Chemical and Physical Properties: Radioactivity & Radioisotopes

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Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.

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  • Definition. Soddy – a protégé of Ernest Rutherford and a graduate of Aberystwyth…the Edward Davies Chemistry labs…now closed, he left there to work at Glasgow University where he worked on alpha radiation and established the existence of isotopes…the term was coined over a Dinner in Glasgow where a local GP Dr Margaret Todd suggested the term isotopes from the Greek: iso – same, topos – place. Soddy moved to Aberdeen and then to be Professor of Chemistry at Oxford. He received his Nobel Prize in 1921 for Chemistry.
  • Hydroxyl free radical also produces hydrogen peroxide – TOXIC to cells – symptoms of radiation sickness are identical to peroxide poisoning
  • Discuss interaction of radiation with material – the greater the interaction (more ionising power), the shorter the path travelled
  • Chemical and Physical Properties: Radioactivity & Radioisotopes

    1. 1. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Radioactivity & Radioisotopes University of Lincoln presentation
    2. 2. Isotopes <ul><li>In 1913 Soddy proposed the existence of ISOTOPES </li></ul><ul><li>Definition : Atoms of the same elements with different atomic masses </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Frederick Soddy Nobel Prize (Chemistry) 1921
    3. 3. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Henri Becquerel Marie & Pierre Curie Radioactivity discovered in 1896
    4. 4. Stable v. Radioactive Isotopes This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License There are approximately 1,700 isotopes known to exist
    5. 5. Chart of the Nuclides This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    6. 6. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Black squares denote STABLE isotopes Z N
    7. 7. Nuclear Stability <ul><li>The stability of the nucleus depends on both N and Z </li></ul><ul><ul><li>Z≤20 N=Z N/Z = 1 </li></ul></ul><ul><ul><li>20<Z≤92 N>Z N/Z = 1–1.6 </li></ul></ul><ul><ul><li>Z>92 Spontaneous fission </li></ul></ul><ul><li>If N/Z < or > stable ratio, the nucleus is radioactive </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    8. 8. Chart of the Nuclides & Radioactivity This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Z N Neutron RICH Neutron DEFICIENT N/Z = 1–1.6 N/Z > 1.6 N/Z < 1
    9. 9. Chart of the Nuclides & Radioactivity This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Neutron RICH Neutron DEFICIENT E STABLE N/Z <1 Need to gain n  + N/Z>1.6 Need to lose n  -
    10. 10.  – Decay (Negatron emission) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License X  X +  – A A Z Z+1 n  p Parent Daughter Negatron It is easier to convert a neutron to a proton, than expel a neutron from the nucleus
    11. 11.  Decay This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License E A Z X A m Z+1 X  – A Z+1 X   – decay (nearly) always results in a daughter in an excited state – if this excited state is fairly long-lived it is called a meta-stable state (m) XS energy is lost by expelling a  -ray
    12. 12.  + Decay (Positron emission) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License X  X +  + A A Z Z-1 p  n Parent Daughter Positron It is easier to convert a proton to a neutron, than expel a proton from the nucleus
    13. 13.  Decay <ul><li>Nuclei that are simply too big (too many n and too many p) need to lose both n and p as quickly as possible </li></ul><ul><li> = Helium nucleus He </li></ul><ul><li>2 protons + 2 neutrons </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 4 2
    14. 14. Chart of the Nuclides This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License  -emitters
    15. 15. Common Radioactive Emissions This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License 0 1.0087 neutron n Neutron 1+ 1.0073 Proton p Proton 1+ 0.00055 positively charged electron  + Positron 0 None EMR  Gamma 0 None EMR X-ray X-ray 1– 0.00055 electron  Beta 2+ 4.0026 He nucleus  Alpha Charge Mass Nature Symbol Emission
    16. 16. Half-life (t ½ ) <ul><li>The time taken for the activity of a radioisotope to reach half it’s original value </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    17. 17. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Half-Life (t ½ ) For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after: 12.5% 2,500 3 hours (Three lifetimes) 25% 5,000 2 hours (Two lifetimes) 50% 10,000 1 Hour (one lifetime) % of atoms remaining Number of atoms remaining Time
    18. 18. Radioactivity This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License One half life Two half lifes
    19. 19. Radioactivity <ul><li>Decay Equation: </li></ul><ul><ul><li>A t = A 0 e -  t </li></ul></ul><ul><ul><li>A t = activity at time t </li></ul></ul><ul><ul><li>A 0 = activity at time 0 (initial activity) </li></ul></ul><ul><ul><li> = decay constant (rate constant) </li></ul></ul><ul><ul><li>t = time </li></ul></ul><ul><ul><li>First Order reaction </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    20. 20. Radioactivity <ul><li>Decay Equation: </li></ul><ul><li>Ln(A t ) = Ln(A 0 ) -  t </li></ul><ul><li> Intercept Gradient </li></ul><ul><ul><li>Straight line graph </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    21. 21. Biological Effects of Radiation <ul><li>Radiation passing through cells of living tissue  ions and free radicals </li></ul><ul><li>These react with compounds in the cell, disrupting or altering the normal metabolic processes </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    22. 22. Biological Effects of Radiation <ul><li>These changes can result in: </li></ul><ul><ul><li>Death of the organism or animal </li></ul></ul><ul><ul><li>Reduced ability of cells to divide </li></ul></ul><ul><ul><li>Abnormal cell division </li></ul></ul><ul><ul><li>Changes in genetic material </li></ul></ul><ul><ul><li>Increase in the rate of aging </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    23. 23. Biological Effects of Radiation <ul><li>Mainly due to the radiolysis of water: </li></ul><ul><li>H 2 O + radiation  H + + OH  + e – </li></ul><ul><li>OH  immediately reacts with neighbouring molecules, such as proteins and DNA </li></ul><ul><li> foreign substances (also H 2 O 2 is formed) </li></ul><ul><li> disrupt/change normal metabolic processes </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License The hydroxyl free radical is very reactive
    24. 24. Cascade effect This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Radiation Initial disruption 1 st generation of foreign substances that cause further disruption Initial disruption has now been magnified 8 times Continuation in cascade leads to a level of disruption with which the body cannot cope
    25. 25. Penetrating Power of Radiation This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License    n Skin & paper 5mm brass 6mm Al Pb & concrete Very thick concrete (2m)
    26. 26. Absorbed Dose <ul><li>The amount of energy absorbed by the tissue </li></ul><ul><li>Units – the Gray (Gy) </li></ul><ul><ul><li>1 Gy = 1 Jkg -1 </li></ul></ul><ul><ul><li>An absorbed dose of 10 Gy is lethal for most mammals </li></ul></ul><ul><ul><ul><li>Although the absorbed energy is very low (10 Jkg -1 ), the disruption it causes to biological processes in the tissue will result in death </li></ul></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    27. 27. Dose Equivalent <ul><li>Different radiation types cause different amounts of damage </li></ul><ul><ul><li>In order for ‘dose’ to meaningful, need to be able to define it in terms of ‘damage done’ </li></ul></ul><ul><ul><ul><li>Dose equivalent defines the damage done in man </li></ul></ul></ul><ul><li>Units – Sievert (Sv) </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    28. 28. Dose Equivalent <ul><li>Dose Equivalent = Absorbed Dose (Gy) x Q </li></ul><ul><li>Where Q is the empirical quality factor </li></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License  , X Q = 1 Fast n, p Q =10  Q =20
    29. 29. Dose Equivalent This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License In theory, 100 Sv  -radiation will cause the same biological effect in man as a dose of 100 Sv  radiation BUT the absorbed doses are 100 Gy and 5 Gy, respectively
    30. 30. Illicit Radioactive Sources Dirty Bombs – Radiation Dispersal Devices (RDD) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    31. 31. Dirty Bombs <ul><li>Conventional explosives wrapped in radioactive material </li></ul><ul><ul><li>NOT atomic bombs </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    32. 32. Dirty Bombs This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License A SMART PHONE that can detect radiation may soon be helping the police to find the raw materials for radioactive “dirty bombs” before they are deployed. The phones will glean data as the officers carrying them go about their daily business, and the information will be used to draw up maps of radiation that will expose illicit stores of nuclear material. New Scientist (December 2004)
    33. 33. Depleted Uranium <ul><li>t ½ U-238 = 4.5 x 10 9 y </li></ul><ul><ul><li>Not exactly ‘radioactive’ </li></ul></ul><ul><ul><li>1 atom will decay every 4.5 x 10 9 y </li></ul></ul>This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
    34. 34. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Acknowledgements <ul><li>JISC </li></ul><ul><li>HEA </li></ul><ul><li>Centre for Educational Research and Development </li></ul><ul><li>School of natural and applied sciences </li></ul><ul><li>School of Journalism </li></ul><ul><li>SirenFM </li></ul><ul><li>http:// tango.freedesktop.org </li></ul>

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