus by 2 + nucleon number by 4

  
  

  speed: 15,000 km/s

  
• gamma ray

  - high-frequency electromagnetic wave

  -emitted after beta or alpha decay

  - very short wavelength

  - no mass (just energy in form of electromagnetic wave)

  - penetrate a long way into materials without being stopped

  - weakly ionising - tend to pass through rather than collide with atoms, eventually hit something + do damage

  - no charge ∴ not deflected by by electric or magnetic fields

  - emission has no effect on proton or nucleon number

  - if nucleus has too much energy: loses energy by emitting gamma ray

  
  

  speed: 3x10⁸ m.s

  
• decay (radioactive)


  - when an unstable nucleus breaks down

  - random process

  ↓ unaffected by physical conditions

  - when nucleus decays: emits α β γ or n

  ↓ often changes into a new element
• unstable

  An unstable nucleus in an atom is one that will decay and give out ionising radiation.
• activity

  The number of emissions of ionising radiation from a sample in a given time. Activity is usually given in becquerels (Bq).
• becquerel (Bq)

  The units for the activity of a radioactive object. One becquerel is one radioactive decay per second.
• half-life

  The average time taken for half of the radioactive nuclei in a sample of radioactive material to have decayed

  
  

  It is also the time taken for the activity of a source to fall to half its value.
• irradiate

  To expose something to ionising radiation (e.g. in order to sterilise food or medical equipment with gamma rays).
• sterilise


  To destroy microorganisms (e.g. bacteria, viruses and fungi) in or on an object. It can be carried out using radioactive sources.
• tracer


  A radioactive substance that is deliberately injected into the body or into moving water. It allows the movement of the substance to be followed by detecting the ionising radiation emitted.
• external radiotherapy


  Treatment of cancer by sending radiation into the body from outside.
• gamma camera


  A camera that detects gamma rays.
• internal radiotherapy


  Treatment of cancer by putting a radioactive source inside the body.
• tumour


  A lump formed of cancer cells.
• nuclear fission


  The reaction in which the nucleus of a large atom, such as uranium, splits into two smaller nuclei.
• nuclear fusion


  The reaction in which nuclei of light atoms, such as hydrogen, combine to make the nucleus of a heavier atom.
• chain reaction


  The sequence of reactions produced when a nuclear fission reaction is triggered.
• control rod


  A rod that can be lowered into the core of a nuclear reactor to absorb neutrons and slow down the nuclear chain reaction.
• daughter nucleus


  A nucleus produced when the nucleus of an unstable atom splits into two during fission or when a radioactive nucleus decays by emitting an alpha or beta particle.
• fuel rod


  A rod containing the nuclear fuel for a nuclear reactor.
• moderator


  A substance in a nuclear reactor that slows down neutrons, so that the nuclear fuel can absorb them more easily.