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Radioactivity 1 輻 射

Radioactivity 1 輻 射. Presented by Mr. Y. N. Chan LIU PO SHAN MEMORIAL COLLEGE. History of Radioactivity. In 1896, Becquerel noted that radiation from uranium affected photographic plates. In 1899, Curie noted that thorium and radium showed also the same effect on photographic plates.

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Radioactivity 1 輻 射

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  1. Radioactivity 1輻 射 Presented byMr. Y. N. ChanLIU PO SHAN MEMORIAL COLLEGE

  2. History of Radioactivity • In 1896, Becquerel noted that radiation from uranium affected photographic plates. • In 1899, Curie noted that thorium and radium showed also the same effect on photographic plates.

  3. What is Radioactivity ? • Radioactivity are reactions through which the unstablenuclei become more stable. • Energetic radiations will be emitted during the process. Unstable Nucleus More Stable Nucleus + Radiation

  4. Types of Radiation • There are THREE types of radiation: -rays  -rays  -rays Helium Nucleus Fast-moving Electrons Light waves with very short wavelength

  5. Revision Beta Particle Alpha Particle Gamma Ray More Stable Nucleus Unstable Nucleus

  6. Properties of Radiation • Charge and Mass • Deflection in Electric Field • Deflection in Magnetic Field • Ionization Power • Penetration Power • Range in air

  7. Charge and Mass  -particle  -particle  -ray Helium Nucleus Light Wave (short ) Electron -1 Charge +2 Nil 4 Nil Mass Negligible

  8. Deflection of Electric Field -ve    +ve

  9. Deflection of Magnetic Field -ray -ray What is the direction of the magnetic field ? + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + -ray Magnetic Field

  10. What are the penetrating power ofa , bandgray ?  - rays  - rays  - rays

  11. The penetrating power ofa , bandgradiation (1) Paper  - rays  - rays  - rays

  12. The penetrating power ofa , bandgradiation (2) Paper 5mmAl  - rays  - rays  - rays

  13. The penetrating power ofa , bandgradiation (3) Paper 5mmAl Lead  - rays  - rays  - rays 100% 50% 2 cm

  14. Ionization Power (1) • It is the ability of the radiation to ionize the air molecule. • Ionization Power:  >  > 

  15. Ionization Power (2) • (1) Its momentum is the greatest • (2) Its charge is the greatest • (3) Its speed is the slowest -ray has the greatest ionization power because

  16. The range in air ofa , bandgradiation  - rays 5 cm  - rays about 5 m  - rays Over 100 m

  17. Detectors of Radiation • Photographic Film • G.M. tube • Cloud Chamber

  18. Tracks in Cloud Chamber (1) -particles -particles -rays

  19. Short Thick Straight Fork track may be seen Range is small Ionization is great Momentum is large Elastic collision with helium gas atom Tracks in Cloud Chamber (2) -particles Characteristics Reason

  20. Zig-zag path diffuse Mass is smaller Range is longer Tracks in Cloud Chamber (3) -particles Characteristics Reason

  21. Radiation is detected even when no radioactive substance is present. Cosmic Radiation (from outer space) Radiation coming from the environment (e.g. rock, concrete, artificial sources) Radon gas Background Radiation Experimental Result : Sources:

  22. Biological Hazards (1) • immediate death • cause cancer • genetic changes • Large Dose • Small Dose • Very small Dose

  23. Biological Hazards (2) • -rays is the most dangerous. (penetrating power is highest) • -rays is the most dangerous. (ionization power is highest.) • Outside the body • Inside the body

  24. Radioactivity 1 END

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