Radioactive Nuclide Nuclide which is unstable. It emits radiation & changes into another kind of atom.

Nuclide An atom with a specific number of protons and a specific number of neutrons. 14 C 12 C 14 N are all nuclides 6 6 7

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 Alpha, Beta, Gamma Separated by electric or magnetic fields. Opposites attract.  Rays are pure energy. No charge so they are not deflected by an electric field.

Least penetration power Alpha radiation. Shielding can be paper or cloth.

Most penetration power Gamma radiation. Requires lead/concrete shielding.

2 He or 2  Symbol for alpha radiation Same as the nucleus of a helium atom Mass = 4 amu Charge =

-1 e or -1  or  - or  Symbol for beta particle Fast moving electron originating from nucleus Mass = “zero” Charge = -1 00

+1 e or +1  or  + Symbol for positron. Mass = “zero.” Charge = +1. Positive electron 00

0  or  Symbol for gamma radiation. Pure Energy 0 mass 0 charge 0

0 n or n Symbol for neutron 1

1 H or 1 p Symbol for proton 1 1

Have mass numbers & atomic numbers Describes changes in the nucleus of an atom Nuclear Equations

Alpha Decay Unstable nucleus emits an alpha particle. Atomic #  by 2. Mass #  by 4.

220 Fr  4  At Alpha Decay Atomic #  by 2. Mass #  by

220 Fr  4  At Equation represents natural transmutation. 1 term on reactant side

220 Fr  4  At Balance nuclear equations using conservation of atomic number & conservation of mass number =220 87=

Predicting Decay Modes Use a nuclide chart! 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.

42 K  0 e + 42 Ca Beta Decay Atomic #  by 1. Mass # stays the same

19 Ne  0 e + 19 F Positron Emission Atomic #  by 1. Mass # stays the same

# of Half-Lives = Elapsed time Length of H.L.

Half-Life Map Fraction Remaining Amount (mass) Elapsed Time # of Half Lives 1Initial Mass00 ½1 X H.L.1 ¼2 X H.L.2 1/83 X H.L.3 1/164 X H.L.4 Fraction = 1/2 n 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.

Cl has 2 isotopes: 25% Cl-37 & 75% Cl-35 How to calculate the Average Atomic Mass of Cl 1)Convert percent abundances to decimal format 2)Multiply each abundance factor by the appropriate isotopic mass 3)Sum 4)Do a reality check. 0.25(37) + (0.75)(35) = = is in between the high & the low, and it is closer to the more abundant isotopic mass.

Artificial Transmutation Particle “bullet” hits target nucleus & new isotope is produced. 2 terms on reactant side.

Artificial Transmutation 32 S + 1 n  32 P + 1 H bullettarget

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.

239 Pu + 1 n  90 Sr Ba n Fission

Fusion Fusion: U for unite and U for sun. Very small nuclei (H & He) are jammed together. Huge amounts of energy are released.

1 H + 2 H  3 He Fusion 1 1 2

Identify each of the rxns a) 1 n U  142 Ba + 91 Kr n + energy b) 59 Co + 1 n  60 Co c) 3 He + 1 H  4 He + 0 e d) 14 C  14 N + 0 e fission Artificial transmutation fusion Natural transmutation

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.

Potential Well Diagram Potential Energy of System Separate Nucleons Stable Nucleus Reference level r, distance between nucleons 4 He + energy  2 protons + 2 neutrons 2 Represents potential energy changes during a process Yellow arrow shows the binding energy!

E = mc 2 or  E =  mc 2 Einstein’s Equation relating energy and mass! Recall that to use this equation, the mass needs to be in kilograms, not amu’s.

STEPS TO CALCULATE BINDING ENERGY 1.Count up protons, neutrons, & electrons. 2.Multiply the number of particles X the mass of the particles. 3.Sum the terms. 4.Subtract the isotopic mass. This is  m in amu’s. 5.Convert to kg. 6.Plug into Einstein’s famous equation, E = mc 2 or  E =  mc 2. 7.Divide by the number of nucleons to get BE per nucleon. 8.Multiply by Avogadro’s number to get binding energy per nucleon for 1 mole of substance.

Curve of 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

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. 1 n U  142 Ba + 91 Kr n + energy Slow neutrons work better! But fast neutrons come off here!

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.

Chain Reaction One of the products is also one of the reactants Neutron reactant Neutron products

Critical Mass The minimum amount of U-235 or Pu-239 that will undergo a self- sustaining chain reaction.

Uses of radioisotopes Radioactive Dating: C-14 to C-12 for organic material. U-238 to Pb-206 for rocks. Killing bacteria/spores in food and mail. Chemical tracers: follow the path of material in a system. Used to study organic reaction mechanisms. Medical uses: I-131, Tc-99