PHYSICS OF NUCLEAR WEAPONS
Nuclear Binding Energy
Nuclear Stability
Weapon Types
• Fission
“Little Boy”
“Fat Man”
Weapon Size
Nuclear Weapons & States
The Fission Reaction
200 MeV/240 ≈ 0.8 MeV/nucleon
≈ 1,000,000 X Echemical
Weapon Types
• Fusion
Two-Stage Thermonuclear
The Fusion Reaction
17.6 MeV/5 ≈ 3.5 MeV/nucleon ≈ 5 X Efission
Comparison of Fission & Fusion
Nuclear Fission
Definition:
Natural occurrence of the process:
Byproducts of the reaction:
Conditions:
Energy Requirement:
Nuclear Fusion
Fission is the splitting of a large atom into Fusion is the fusing of two or more lighter
two or more smaller ones.
atoms into a larger one.
Fission reaction does not normally occur
in nature.
Fusion occurs in stars, such as the sun.
Few radioactive particles are produced by
Fission produces many highly radioactive fusion reaction, but if a fission "trigger" is
particles.
used, radioactive particles will result from
that.
Critical mass of the substance and highspeed neutrons are required.
High density, high temperature
environment is required.
Extremely high energy is required to bring
Takes little energy to split two atoms in a two or more protons close enough that
fission reaction.
nuclear forces overcome their
electrostatic repulsion.
Energy Released:
The energy released by fission is a million
times greater than that released in
chemical reactions; but lower than the
energy released by nuclear fusion.
The energy released by fusion is three to
four times greater than the energy
released by fission.
Nuclear weapon:
One class of nuclear weapon is a fission
bomb, also known as an atomic bomb or
atom bomb.
One class of nuclear weapon is the
hydrogen bomb, which uses a fission
reaction to "trigger" a fusion reaction.
Paths to Fissionable Material
Nuclear Fuel - Uranium
• Ore → Yellow Cake → Enriched
Uranium Deposits
Uranium Deposits
Uranium
Enrichment
Slightly Enriched (SEU): 0.9%-2.0%
Used in Heavy-Water Reactors (HWR)
Low-Enriched (LEU): 2%-20%
3%-5% used in Light-Water Reactors (LWR)
12%-19.75% used in Research Reactors
Highly Enriched (HEU): >20%
≥ 85% used in weapons primaries
≥ 20% ‘weapons-usable’ in implosion designs
40%-80% used in secondary of two-stage
≥ 20% used in fast neutron reactors
50%-90% used in naval reactors
26.5% in commercial fast reactors
Critical
Mass
Critical Masses
Isotope or
Mixture
Critical Mass Half Life
(kg)
(years)
Decay Heat
(watts/kg)
U-233
16
160,000
0.28
U-235
Np-237
Pu-238
Pu-239
Pu-240
Pu-241
48
59
10
10
37
13
700,000,000
2,100,000
88
24,000
6,600
14
Pu-242
Am-241
89
57
380,000
430
Neutron
Production
From
Spontaneous
Fission (per
kg-sec)
1.2
Main Gamma
Energies
(MeV)
2.6 from Tl208
Properties of Nuclear-Explosive
Nuclides
0.00006TABLE A-10.36
0.19
0.021
0.14
0.087
560
2,700,000
0.100
2.0
22
0.41
7.0
1,000,000
0.10
6.4
49
0.66 from Am241
0.12
1,700,000
0.045
110
1,500
0.66
Comparison of Energy Content
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Fission of U-233: 17.8 kt/kg
Fission of U-235: 17.6 kt/kg
Fission of Pu-239: 17.3 kt/kg
Fusion of pure deuterium: 82.2 kt/kg
Fusion of tritium and deuterium (50/50): 80.4 kt/kg
Fusion of lithium-6 deuteride: 64.0 kt/kg
Fusion of lithium-7 deuteride:
Total conversion of matter to energy: 21.47 Mt/kg
Fission of 1.11 g U-235: 1 megawatt-day (thermal)
Broader comparison of Energy Densities
Enrichment Process
Uranium
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•
•
Isotopic Masses and Abundances
•
•
235U
235U
238U
238U
Abundance = 0.720%
Abundance = 99.274%
Mass = 235.04393 (UF6, 349.03433)
Mass = 238.05079 (UF6, 352.04119)
• m238/ m235 = 1.0086
•
m238/ m235 = 1.0043 →
v235/ v238 = 1.0043
UF6
Enrichment Methods
• Electromagnetic (Calutron)
(≤ 15% enrichment)
Enrichment Methods
• Gaseous Diffusion
Enrichment Timeline
Enrichment Methods
• Thermal Diffusion
Enrichment Methods
• Gas Centrifuge
Centrifuges
• Materials:
Aluminum → Maraging Steel → Carbon Fiber Composite
• 100,000 rpm (balanced, magnetic bearings)
• STUXNET
Enrichment Methods
• LASER Techniques
(AVLIS/MLIS)
Method Comparison
Resources
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IAEA/INFCIS
The Atomic Archive
World Nuclear Association
Nuclear Chemistry
Federation of American Scientists
Nuclear Pathways
ALSOS Digital Library
Nuclear Safeguards Education Portal
World Information Service on Energy (WISE) Uranium Project