The ultimate pocket protector--radiation detection made easy

August 17, 2000

If you're trying to smuggle nuclear material into or out of the United States, getting through Customs is even tougher now thanks to an award-winning, pocket-sized device developed at the Idaho National Engineering and Environmental Laboratory.

Nuclear scientist Rahmat Aryaeinejad designed a device to simultaneously detect two types of radiation-bundles of massless energy called gamma rays and tiny particles called neutrons. The device, called a dosimeter, has been recognized as one of the 100 most significant technological achievements for the year 2000 by R&D Magazine. Aryaeinejad will receive his award at a gala at the Museum of Science and Industry in Chicago, on Sept. 27, 2000.

A dosimeter is an instrument that responds to the presence of radiation, and measures the dose or amount of exposure. Used at hospitals, nuclear power plants, and research labs, these devices are an important part of personnel workplace safety. Aryaeinejad is putting the instrument to use for national security-a primary mission of the Department of Energy and the INEEL as well.

"This year's R&D 100 awards recognize the Department of Energy's continued contribution to our Nation's economic prosperity and well-being," said Secretary of Energy Bill Richardson. "Energy Department laboratories are a wellspring of innovation, and I congratulate the researchers on their success."

Aryaeinejad began work on his battery-operated detector in 1997 in response to a technology need of the U.S. Customs office. In the day-to-day duties of national defense, commonly transported radioactive medical isotopes were a constant source of false security alarms for Customs officials. They wanted an instrument that could quickly detect the kinds of radioactive materials they really worry about-materials such as weapons-grade plutonium.

To detect materials such as plutonium, Aryaeinejad needed to be able to measure both gamma rays and neutrons-a challenge because they interact differently with the matter around them. Gamma rays are essentially massless energy that can pass through all but the heaviest forms of matter, such as lead or concrete. Neutrons are atomic particles-tiny pieces of the radioactive element's mass that crash into other atoms like a cue ball in a game of pool. The neutrons are then bounced away in other directions.

"It's harder to detect the neutron particles because they don't interact with matter in the same way that the gamma energy does," says Aryaeinejad.

He solved the problem by combining two similar sensors that use two variations, or isotopes, of the element lithium-Li-6 and Li-7. The Li-7 isotope is sensitive to gamma rays only, and the Li-6 isotope is sensitive to both gamma rays and neutrons. The sensors emit a tiny bit of light each time they detect either type of radiation. The light is translated into electronic pulses and recorded. The sensitive INEEL dosimeter takes less than 10 seconds to make a reading.

The microprocessor then subtracts the "counts" of light for the Li-7 sensor from those of the Li-6 sensor to determine the number of neutrons. Subtracting the number of neutrons from the total number of counts from both sensors calculates the gamma rays.

The sandwich-sized sensor can tell the user about the presence of radiation in three ways-visually on a tiny display screen, audibly through an alarm, or tangibly through vibrations. Small enough to be worn on a belt, the dosimeter is discrete-a plus for Customs workers, and the availability of comprehensive real-time data enables the quick responses needed to apprehend potential smugglers.

"The mathematics are simple," insists Aryaeinejad, "but no one has made a detector combining two sensors like this before." Competing instruments are outclassed because the INEEL dosimeter provides both gamma and neutron data in real time with one instrument. The dosimeter eliminates the need to carry two instruments, one for gamma rays and another for neutrons, or to develop films, employ highly trained staff, and lug around bulky equipment. The dosimeter is powered by just four AA-batteries and has a data port for downloading information into a computer.

Getting an accurate count of the neutrons is the tricky part. Aryaeinejad includes a piece of polyethylene in the sensor because it slows down the fast neutrons so they can be captured and measured. "Measuring the slow neutrons isn't a problem," he said. "But I needed to slow down the faster neutrons or the sensor would miss them." Polyethylene works well as a neutron absorber because the chemical makeup is rich in hydrogen which is efficient at slowing down neutrons. "Neutrons come into the detector at a millionth of the energy they were traveling at before," he says.

Because the dosimeter uses one sensor for neutrons and another sensor for gamma rays, Aryaeinejad's detector can outperform competing instruments. Other instruments cannot measure low-level neutrons in high gamma radiation fields as accurately.

"The good thing about this detector is that you can easily change the detector size and geometry to do different applications," says Aryaeinejad. Using a larger-size detector makes the device more sensitive-but also bigger. The design can be changed depending on how portable the customer needs the detector to be and how fast the measurements need to be taken. In this case, the design requirement was for a visually discrete, portable instrument that didn't need to be plugged into an electrical source.

The dosimeter has broad applicability in any environment where real-time radiation detection is important, such as personnel monitoring at nuclear power plants, monitoring of patients undergoing radiation therapy, monitoring spent nuclear fuel in storage, or monitoring remediation sites containing radioactive material.

Aryaeinejad has plans for future development of his device. He hopes to miniaturize the dosimeter even more, making it the size of a pack of cigarettes, and also to modify it for use in the subsurface-helping researchers to locate and identify radioactive contamination in the ground and measure the rate of migration.
The early research on the Li-6 and Li-7 sensors was funded by the Department of Energy Office of Nonproliferation and National Security. Later, The Department of Energy Special Technologies Program supported the development of the dosimeter, with follow-on funding by the INEEL Laboratory Directed Research and Development Program.

R&D Magazine has sponsored the international R&D 100 Awards program since 1963. This is the 26th such award for the INEEL and the second for Aryaeinejad, who won the award in 1995 for an assay system. For more information about the awards program and this year's winners, access the web site at

The INEEL is a science-based, applied engineering national laboratory dedicated to supporting the U.S. Department of Energy's missions in national security, environment, energy and science. The INEEL is operated for the DOE by Bechtel BWXT Idaho, LLC, in partnership with the Inland Northwest Research Alliance.

Technical contact: Rahmat Aryaeinejad, 208-526-1670,

Media contacts: Deborah Hill, 208-526-4723,
Mary Beckman, 208-526-0061,
Teri Ehresman, 208-526-7785,

Visit our web site at

DOE/Idaho National Laboratory

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