P6

• Isotopes

  • atoms of the same element - same number of protons but different number of neutrons
  • different nuclear mass but same nuclear charge
  • most are unstable and radioactive isotopes
  • Give out nuclear radiation and may decay into another element
• Nuclei decay

  • spit out one or four types of radiation
  • Alpha, gamma , beta , neutron
  • nucleus change into new element
  • charge changes and mass
• Alpha particles

  • alpha particle
  • two neutrons and two protons
  • relative mass of 4 and charge of +2
  • Big, heavy and slow moving
• beta particles

  • an electron with no mass
  • Charge of -1
  • move quite fast and are quite small
  • every beta particle emitted- neutron turns into a proton
• Gamma ray

  • EM wave
  • get rid of extra energy after alpha and beta
  • no mass, no charge
  • Just energy and don't change element of nucleus
• Neutron

  • nucleus has a lot of neutrons
  • protons stay the same and has a different nuclear mass
  • becomes an isotope of same element
• Penetration

  • when radiation travels through a material- collides with atoms in the material
  • only penetrate till m material absorbs radiation
• Penetration- Alpha

  • don't get far - shortest range in a material
  • blocked by paper
• Penetration- Beta

  • travel quite far before hitting an atom
  • blocked by thin aluminium
• Penetration- Gamma

  • travel a long way before hitting an atom
  • longest range
  • Blocked by thick lead
• Count rate

  • Number of radioactive particles that reach a detector in a given time
  • the further the radiation travels, the higher chance it will be absorbed ny the material
  • Count rate decreases the further the detector from the radioactive source
• Alpha radiation α

  • mass number increases by 4- loses two protons and two neutrons
  • Atomic number decreases by 2- two less protons
• Beta radiation β

  • mass number doesn't change- lost a neutron but gained a proton
  • atomic number increased by 1 - new proton
• Gamma radiation γ

  • mass num er and atomic number doesn't change
• energy levels

  • electrons sit in different energy levels or shells
  • energy levels at different distance form nucleus
  • inner electron can move up levels if it absorbs EM radiation with the right amount of energy
  • moves up to partially filled or empty shell and is considered excited
  • Moves down a level- to original level , energy carried away by EM radiation
  • Em spectrum radiation depends on its energy
  • Higher energy means higher frequency of EM radiation
• Ionises

  • An atom is ionised if it loses an electron
  • outer electron absorbs radiation with enough energy so it can leave the atmosphere and is now a free electron
  • atom is now positive- more protons than electrons
  • atoms can lose more than one electron- the more electrons the greater the positive charge
• Nuclear radiation

  • Alpha, beta, gamma radiation- ionise atoms and called ionising radiation
  • ionisation power is different for different ionising radiation
  • alpha particles have highest ionising power as it doesn't travel far into material before hitting an atom
  • Gamma particles- lowest ionising power
• Fluorescent tubes

  • use excited electrons to produce light
  • tubes contain mercury vapour- electrons ionised some of the mercury atoms producing more free electrons
  • flow of free electrons collide with electrons in the mercury atoms, mercury atoms are excited to higher energy levels
  • when return to original energy levels they emit radiation in the UV rage of EM spectrum
  • phosphor coats the inside of the tubes and absorb the radiation exciting its electrons to higher levels
  • elects cascade down the energy levels emitting many different frequencies of radiation all in the visible part of EM
• Half life

  • radioactivity of a sample always decreases over time
  • radioactivity decay is a random process
  • make predictions of large umbers of nuclei in isotope
  • radioactive isotopes decay at different rates
  • activity- number of unstable nuclei that decay measured in (Bq)
  • Geiger muller tube detects radiation from decaying nucleus
  • as more unstable nuclei decay, activity decreases
  • HALF LIFE- half-life of a source is the average time taken for its activity to half
  • Short life- activity falls quickly- lots of decay in a short time
  • Long life falls more slowly- most nuclei don't decay
• Ionising radiation harms living cells

  • some materials absorb ionising radiation - enter living cells and interact with molecules
  • lower doses of ionising radiation can cause mutations in DNA which causes cells to divide uncontrollably - cancer
  • higher doses kill living cells - radiation sickness
• Outside the body

  • beta and gamma is most dangerous
  • can still get inside delicate organs as they can pass through skin
  • Alpha can't penetrate the skin
• Inside the body

  • Alpha particles most harmful because its most ionising and do all their damage in local areas
  • Beta and gamma are less dangerous as they're less ionising
  • Gamma will most likely pass straight out
• Irradiation 


  irradiation- radiation from a radioactive source reaches an object

  • risk of irradiation is how likely ab object will be irradiated by the source and depends on the distance from he source and the type of radiation that the source emits
  • As distance increased from source, amount of radiation reaching the point decreases as is the irradiation rush for any source is lower at larger distance
  • irradiation is shorter with shorter range of radiation such as alpha
• Contamination

  • How likely an object can be contaminated
  • No contamination with a solid if not touched
  • Contamination with gas as it can move around and come into contact with an object
  • gases are dangerous as they can be inhaled contaminating from the inside
  • contamination leads to high risk of irradiation as the distance is so small
  • irradiation is temporary if source is taken away
  • Contamination acts longer- as atoms causing contamination lingers and can cause more harm
• Hazards and dependent on half-life

  • the Lower the activity- the safer it is
  • Lower activity- longer half-life
  • after a while, longer half-life lasts longer and is more dangerous to be around
  • balance source of being high enough activity but least harmful
• Tracers in medicine

  • radioactive isotope that emit gamma radiation are used as tracers
  • injected or injected to see how parts of the body work
  • progress is followed externally by radiation detectors
  • relatively short half-life so that radioactivity quickly disappears
  • all use gamma sources- can penetrate tissue so pass out the body and are detected as alpha is more dangerous inside the body
• radiotherapy

  • used to treat cancers
  • radiation directed carefully and at a specific dosage so it doesn't kill too many normal cells
  • makes patient ill as a little damage is done to normal cells
• Treat cancer externally

  • gamma rays
  • focused on tumour using narrow beam
  • patient stays still and beam is rotated round them
  • minimised exposure to normal cells so damage is limited
  • dose with time in between to let cells repair and replace
• Treat cancer internally

  • implants contain beta-emittiners are placed next to or inside tumour
  • beta particles damage the tumour cells with short range so damage to healthy cells ar limited
  • alpha particles injected into tumour- strongly ionising and does a lot of damage with a short range
• Nuclear fission

  • splitting up of big atomic nuclei
  • used to release energy from large unstable nuclei by splitting into smaller nuclei

  Two ways it can occur:

  • Spontaneously - fission is unforced and happens by itself
  • By absorbing a neutron - nucleus absorbs neutron making it unstable and splits

  Gives out a lot of energy - transferred into kinetic energy store of the fusion product or carried away by gamma rays
• Nuclear fission - chain reaction

  1. Nuclear fission of Uranium- shapes if a slow moving neutron is absorbed into uranium nucleus- makes nucleus unstable and split
  2. each time uranium nucleus splits up, spits out two or three neutrons some absorbed by other nuclei causing them so split (chain reaction)
  3. nuclear powers generate electricity through chain reaction to heat water to make steam and drive a turbine connected to a generator
• Disadvantages of nuclear power

  • disposal of waste - highly reactive and have long half-lives
  • difficult and expensive to dispose safely
  • Nuclear fuel is cheap but initial set up is expensive
  • Dismantling nuclear plants takes decades
  • uncle power carry risks of leaks
• Nuclear fusion

  • Two light nuclei join to create a large nucleus
  • Fusion releases a lot of energy - all energy released in stars come from fusion
  • energy is difference in mass between the original nuclei and the new nucleus
  • xtra mass is converted into energy and released
  • Doesn't create radioactive waste
  • Only happens at high temperatures about 10 million degrees and high pressured and strong electromagnetic field to keep the hydrogen