Implosion (mechanical process)

Implosion is a process in which objects are destroyed by collapsing (or being squeezed in) on themselves. The opposite of explosion (which expands the volume), implosion reduces the volume occupied and concentrates matter and energy. True implosion usually involves a difference between internal (lower) and external (higher) pressure, or inward and outward forces, that is so large that the structure collapses inward into itself, or into the space it occupied if it is not a completely solid object. Examples of implosion include a submarine being crushed from the outside by the hydrostatic pressure of the surrounding water and the collapse of a massive star under its own gravitational pressure. An implosion can propel material outward (for example due to the force of inward falling material rebounding, or peripheral material being ejected as the inner parts collapse), but this is not an essential component of an implosion and not all kinds of implosion will do so. If the object was previously solid, then implosion usually requires it to take on a more dense form—in effect to be more concentrated, compressed, or converted into a new material that is denser than the original. In an implosion-type nuclear weapon design, a sphere of plutonium, uranium, or other fissile material is imploded by a spherical arrangement of explosive charges. This decreases the material's volume and thus increases its density by a factor of two to three, causing it to reach critical mass and create a nuclear explosion. In some forms of thermonuclear weapons, the energy from this explosion is then used to implode a capsule of fusion fuel before igniting it, causing a fusion reaction (see Teller–Ulam design). In general, the use of radiation to implode something, as in a hydrogen bomb or in laser driven inertial confinement fusion, is known as radiation implosion. Cavitation (bubble formation/collapse in a fluid) involves an implosion process. When a cavitation bubble forms in a liquid (for example, by a high-speed water propeller), this bubble is typically rapidly collapsed—imploded—by the surrounding liquid.