Radiation What is it? Where does it come from?

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

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

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

Page 646 Figure 6 Yellow area is stable. Are these stable? yes no yes no Protons Mass number Have to subtract to get neutrons

So, since some nuclei are unstable, they will fall apart This leads to radioactive decay This leads to radioactive decay Radioactivity – the process by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation Radioactivity – the process by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation By emitting particles and/or energy, the nucleus can stabilize itself By emitting particles and/or energy, the nucleus can stabilize itself

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

Table 1 – Page 648

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

Beta Particle Emission If N/Z is too large, a neutron may emit a high level electron and turn into a proton. If N/Z is too large, a neutron may emit a high level electron and turn into a proton. 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. Example: C  N + e Example: C  N + e Note: If you treat  as an = sign, numbers should equal

Electron 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. Once again, the element will change Once again, the element will change Example: Cr + e  V +  Example: Cr + e  V +  Note that in this case, extra energy is released. This energy is released as gamma rays Note that in this case, extra energy is released. This energy is released as gamma rays

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

Alpha Particle Emission If N/Z is much larger than 1, then a nucleus can stabilize itself by emitting an alpha particle (Helium Nucleus). If N/Z is much larger than 1, then a nucleus can stabilize itself by emitting an alpha particle (Helium Nucleus). Example: U  Th + He Example: U  Th + He Note again, that every nuclear equation must be balanced. Note again, that every nuclear equation must be balanced. Top number on right must equal top numbers on left and bottom numbers on right must equal the bottom number on left Top number on right must equal top numbers on left and bottom numbers on right must equal the bottom number on left

Examples Write a balanced equation for each nuclear equation Write a balanced equation for each nuclear equation Po  + Pb Po  + Pb Pm +  Nd Pm +  Nd Es + He  n + Es + He  n Alpha emitted Beta captured Alpha captured