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210 Po

210 Po. Polonium 210. Alexander Litvinenko. Nuclear Radiation. We will look at three types of nuclear radiation. α. alpha. few centimetres through air. several centimetres through air. β. beta. γ. gamma. several metres through air. Absorption. A few mm of Aluminium.

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210 Po

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  1. 210 Po Polonium 210 Alexander Litvinenko

  2. Nuclear Radiation We will look at three types of nuclear radiation. α alpha few centimetres through air several centimetres through air β beta γ gamma several metres through air

  3. Absorption A few mm of Aluminium Several cm of Lead Paper Alpha Beta Gamma

  4. Safety Precautions • Always use forceps to lift a source (never bare hands). • Ensure source is pointed away from the body. • Never bring towards eye to examine source. • When in use, always attended by an authorised person. Returned to a locked and labelled store which is shielded after use. • After using radioactive sources, wash hands thoroughly before eating. • In the UK, students under the age of 16 may not handle radiation sources.

  5. Effect on Living Cells • Nuclear radiation can kill or damage living cells. • The extent of damage depends on: • type of tissue • type of radiation • the total amount of energy absorbed. Physicists measure the damage by calculating the equivalent dose. Equivalent dose is measured in units called Sieverts ( S ).

  6. Radiotherapy Radiotherapy uses nuclear radiation to kill cancer cells. A beam of nuclear radiation is fired at the cancer cells from different directions to minimise the damage to the surrounding healthy cells. The cancer cells are damaged which stops them reproducing. The tumour then shrinks.

  7. Brain Tumour A beam of invisible nuclear radiation is fired at the tumour. The direction is changed at the next dose to protect the healthy cells around the tumour.

  8. The Gamma Camera The gamma camera is a detector of gamma radiation. It can be used to produce an image of inside the body. A radioactive chemical called a tracer( which emits gamma radiation ) is usually injected into the patient’s bloodstream. It gives off gamma radiation as it travels around the body. This gamma radiation is detected by the gamma camera. Image of a patient’s kidneys using a gamma camera.

  9. + - - + + - The Atom Nucleus Proton Neutron Electron

  10. The mass of the atom is concentrated in the centre called the nucleus. The nucleus contains positive particles called protons and neutral particles called neutrons. Most of the atom is empty space. Orbiting the nucleus are negative particles called electrons. In an atom there are always the same number of protons and electrons. The positive and negative charges cancel out each other so the atom has an overall neutral charge.

  11. Nucleus Nuclear Radiation + - + - Ionisation Nuclear radiation can change neutral atoms into charged ions.

  12. If nuclear radiation passes through or close to an atom it can remove one or more of the orbiting electrons. This upsets the balance between positive and negative. It is no longer neutral. The neutral atom has been changed into a charged ion. This is called IONISATION. ALPHA causes more ionisation than BETA or GAMMA. If an atom loses an electron it becomes a positive ion. If another atom gains this electron it will become a negative ion.

  13. The Geiger-Muller Tube This is a detector of nuclear radiation. Tube of gas atoms Nuclear Radiation mica window Central Electrode ( high voltage ) Counter

  14. If nuclear radiation enters the G-M tube through the thin mica window it will IONISE some gas atoms in the tube. These charged IONS are attracted to the high voltage central electrode. A pulse of electricity is produced which is recorded by the counter.

  15. Activity & Dose Equivalent Activity The activity of a radioactive source is measured in becquerels ( Bq ) or kilobecquerels ( kBq ). 20 Bq means 20 atoms disintegrating in one second. Dose Equivalent The dose equivalent is a measure of the biological effect of radiation. The dose equivalent is measured in Sieverts ( Sv ) or millisieverts ( mSv ).

  16. Activity ( kBq ) 1000 500 time ( hours ) 3 9 6 Radioactive Decay The amount of radiation emitted from a radioactive source is called its activity. Activity is measured in units called Becquerels ( Bq ). The activity of a radioactive source decreases with time. Half-Life = 3 hours

  17. The half-life of a radioactive source is the time it takes for the activity to half.

  18. Radioactive Liquid G-M Tube Counter Stopwatch Measuring Half-Life • Measure the background count rate. • Place the radioactive source next to the GM tube. • Measure the count rate of the substance every minute. • Subtract the background count rate from every reading.

  19. To Do… 0 100 98 5 64 62 10 43 41 15 29 27 20 21 19 25 18 16 30 17 15 Background radiation = 2 kBq • Use the table of results to plot a graph of corrected activity and time. • Predict from your graph, the half life of the radioactive source.

  20. Half-life = 7 years

  21. 3 days 3 days 3 days Half-Life Calculations Example 1 The Half-Life of a radioactive source is 3 days. (a) How long will it take the Activity to fall from 2000 kBq to 250 kBq? 250 2000 1000 500 It will take 9 days.

  22. 3 days 3 days (b) What will the activity be after a further 6-days? 250 125 62.5 Activity after a further six days is 62.5 kBq.

  23. 1 half-life 1 half-life 1 half-life 1 half-life = 24-hours 3 Example 2 The activity of a radioactive source falls from 200 kBq to 25 kBq in a time of 24-hours. What is the half life of the radioactive source? 25 200 100 50 3 half lives = 24-hours 1 half-life = 8-hours

  24. Attempt the following questions showing ALL your working. Q1. A radioisotope has a half life of 5-hours. If its initial count rate is 320 cps, what is the count rate after 15-hours? Q2. Uranium has a half-life of 4,000 years. If the activity of a sample is 48 kBq in the year 2000 AD, what will its activity be in the year 14000 AD? Q3. The half-life of a radioactive substance is 5,600 years. How long will it take for the activity to fall to one eighth (1/8) of what it was? Q4. The activity of a radionuclide in 1985 was 1,200 Bq. In what year will the activity be 75 Bq if its half-life is 12 years?

  25. Q5. Calculate the half-life of a radioactive sample whose activity falls from 128 kBq to 4 kBq in a time of 40-hours. Q6. The activity of a radioisotope is measured to be 20 MBq. Twelve days later the activity has fallen to 5 MBq. What is the half-life? Q7. A Geiger counter measures the corrected count rate of a radioactive gas to be 80 cpm (counts per minute). One minute later the count rate has decreased to 10 cpm. What is the half- life of this radioactive gas? Q8. In 1970 the activity of a radioisotope is found to be 100 kBq. In 1982 this activity had fallen to 25 kBq. What is the half-life of the radioisotope?

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