The Physics
Opus in profectus

Nuclear Weapons

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  1. Write a fission bomb question that could be used in both the fission and nuclear weapons sections.
  2. The fuel used in most high-yield thermonuclear weapons is solid lithium 6 deuteride (ρ = 820 kg/m3). These weapons, commonly known as "hydrogen bombs" or "H-bombs", use the energy released when a nuclueus of light lithium and heavy hydrogen, also known as deuterium, fuse to form two nuclei of ordinary helium (a two part process).

    63Li + 21H → 242He

    Given the reaction described above, determine…

    1. the mass of one molecule of lithium 6 deuteride
    2. the mass defect when one molecule of lithium 6 deuteride is transformed into two atoms of helium (in atomic mass units and megaelectronvolts)

    A typical thermonuclear weapon has a yield on the order of several million tons of TNT or about as destructive one truck bomb for every person in Brooklyn. (One ton of TNT is equal to 4.184 GJ by definition.) Given a "small" hydrogen bomb with an explosive yield of one megaton, determine…

    1. the mass destroyed in its detonation
    2. the mass of the fuel required
    3. the volume of the fuel required
  3. Write something else.
  4. The text below describes some of the nuclear reactions that occurred during the detonation of the first hydrogen bomb code named "Mike" at Eniwetok Atoll in 1952. Identify the fusion reactions described in these two paragraphs and rewrite them in symbolic form; that is, as reaction equations.

    All these processes, proceeding through microseconds, prepared Mike for thermonuclear burning. Now the escaping X-radiation of the fissioning sparkplug heated the compressed deuterium at its boundaries; the increasing thermal motion of the deuterium nuclei pushed them together until they passed the barrier of electrostatic repulsion between them and came within range of the nuclear strong force, at which point they began to fuse. Some fused to form a helium nucleus — an alpha particle — with the release of a neutron, the alpha and the neutron sharing an energy of 3.27 MeV(1). The neutron passed through the electrified mass of fusing deuterons and escaped, but the positively charged alpha dumped its energy into the heating deuterium mass and helped heat it further.

    Other deuterium nuclei fused to form a tritium nucleus with the release of a proton, the triton and the proton sharing 4.03 MeV(2). The positively charged proton dumped more energy into the deuterium mass. The tritium nucleus fused in turn with another deuterium nucleus to form an alpha particle and a high-energy neutron that shared 17.59 MeV(3). The 14 MeV neutrons from this reaction began to escape the hot, compressed deuterium plasma and encountered the U238 nuclei of the vaporized uranium pusher. U238 fissions when it captures neutrons with energies above 1 MeV; so the U238 of the uranium pusher began to fission then under the intense neutron bombardment, flooding more X rays back into the deuterium mass from the outside just as the sparkplug fission reaction was radiating them from the inside, trapping the deuterium between two violent walls of heat and pressure. Deuterium-bred tritium fused with tritium as well, producing a helium nucleus and two neutrons that shared 11.27 MeV of energy(4). At lower orders of probability, deuterium captured a neutron and bred tritium(5); deuterium-bred helium fused with deuterium and made heavy [ordinary] helium plus a highly energetic proton(6), or captured a neutron and bred tritium plus a proton(7). All these reactions contributed to the force of the Mike explosion.

    Richard Rhodes, 1995 (paid link)


  1. This question is composed of three related parts.
    1. What percentage of the original mass is converted to energy when two heavy hydrogen atoms fuse to form one helium atom?
    2. Calculate the mass destroyed in the detonation of a typical hydrogen bomb if its explosive potential is equivalent to one million tons of TNT. (One ton of TNT possesses 4.184 GJ of chemical energy.)
    3. Using your results from the previous two questions, determine the mass of nuclear fuel needed to make an "H-bomb" capable of leveling hundreds of square kilometers.


  1. yield-to-weight.txt
    The efficiency of a nuclear weapon is often stated as a yield-to-weight ratio — the energy released after the weapon detonated divided by the mass of all its parts (nuclear fuel, conventional explosive, triggers, casing, etc.) before it detonated. The practical limit for all forms of nuclear weapon is thought to be 6 kt/kg (kilotons per kilogram). Identify the weapon that comes closest to this limit and state its yield-to-weight ratio. The accompanying tab-delimited-text file provides the following information for all publicly known weapons designed and built in the United States from 1945–1991:
    1. Designation (the "make and model" of the device)
    2. Type of device (bomb, warhead, artillery shell, or demolition munition)
    3. Weight in English pounds (1 kg = 2.2 lbs)
    4. Maximum explosive yield in kilotons of TNT
    Source: Complete List of All US Nuclear Weapons. Carey Sublette. Nuclear Weapon Archive (2006).


  1. Read this passage.

    The ultimate secret of the W-88 warhead, as with all nuclear bombs, is the mere fact that one kilogram of uranium, when completely fissioned, releases the energy equivalent of 18 thousand tons (18 kilotons) of TNT. Six kilograms of uranium would fit inside a can of soda pop. If the published descriptions are correct, the W-88 will fully fission about 26 kilograms of uranium, a liter and a half, or two wine bottles' worth. A softball bat made of uranium would weigh about 26 kilograms. The Hiroshima bomb reportedly had twice that much uranium-235, but it was only 2% efficient

    Howard Morland, 1999.

    Verify (in whatever order you wish) that…
    1. "[O]ne kilogram of uranium, when completely fissioned, releases the energy equivalent of 18 thousand tons (18 kilotons) of TNT."
    2. "Six kilograms of uranium would fit inside a can of soda pop."
    3. "[T]he W-88 will fully fission about 26 kilograms of uranium, a liter and a half, or two wine bottles' worth."
    4. "A softball bat made of uranium would weigh about 26 kilograms."