CHANTILLY, Va. (AP) _ It looks like any other piece of construction equipment.
But when Alexis Burton lifts a 60-pound soil-testing gauge from the back of her Jeep Cherokee, she's knows it's anything but that.
Inside the gauge, which appears strangely like a small carpet sweeper, two steel-encased capsules contain small amounts of highly radioactive Cesium-137 and Americium-241.
What worries some is that in the hands of terrorists, the radioactive material _ imbedded in a device that has been a staple of the construction and road-building industries for decades _ could be used to make a so-called dirty bomb.
That dozens of gauges keep getting stolen from sites across the country only heightens the fear, officials say.
For two summers, Burton, 21, who is studying civil engineering at the University of Virginia, has been using such gauges to test the density and moisture of soil at construction sites across northern Virginia for Engineering Consulting Services, one of hundreds of companies licensed to use the devices.
In the morning she checks out her gauge, locked in its yellow container, from the ECS building. She keeps it under lock and key when not in use and returns it each evening to the same locked storage room in the ECS compound. She is prohibited from taking it home overnight.
When not in use, the company's 48 nuclear gauges must be under double, sometimes triple, lock and key, even when they are kept _ as is sometimes the case _ overnight at a construction site, said Stan Murphy, ECS's radiation officer.
``We take it pretty seriously,'' Murphy said.
But federal regulators are worried that's not the case everywhere. The Nuclear Regulatory Commission now wants to toughen its security requirements for the gauges _ some 20,000 of them used nationwide by more than 5,100 licensees.
Every year about 50 gauges _ ``practically one a week'' _ are reported stolen, and many are never recovered, said Lydia Chang, an NRC official who has been working on the new requirements. They were approved last month by commission members and are expected to be in place later this year.
NRC officials emphasize there is no evidence that any of the thefts are in any way connected. They also caution that the amount of radioactive material in each device is so small that it would take hundreds of them to produce enough Cesium-137 or Americium-241 to be useful in a dirty bomb, which uses conventional explosives to spread radiation.
Nevertheless, the thefts are worrisome and ``it is time the NRC took action on this,'' said NRC Commissioner Jeffrey Merrifield. The radioactive devices have been a concern for years because many of them end up in landfills or are just discarded beside a road.
The NRC said their safekeeping has become even more urgent since the Sept. 11, 2001, terror attacks and awareness that al-Qaida operatives have discussed the possibility of detonating a radioactive device.
The new government regulations require anyone using nuclear gauges to have two independent physical controls, such as separate locks, to secure the devices when they are not under surveillance. Some states already require even more stringent controls.
For example, the NRC staff dismissed as too costly a requirement in Rhode Island that restricts how far from a company's home base the gauges may be used. The agency estimated the new rules would add $200 to the lifetime cost of a gauge, which typically costs about $5,000 to purchase.
Murphy said that ECS, a nationwide engineering consulting firm, already meets the new NRC requirements and exceeds them in some cases. The room where the gauges are kept is locked. Each device is locked in its own container which, in turn, is chained to a wooden bench. The room is monitored by camera at all times.
But all those precautions didn't prevent one of ECS' gauges from being stolen last April when thieves broke into a trailer at a construction site in Bethesda, Md. The gauge has yet to be found, said Murphy, adding that it was under double lock when it was taken with other tools.
Last year, a nuclear gauge owned by another engineering firm, Chicago-based Professional Service Industries, disappeared from a construction site near Columbia, Md., only to turn up a month later at a pawn shop. The owner noticed the radiation-warning decal on its surface and called police. The radioactive material, secured inside the device and shielded from the environment, was not compromised, officials said.
While there are other technologies for measuring soil moisture and density, ``there is nothing that has the same accuracy and precision'' as the nuclear gauges, nor speed in getting the job done, said Stephen Browne, an executive at Troxler Labs, one of the leading manufacturers of the devices.
Nuclear terrorism experts say it is unlikely the gauges would be of much good to terrorists given the small amount of nuclear material, generally less than one curie and in many cases far less.
``Radioactive sources in this application generally pose minor security risks,'' writes Charles Ferguson of the Center for Nonproliferation Studies at the Monterey Institute.