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Radiation What is it? Where does it come from? Slide 2 Radiation discovered Henri Becquerel discovered an invisible, penetrating radiation emitted spontaneously by Uranium. Henri Becquerel discovered an invisible, penetrating radiation emitted spontaneously by Uranium. Pierre and Marie Curie discovered two other elements that emitted similar radiations. Polonium and Radium. Called the phenomenon "radioactivity". Pierre and Marie Curie discovered two other elements that emitted similar radiations. Polonium and Radium. Called the phenomenon "radioactivity". Now defined as the emission of electromagnetic radiation and/or particles from unstable nuclei Now defined as the emission of electromagnetic radiation and/or particles from unstable nuclei Slide 3 So, it is the unstable nucleus of an atom falling apart The bigger the nucleus, the greater the chance it will fall apart, which brings us to nuclear chemistry Slide 4 Nuclear Stability Not all combinations of protons and neutrons are stable. Not all combinations of protons and neutrons are stable. To determine stability N/Z is examined, where N = neutrons and Z = protons. To determine stability N/Z is examined, where N = neutrons and Z = protons. For small atomic numbers, the atom is stable if N/Z=1 For small atomic numbers, the atom is stable if N/Z=1 For larger atomic numbers, the atom is stable if N/Z is closer to 1.5 For larger atomic numbers, the atom is stable if N/Z is closer to 1.5 Slide 5 Page 646 Figure 6 Yellow area is stable. Are these stable? Slide 6 So, since some nuclei are unstable, they will fall apart This leads to radioactive decay This leads to radioactive decay By emitting particles and/or energy, the nucleus can stabilize itself By emitting particles and/or energy, the nucleus can stabilize itself Slide 7 Four main types of radiation Alpha radiation- does not penetrate the skin, emits positive charge (Helium nucleus), weakest type of radiation Alpha radiation- does not penetrate the skin, emits positive charge (Helium nucleus), weakest type of radiation Beta radiation -penetrates the skin, emits negative charge(fast moving electron) Beta radiation -penetrates the skin, emits negative charge(fast moving electron) Positron penetrates the skin, it is the antiparticle of the electron Positron penetrates the skin, it is the antiparticle of the electron Gamma radiation- emits high energy, penetrates the skin fully Gamma radiation- emits high energy, penetrates the skin fully Slide 8 Table 1 Page 648 Slide 9 These particles can either be captured or emitted If they are absorbed by the reactants, they are captured If they are absorbed by the reactants, they are captured In other words, if they appear on the left side of the equation In other words, if they appear on the left side of the equation If they are given off the reactants, they are emitted If they are given off the reactants, they are emitted In other words, if they appear on the right side of the equation In other words, if they appear on the right side of the equation Take a look at the following examples Take a look at the following examples Slide 10 Beta Particle Capture If N/Z is too small, a proton may absorb a high level electron and turn into a neutron. If N/Z is too small, a proton may absorb a high level electron and turn into a neutron. Question: What happens if the number of protons change? Question: What happens if the number of protons change? Answer: The atom changes to a new element. Answer: The atom changes to a new element. Slide 11 Beta Particle Capture Example: Cr + e V + Example: Cr + e V + Note: If you treat as an = sign, numbers should equal Note: If you treat as an = sign, numbers should equal Also note that in this case, extra energy is released. This energy is released as gamma rays Also note that in this case, extra energy is released. This energy is released as gamma rays 51 24 51 23 0 Slide 12 Positron Emission If N/Z is too small, a proton may release a positron, (antiparticle of an electron) and turn into a neutron. If N/Z is too small, a proton may release a positron, (antiparticle of an electron) and turn into a neutron. Once again, the element will change Once again, the element will change Example: Cr V + e Example: Cr V + e If a positron meets an electron, all the mass will be annihilated and is converted to energy (gamma rays) If a positron meets an electron, all the mass will be annihilated and is converted to energy (gamma rays) Positron + electron = 2 gamma rays Positron + electron = 2 gamma rays 49 24 49 23 0 +1 Slide 13 Examples Write a balanced equation for each nuclear equation Write a balanced equation for each nuclear equation Po He+ Po He+ Pm + Nd Pm + Nd Es + He 3 n + Es + He 3 n + 218 84 253 99 142 61 142 60 1010 4242 Alpha emitted Beta captured Alpha captured 4242 Slide 14 Homework Page 670: 30, 31, 34, 35, 43 Page 670: 30, 31, 34, 35, 43