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Radiation

Radiation. What is it? Where does it come from?. Radiation discovered. Henri Becquerel discovered an invisible, penetrating radiation emitted spontaneously by Uranium .

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Radiation

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  1. Radiation What is it? Where does it come from?

  2. Radiation discovered • 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". • Now defined as the emission of electromagnetic radiation and/or particles from unstable nuclei

  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

  4. Nuclear Stability • Not all combinations of protons and neutrons are stable. • 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 larger atomic numbers, the atom is stable if N/Z is closer to 1.5

  5. Page 683 Figure 2 Yellow area is stable. Are these stable?

  6. So, since some nuclei are unstable, they will fall apart • This leads to radioactive decay • By emitting particles and/or energy, the nucleus can stabilize itself

  7. Four main types 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) • Positron – penetrates the skin, it is the antiparticle of the electron • Gamma radiation- emits high energy, penetrates the skin fully

  8. These particles can either be captured or emitted • If they are absorbed by the reactants, they are captured • In other words, if they appear on the left side of the equation • If they are given off the reactants, they are emitted • In other words, if they appear on the right side of the equation • Take a look at the following examples

  9. Beta Particle Capture • 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? • Answer: The atom changes to a newelement.

  10. Beta Particle Capture 51 23 51 24 0 -1 • Example: Cr + e V +  • 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

  11. Positron Emission • 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 • Example: Cr  V + e • If a positron meets an electron, all the mass will be annihilated and is converted to energy (gamma rays) • Positron + electron = 2 gamma rays 49 24 49 23 0 +1

  12. Examples • Write a balanced equation for each nuclear equation • Po  He + • Pm +  Nd • Es + He 3 n + 218 84 4 2 Alpha emitted 142 61 142 60 Beta captured 253 99 1 0 4 2 Alpha captured

  13. Homework • Page 703: 9, 11, 12, 13

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