Physics-> Radioactivity

• Describe an experiment to show that only beta particles are emitted?

  1) Take background radiation reading (without the source)

  2)Use a piece of paper between the source and the detector (alpha particles would be stopped by paper, however beta particles should be able to pass through) The reading on the detector would be unchanged, suggesting no alpha particles are emitted.

  3)Use a few mm of aluminium between the source and the detector.

  
  

  4)The reading on the detector should now be equal/similar to the background reading, because the beta particles are stopped by a few mm of aluminium.
• Use shielding:

  wear gloves when handling a radioactive material and store it in a lead-lined box when not in use to absorb the radiation
• Increase the distance between source and living tissue:

  use tongs to

  handle the radioactive source and keep your distance so that some of the radiation is absorbed by the air before it reaches you.
• Reduce the exposure time:


  spend as little time as possible with the material

  to reduce the exposure to its emissions.
• When handling a radioactive source:

  • Wear gloves.

  • Minimise your exposure time.

  • Maintain your distance from the source.

  • Use tongs to increase your distance from the material.

  When storing a radioactive source:

  • Keep it in a lead-lined container.
• What can ionizing radiation do to cells ?

  Ionising nuclear radiation can kill cells or mutate them which can lead to cancer.
• Why is the half life not more than 6 hours ?

  If the half-life was longer than 6 hours, then a radioactive substance would be active in the body for a long time.
• Why is the the half life of the tracer not shorter that 6 hours ?

  If the half-life was shorter than 6 hours, it might be insufficient time for investigation. Also, it takes a few hours for the tracer to spread round the body.
• What happens in radiotherapy?

  In radiotherapy, a high dose of gramma rays is carefully directed to cancerous cells in order to kill them, while keeping

  the dose to the rest of the body as low as possible.
• Why is it good That gamma rays are highly penetrative and have low ionizing effect?

  Gamma rays are highly penetrative, so they pass out of the

  body easily and be detected, and they are weakly ionising, so they don't cause

  much damage to the patient's cells.
• How are gamma rays used to diagnose cancer?


  The path of the substance is tracked by a detector outside of the body in order to diagnose cancer.
• What is a medical tracer?

  A medical tracer is a radioactive substance that is put into a patient's body.
• What can gamma rays be used for ?

  Gamma rays can be used to diagnose and treat cancer.
• Why should the half life of the beta source be long ?

  The half-life of the β-source should be

  long, so that the count rate stays fairly constant making it easier to control thickness with and so

  that it doesn't need replacing too often.
• What happens when the radiation level changes ?

  When the detected radiation level changes, it means the paper is coming out too thick or too thin, so the

  control unit adjusts the rollers to give the correct thickness.
• How is radiation used to control the thickness of paper ?

  Radiation is directed

  through the paper being made with a detector on the other side, connected to a control unit.
• What is beta radiation used in ?

  Beta radiation, for example, is used in thickness gauges in paper making.
• What can radiation be used for ?


  Radiation can be used to measure and control the thickness of materials.
• What source does sterilizing use and why ?


  A γ-source with at least several months-long half-life is used so that it doesn't need replacing too often
• Why can fresh fruit be sterilized without being damaged ?

  Unlike boiling, gamma rays

  don't involve high temperatures, so fresh fruit or plastic instruments can be sterilised without being

  damaged.
• How is gamma used in sterilization ?

  A high dose of gamma rays can kill the bacteria in food by irradiation, sterilising it to keep it fresh

  for longer. Medical equipment can also be sterilised with this method.
• What can gamma rays be used for ?


  Gamma rays can be used to irradiate food to kill bacteria and to sterilise equipment.
• Why is the half life of the source

  If the half-life of the a-source wasn't long, it would need replacing more often as the activity would drop down in a short amount of time.
• Why are alpha particles used in smoke alarms ?

  a-particles are more ionising so they can easily ionise the air particles and they would not be harmful to humans (they would be absorbed by a few cm of air). a-particles are less penetrative so they can be stopped by the smoke.
• How do alpha particles ionize the air ?


  Alpha particles ionise the air particles by hitting/colliding with them and removing their electrons.
• How does a smoke detector work ?

  A smoke detector circuit consists of a source of alpha particles (usually americium-241) and two metal plates

  (electrodes) with a small potential difference between them. The alpha particles ionise the air between the

  plates causing an electric current between the

  electrodes. If there is smoke, it will absorb the alpha particles, the current will be stopped, and an alarm will

  go off.
• Where are alpha emitters are used in?

  Alpha emitters are used in household fire (smoke) alarms.
• How else can the half life be defined ?

  Half-life can also be defined as the time taken for the count rate (or activity) of a sample of a

  radioactive isotope to drop to half of its original value.
• What is the half life defined as ?


  The time taken for half the nuclei in a sample of a radioactive isotope to decay is defined as

  its half-life.
• What must we do to remove the background radiation?

  Therefore, an average reading

  for the background radiation must first

  be found and then subtracted from the

  total to get the corrected count rate.
• What happens when the radiation of a source is measured ?

  When the radiation of a source is measured,

  the reading includes any background

  radiation.
• Where does background radiation come from ?

  Background radiation comes mostly from radon gas in the air, rocks and buildings, food and

  drink, and cosmic rays.
• What is background radiation?

  The low-level, random radiation that's around us all the time is called background radiation.
• How can Ionising radiation be measured ?

  Ionising nuclear radiation can be measured using a detector (Geiger-Müller or GM tube)

  connected to a counter as a count rate in counts/s or counts/minute.
• What happens in gamma decay

  nothing changes but asterix removed from product
• What happens when alpha decay takes place ?

  When alpha decay takes place, the nucleus emits 2 protons and 2 neutrons.
• What happens when beta decay takes place to a neutron ?

  When beta decay takes place, a neutron in the nucleus changes into a proton and an electron (and an antineutrino).
• What happens during alpha or beta decay

  During α-decay or β-decay, the number of protons changes, so the nucleus changes to that of a different element
• What is radioactive decay?

  Spontaneous and random
• What kind of change in an unstable nucleus result in?

  And what is it know as ?

  A change in an unstable nucleus that can result in the emission of α-particles, β-particles and/or

  γ-radiation is known as radioactive decay..