Radioactive Nuclide Nuclide which is unstable. It emits radiation & changes into another kind of atom.
Nuclide 14C 12C 14N are all nuclides 6 6 7 An atom with a specific number of protons and a specific number of neutrons.
Isotopes Two atoms with the same atomic number but different mass numbers.
Transmutation Reaction A change in the identity of a nucleus as a result of a change in the number of its protons.
Relationship between stability and energy As stability , energy .
Nuclear Strong Force Attractive force between all nucleons. Holds the nucleus together. But it is a very short-range force.
Electrostatic repulsive forces Occur between like charges. Occur between protons in the nucleus. Longer-range force.
Stability of nuclide - Can be assessed by neutron to proton ratio. - A certain number of neutrons are needed to increase the strong nuclear force (the attractive force) enough to hold the nucleus together. Small atoms, a stable N/P ratio is 1:1 Large atoms: 1.5:1
Which elements are unstable? All the elements with atomic number > 83 (or beyond Bismuth) That’s all nuclides 84!
Types of Radiation Opposites attract. Rays are pure energy. No charge so they are not deflected by an electric field. Alpha, Beta, Gamma Separated by electric or magnetic fields.
Least penetration power Alpha radiation. Shielding can be paper or cloth.
Most penetration power Gamma radiation. Requires lead/concrete shielding.
2He or 2 Symbol for alpha radiation Same as the nucleus of a helium atom Mass = 4 amu Charge = +2 4 4
-1e or -1 or - or Symbol for beta particle Fast moving electron originating from nucleus Mass = “zero” Charge = -1 0 0
+1e or +1 or + Symbol for positron. Mass = “zero.” Charge = +1. Positive electron 0 0
0 or Symbol for gamma radiation. Pure Energy 0 mass 0 charge 0
0n or n Symbol for neutron 1
1H or 1p Symbol for proton 1 1
Have mass numbers & atomic numbersDescribes changes in the nucleus of an atom Nuclear Equations
Alpha Decay Unstable nucleus emits an alpha particle. Atomic # by 2. Mass # by 4.
220Fr 4 + 216At Alpha Decay Atomic # by 2. Mass # by 4. 2 85 87
220Fr 4 + 216At Equation represents natural transmutation. 1 term on reactant side. 2 85 87
220Fr 4 + 216At 220 = 4 + 216 Balance nuclear equations using conservation of atomic number & conservation of mass number. 2 85 87 2 + 85 87 =
Predicting Decay Modes For elements 1-20: If the n/p ratio is too high, beta emission happens. If the n/p ratio is too low, positron emission happens. Use a nuclide chart!
42K 0e + 42Ca Beta Decay Atomic # by 1. Mass # stays the same. -1 20 19
19Ne 0e + 19F Positron Emission Atomic # by 1. Mass # stays the same. 10 +1 9
# of Half-Lives = Elapsed time Length of H.L.
Half-Life Map Fraction = 1/2n where n = # of half-lives
Decay Mode Same as type of particle emitted
Average Atomic Mass Weighted average of the masses of the naturally occurring isotopes.
Convert percent abundances to decimal format • Multiply each abundance factor by the appropriate isotopic mass • Sum • Do a reality check. Cl has 2 isotopes: 25% Cl-37 & 75% Cl-35 0.25(37) + (0.75)(35) = 9.25 + 26.25 = 35.5 35.5 is in between the high & the low, and it is closer to the more abundant isotopic mass. How to calculate the Average Atomic Mass of Cl
Artificial Transmutation Particle “bullet” hits target nucleus & new isotope is produced. 2 terms on reactant side.
Artificial Transmutation target bullet 32S + 1n 32P + 1H 1 16 0 15
Artificial Transmutation Particle “bullet” may be proton or alpha particle. To react with a nucleus, must overcome + + repulsive forces by accelerating bullet to high speeds. Particle “bullet” may be a neutron. Neutrons have no charge, so no repulsive forces to overcome. No acceleration necessary. Target can be anything from PT.
Fission Fission is division. Large nucleus (U-235 or Pu-239) is split into 2 medium sized nuclei by a neutron bullet. Excess neutrons & a great deal of energy are also produced.
239Pu + 1n 90Sr + 147Ba + 3 1n Fission 94 0 38 56 0
Fusion Fusion: U for unite and U for sun. Very small nuclei (H & He) are jammed together. Huge amounts of energy are released.
1H + 2H 3He Fusion 1 1 2
fission 0 92 56 36 0 Artificial transmutation 27 0 27 Identify each of the rxns fusion 1 2 2 +1 Natural transmutation 6 7 -1 1n + 235U 142Ba + 91Kr + 3 1n + energy 59Co + 1n 60Co 3He + 1H 4He + 0e 14C 14N + 0e
Mass Defect, m The difference between the mass of a specific atom and the sum of the masses of its protons, neutrons, & electrons. Can be expressed in amu or kg. In nuclear reactions, a small amount of mass is converted to a huge amount of energy.
Nuclear Binding Energy The energy released when a nucleus is formed from its nucleons. Often expressed per nucleon.
4He + energy 2 protons + 2 neutrons 2 Potential Well Diagram Reference level Yellow arrow shows the binding energy! Separate Nucleons Potential Energy of System r, distance between nucleons Stable Nucleus Represents potential energy changes during a process
E = mc2 or E = mc2 Recall that to use this equation, the mass needs to be in kilograms, not amu’s. Einstein’s Equation relating energy and mass!
Count up protons, neutrons, & electrons. Multiply the number of particles X the mass of the particles. Sum the terms. Subtract the isotopic mass. This is m in amu’s. Convert to kg. Plug into Einstein’s famous equation, E = mc2 or E = mc2. Divide by the number of nucleons to get BE per nucleon. Multiply by Avogadro’s number to get binding energy per nucleon for 1 mole of substance. Steps to calculate binding energy
Binding Energy & Stability Fe and Ni have the highest binding energies. The higher the binding energy, the more energy is released when the nucleus is formed. So the nucleus is in a deeper potential well, and it is MORE stable.
Nucleon Protons and Neutrons Mass # = # of nucleons
Parts of a nuclear reactor Fuel Control rods Containment or shielding Coolant Moderator
Moderator 1n + 235U 142Ba + 91Kr + 3 1n + energy 92 0 0 56 36 Slow neutrons work better! But fast neutrons come off here! Substance that slows down fast neutrons. Increases the efficiency of the fission process. Sometimes the moderator is also the coolant. Sometimes it is in the fuel rods.
Control Rods Contain a substance that absorbs neutrons, removing them from the reaction. On days with high electrical demand, the control rods would be removed from the core.