Radioactive Nuclide Nuclide which is unstable. It emits radiation & changes into another kind of...
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Radioactive Nuclide
Nuclide which is unstable. It emits radiation &
changes into another kind of atom.
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Nuclide
An atom with a specific number of protons and a
specific number of neutrons.
14C 12C 14N are all nuclides6 6 7
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Isotopes
Two atoms with the same atomic number but
different mass numbers.
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Transmutation Reaction
A change in the identity of a nucleus as a result of a change in the number of
its protons.
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Relationship between stability and energy
As stability , energy .
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Nuclear Strong Force
Attractive force between all nucleons. Holds the nucleus together.But it is a very short-range force.
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Electrostatic repulsive forces
Occur between like charges.Occur between protons in the nucleus.Longer-range force.
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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
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Which elements are unstable?
All the elements with atomic number > 83 (or
beyond Bismuth) That’s all nuclides 84!
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Types of Radiation
Alpha, Beta, GammaSeparated by electric or
magnetic fields.
Opposites attract.
Rays are pure energy. No charge so they are not deflected by an electric field.
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Least penetration power
Alpha radiation. Shielding can be paper or cloth.
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Most penetration power
Gamma radiation. Requires lead/concrete
shielding.
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2He or 2
Symbol for alpha radiationSame as the nucleus of a helium
atomMass = 4 amuCharge = +2
4 4
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-1e or -1 or - or
Symbol for beta particleFast moving electron
originating from nucleusMass = “zero”Charge = -1
0 0
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+1e or +1 or +
Symbol for positron.Mass = “zero.”Charge = +1.
Positive electron
0 0
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0 or
Symbol for gamma radiation.Pure Energy
0 mass0 charge
0
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0n or n
Symbol for neutron
1
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1H or 1p
Symbol for proton
1 1
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Have mass numbers & atomic numbers
Describes changes in the nucleus of an atom
Nuclear Equations
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Alpha Decay
Unstable nucleus emits an alpha particle.
Atomic # by 2. Mass # by 4.
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220Fr 4 + 216At
Alpha Decay
Atomic # by 2. Mass # by 4.
87 2 85
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220Fr 4 + 216At
Equation represents natural transmutation. 1 term on reactant side.
87 2 85
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220Fr 4 + 216At
Balance nuclear equations using conservation of
atomic number & conservation of mass
number.
87 2 85
4 + 216=220
87 = 2 + 85
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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.
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42K 0e + 42Ca
Beta Decay
Atomic # by 1.Mass # stays the same.
19 -1 20
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19Ne 0e + 19F
Positron Emission
Atomic # by 1.Mass # stays the same.
10 +1 9
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# of Half-Lives =
Elapsed timeLength of H.L.
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Half-Life Map
Fraction Remainin
g
Amount (mass)
Elapsed Time
# of Half Lives
1 Initial Mass 0 0
½ 1 X H.L. 1
¼ 2 X H.L. 2
1/8 3 X H.L. 3
1/16 4 X H.L. 4
Fraction = 1/2n where n = # of half-lives
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Decay Mode
Same as type of particle emitted
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Average Atomic Mass
Weighted average of the masses of the naturally
occurring isotopes.
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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) Sum4) Do a reality check.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.
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Artificial Transmutation
Particle “bullet” hits target nucleus & new isotope is produced.
2 terms on reactant side.
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Artificial Transmutation
32S + 1n 32P + 1H16 0 15 1
bullettarget
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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.
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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.
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239Pu + 1n 90Sr + 147Ba + 3 1n
Fission
94 0 038 56
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Fusion
Fusion: U for unite and U for sun.
Very small nuclei (H & He) are jammed together. Huge amounts of energy are released.
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1H + 2H 3He
Fusion
1 1 2
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Identify each of the rxns
a) 1n + 235U 142Ba + 91Kr + 3 1n + energy
b) 59Co + 1n 60Co
c) 3He + 1H 4He + 0e
d) 14C 14N + 0e
0 92 56 36 0
27 0 27
2 1 2 +1
6 7 -1
fission
Artificial transmutation
fusion
Natural transmutation
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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.
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Nuclear Binding Energy
The energy released when a nucleus is formed from its nucleons.
Often expressed per nucleon.
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Potential Well Diagram
Po
ten
tial E
ner
gy o
f Sys
tem
Separate Nucleons
Stable Nucleus
Reference level
r, distance between nucleons
4He + energy 2 protons + 2 neutrons2
Represents potential energy changes during a process
Yellow arrow shows the binding energy!
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E = mc2 or E = mc2
Einstein’s Equation relating energy and mass!
Recall that to use this equation, the mass needs to be in kilograms, not amu’s.
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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 = mc2
or E = mc2.7. 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.
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Curve of Binding Energy
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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.
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Nucleon
Protons and Neutrons
Mass # = # of nucleons
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Parts of a nuclear reactor
FuelControl rodsContainment or shieldingCoolantModerator
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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.1n + 235U 142Ba + 91Kr + 3 1n + energy
0 92 03656
Slow neutrons work better!
But fast neutrons come off here!
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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.
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Chain Reaction
One of the products is also one of the reactants
Neutron reactant
Neutron products
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Critical Mass
The minimum amount of U-235 or Pu-239 that will undergo a self-sustaining chain reaction.
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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