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Nuclear accidents and threat of terrorists undertaking dirty bomb attack require improved Radiation detecting technologies

Following a demonstration earlier this year with the Port Authority of New York and New Jersey involving more than 100 SIGMA sensors, the DARPA field test that saw a thousand volunteers equipped with smartphone-sized radiation detectors fan out over the National Mall in a radioactive scavenger hunt to test the progress of the agency’s SIGMA project.  1,000-detector deployment in Washington, D.C., marked the largest number of SIGMA mobile detectors ever tested at one time and was a demonstration of the program’s ability to fuse the data provided by all those sensors to create minute-to-minute situational awareness of nuclear threats.

A key element of SIGMA, which began in 2014, has been to develop and test low-cost, high-efficiency, radiation sensors that detect gamma and neutron radiation. The detectors, which do not themselves emit radiation, are networked via smartphones to provide city, state, and federal officials real-time awareness of potential nuclear and radiological threats such as dirty bombs, which combine conventional explosives and radioactive material to increase their disruptive potential. Next steps in the SIGMA program include continuing to test full city- and regional-scale, continuous wide-area monitoring capability in 2017 and then transition the operational system to local, state, and federal entities in 2018.

Recently a secret group of fewer than 10 people in undercover congressional operation was easily able to buy the raw ingredients for a dirty bomb in US. This exposed gaps in U.S. regulations and undermines Washington’s claim to be the best in the world at blocking this potential terrorist threat. This has set off alarms among some lawmakers and officials in Washington about risks that terrorists inside the United States could undertake a “dirty bomb” attack and the harmful effects of radiation from such an event.

Apart from terrorists, there is also threat of accidents involving nuclear material. The government of Kazakhstan said in Sept 2014 that it was searching for a container of radioactive cesium-137 that fell off a truck in the western part of the country. The material was recovered, but the incident highlighted the risks of radioactive material falling into the wrong hands.

In 1987, a small radiotherapy capsule of cesium chloride salt was accidentally broken open in Goiania, Brazil, after being salvaged from a radiation therapy machine at an abandoned health care facility. In all, more than 1,000 people were contaminated during the incident, and some 244 were found to have significant radioactive material in or on their bodies. In another case, this time in a slum outside New Delhi, India, eight people were admitted to hospitals in 2010 for radiation exposure after a scrap dealer dismantled an object containing cobalt-60.

Radioactive materials (RM) are widely used in industry, medicine, agriculture and scientific research. When radioactive elements decay, they produce energetic emissions (alpha particles, beta particles, or gamma rays) that can cause chemical changes in tissues. High-activity RM in several physical and chemical forms can cause severe deterministic effects to individuals in a short period of the exposure time, as well as induce long-term radioactive contamination, if not managed safely and securely during their production, use, transportation, storage and disposal.


Dirty bombs and Nuclear bombs

A “dirty bomb” is one type of a radiological dispersal device (RDD) that combines conventional explosives, such as dynamite, with radioactive material.  The dirty bomb is often employed to frighten people and make buildings or land unusable for a long period of time.

No special assembly is required to make a dirty bomb; the regular explosive would simply disperse the radioactive material packed into the bomb. Most RDDs would not release enough radiation to kill people or cause severe illness – the conventional explosive itself would be more harmful to individuals than the radioactive material.” However, depending on the situation, an RDD explosion could create fear and panic, contaminate property, and require potentially costly cleanup. Making prompt, accurate information available to the public may prevent the panic sought by terrorists,” explains US NRC.

A dirty bomb is in no way similar to a nuclear weapon or nuclear bomb. A nuclear bomb creates an explosion that is millions of times more powerful than that of a dirty bomb. The cloud of radiation from a nuclear bomb could spread tens to hundreds of square miles, whereas a dirty bomb’s radiation could be dispersed within a few blocks or miles of the explosion. A dirty bomb is not a “Weapon of Mass Destruction” but a “Weapon of Mass Disruption,” where contamination and anxiety are the terrorists’ major objectives, says NRC.

The effects of radiation exposure would be determined by: the amount of radiation absorbed by the body; the type of radiation (gamma, beta, or alpha); the distance from the radiation to an individual; the means of exposure-external or internal (absorbed by the skin, inhaled, or ingested); and the length of time exposed. The health effects of radiation tend to be directly proportional to radiation dose. In other words, the higher the radiation dose, the higher the risk of injury.

Radiation can be readily detected with equipment carried by many emergency responders, such as Geiger counters, which provide a measure of radiation dose rate. Other types of instruments are used to identify the radioactive element(s) present. But they only work within a range of a few metres.

How lasers can spot a dirty bomb in the making

The University of Maryland’s Joshua Isaacs and colleagues reported their device, which may uncover a nuclear threat hundreds of metres away, in the journal Physics of Plasmas. They claim their device could detect 10 milligrams (one one-hundredth of a gram) of cobalt-60 from several hundred metres away. This is a much smaller amount than needed for an effective dirty bomb.

Some radioactive materials, such as cobalt-60 and isotopes of polonium, emit gamma-rays. These collide with air molecules around them and create a cascade of electrons. In turn, these electrons seek out and cling to oxygen molecules, “ionising” them. In other words, any material containing those radioactive sources will be enveloped by a cloud of oxygen ions. And the new detection technology, developed at the University of Maryland, hinges on revealing this ion cloud.

The team first fires a low-intensity laser beam at the air surrounding a radioactive source, followed by a second, high-intensity laser. The combination makes any oxygen ions spark like a miniature crackle of lightning. The sparking air acts like a mirror to the laser, reflecting the pulse back to the detector and indicating the presence of nuclear material.

Currently, the technique only works for gamma-ray emitting materials. Other types of radiation, such as alpha or beta radiation, have too short a range to be detected. The concept also requires a clear line-of-sight towards the suspect which may limit its usefulness.


Passport Systems Inc. Reaffirms That Its Cargo Radiation Detection Technology Can Solidify Security at Seaports around the Globe

Jennifer Grover, Director of Homeland Security and Justice Issues at the Government Accounting Office, testified that “with about 12 million cargo shipments arriving each year in the U.S. – the U. S. maritime ports do indeed remain vulnerable to nuclear smuggling risks. CBP {U.S. Customs and Border Protection} has determined that it does not have the resources to examine every shipment.  “At the hearing, subcommittee members cited the need for technology that can accurately detect nuclear threats and contraband without significantly slowing the shipping process,” Dr. Ledoux said.

Our SmartScan 3D™ cargo scanner can protect people and property from dirty bombs and other nuclear threats.” Dr. Ledoux said the SmartScan 3D system automatically identifies any radioactive material, including “actinides” that may signal a weapon of mass destruction or smuggled special nuclear materials, after the cargo has been unloaded onto conveyances. The non-intrusive cargo inspections also detect explosives and contraband such as drugs, tobacco, and firearms – a growing concern among security professionals and lawmakers.

As noted at the subcommittee hearing, a limited X-ray scanning process is used at most ports today. Dense or thick objects, which could hide nuclear threats or contraband, require that individuals open the containers and inspect the objects by hand; it slows the shipping process by hours and the process could be dangerous for inspectors.

By contrast, SmartScan doesn’t require that containers be opened. The technology scans a container, provides a three-dimensional map of the cargo, and sends alerts to flag suspicious cargo. Within minutes, it determines if an actinide is present and whether it is a bomb.


New technique could improve detection of concealed nuclear materials in cargo containers

Scientists from the Georgia Institute of Technology, the University of Michigan, and the Pennsylvania State University have demonstrated proof of concept for a novel low-energy nuclear reaction imaging technique designed to detect the presence of “special nuclear materials” — weapons-grade uranium and plutonium — in cargo containers arriving at U.S. ports. The method relies on a combination of neutrons and high-energy photons to detect shielded radioactive materials inside the containers.

The technique can simultaneously measure the suspected material’s density and atomic number using mono-energetic gamma ray imaging, while confirming the presence of special nuclear materials by observing their unique delayed neutron emission signature.

“Once heavy shielding is placed around weapons-grade uranium or plutonium, detecting them passively using radiation detectors surrounding a 40-foot cargo container is very difficult,” said Anna Erickson, an assistant professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering. “One way to deal with this challenge is to induce the emission of an intense, penetrating radiation signal in the material, which requires an external source of radiation.”

The technique begins with an ion accelerator producing deuterons, heavy isotopes of hydrogen. The deuterons impinge on a target composed of boron, which produces both neutrons and high-energy photons. The resulting particles are focused into a fan shaped beam that could be used to scan the cargo container.

The transmission of high-energy photons can be used to image materials inside the cargo container, while both the photons and neutrons excite the special nuclear material — which then emits gamma rays and neutrons that can be detected outside the container. Transmission imaging detectors located in the line of sight of the interrogating fan beam of photons create the image of the cargo.

When the neutrons interact with fissile materials, they initiate a fission reaction, generating both prompt and delayed neutrons that can be detected despite the shielding. The neutrons do not prompt a time-delayed reaction with non-fissionable materials such as lead, providing an indicator that materials of potential use for development of nuclear weapons are inside the shielding.

“If you have something benign, but heavy — like tungsten, for instance — versus something heavy and shielded like uranium, we can tell from the signatures of the neutrons,” Erickson said. “We can see the signature of special nuclear materials very clearly in the form of delayed neutrons. This happens only if there are special nuclear materials present.”

It could significantly improve the ability to prevent the smuggling of dangerous nuclear materials and their potential diversion to terrorist groups.


DHS Human Portable Tripwire (HPT) systems

Recently, the Domestic Nuclear Detection Office (DNDO) awarded a multimillion dollar contract that will equip U.S. Coast Guard (USCG), U.S. Customs and Border Protection (CBP), and Transportation Security Administration (TSA) frontline personnel with a new capability to detect and interdict radiological or nuclear threats.

The award is for small, wearable radiation detector devices that passively monitor the environment and alert the user when nuclear or other radioactive material is present. Known as the Human Portable Tripwire (HPT), this device has the capability to identify the source of radiation and allow personnel to take appropriate action.

The technology can also locate the source of the detected radiation and includes communication features that allow the user to easily seek additional technical assistance from experts if needed. These devices are a critical tool for personnel who operate in the maritime environment, at land and sea ports of entry, and within the United States.

Domestic Nuclear Detection Office (DNDO)’s mission is to protect the United States, its people, territory, and its interests against the unauthorized importation, possession, storage, transportation, development, or use of an unauthorized nuclear explosive system, fissile material, or radiological material and protect against attacks using such systems or material.

Kromek to support DARPA’s SIGMA dirty bomb detection programme

UK-based radiation detection company Kromek has secured two separate contracts from the US Department of Defense (DoD) to support the Defense Advanced Research Projects Agency’s (DARPA) SIGMA programme. Valued at $6m, the deal requires the company to supply spectroscopic personal radiation detectors (D3S) in support of the programme.

The SIGMA programme aims to develop an advanced personal detection system for gamma and neutron radiation that can be combined with other such systems to form large networks to detect radiation signatures over an extended area. The technology used could provide early warning about acts of terrorism such as a ‘dirty bomb’.

The second contract, which is valued at $0.75m, covers the supply of 12,000 inductive charging packs for D3S detectors and associated mobile devices. The inductive charging pack provides a long battery life for the detectors, and can be recharged and recalibrated when necessary.

Kromek CEO Arnab Basu said: “The D3S is the world’s first fully approved combined gamma and neutron detector available in volume shipment and at a market leading unit price of $400, which is also available to other user organisations buying over 10,000 detectors in a single procurement.


DARPA’s SIGMA program

U.S. ‘s Defense Advanced Research Projects Agency (DARPA) had asked industry to design a pocket-sized radiation detector to help foil terrorists attempting to detonate concealed dirty bombs or full-blown nuclear weapons in or around U.S. cities and crucial government and industrial infrastructure. Direct measurement of gamma and neutron emission remains one of the few definitive to detect and identify special nuclear materials and radiological sources, DARPA officials say.

Needed are belt-worn, pocket-size, wearable, and large-area radiation detectors that represent an order of magnitude less expensive with substantially increased detection capability than what is available today, researchers say. DARPA is interested in new packaged dual-mode gamma and neutron detector concepts with an order of magnitude reduction in cost per unit while achieving 5 x and 10 x greater sensitivity in gamma and neutron detection, respectively, compared to the state-of-the art.

For gamma detection, spectroscopy is required, whereas for neutron detection, counting is sufficient. The user interface is expected to be provided by a user-owned mobile device with both USB and wireless secure connection options, and the detector is expected to be worn (e.g., on a belt or in pocket), not held.


DARPA program seeks highly portable neutron sources to complement X-ray capabilities

X-Ray imaging has proven invaluable in a host of military and commercial applications—from spotting tiny cracks in aircraft wings, to making medical diagnoses, to scanning passengers’ bags to keep the flying public safe. As useful as X-ray scanning is, however, it is limited in what it detects. For example, while X-ray radiography can highlight heavier chemical elements very well (think of shiny silver fillings on a dental X-ray), it’s not very good at revealing lighter elements, such as hydrogen. That’s why X-ray radiography machines are generally “blind” to water or other liquids.

By contrast, neutron radiography—which uses neutrons to image objects—is very good at visualizing lighter elements and liquids, in some cases even identifying a substance’s atomic makeup. Unfortunately, neutron sources are not nearly as portable and practical as X-ray machines, typically extending up to tens of meters in length and requiring powerful energy sources to generate the neutrons.

DARPA’s new Intense and Compact Neutron Sources (ICONS) program seeks to develop a portable unit able to generate both neutrons and X-rays. Such a device would harness the complementary strengths of the two imaging sources and enable much more detailed radiography in field settings.

“Creating a high-yield, directional neutron source in a very compact package is a significant challenge,” said Vincent Tang, DARPA program manager. “But a successful ICONS program would provide an imaging tool with significant national security applications, able to deliver very detailed, accurate internal imaging of objects in any setting.”

For example, Tang said, ICONS could enable non-destructive evaluation of military equipment with greater fidelity than X-rays, revealing water penetration and corrosion in aircraft wings and welds on ships. Neutron imaging could also help detect explosives and contraband by identifying the chemical and atomic make-up of an object or its contents. And it could assist in forensics and attribution, such as differentiating sources of ammunition through imaging of the propellant fill levels.


Radiation Detectors

As the requirements for greater accuracy, efficiency, or sensitivity increases, so does the complexity of the detector and its operation. The following list presents some types of commonly used detectors and includes comments on each of them:


Geiger counter

The most common detector is the Geiger-Mueller counter, commonly called the Geiger counter. It uses a gas-filled tube with a central wire at high voltage to collect the ionization produced by incident radiation. It can detect alpha, beta, and gamma radiation although it cannot distinguish between them. Because of this and other limitations, it is best used for demonstrations or for radiation environments where only a rough estimate of the amount of radioactivity is needed.


Scintillation detectors

Scintillators are usually solids (although liquids or gases can be used) that give off light when radiation interacts with them. The light is converted to electrical pulses that are processed by electronics and computers. Examples are sodium iodide (NaI) and bismuth germanate (BGO). These materials are used for radiation monitoring, in research, and in medical imaging equipment.


Solid state X-ray and gamma-ray detectors

Silicon and germanium detectors, cooled to temperatures slightly above that of liquid nitrogen (77 K), are used for precise measurements of X-ray and gamma-ray energies and intensities. Silicon detectors are good for X-rays up to about 20 keV in energy.

Germanium detectors can be used to measure energy over the range of >10 keV to a few MeV. Such detectors have applications in environmental radiation and trace element measurements. Germanium gamma ray detectors play the central role in nuclear high-spin physics, where gamma rays are used to measure the rotation of nuclei. Large gamma-ray detection systems, such as Gammasphere and Eurogam are made of these detectors.


Neutron detectors

Neutrons are much harder to detect because they are not charged. They are detected by nuclear interactions that produce secondary charged particles. For example, boron trifluoride (BF3) counters make use of the 10B(n,a)7Li reaction to detect neutrons.

Often one uses a moderator, such as paraffin, to slow the neutrons and thus increase the detection efficiency. These detectors are used to monitor the neutron fluxes in the vicinity of a reactor or accelerator. Liquid scintillators can measure both neutrons and gamma rays. By carefully measuring the shape of the electronic signal, scientists can and distinguish between these two types of particles.


Ionizing Radiation

When radioactive elements decay, they produce energetic emissions (alpha particles, beta particles, or gamma rays) that can cause chemical changes in tissues. Gamma and X-rays can travel long distances in air and can pass through the body exposing internal organs; it is also a concern if gamma emitting material is ingested or inhaled.

Beta radiation can travel a few yards in the air and in sufficient quantities might cause skin damage; beta-emitting material is an internal hazard if ingested or inhaled. Alpha radiation travels only an inch or two in the air and cannot even penetrate skin; alpha-emitting material is a hazard if it is ingested or inhaled.

Alpha Particles are the cores (nucleus) of helium atoms. Even though they are easily stopped, they can damage the atoms of whatever they strike. Beta Particles – Beta particles are electrons flying along without the rest of the atom. It takes a little more to stop a beta particle, but thin metal – even tinfoil will stop most of them. Gamma Radiation – Gamma rays are made of the same particles as non-ionizing radiation, but at much, much higher energies. Gamma Rays come from the decay of radioactive elements here on Earth. Gamma Rays are very hard to stop, and a Gamma source even quite distant from the body can be very dangerous.

The average person in the United States receives a “background” dose of about one-third of a rem* per year— about 80% from natural sources including earth materials and cosmic radiation, and the remaining 20% from man-made radiation sources, such as medical x-rays.


* A rem is a measure of radiation dose, based on the amount of energy absorbed in a mass of tissue. Dose can also be measured in Sieverts (1 Sievert=100 rem).


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