Radiation Uses and Safety. BI 245. A plant cell. Sucrose. Sucrose. How can you measure sucrose molecules taken in by the cell?. Weise et al.2000. Plant Cell 12:1345. Expose to Epidermal Growth Factor. Untreated Fibroblast Treated Fibroblast.
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Radiation Uses and Safety BI 245
A plant cell Sucrose Sucrose How can you measure sucrose molecules taken in by the cell? Weise et al.2000. Plant Cell 12:1345
Expose to Epidermal Growth Factor Untreated Fibroblast Treated Fibroblast How would you find out what new proteins are synthesized in the treated fibroblasts?
Labeling with Radioisotopes • Radioisotopes are isotopes of atoms that decay and release energy in the form of particles or electromagnetic energy. • The energy released is a form of electromagnetic radiation (like light), but very energetic (short wavelengths) • This means if you put a radioisotope on a molecule, you can find it with radiation detection instruments or film – just like light.
Radioactive Materials in biomedical research • Most commonly used radioisotopes • H3, C14, P32, P33, S35 -- all beta emitters • In vivo and in vitro labeling • Na22, K40, Ca45, I125 -- all beta/gamma emitters • Uptake studies for the ions, in vitro labeling for I125
A plant cell Sucrose Sucrose How can you measure sucrose molecules taken in by the cell? What isotopes would be best to label sucrose? How could you find out how much was in the cells? Weise et al.2000. Plant Cell 12:1345
Expose to Epidermal Growth Factor Untreated Fibroblast Treated Fibroblast How would you find out what new proteins are synthesized in the treated fibroblasts? What isotopes could you use to label newly synthesized proteins? How would you find those proteins?
Suppose you wanted to label a DNA molecule? • What isotopes could you use? • How could you find the labeled DNA molecule.
The radioactive molecules used in these experiments are sometimes called tracers • Sugars, Lipids…C-14 or H-3 • Proteins, C-14, S-35, or H-3 labeled amino acids • Nucleic acids P-32, either as a P32-labeled nucleotide or as P-32 added to one end of the molecule.
Radioactivity vs Radiation • Radioactivity • Any spontaneous change in the state of the nucleus accompanied by the release of energy. Alpha, beta, gamma, neutrons • Radiation • Refers to the actual particles or photons emitted and the energy they carry.
Electromagnetic Radiation Non-ionizing Ionizing
What defines the differences in radionuclides and the radiation they emit • What type of radiation (alpha, beta, gamma)? • How does that radiation interact with matter? • How much energy does the radiation have? • How long with the radiation last (half-life of the radionuclide.
Move in straight line Lose little energy in each interaction But have many interactions in the path Consequently don’t travel very far Alpha particles
Electrons and Positrons (betas) • Path Length > Range • Interaction Characteristics: • Ionize and excite atomic electrons • Few interactions per unit path length – few ions produced and low energy transfer. • Large energy loss per collision • Path isnot straight • Higher energy deposition at end of path • (more interactions at end of path)
Energy differences • Betas • H3 = 0.018 MeV • C14 = 0.156 MeV • P32 = 1.71 MeV • Gammas • Co60 = 1.33 MeV • Cs137 = 0.66 MeV
Half-Lives of Radionuclides • H-3 12.26 years • C-14 5730 years • S-35 87 days • P-32 14.3 days • Am-241 432 years
Radiation Risk • All higher energy radiation poses some risk to cells. • UV – induces thymine dimers in DNA • Betas—induce changes in DNA, potentially breakage • Gammas and alphas -- the same as beta, but generally more energetic, so more potential for damage. • X-rays -- same • DNA repair systems are activated, but not perfect.
High Dose (acute) 100-400 rem –effects blood cell counts, but people usually recover 400-1400 rem – GI track, and epithelial cells effected. Lower end survive,. Upper end don’t Above 1400 rem..death likely Atomic Bomb Victims Chernobyl nuclear meltdown Low Dose Risk related to chance of mutation Above 50 rem, risk proportional to dose Below 50 rem, risk assessment less clear. Effects below 10 rem unknown. Primary risk is induction of cancer Radiation Risk
What factors influence probability of radiation damage? • Radiation Dose • Type • Activity (how much) • Time of exposure
Types of exposure External Exposure High energy Betas Gammas Internal exposure – requires intake of radioisotope – Alpha, Beta and Gamma
External Exposure Reduction • Time: • reduce time spent in radiation area • Distance: • stay as far away from the radiation source as possible • Shielding: • interpose appropriate materials between the source and the body
Controlling Internal Exposure • PREVENT INTAKE! • Safe Handling Practices! • Contamination Control • removable surface contamination • airborne contamination • Standard Procedures help! • Personal • No eating, drinking, smoking, make-up application, etc when working with RAM • Procedures • Work in hood • Wear PPE • Clean up contamination • Survey to make sure no contamination exists • Monitor Air, to make sure procedure doesn’t release dust or volatiles
Gloves Labcoat Dosimeters Safety glasses Required PPE Appropriate PPE, shielding, and monitoring Inappropriate PPE!
Exposures in perspective • You are exposed to ionizing radiation all the time. This is called background radiation.
DOSE LIMITS What’s my risk of getting cancer from a radiation exposure? This is hard to determine. The most quoted estimate is that an exposure of 10000 workers to 1 rem of radiation would produce 4 cancers = 0.04%. Consider that in the US as a whole the risk of cancer is about 25%
BUT! • The public perception of radiation risk is that it is always “DEADLY RADIATION”! • This graphic shows how the media place stories on radiation out of proportion to risk. nb. There were NO documented deaths due to radiation in the time shown here.
Some Risk ComparisonsOne-in-a million chances of dying SituationCause of death 2.0 mrem cancer from radiation travelling 700 miles by air accident crossing the ocean by air cancer from cosmic rays traveling 60 miles by car accident living in Denver for 2 months cancer from cosmic rays living in a stone building for 2 months cancer from radioactivity working in a factory for 1.5 wk accident working in a coal mine for 3 hr accident smoking 1-3 cigarettes cancer; heart-lung disease rock-climbing for 1.5 minutes accident 20 min being a man aged 60 mortality from all causes living in New York City for 3 days lung cancer from air pollution
How do you find radiation or radioactive materials • Radiation • With an exposure meter (reads the radiation field)..These are called ion chambers • Radioactive materials • With a counter (like a Geiger counter). These measure individual radioactive particles.