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.
What is Radioactivity ? Radioactivity are reactions through which the unstable nuclei become more stable. Energetic radiations will be emitted during the process. Unstable Nucleus More Stable Nucleus + Radiation
Types of Radiation -rays -rays -rays There are THREE types of radiation: Helium Nucleus Fast-moving Electrons Light waves with very short wavelength
Unstable Nucleus Revision Alpha Particle Gamma Ray Beta Particle More Stable Nucleus
Properties of Radiation Charge and Mass Deflection in Electric Field Deflection in Magnetic Field Ionization Power Penetration Power Range in air
Charge and Mass Electron Light Wave (short ) -particle -particle -ray Charge Mass +2 Nil 4 Negligible Nil Helium Nucleus
Tracks in Cloud Chamber (2) Short Thick Straight Fork track may be seen Range is small Ionization is great Momentum is large Elastic collision with helium gas atom -particles CharacteristicsReason
Tracks in Cloud Chamber (3) Zig-zag path diffuse Mass is smaller Range is longer -particles CharacteristicsReason
Background Radiation 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 Sources: Experimental Result :
Biological Hazards (1) immediate death cause cancer genetic changes Large Dose Small Dose Very small Dose
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
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