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An electromagnetic pulse (commonly abbreviated as EMP, pronounced ) is a burst of electromagnetic radiation. Nuclear explosions create a characteristic pulse of electromagnetic radiation called a nuclear EMP or NEMP. The resulting rapidly changing electric and magnetic fields may couple with electrical and electronic systems to produce damaging current and voltage surges. The specific characteristics of any particular nuclear EMP event vary according to a number of factors, the greatest of which is the altitude of the detonation. The term "electromagnetic pulse" generally excludes optical (infrared, visible, ultraviolet) and ionizing (such as X-ray and gamma radiation) ranges. In military terminology, a nuclear warhead detonated hundreds of kilometers above the Earth's surface is known as a high-altitude electromagnetic pulse (HEMP) device. Effects of a HEMP device depend on factors including the altitude of the detonation, energy yield, gamma ray output, interactions with the Earth's magnetic field and electromagnetic shielding of targets. ==History== The fact that an electromagnetic pulse is produced by a nuclear explosion was known in the earliest days of nuclear weapons testing. The magnitude of the EMP and the significance of its effects, however, were not immediately realized.〔Broad, William J. "Nuclear Pulse (I): Awakening to the Chaos Factor", Science. 29 May 1981 212: 1009–1012〕 During the first United States nuclear test on 16 July 1945, electronic equipment was shielded due to Enrico Fermi's expectation of the electromagnetic pulse. The official technical history for that first nuclear test states, "All signal lines were completely shielded, in many cases doubly shielded. In spite of this many records were lost because of spurious pickup at the time of the explosion that paralyzed the recording equipment."〔Bainbridge, K.T., (Report LA-6300-H), Los Alamos Scientific Laboratory. May 1976. p. 53 (''Trinity'' )〕 During British nuclear testing in 1952–1953 instrumentation failures were attributed to "radioflash", which was their term for EMP.〔Baum, Carl E., IEEE Transactions on Electromagnetic Compatibility. Vol. 49, No. 2. pp. 211–218. May 2007. (''Reminiscences of High-Power Electromagnetics'' )〕〔Baum, Carl E., Proceedings of the IEEE, Vol.80, No. 6, pp. 789–817. June 1992 (''From the Electromagnetic Pulse to High-Power Electromagnetics'' )〕 The first openly reported observation of the unique aspects of high-altitude nuclear EMP occurred during the helium balloon lofted Yucca nuclear test of the Hardtack I series on 28 April 1958. In that test, the electric field measurements from the 1.7 kiloton weapon went off the scale of the test instruments and was estimated to be about 5 times the oscilloscope limits. The Yucca EMP was initially positive-going whereas low-altitude bursts were negative pulses. Also, the polarization of the Yucca EMP signal was horizontal, whereas low-altitude nuclear EMP was vertically polarized. In spite of these many differences, the unique EMP results were dismissed as a possible wave propagation anomaly.〔Defense Atomic Support Agency. 23 September 1959. Operation Hardtack Preliminary Report. Technical Summary of Military Effects. Report ADA369152. pp. 346-350. ()〕 The high-altitude nuclear tests of 1962, as discussed below, confirmed the unique results of the Yucca high-altitude test and increased the awareness of high-altitude nuclear EMP beyond the original group of defense scientists. The larger scientific community became aware of the significance of the EMP problem after a three-article series on nuclear EMP was published in 1981 by William J. Broad in ''Science''.〔〔Broad, William J. "Nuclear Pulse (II): Ensuring Delivery of the Doomsday Signal", Science. 5 June 1981 212: 1116–1120〕〔Broad, William J. "Nuclear Pulse (III): Playing a Wild Card", Science. 12 June 1981 212: 1248–1251〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nuclear electromagnetic pulse」の詳細全文を読む スポンサード リンク
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