Editing Exploding-bridgewire detonator (section)

== Mechanism of operation ==

The bridgewire is usually made of [[gold]], but [[platinum]] or gold/platinum alloys can also be used. The most common commercial wire size is 0.038&nbsp;mm (1.5 [[thousandth of an inch|mils]]) in diameter and 1&nbsp;mm (40 mils) in length, but lengths ranging from 0.25&nbsp;mm to 2.5&nbsp;mm (10 mils to 100 mils) can be encountered. From the available explosives, only [[PETN]] at low densities can be initiated by sufficiently low shock to make its use practical in commercial systems as a part of the EBW initiator. It can be chained with another [[explosive booster]], often a pellet of [[tetryl]], [[RDX]] or some [[polymer-bonded explosive|PBX]] (e.g., PBX 9407). Detonators without such booster are called ''initial pressing detonators'' (IP detonators).<!-- Paul Cooper: Introduction to the Technology of Explosives, chapter 4.5 -->

During initiation, the wire heats with the passing current until melting point is reached. The heating rate is high enough that the liquid metal has no time to flow away, and heats further until it vaporizes. During this phase the electrical resistance of the bridgewire assembly rises. Then an [[electric arc]] forms in the metal vapor, leading to drop of electrical resistance and sharp growth of the current, quick further heating of the ionized metal vapor, and formation of a [[shock wave]]. To achieve the melting and subsequent vaporizing of the wire in time sufficiently short to create a shock wave, a current rise rate of at least 100 amperes per microsecond is required.

If the current rise rate is lower, the bridge may burn, perhaps causing deflagration of the PETN pellet, but it will not cause detonation. PETN-containing EBWs are also relatively insensitive to a static electricity discharge. Their use is limited by the thermal stability range of PETN.  [[Slapper detonator]]s, which can use high density [[hexanitrostilbene]], may used in temperatures up to almost {{Convert|300|C|F}} in environments ranging from vacuum to high pressures.<!-- Paul Cooper: Introduction to the Technology of Explosives, chapter 4.5 --><ref name="Cooper-Intro">
{{cite book
 |last=Cooper
 |first=Paul W.
 |title=Introduction to the Technology of Explosives
 |year=1996
 |publisher=Wiley-VCH
 |chapter=Chapter 4.5 Exploding bridgewire detonators
 |isbn=978-0471186359
}}</ref>