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.
Nuclide
An atom with a specific number of protons and a
specific number of neutrons.
14C 12C 14N are all nuclides6 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, GammaSeparated 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.
2He or 2
Symbol for alpha radiationSame as the nucleus of a helium
atomMass = 4 amuCharge = +2
4 4
-1e or -1 or - or
Symbol for beta particleFast moving electron
originating from nucleusMass = “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 mass0 charge
0
0n or n
Symbol for neutron
1
1H or 1p
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.
220Fr 4 + 216At
Alpha Decay
Atomic # by 2. Mass # by 4.
87 2 85
220Fr 4 + 216At
Equation represents natural transmutation. 1 term on reactant side.
87 2 85
220Fr 4 + 216At
Balance nuclear equations using conservation of
atomic number & conservation of mass
number.
87 2 85
4 + 216=220
87 = 2 + 85
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.
42K 0e + 42Ca
Beta Decay
Atomic # by 1.Mass # stays the same.
19 -1 20
19Ne 0e + 19F
Positron Emission
Atomic # by 1.Mass # stays the same.
10 +1 9
# of Half-Lives =
Elapsed timeLength of H.L.
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
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) 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.
Artificial Transmutation
Particle “bullet” hits target nucleus & new isotope is produced.
2 terms on reactant side.
Artificial Transmutation
32S + 1n 32P + 1H16 0 15 1
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.
239Pu + 1n 90Sr + 147Ba + 3 1n
Fission
94 0 038 56
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
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
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
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!
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.
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.
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
FuelControl rodsContainment or shieldingCoolantModerator
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!
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
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