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Posted on 03/02/2002 9:32:34 PM PST by kattracks
WASHINGTON (Reuters) - Fearing Osama bin Laden's al Qaeda network may be making progress in obtaining nuclear weapons, the Bush administration has been placing sophisticated radiation sensors at U.S. border positions and key locations around Washington, the Washington Post reported on Sunday.
The administration also has placed the elite U.S. commando unit Delta Force on a new standby alert to seize any nuclear materials that the sensors may detect, the newspaper added. The Delta Force has been given the task of killing or disabling anyone with a suspected nuclear device and turning the bomb over to scientists to be disarmed, the Post added.
The sensors, known as gamma ray and neutron flux detectors, have been deployed since November at U.S. borders, certain overseas facilities and choke points around Washington, the newspaper said, citing U.S. government policymakers.
The sensors also have been used at designated "national-security special events" such as the Olympics in Utah, the Post said. Allied countries, including Saudi Arabia, have rushed new detectors to their borders after U.S. intelligence warnings, the newspaper added.
Up until now, the devices were carried only by nuclear search teams dispatched when extortionists claim to have radioactive materials, the Post reported.
The Post reported that President Bush has ordered his national security team to give nuclear terrorism priority over every other threat to the United States after an October briefing by CIA Director George Tenet on al Qaeda's nuclear aspirations.
"Clearly ... the sense of urgency has gone up," the newspaper quoted a senior policymaker on nuclear, biological and chemical weapons terrorism as saying.
Another official was quoted as saying, "The more you gather information, the more our concerns increased about al Qaeda's focus on weapons of mass destruction of all kinds."
The consensus U.S. government view is that Saudi-born extremist Osama bin Laden's al Qaeda network likely has acquired the lower-level radionuclides strontium 90 and cesium 137, which cannot produce a nuclear detonation but are radioactive contaminants. Conventional explosives could scatter them in what is known as a radiological dispersion device, better known as a "dirty bomb."
The number of deaths that might follow is hard to estimate but would probably be modest but it could be a potent weapon of terror, the paper added.
Not necessarily. The extinction function is exponential, so some is still going to leak out no matter how much lead you have. Suppose that for neutrons of a given energy, half of them are absorbed by a centimeter of lead. If you want to want to decrease the emission by a factor of four, you need two centimeters of lead, and so on. It will never go to zero.
There's a practical limit to how much shielding they can use. For any given amount of shielding, it's a question of how close you can get the detector to the source, to distinguish the signal from the background.
What helps is that the neutrons and gammas coming from radionuclides tend to have well-defined energies, which cuts down the effective background dramatically. Instead of simply counting neutrons or gammas and looking for an excess, bin them according to energy and look for an excess in any one energy bin. With fine enough energy resolution, the background will be effectively zero, and a few neutrons or gammas will be enough for a signal. You could even determine what material was present (which is probably necessary; you don't want to pull over every schmoe bringing home a smoke alarm from the Wal-Mart).
In principle, such a sensor should be pretty effective. I myself would put them under the road surfaces at places where the traffic moves slowly (toll booths?); that should solve the distance problem.
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