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Acknowledgements/Disclaimer

• All information in this presentation is in the public domain

• This information is insufficient to actually build a nuclear device

• Historical material, including video clips, has been taken mainly from US government websites, atomic weapons archive

• Guide to nuclear weapons, Federation of American Scientists, Membrane domain (garwain.membrane.com/hew)

• Some animations are taken from the website “HowStuffWorks”

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Physical Foundation of Nuclear Fission Weapons

235 236 *

239 240 *

2 2.4

2 2.5

U n U FF n Q

Pu n Pu FF n Q

Fission based “atomic” bombs

Task:

•Initially stable, sub-critical configuration of fissile material

•produce prompt criticality, a self-sustained super-critical fission chain reaction with fast neutrons,

•produce exponential n multiplication explosion

•explosive disassembly in short time, internal expansion+surface blow-off decreases density

•prevent premature rediation of energy to outside tamper, using most of material

use U or Pu metal

Typical conversion in a weapon: 1 kg U/Pu 17 kT TNT + 5·1024 n

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Critical Masses

Critical Masses for Plutonium Compositions Total mass Pu (kg)/239Pu (kg), density = 19.4 . Isotopic Composition Reflector . atomic % None 10 cm nat. U . 239 240 . 100% 0% 10.5/10.5 4.4/4.4 90% 10% 11.5/10.3 4.8/4.3 80% 20% 12.6/10.0 5.4/4.3 70% 30% 13.9/ 9.7 6.1/4.3 60% 40% 15.4/ 9.2 7.0/4.2 50% 50% 17.2/ 8.6 8.0/4.0 40% 60% 20.0/ 8.0 9.2/3.7 20% 80% 28.4/ 5.7 13. /2.6 0% 100% 40. / 0.0 20. /0.0 .

Pu-238 9 kg Pu-239 10 kg Pu-240 40 kg Pu-241 12 kg Pu-242 90 kg Am-241 114 kg

All Pu mixture have critical masses all produce nuclear explosion, if supercriticality is reached fast enough geometry, reflectors, tampers

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Effect of Reflector

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The US Manhattan Project

1941: Rudolph Frisch & Otto Peierls (in UK) calculate critical mass 235U (~10 lbs)

Dec. 1942: Fermi’s reactor in Chicago went critical April 1943: Site Y: Los Alamos/NM laboratory

Industrial Scale Test Experiments

Pu prod

U enrichmt

ORNL K-35 Plant

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Atomic-Bomb Gun Design

“fool proof” design, had not been tested before deployment

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Trinity Site Atomic Bomb Tests

July 16, 1945July 16, 1945

First explosion of a nuclear device.First explosion of a nuclear device.North of Alamogordo/NMNorth of Alamogordo/NM

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The Hiroshima Bomb

60 kg U0.8 kg used in fission (=1.3%) rest dispersed into atmosphere

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Pu Nuclear Fission Bomb

Deployed in Nagasaki, 1945

ignition by n from

PuBe internal initiator6 kg Pu 22kt (fission of 1.3 kg Pu) more efficient: = 20%

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The Nagasaki Bomb

Designed and built in Los Alamos

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““LittleBoy” and “Fat Man” in Los Alamos MuseumLittleBoy” and “Fat Man” in Los Alamos Museum

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Hiroshima, August 6, 1945

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Memorable Events

August 6, 1945 Hiroshima: “Little Boy” fission bomb (gun design, 60 kg 239U, 14.5 kt TNT) dropped by Enola Gay B-29 bomber

August 9, 1945 Nagasaki “Fat Man” (implosion design), 6.2 kg 239Pu 22 kt TNT

November 1, 1952, Eniwetok Atoll: “Mike” 10Mt thermo-nuclear (hydrogen) bomb (radiation implosion),

1961, Soviet Union: 60 MT hydrogen bomb

Fat Man

Mike

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Physical Foundations of Thermonuclear Bombs

235 236 *

239 240 *

2 2.4

2 2.5

th

th

U n U FF n Q

Pu n Pu FF n Q

3

3 4

6 4

7

4

4

3.25

4.0

18.3

2 22.4

2 17.3

17.6

d d He MeV

d d t p MeV

fast

d H

d t He

e He p MeV

d Li H

n MeV

e MeV

p Li He MeV

Fission bomb as ignition of hydrogen device

Fusion based “thermo-nuclear” bombs

6 4

7 4

4.8

2.5

n Li t He MeV

n Li t n He MeV

t-”breeding” reactionst1/2 = 12.35 a

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Boosted Thermonuclear Bombs

X-ray radiation transfers energy to fusion chamber

fission n render rod super-critical

n+6Li4He+t ignites d-d, d-t

fusion

Staged radiation implosion

Teller-Ulam design (1951): chemical explosive implodes kg-Pu chargeexploding Pu produces many (80%) soft X rays transferring energy fast (10-8 s) to secondary Li/D fusion charge 10-9 s dd, dt reactions

Edward Teller

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2-Stage Radiation-Implosion Bomb

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Effects of Nuclear Weapons

•Radiation, direct and delayed (fall-out), soil contamination

•Thermal

•Blast effects, direct dame, material in atmosphere

•Electromagnetic pulse EMP effects

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