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Unformatted text preview: Chapter 29, part 2 PHY213 1 Marie Curie and Radioactivity s 1867 1934 s Discovered new radioactive elements s Shared Nobel Prize (physics in 1903) s Nobel Prize (chemistry in 1911) s Radioactivity is the spontaneous emission of radiation s Experiments suggested that radioactivity was the result of the decay, or disintegration, of unstable nuclei Radioactivity Types s Three types of radiation can be emitted s Alpha particles ( ) s The particles are 4 He nuclei s Beta particles ( + or - ) s The particles are either electrons or positrons s A positron is the antiparticle of the electron s It is similar to the electron except its charge is +e s Gamma rays ( ) s The rays are high energy photons Distinguishing Types of Radiation s A radioactive beam is directed into a region with a magnetic field s The gamma particles carry no charge and they are not deflected s The alpha particles are deflected upward s The beta particles are deflected downward s A positron would be deflected upward Penetrating Ability of Particles s Alpha particles s Barely penetrate a piece of paper s Beta particles s Can penetrate a few mm of aluminum s Gamma rays s Can penetrate several cm of lead Chapter 29, part 2 PHY213 2 The Decay Constant s The number of particles that decay in a given time is proportional to the total number of particles in a radioactive sample s N = - N t s is called the decay constant and determines the rate at which the material will decay s The decay rate or activity , R, of a sample is defined as the number of decays per second N R N t = = Decay Curve s The decay curve follows the equation, N = N o e- t s The half-life is also a useful parameter s The half-life is defined as the time it takes for half of any given number...
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