The gedanken experiment as introduced recently by Pirani to demonstrate the noncausal behavior of classical tachyons is reconsidered and analyzed in Minkowski space. Upon adhering to the principles used by Sudarshan and Feinberg with respect to the possible existence of tachyons, it i s shown that the noncausal behavior of classical tachyons as deduced from this experiment is inconclusive.
We propose and study a new technique for estimating the weight of very heavy objects. This new technique is based on measurements made by a device, a gravity gradiometer, that is capable of measuring subtle changes in the gravitational field produced by an object with respect to distance. The physical observables, known as gravity gradients, depends upon the mass density distribution of an object and the relative distance between the object and the measurement device. We show that, for very heavy objects, gravity gradient measurements can be used to make accurate weight estimates. This technology could be potentially important in the eventual implementation of arms control agreements or for application in the transportation industry.
Efforts to halt proliferation of nuclear weapons are threatened by vulnerability of weapons-usable material to smuggling especially in Russia. Mixing 232 U into highlyenriched uranium (HEU) makes it readily observable and harder to steal. Adding a proportion of 233 U associated with a specific storage site enables attribution to be performed on stolen HEU that has been recovered. Incorporating 244 Pu into plutonium does the same for this material. U.S. programs for radioactive surplus disposition could provide a source for tags. Current U.S.-Russian efforts to dispose of surplus nuclear weapons open opportunities to incorporate tags into large amounts of weapons-usable material. The 232 U detection tag would also enhance ongoing US-Russian efforts to detect smuggling of weapons-usable materials out of Russia.While the end of the Cold War greatly reduced the threat of an all-out nuclear war between the United States and the Russian Federation, it created a new set of challenging national security concerns. The political and economic volatility in Russia has resulted in growing fears about the lack of fissile material security there and raised the specter of this material falling into the hands of 'rogue' nations, terrorists, and other opportunists. [1][2][3] In this report we describe a way of significantly reducing this threat by making it easier to detect smuggled fissile material and by creating a nuclear fingerprint to aid law enforcement in identifying the source of a 'leak.' We also describe a unique confluence of opportunities that make this nuclear tagging feasible at this time.We propose uniformly mixing specific substances into fissile materials to act as intrinsic tags. The tags work in two ways. First, they brighten the radioactive signature of highly-enriched uranium (HEU) making it easier to detect. HEU emits far less radiation than plutonium and is more difficult to detect.
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