Radiation

• 2 uses of an ultra sound 


  Evaluate blood flow

  scan babies
• what stops each radiation

  
• are xrays, gamma rays, beta and alpha rays the most harmful?

  Gamma rays are the most harmful external hazard. Beta particles can partially penetrate skin, causing “beta burns”. Alpha particles cannot penetrate intact skin. Gamma and x-rays can pass through a person damaging cells in their path.
• Why is gamma used to treat cancer?

  gamma rays damages the cancer cells and prevents them from multiplying. After treatment, the tumor stops growing and, in many cases, it disappears over time.
• what is half life?


  Radioactive decay is a random process. A block of radioactive material will contain many trillions of nuclei and not all nuclei are likely to decay at the same time so it is impossible to tell when a particular nucleus will decay.It is not possible to say which particular nucleus will decay next, but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. they can use statistical methods to tell when half the unstable nuclei in a sample will have decayed. This is called the half-life.
• nuclear equation example...


  here helium's mass number is 4 and the atomic number is 2. therefore you take away 2 and 4 as seen in the diagram.

  
• What happened in Rutherford's gold foil experiment?

  Rutherford's gold foil experiment showed that atoms are mostly empty space, with the positive charge concentrated in a nucleus. He realized this because most of the alpha particles passed straight through the piece of gold foil, with just a few deflected at huge angles.
• The pupil records 45 disintegrations in 60 seconds.What is the background activity in the room?



  activity=number of disintegrations/time taken. 45/60=0.75Bq

  
• a Geiger counter...

  is an instrument that can detect radiation
• what is radioactive decay?


  Radioactive decay is the random process in which a nucleus loses energy by emitting radiation.
• why is radioactive decay spontaneous and random?

  Radioactive decay is a random process, which means that it is impossible to predict when a particular radioactive nucleus will decay. It is also spontaneous - you cannot cause or influence the decay.
• helium has a mass number of 4 as 219-215=4 as seen in diagram

  
• Doctors also use radioactive sources for a number of reasons, eg:

  • sterilisation of surgical instruments
  • beams of gamma rays, called a gamma knife, can be used to kill cancerous tumours deep inside the body

  These beams are aimed at the tumour from many different directions to maximise the dose on the tumour but to minimise the dose on the surrounding soft tissue. This technique can damage healthy tissue, so careful calculations are done to establish the best dose - enough to kill the tumour, but not so much so that the healthy tissue is damaged.
• In medical applications that involve using radioactive sources, efforts are made to ensure that irradiation does not cause any long-term effects. This is done by considering:

  • the nature of decay (alpha, beta or gamma)
  • the half-life (long enough for the isotope to produce useful measurements, but short enough for the radioactive sources to decay to safe levels soon after use)
  • toxicity
• disadvantages of irradiation

  • it may not kill all bacteria on an object
  • it can be very harmful - standing in the environment where objects are being treated by irradiation could expose people’s cells to damage and mutation
• Advantages of irradiation

  • sterilisation can be done without high temperatures
  • it can be used to kill bacteria on things that would melt
• what are the effects of radiation?

  effects of radiation on the body....

  
• Managing the risks

  The risk associated with radioactive materials depends on the amount of exposure. Being exposed to highly radioactive materials or being exposed to radioactive materials for long periods of time or on a regular basis increases the dose received which, in turn, increases the risk.
• Background radiation

  Radioactive materials occur naturally and, as a result, everyone is exposed to a low-level of radiation every day. This exposure comes from a mixture of natural and man-made sources.

  
• most common measure of radiation...

  The simplest measure of radioactivity is the Becquerel (Bq). This is a measure of the activity of the nucleus. The activity is the number of decays per second from an unstable nucleus.
• why is alpha radiation the least dangerous?


  alpha radiation has a low penetrating ability, so alpha radiation is stopped by skin (so is low risk)
• what is half life?


  Half-life is the time it takes for half of the unstable nuclei in a sample to decay
• describe alpha radiation


  has 2 protons and 2 neutron's (helium nucleus)
• describe beta radiation


  high energy electron
• describe gamma radiation 


  an electromagnetic wave
• strontium 90 has a half life of 28 years, how long will it take to fall to less than 1% of its original activity? 


  Start with 100% of the original activity:

  • After 1 half-life (28 years):  100 \ 2 = 50\%

  • After 2 half-lives (56 years):  50 \ 2 = 25\%

  • After 3 half-lives (84 years):  25 \ 2 = 12.5\%

  • After 4 half-lives (112 years):  12.5 \ 2 = 6.25\%

  • After 5 half-lives (140 years):  6.25 \ 2 = 3.125\%

  • After 6 half-lives (168 years):  3.125 \ 2 = 1.5625\%

  • After 7 half-lives (196 years):  1.5625 \ 2 = 0.78125\% so approximately it will take 169 years.
• what is background radiation?


  the amount of ionizing radiation that is always present in the environment, and is not caused by deliberate human activity.