NE 301 - Introduction to Nuclear Science Spring 2012
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NE 301 - Introduction to Nuclear Science Spring 2012 Classroom Session 2: • Natural Radioactivity • Chart of the Nuclides • Nuclear Stability (Binding Energy, BE) • Radioactive Decay Types • Radioactive Decay and Growth • Isotopes and Decay Diagrams • Nuclear Reactions • Energy of nuclear reactions • Neutron Cross Sections
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NE 301 - Introduction to Nuclear Science Spring 2012. Classroom Session 2: Natural Radioactivity Chart of the Nuclides Nuclear Stability (Binding Energy, BE) Radioactive Decay Types Radioactive Decay and Growth Isotopes and Decay Diagrams Nuclear Reactions Energy of nuclear reactions - PowerPoint PPT Presentation
Transcript of NE 301 - Introduction to Nuclear Science Spring 2012
NE 301 - Introduction to Nuclear ScienceSpring 2012
Classroom Session 2:
•Natural Radioactivity•Chart of the Nuclides•Nuclear Stability (Binding Energy, BE)•Radioactive Decay Types•Radioactive Decay and Growth•Isotopes and Decay Diagrams•Nuclear Reactions
• Energy of nuclear reactions• Neutron Cross Sections• Activation Calculations
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Prelude…Please bring clickers to class.
Please bring calculators.
Get in pairs/groups, feel free to talk across tables.
Time on task please. I want everybody working to get answers.
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Radioactivity in Nature
Discovered in 1896 by Henri Becquerel Using photographic plates Notice: no natural sensors for radiationMarie Curie: differences between radioactivity of Uranium and Uranium minerals Discovered Polonium then Radium (both
1898) Main radioactive minerals are:
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Main Radioactive Minerals
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Main Naturally Occurring Isotopes:
Trivia:14C production:
~22,000 at/s/m2 of earth surface
3H production:~2,500 at/s/m2
Global Planetary Equilibrium Inventory of:
63 tons of 14C3.5 kg of 3H
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A Bit of History… Filling the Periodic Table
The Periodic Table of the Elements 1869 by Dmitri Mendeleev
a) Elements Known: 1 – H to 83 – Bi. Plus U and Th. Some stable elements later (Hf -1922, Re-
1925)b) Natural Unstable Elements:
Po, Rn, Fr, Ra, Ac, and Pa (mainly by Curies)
c) Artificial Elements 43-Tc , 61-Pm , 85-At, and Transuranics (Np,
Pu, Am, etc)
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Isotopes…40 kinds of atoms with different half-lives were foundProblem: Only 13 spots available in the Periodic TableFrederick Soddy in 1913: Isotopes = “In the Same Place” Nobel Prize 1921 It was later discovered that stable atoms also can have isotopes (e.g.
Sn has 10 stable and 18 unstable ones).
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Atomic and Nuclear Nomenclature
X element symbol (H, He, Na, Xe, U, etc.) represents the number of charges in the nucleus (thus electrons, thus chemical behavior).
A = Mass number = protons + neutrons = Nucleons.
Z = atomic number = protons. X and Z are redundant and normally we only
write AX.e.g. 235U, 16O, 3H, 14C
ZAX
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NuclidesAtoms differing by atomic number of mass number
Radionuclide: Unstable
nuclide
Table of nuclidesProvide accurate mass of each nuclide
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Chart of the Nuclides
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Chart of the Nuclides
Z
N
IsobarsIsotopes
Isotones
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Trivia:Nuclides
known:
Found in Nature:
Main Nat. Radioactive:
Produced by cosmic rays:
~2800
258 Stable25 with Z<80 reported radioactive (7 not confirmed)
235U, 238U, 232Th and decay families.
14C, 10Be, 7Be, 3H
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Nuclear IsomersCertain Nuclides with different physical properties Half-lives Modes of decayMetastable states of the same nuclide Either decay by -emission Transmute to other nuclides (,
decay, etc)Suffix “m” next to A. (i.e. 60mCo, 99mTc)
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DownloadRadDecay, by Charles Hacker
Play with it:
1. How to find nuclides2. Half-life3. Understand Decay products
) ’s) ’sc) ’sd) X-Rayse) electrons
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Nuclear Stability
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Stability of Nuclei – General Observations
In general, nuclei with an even number of protons or neutrons are more stableAs the protons increase electromagnetic forces increase and more neutrons are needed to provide attractive nuclear force to keep the nucleus togetherCertain Z or N numbers are particular stable (Higher BE) 2, 8, 20, 28, 50, 82, 126
Magic Numbers
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Stability with Even or Odd Z
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Stability with Even or Odd N
Even Z, Even N = 159
Even Z, Odd N = 53Odd Z, Even N = 50Odd Z, Odd N = 4
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Let’s do some accounting…For example: Mass of Oxygen Atom:
Mp=1.007276 amuMn=1.008665 amuMe=5.48e-4 amu
168
16.131912 amu
8 1.007276 amu
( ) 8 1.008665 amu 15.994915 amu8 5.48 4 amu
p
n O
e
Zm
A Z m MZm e
Mass Defect = Binding
Energy (BE)
1 amu = 931.49 MeV
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Nuclear Stability and Binding Energy (BE)
Higher BE = Higher Stability
Compare BE of 12C and 14C:
To understand stability and radioactive decay, please calculate BE for the following ISOBARS (A=73):
73Zn, 73Ga, 73Ge, 73As, 73Se, 73Br, 73KrEverybody!
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Isobars = A
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Notice radioactive decay stabilizes atoms:
Question:
Do fission products normally have - or + decay?
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Chart of the Nuclides
Z
N
Z=N
i.e. Fission products are neutron rich
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Another
Example:Notice several stable possibilities
If we graph naturally occurring atoms…
Fission
Fusion
Reaction EnergeticsReaction reactants and products
If E is positive: reaction exothermic
releases energyIf E is negative, reaction endothermic
requires energyEndoergic and exoergic is sometimes used
A + B C + D + E
Please remember…
BALANCE!
Before starting to work
Balancing Reactions
nucleons 1 +16 = 16+1Charges
01n 8
16O 716N1
1p
1 16 16 0 10 8 7 1 1
1 16 16 10 8 7 1
n O N e p or
n O N H
(+) 0 + 8 = 7 + 1(-) -0 -8 = -7 -0 e- missing
0 1So in reality the reaction is:
Calculating Q…
Q-value for the reaction is:
Using atomic mass tables:
1 16 16 10 8 7 1n O N H
( )1.008665 15.994915 16.006101 1.007825 0.010346 amu
931.494 MeV 0.010346 amu 9.637 MeV1 amu
A B C DM M M M MM
Endothermic reaction. Only a few fission neutrons can do it
