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Deployments of passive sensors for nuclear and conventional explosives

As part of the US National Nuclear Security Administration annouced that as part of their "Megaports Initiative," the Belgian seaport of Antwerp will be getting radiation sensors.

Separately, Implant Sciences annouced that they recieved an order for their passive detection system to be deployed at Pakistani airports. The handheld system can detect conventional explosives at a distance without the swabbing required by most other systems deployed throughout the world.

How to detect an atomic bomb (3)

Found a few cold-war era papers on detection of nuclear weapons. The first is "Gamma-Ray Measurements of a Soviet Cruise-Missile Warhead" in which an American team of nuclear scientists were asked to board a Soviet cruiser ship and detect the nuclear weapons onboard. They used high-res gamma spectroscopy to detect the weapon at a distance of 4 meters. The second is paper describes the efforts of Soviet scientists to use of neutrons to detect nukes at a distance of tens of meters from a helicopter, called "The Use of Helicopter-Borne Neutron Detectors to Detect Nuclear Warheads in the USSR-US Black Sea Experiment." The paper suggests that neutron emissions from Plutonium-based nukes can be useful for detection. Both these papers are referenced by the NTI writeup on nuclear detection, "A Tutorial on Nuclear Weapons and Nuclear-Explosive Materials."

In addition, there is a report from Los Alamos National Lab called "Nondestructive Assay of Special Nuclear Material for Uranium Fuel-Fabrication Facilities," similar to the report by the British National Physical Laboratory that I blogged earlier. Except, this report provides more quantitative models/estimates of things like self-shielding and the times required to take a measurement using gamma ray spectroscopy. One thing they note here is that unlike Plutonium as discussed in the Soviet report above, passive neutron detection of Uranium is likely to be less effective due to the small number of neutrons emitted.

Insects could be used to detect chemical and biological threats

The DoD is investigating whether insects, weeds, bacteria, and fish can be used to detect biological and chemical toxins: US Military Taps Bugs and Weeds in War on Terror.

This builds on the theme of using dogs to sniff out bombs and  dolphins to find underwater terror threats: Dolphins Valuable to US in Arabian Gulf.

How to detect an atomic bomb (2)

Buried somewhere in the Nuclear Threat Initiative website is a readable summary called Detecting Nuclear Materials and Nuclear Weapons (see first 10 paragraphs or so). In particular, they discuss the tradeoffs of

1. active versus passive scanning
2. detecting highly enriched uranium (HEU) versus plutonium (Pu) and dirty bombs
3. Nuclear Emergency Search Teams (NEST)

What they say here is consistent with what I have found in other references.

Due to its low level of radioactivity, passive HEU detection appears to be significantly harder than detecting Pu or dirty bombs. The following references discuss specifically how HEU might be detected:

1. Uranium Attributes and Measurements by Lawrence Livermore National Lab
2. Emission and Absorption of Radiation in Science and Global Security.

Active neutron scanning of shipping containers

To detect the presence of concealed nuclear or chemical material/weapons in cargo shipping containers, US national labs and defense contractors are investigating an approach where the container is sent through a scanner that floods the container with high energy neutrons (~14MeV). The energetic neutrons are penetrate almost anything that gets in their way and they will excite shielded contraband material (Uranium, Plutonium, etc.) into emitting detectable high-energy gamma rays (several MeV). Unlike the spontaneous radioactivity, these induced gamma rays are not usually present in the background and can be identified readily by the scanner.

Several articles have appeared in the press about this, but here is a technical feasibility study by Lawrence-Livermore National Labs that answers just about any question you could possibly ask "Detection of special nuclear material in cargo containers using neutron interrogation" (August, 2003). The study draws two interesting conclusions:

1. The radiation produced by the scanning is a potential concern, but it will drop to acceptable levels within minutes.
2. The scans will take about a minute, and they envision only suspect containers will be diverted through the scan after first being screened by passive techniques and traditional inspections.

An article describing the personal story of the dedicated physicists behind this effort appeared in the Daily Californian, Innovative Detection Methods May Help Tighten U.S. Security. The effort began in 2001 immediately after 9/11, and it is in laboratory testing as of mid-2004. They optimistically expect to achieve widespread deployment at ports by 2007.

Books on WMD & terrorism

The following books to help in understanding the nature of nuclear, biological, and chemical threats. In particular, they give you a good sense for how what threats are most likely to materialize based on the type of perpretrator (terrorist, nation-state, individual, etc.). These books also expose what the US government is not doing, but could be doing, to protect us against these threats.

1. Nuclear Terrorism is short and reads very easily, sparing lots of detail to give you the big picture. It is written by the founder of the Kennedy School of Government.
2. The Four Faces of Nuclear Terrorism by the Monterey Institute of International Studies is the most recent, most comprehensive, and has an extensive bibliography. It covers policy recommendations and also includes technical details, such as the amount of U or Pu  needed for a improvised nuclear device (IND). The full text is available online as a pdf, so you don't have to buy it unless you prefer the book format.
3. America's Achilles' Heel, written back in 1998 by another Kennedy School professor (Falkenrath) who was subsequently tapped by Tom Ridge for the newly formed Department of Homeland Security, covers a wide variety of possibilities spanning nuclear, biological, and chemical threats.

Another reference is a report on WMD by the Office of Technology Assessment.

U.S. Congress, Office of Technology Assessment. 1993. Proliferation of Weapons of Mass Destruction: Assessing the Risks. OTA-ISC-559.

Muon detection

Earlier this year, researchers at Los Alamos National Lab discovered a new passive detection technique for heavy elements that works better the more the shielding... their idea involves cosmic muons. Read about it in a BBC science article or the original article in Nature cited below.

These highly energetic particles (GeV range) shower the earth at the rate of 10,000 per sq. meter per minute and mostly pass right through anything they encounter. However, they will scatter just slightly and the scattering angle is highly dependent on the atomic mass. Although it is not specific to nuclear materials, this technique can therefore differentiate between ordinary materials in say a container or truck and heavier materials like Uranium/Plutonium and shielding such as lead . So a property of this approach is that greater or denser the shielding, the greater the angle of scattering. This forms a passive substitute for (active) X-ray scanning that can even be used on live cargo, such as sheep, to detect a concealed cargo.

The original article appearing in Nature (below), which have to have online access to or purchase, shows the shape of shielded matter can reconstructed exhibiting the detection capability and providing formulas on how the scattering works.

Nature 422, 277 (20 March 2003); doi:10.1038/422277a, "Surveillance: Radiographic imaging with cosmic-ray muons"

How to detect an atomic bomb

If only U2 had dedicated their new album to detection, not dismantling...  I found a few "practical" guides that explain how to do precisely that.

1. Longer: "Radiometric Non-Destructive Assay" by UK's National Physical Lab
2. Shorter: "Comparison of Several Detector Technologies for Measurement of Special Nuclear Materials" based on experiments at Los Alamos National Lab.

The idea is that nuclear materials naturally decay and emit gamma-rays, X-rays, neutrons which can travel through shields (with some attenuation) since these are chargless particles.

I'd recommend the following book for a clearly-written, engaging, and systematic introduction to how things work at the nuclear level. Starting with the basic physics, topics covered include things like natural decay, fission, fusion, shielding, as well as the internal dynamics of nuclear reactors and stars.

US ports and border crossings to get radioactivity monitors over the next couple of years

Today, the Chicago Tribune writes that monitors for detecting radioactivity inside shipping containers will be rolled out at US ports and border crossings over the next couple years (see "U.S. ports face daunting task: Screening process targets 5% of cargo") and that they have already been installed in the New York area. The article goes on to point out that drive-thru truck monitors, costing $1M each, experience a false positive rate of 2% from naturally occuring low-level radioactivity from things like ceramic tiles or slabs of stone.

Wide-area nuke detection?

A product from Thermo Electron Corporation (Waltham, MA) launched this past September is a step towards metro-scale monitoring using distributed nuclear detectors. It's called Matrix Mobile Radiation Detection System (MRDS) and includes centralized monitoring over a wireless 2.4GHz Wi-Fi network.