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Physics a Nuclear Bomb

Extracts from this document...


                 Nuclear Physics                            Page |

 Table of Contents

Page Number



















Appendix A


Appendix B


Appendix B


Appendix C


Appendix C


Appendix D




The Nuclear bomb is a well known and greatly feared weapon. Its often categorized as a weapon of mass destruction, and appropriately named so after its detonation in Hiroshima, Japan on Monday, August 6, 1945. This bomb, named 'Little boy', instantly incinerated approximately 90,000-166,000 innocent Japanese lives. 2   Little boy was a uranium bomb which was capable of destroying houses from around 1.6 km away from the area of detonation with an overpressure of approximately 5 psi. 2 The Destruction displayed by this bomb in particular was due to X-ray heated fireballs, hyper intensified soundwaves, and gamma radiation.

These X-ray heated fireballs burned at around 3980ᵒC  . Everything near the fireball would spontaneously burst into flames and sand would melt and form glass. 2,3 All human life was incinerated instantly, so quickly that their shadows were etched into the ground beneath them. The premature extinguishing of this fireball was due to the hyper intensified sound waves emitted from the explosion. The hyper intensified soundwaves in fact travelled at speeds much higher than that of the sound barrier, and within the kill zone of the bomb, output a pressure of 5 psi3,  which could easily destroy homes and other buildings.

After the initial effect of the blast there was still the daunting affects of nuclear radiation and nuclear decay. Radioactive decay is the process of atoms splitting apart, and the small parts of the atom being shot outward at high speeds, thus being called rays, and soon after colliding into and splitting apart surrounding atoms and creating a chain effect. There are different types of radioactive decay which are separately named accordingly as Alpha decay, Beta Decay, and Spontaneous fission. 2

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This method of detonation was used in the atomic bomb named "Little Boy", which was dropped on Hiroshima. Essentially what happens is a small 'bullet' of uranium is displaced by an explosion, which propels it towards and into a larger sphere of uranium (both at subcritical mass) through a canon, and thus creating the supercritical mass of uranium. This supercritical mass is then bombarded with neutrons and is kept under pressure, with external explosives and the bomb casing, to allow fissionable material to fully fission. This is then followed by a massive release of energy and radiation (Refer to Appendix A).


With nuclear radiation comes nuclear decay. They are essentially the same concept. In the regards to fission electromagnetic radiation, in the form of gamma rays, is the most common type of radiation. 4 Gamma rays are the emission of high energy photons. These high energy photons move at a very high frequency of approximately 1019 Hz, and retain very short wavelengths of less than 10 picometers. 4 Often gamma rays retain energy measuring around 100MeV, but Gamma radiation decay photons retains exceedingly more (usually around a few hundred MeV more). What makes gamma radiation so harmful to living tissue (i.e. Humans) is that gamma radiation is a type of ionizing radiation. 7 The photon particles in gamma rays are so energetic that they are able to strip other atoms of their electrons, and in turn giving that atom a more positive charge (A.K.A. Ionizing the atoms). 7 This can lead to many health issues for any living organism causing skin damage and burns, radiation sickness, and forms of cancer. 4

Another form of radiation and nuclear decay commonly found in the by-products of fission reactions beta decay and radiation.4

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Table 2 - Thermal Flash effects range from ground zero (GZ) and slant range (Airburst) 6

Appendix C --> Fission Bomb6


Numbered parts:

  1. bomb casing
  2. detonators
  3. conventional high explosion
  4. pusher (aluminum, others) and reflector (beryllium, tungsten)
  5. tamper (uranium-238)
  6. fissile core (plutonium or uranium-235)

Sequence of events in explosion: Numbered parts:

  • Multiple detonators (2) simultaneously initiate detonation of high explosives (3).
  • As detonation progresses through high explosives (3), shaping of these charges transforms the explosive shock front to one that is spherically symmetric, travelling inward.
  • Explosive shock front compresses and transits the pusher (4) which facilitates transition of the shock wave from low-density high explosive to high-density core material.
  • Shock front in turn compresses the reflector (4), tamper (5), and fissile core (6) inward.
  • When compression of the fissile core (6) reaches optimum density, a neutron initiator (either in the centre of the fissile core or outside the high explosive assembly) releases a burst of neutrons into the core.
  • The neutron burst initiates a fission chain reaction in the fissile core (6): a neutron splits a plutonium/uranium-235 atom, releasing perhaps two or three neutrons to do the same to other atoms, and so on; energy release increases geometrically.
  • Many neutrons escaping from the fissile core (6) are reflected back to it by the tamper (5) and reflector (4), improving the chain reaction.
  • The mass of the tamper (5) delays the fissile core (6) from expanding under the heat of the building energy release.
  • Neutrons from the chain reaction in the fissile core (6) cause transmutation of atoms in the uranium-235 tamper (5).
  • As the superheated core expands under the energy release, the chain reaction ends; the entire weapon is vaporized.
  • Total elapsed time: about 0.00002 seconds.

Appendix   D - Teller-Ulam Fusion Bomb3



Airburst   -   An above ground detonation of a bomb

Ground Zero (GZ)   -   An on ground detonation(point of detonation referred to as ground zero)

Kiloton(kt)   -   Equivalent in TNT (eg. 1kt = 1000 tons of TNT)

Fizzle- Occurs when fissionable material in a bomb is blown away before it can completely fission

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