2005 Archive

Los Alamos Muon Detector Could Thwart Nuclear Smugglers, ScienceDaily.com

Los Alamos, NM – Trillions of cosmic rays that constantly bombard Earth could help catch smugglers trying to bring nuclear weapons or materials into the United States.

Los Alamos National Laboratory scientists have developed a detector that can see through lead or other heavy shielding in truck trailers or cargo containers to detect uranium, plutonium or other dense materials. Their technique, muon radiography, is far more sensitive than x-rays, with none of the radiation hazards of x-ray or gamma-ray detectors now in use at U.S. borders.

Chris Morris of Los Alamos' Physics Division and Rick Chartrand of the Theoretical Division discussed recent improvements to the technique and their efforts to build a prototype detector today at the Annual Meeting of the American Association for the Advancement of Science during a symposium, "Detecting the Unseen with Cosmic-Ray Muons, scheduled for 9:45 - 11:15 a.m., EST.

Both 2004 U.S. presidential candidates declared nuclear terrorism the greatest threat facing the United States. National security experts have speculated that detonation of a nuclear weapon or radiological dispersion device on U.S. soil could create global chaos by shutting down trade.

Existing radiographic methods are inefficient for detecting shielded nuclear materials and present radiation hazards to inspectors and vehicle passengers. Muon radiography uses the natural scattering of muons - produced by the decay of cosmic rays showering down on Earth - as a radiographic probe. In fact, efforts to shield nuclear materials with lead or similar heavy metals make a smuggled object easier to detect with muons.

"We believe we've worked through all of the major obstacles to building a prototype system for a range of security scenarios," Morris said. Muon radiography works because muons are energetic enough to penetrate thick rock or heavy metals. Materials with large numbers of protons and tightly packed nuclei, such as plutonium and uranium or metals like lead and tungsten, produce stronger electromagnetic forces and therefore deflect muons more than less dense materials such as steel, aluminum or plastic.

A pair of detectors above and another pair beneath a truck, cargo container or other suspect object record each muon's path before and after it passes through the cargo. By analyzing changes in energy and trajectory, computer algorithms build a three-dimensional mathematical map of dense items in the cargo. In the 1960s, Luis Alvarez used muon counters to seek hidden chambers inside the Second Pyramid of Giza.

Muons strike the Earth from every angle, so the key to a workable detection system is to keep improving the computer algorithms for tomographic reconstruction. "If we measure the muon's path and energy with two detectors going in and two coming out, we have a straight line on either side that tells us how much the target deflects the muon, and we can locate highly dense objects, as well distinguishing between materials," said Larry Schultz, a member of the Los Alamos team.

One advantage of muon radiographs is their ability to discriminate between shielding materials and less dense metals. With an average energy of 3 billion electron volts, most muons can penetrate about six feet of lead. Gamma-ray detectors are far less penetrating, produce only cluttered, two-dimensional views that need additional interpretation and require hazardous materials such as cobalt.

One drawback of detection systems such as airport screeners is the need for people to interpret images and data. The automation built into the Los Alamos computer algorithm makes inspectors' jobs easier because it doesn't convert data from nearly a million detector coordinates into images, Chartrand explained. Instead, using machine learning techniques, the algorithm is trained with known examples until it can decide directly whether a bomb, nuclear materials or shielding are present.

"We've shown we can put the data through a machine-learning algorithm and train the system to spot objects of interest with a rate of false positives and false negatives that is less than 3 percent," Chartrand said. "We think we can continue to improve that."

Working at the Los Alamos Neutron Science Center, the team is building a prototype set of detectors big enough to radiograph in 60 seconds large metal objects such as auto engines or transmissions. With refinement, inspectors could declare most vehicles harmless in a border setting with as little as 20 seconds of muon exposure.

Muon Opportunists: Detecting the Unseen with Natural Probes, ScienceDaily.com

Earth is showered constantly by particles called muons that are created by cosmic rays, and clever scientists are finding ways to use them as probes of dense objects, including a massive pyramid in Mexico and volcanoes in Japan. American researchers also have proposed using the energetic particles to detect smuggled nuclear materials in vehicles and cargo containers.

Muons are formed when cosmic rays from deep space interact with the atmosphere. The particles, which strike earth's surface at the rate of about 10,000 per square meter per minute, pass through large amounts of rock or metal with ease, yet their charge makes them easy to track.

Researchers described several promising uses for muon radiography, as it is called, at the annual meeting of the American Association for the Advancement of Science (AAAS).

Arturo Menchaca-Rocha, director of the physics institute at the National Autonomous University of Mexico leads a team that is deploying muon detectors in a tunnel 26 feet below the base of the Pyramid of the Sun in Teotihuacan, about 30 miles northeast of Mexico City. The researchers hope to find any hidden burial chambers or other interior features of the massive pyramid, which is about 740 feet on each side and 215 feet tall. Linda Manzanilla, an archaeologist, is collaborating in the research effort.

Menchaca-Rocha's team has been doing calibration of its instruments in preparation for taking a year's data on muon flux through the pyramid. The team will be looking for any surplus of muons striking a portion of its detector array compared to the background flux. That would be an indication that voids in the pyramid have allowed more particles to pass through to the detectors than expected. The denser an object, the less likely the muons are to pass through. The detector consists of an array of thin wires immersed in a gas. A muon passing through the detector will create an electric charge in the gas that can be picked up as a localized current in the wires.

Menchaca-Rocha and his colleagues are following in the footsteps of the late Luis Alvarez, a Nobel physics laureate from the University of California, Berkeley. In the late 1960s, Alvarez placed muon detectors in a tunnel beneath the Great Pyramid of Chefren in Egypt in search of hidden burial chambers. None were discovered.

Another speaker at the meeting, Kanetada Nagamine of the KEK Muon Science Laboratory in Japan, reports on his team's use of cosmic-ray muons to essentially take X-rays of the interior of volcanoes for hints of their eruption potential. Nagamine and his colleagues exploit the fact that some high-energy muons are traveling almost horizontally when they reach Earth's surface. By placing multiple muon detectors around a mountain, the scientists can measure its shape and look for interior channels where molten rock may be rising, an early sign of a potential eruption. The research team has studied several volcanoes in Japan, including as assessment of the amount of molten rock within the crater of Mt. Asama.

Closer to home, scientists at Los Alamos National Laboratory in New Mexico have been exploring the use of muon radiography to detect illicit nuclear materials in cargo containers or trucks. Existing X-ray devices, already being deployed at ports and border crossings, cannot readily detect a well-shielded cache of highly enriched uranium, material that could be used in a devastating nuclear bomb. Newer scanning methods, using either dual-beam X-rays or neutrons, can pose radiation hazards to security personnel or illegal immigrants who might stow away in a container.

The muon detection method would involve passive monitoring of vehicles and cargo containers, with no artificial dose of radiation involved, according to the Los Alamos researchers. Truck drivers could remain in their vehicles while the scan is underway. "We measure the angle of a muon coming in and the angle going out," said Christopher Morris, a member of the Los Alamos team. "The change in angle tells us how much material was in the path."

It takes about 30 to 60 seconds to track enough muons for each cargo container screened, Morris said. There have been questions on whether the method is quick enough to allow prompt screening of large numbers of vehicles or cargo containers. "We've been fighting the general perception that there are not enough muons to measure," Morris said. "There really are." The team is developing better software techniques to allow rapid 3-dimensional images of the volumes being screened. They can reliably detect a small cube of uranium - about 4 inches on a side - within a large metal container full of sheep.

While the Los Alamos research is still in its developmental phase, Morris said he is confident a muon detectors, probably at an initial cost of about $1 million each, could make a significant contribution to efforts to tighten screening of vehicles and cargo containers entering the United States.

This AAAS session was organized by Rick Chartrand of the Los Alamos National Laboratory.

Muons Will Be Used to Protect You from Terrorist Attacks, SixWise.com

Nuclear terrorism is the greatest threat facing the United States today, according to last fall's campaign debates of both President Bush and Senator John Kerry. Yet despite the worries over this massive threat, less than 5 percent of the cargo entering the United States is examined for it -- largely because the U.S. government lacks a capable and reliable means of carrying out such a task. But a solution may now have been discovered.

Scientists at Los Alamos National Laboratory are testing technology that uses muons to detect potential nuclear materials in vehicles or ship containers. What are muons? Muons are tiny charged particles that occur naturally in the atmosphere. They are able to penetrate virtually all substances; they are deflected to varying degrees by denser materials such as lead and aluminum. With an average energy of three billion electron volts, most muons can penetrate about 1.8m of lead.

And while scientists had been studying the possibility of using muon cosmic rays for screening purposes, the project did not gain full swing until the Sept. 11 terror attacks occurred. Principal funding was received in October 2003 -- two years following the attacks.

By utilizing these tiny charged particles, the scientists at Los Alamos National Laboratory have developed a muon cosmic ray screening device that can accurately detect smuggled nuclear weapons and materials in any vehicle or container.

(Image)
Image Caption: Muons are formed when cosmic rays heading toward Earth interact with atmospheric gases and produce electrically charged subatomic particles. These particles (or muons) have a mass 207 times that of an electron. They strike Earth at the rate of 10,000 per square meter every minute, moving through most materials, scattering when they come in contact with high-density materials.

How Does the Muon Cosmic Ray Screening Device Work?

The essential parts of the device consists of two sets of parallel tubular sensor constructed so: 

• Trucks and other vehicles can drive through
•  Sensors would fit over ship containers 

By placing detectors above and below a vehicle, scientists are able to monitor muon interaction with different materials in the vehicle's cargo. The denser a material is, the more muons will scatter when they make contact. Using the scatter data, a computer creates an image of the different materials in the vehicle. This way, instead of relying on the interpretation of images on a screen, operators only need to consult the device's readings.

According to one scientist, the muon cosmic ray screening device is basically a data analysis system that measures the exact amount of deflection caused by the rays bouncing off different materials and identifies them according to the degree of deflection.  

Questions have been raised, however, concerning the speed of the device and whether or not it is fast enough to allow prompt screening of large numbers of vehicles or cargo containers. Currently, the system takes 30 to 60 seconds to complete an examination of a vehicle or object; however, scientists foresee reducing that time to a mere 20 seconds, making it possible for use with a large volume of motor traffic or cargo.

(Image)
Image Caption: The new device is large enough to scan a 50-foot trailer truck or a 20-foot-long ship container. It would cost about $1 million each and could be used for screening vehicles at border crossings or ship cargo at major ports. 

Mouns vs. X-Rays 

Scientists agree X-rays (and gamma ray) detectors that are currently being used at U.S. borders are inefficient for detecting nuclear materials shielded with lead and steel.  

The bottom line is that the muon cosmic ray screening device is superior to X-ray devices -- such as those used at airports -- which require the generation and focusing of radiation beams that can penetrate luggage or metal packaging material but not highly dense lead and similar shielding.  

Moreover, any X-ray systems large and powerful enough for motor vehicles and ships' containers would not only generate a poor success rate, but would also pose a significant health hazard. In fact, on scientist commented, "If you had illegal migrants inside a container you would kill them [with X-rays]."

(Image)
Image Caption: The new system has proven to be accurate within a 3 percent margin for error, and scientists believe they can improve that. Better software techniques are being developed to allow rapid 3-dimensional images of the volumes being screened. Scientists can consistently detect a small cube of uranium--about 4 inches on a side--within a large metal container full of sheep.

Muons In Search For Hidden Pyramid Chambers, Physorg.com

Earth is showered constantly by particles called muons that are created by cosmic rays, and clever scientists are finding ways to use them as probes of dense objects, including a massive pyramid in Mexico and volcanoes in Japan. American researchers also have proposed using the energetic particles to detect smuggled nuclear materials in vehicles and cargo containers. Muons are formed when cosmic rays from deep space interact with the atmosphere. The particles, which strike earth's surface at the rate of about 10,000 per square meter per minute, pass through large amounts of rock or metal with ease, yet their charge makes them easy to track.

Researchers described several promising uses for muon radiography, as it is called, at the annual meeting of the American Association for the Advancement of Science (AAAS).

Arturo Menchaca-Rocha, director of the physics institute at the National Autonomous University of Mexico leads a team that is deploying muon detectors in a tunnel 26 feet below the base of the Pyramid of the Sun in Teotihuacan, about 30 miles northeast of Mexico City. The researchers hope to find any hidden burial chambers or other interior features of the massive pyramid, which is about 740 feet on each side and 215 feet tall. Linda Manzanilla, an archaeologist, is collaborating in the research effort.

Menchaca-Rocha's team has been doing calibration of its instruments in preparation for taking a year's data on muon flux through the pyramid. The team will be looking for any surplus of muons striking a portion of its detector array compared to the background flux. That would be an indication that voids in the pyramid have allowed more particles to pass through to the detectors than expected. The denser an object, the less likely the muons are to pass through. The detector consists of an array of thin wires immersed in a gas. A muon passing through the detector will create an electric charge in the gas that can be picked up as a localized current in the wires.

Menchaca-Rocha and his colleagues are following in the footsteps of the late Luis Alvarez, a Nobel physics laureate from the University of California, Berkeley. In the late 1960s, Alvarez placed muon detectors in a tunnel beneath the Great Pyramid of Chefren in Egypt in search of hidden burial chambers. None were discovered.

Another speaker at the meeting, Kanetada Nagamine of the KEK Muon Science Laboratory in Japan, reports on his team's use of cosmic-ray muons to essentially take X-rays of the interior of volcanoes for hints of their eruption potential. Nagamine and his colleagues exploit the fact that some high-energy muons are traveling almost horizontally when they reach Earth's surface. By placing multiple muon detectors around a mountain, the scientists can measure its shape and look for interior channels where molten rock may be rising, an early sign of a potential eruption. The research team has studied several volcanoes in Japan, including as assessment of the amount of molten rock within the crater of Mt. Asama.

Closer to home, scientists at Los Alamos National Laboratory in New Mexico have been exploring the use of muon radiography to detect illicit nuclear materials in cargo containers or trucks. Existing X-ray devices, already being deployed at ports and border crossings, cannot readily detect a well-shielded cache of highly enriched uranium, material that could be used in a devastating nuclear bomb. Newer scanning methods, using either dual-beam X-rays or neutrons, can pose radiation hazards to security personnel or illegal immigrants who might stow away in a container.

The muon detection method would involve passive monitoring of vehicles and cargo containers, with no artificial dose of radiation involved, according to the Los Alamos researchers. Truck drivers could remain in their vehicles while the scan is underway. "We measure the angle of a muon coming in and the angle going out," said Christopher Morris, a member of the Los Alamos team. "The change in angle tells us how much material was in the path."

It takes about 30 to 60 seconds to track enough muons for each cargo container screened, Morris said. There have been questions on whether the method is quick enough to allow prompt screening of large numbers of vehicles or cargo containers. "We've been fighting the general perception that there are not enough muons to measure," Morris said. "There really are." The team is developing better software techniques to allow rapid 3-dimensional images of the volumes being screened. They can reliably detect a small cube of uranium - about 4 inches on a side - within a large metal container full of sheep.

While the Los Alamos research is still in its developmental phase, Morris said he is confident a muon detectors, probably at an initial cost of about $1 million each, could make a significant contribution to efforts to tighten screening of vehicles and cargo containers entering the United States.

This AAAS session was organized by Rick Chartrand of the Los Alamos National Laboratory.

Nanotechnology
Muons