Exploding - bridgewire detonator The exploding - bridgewire detonator ( " EBW " , also known as exploding wire detonator ) is a type of detonator used to initiate the detonation reaction in explosive materials , similar to a blasting cap in that it is fired using an electric current . EBWs use a different physical mechanism than blasting caps , using more electricity delivered much more rapidly , and explode in a much more precise timing after the electric current is applied . This has led to their common use in nuclear weapons . The slapper detonator is a more recent development along similar lines . History . The EBW was invented by Luis Alvarez and Lawrence Johnston for the Fat Man - type bombs of the Manhattan Project , during their work in Los Alamos National Laboratory . The Fat Man Model 1773 EBW detonators used an unusual , high reliability detonator system with two EBW " horns " attached to a single booster charge , which then fired each of the 32 explosive lens units . Description . EBWs were developed as a means of detonating multiple explosive charges simultaneously , mainly for use in plutonium - based nuclear weapons in which a plutonium core ( called a “ pit ” ) is compressed very rapidly . This is achieved via conventional explosives placed uniformly around the pit . The implosion must be highly symmetrical or the plutonium would simply be ejected at the low - pressure points . Consequently , the detonators must have very precise timing . An EBW has two main parts : a piece of fine wire which contacts the explosive , and a “ strong ” source of high - voltage electricity — strong , in that it holds up under sudden heavy load . When the wire is connected across this voltage , the resulting high current melts and then vaporizes the wire in a few microseconds . The resulting shock and heat initiate the high explosive . This accounts for the heavy cables seen in photos of the Trinity “ Gadget ” ; high voltage cable requires good insulation and they had to deliver a large current with little voltage drop , lest the EBW not achieve the phase transition quickly enough . The precise timing of EBWs is achieved by the detonator using direct physical effects of the vaporized bridgewire to initiate detonation in the detonator ’ s booster charge . Given a sufficiently high and well known amount of electric current and voltage , the timing of the bridgewire vaporization is both extremely short ( a few microseconds ) and extremely precise and predictable ( standard deviation of time to detonate as low as a few tens of nanoseconds ) . Conventional blasting cap s use electricity to heat a bridge wire rather than vaporize it , and that heating then causes the primary explosive to detonate . Imprecise contact between the bridgewire and the primary explosive changes how quickly the explosive is heated up , and minor electrical variations in the wire or leads will change how quickly it heats up as well . The heating process typically takes milliseconds to tens of milliseconds to complete and initiate detonation in the primary explosive . This is roughly one to ten thousand times longer and less precise than the EBW electrical vaporization . Use in nuclear weapons . Since explosives detonate at typically 7 – 8 kilometers per second , or 7 – 8 meters per millisecond , a one millisecond delay in detonation from one side of a nuclear weapon to the other would be longer than the time the detonation would take to cross the weapon . The time precision and consistency of EBWs ( 0 . 1 microsecond or less ) are roughly enough time for the detonation to move 1 millimeter at most , and for the most precise commercial EBWs this is 0 . 025 microsecond and about 0 . 2 mm variation in the detonation wave . This is sufficiently precise for very low tolerance applications such as nuclear weapon explosive lens es . Due to their common use in nuclear weapons , these devices are subject to the nuclear control authorities in every state , according to the Guidelines for the Export of Nuclear Material , Equipment and Technology . In the US , EBWs are on the US State Department Munitions Control List , and exports are highly regulated . Civilian use . EBWs have found uses outside nuclear weapons , such as the Titan IV , safety conscious applications where stray electrical currents might detonate normal blasting caps , and applications requiring very precise timing for multiple point commercial blasting in mines or quarries . Mechanism of operation . The bridgewire is usually made of gold , but platinum or gold / platinum alloys can also be used . The most common commercial bridgewire diameter and length is 1 . 5 and 40 mils ( 0 . 038 mm and 1 mm ) , but lengths ranging from 10 mils to 100 mils ( 0 . 25 mm to 2 . 5 mm ) 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 PBX ( e . g . PBX 9407 ) . Detonators without such booster are called " initial pressing detonators " ( IP detonators ) . 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 . ( " Cf . " slapper detonator s , which can use high density hexanitrostilbene , allowing their use in temperatures up to almost 300 °C and at both vacuum and at high pressures . ) Firing system . The EBW and the slapper detonator are the safest known types of detonators , as only a very high - current fast - rise pulse can successfully trigger them . However , they require a bulky power source for the current surges required . The extremely short rise times are usually achieved by discharging a low - inductance , high - capacitance , high - voltage capacitor ( e . g . oil - filled , Mylar - foil , or ceramic ) through a suitable switch ( spark gap , thyratron , krytron , etc . ) into the bridge wire . The ballpark figures are 5 kilovolt and 1 microfarad rating for the capacitor , and the peak current required ranges between 500 and 1000 amperes . The wire used in the bridge tends to be highly pure gold or platinum , 0 . 02 – 0 . 05 mm in diameter , and 1 mm long . The high voltage may be generated using a Marx generator . Low - impedance capacitors and low - impedance coaxial cable s are required to achieve the necessary current rise rate . A possible alternative for bulky ( * see note below ) capacitors is the flux compression generator . When fired , it creates a strong electromagnetic pulse , which is inductively coupled into one or more secondary coils connected to the bridge wires or slapper foils . In a fission bomb the same or similar circuit is used for powering the neutron trigger , the additional booster source of fission neutrons . The energy in such a capacitor would be 1 / 2 C V , which for the above mentioned cap is 12 . 5 J . The capacitor would be small even if a low energy density one was used ( soda can size ) . By comparison , a defibrillator delivers ~ 200 J from 2 kV and perhaps 20 µF . The flash - strobe in a disposable camera is typically 3 J from a 300 V capacitor of 100 µF .