|As with other subjects of possible terrorist use, this article gives capabilities and policies and general technical characteristics, but deliberately does not go into detailed operational usage techniques. Do not attempt to use any substance described here. If you are threatened by one, move away from it and call the appropriate civilian or military emergency response agency.|
A radiological weapon or radiological dispersal device (RDD) uses a conventional explosive or other mechanical means to disperse a hazardous radioactive and thus contaminate an area. While the radioactive material might have been generated in a nuclear reactor, or even collected from a nuclear weapon test site, the radiological weapon does not, itself, use fission or fusion.
The U.S. military uses some simplified terminology to discuss the problem at the policy level. They use the generic term TIM for toxic, infectious, or radioactive compounds in solid, liquid, aerosolized, or gaseous form; it can also stand for toxic industrial material, as in the Bhopal Disaster. TIMs may be used or stored for use for industrial, commercial, medical, military or domestic purposes. An example of toxic dispersal, comparable to what might be done with a crude radiological attack, has been seen in Iraq, where terrorists attached improvised explosive devices to industrial tank trucks of chlorine. A simple explosion, however, is not efficient for releasing TIM.
Especially if those constructing the weapon are not concerned with their own health or survival, such a weapon is quite simple to make, assuming radioactive material is available. Between 1994 and 2003, there were at least several hundred illicit transfers of radioactive material, relatively little of which was of bomb grade.  Many experts consider radiological weapons the most plausible means of terrorist use of weapons of mass destruction.
The main purpose of a dirty bomb remains frightening people by contaminating their environment with radioactive materials and threatening large numbers of people with exposure. Well-engineered weapons may also result in area denial and costly cleanup or decontamination.
STRATFOR has observed "media coverage of the threat posed by dirty bombs runs in a perceptible cycle with distinct spikes and lulls." No terrorist group has actually completed a radiological attack, although there have been accidents, some of which had greater effects than any plausible terrorist operation.
RDDs are designed to disperse radiation and/or contamination. The explosive itself may cause blast injuries. Unless an unusually efficient dispersion technique were used (e.g., aerosol spray from an aircraft), the actual area of contamination of a practical "dirty bomb" will not be that great; the quantity of radioactive material is far less than was generated by a high-fallout bomb test such as CASTLE BRAVO, or a major reactor catastrophe such as Chernobyl. Nevertheless, effective dispersion remains the worst-cases scenario, and more and more resources are available to manage such events, such as the National Atmospheric Release Advisory Center.
Given the danger of smuggled nuclear weapons, as well as the special nuclear materials (SNM) to build them, intense attention is being paid to detecting them. The problem divides roughly into systems practical for fixed or minimally mobile installation at transportation ports of entries, and for field searches for weapons development.  A representative set of technologies includes:
- A new scintillator material to improve detector performance and lower cost. This project was terminated in January 2010.
- GADRAS, an application using multiple algorithms to determine the materials in a container by analyzing gamma-ray spectra. If materials are the “eyes and ears” of detectors, algorithms are the “brains.”
- A project to simulate large numbers of experiments to improve detection system performance.
- Two Cargo Advanced Automated Radiography Systems (CAARS) to detect high-density material based on the principle that it becomes less transparent to photons of higher energy, unlike other material.
- third CAARS to detect material with high atomic number (Z, number of protons in an atom’s nucleus) based on the principle that Z affects how material scatters photons. This project was terminated in March 2009.
- A system to generate a 3-D image of the contents of a container based on the principle that Z and density strongly affect the degree to which muons (a subatomic particle) scatter.
- Nuclear resonance fluorescence imaging to identify materials based on the spectrum of gamma rays a nucleus emits when struck by photons of a specific energy.
- The Photonuclear Inspection and Threat Assessment System to detect SNM up to 1 km away, unlike other systems that operate at very close range. It would beam high energy photons at distant targets to stimulate fission in SNM, producing characteristic signatures that may be detected.
Medical and response considerations
Typically, acute radiation syndrome will result if individuals are exposed, over a short period of time, to 75 rad/0.75 Gray of penetrating radiation; the threshold may be lower if neutrons rather than gamma or X-ray source.
Given the need for training, organization, and possibly specialized equipment, preparedness is essential. 
Response will vary with the nature of the contamination, the awareness and resources of the emergency services and public health authorities that become involved, news and rumor with their psychological effect, and the availability and political acceptability of foreign help.
In the Chernobyl disaster, it is not clear that outside help would have been useful in dealing with the massive contamination, far greater than virtually any plausible terrorist device. The time to mitigate it was in the missing safety designs of the reactor, and of a test in which multiple safety systems were disabled. A substantial number of plant, fire service, and helicopter pilots took action to contain it, and many knew that they would suffer fatal radiation exposures.
Incidents with comparable effects
Unfortunately, isotopes with appropriate medical or industrial uses may not be as well-guarded as military-grade nuclear material. Some accidents have been well-handled without casualties, while others have not. There are lessons to be learned from one assassination.
In an incident that was almost certainly an assassination, "Aleksander Litvinenko died in London in 2006 from poisoning with the radioisotope polonium-210, public health agencies in the United States were affected. Polonium was spread to many places in London, potentially contaminating thousands of persons, including foreign visitors. In the United Kingdom, approximately 8,000 persons contacted public health authorities, and citizens from 52 countries potentially were involved, including 160 U.S. citizens. Approximately 20 U.S. state and local public health agencies worked with CDC to notify involved citizens and to coordinate laboratory testing."
New York post office
"In August 2004, the day before the Republican National Convention, the New York City Department of Health and Mental Health (DOHMH) responded to a radiation incident at a mid-town Manhattan post office. A radiation source failed to retract into its protective shielding, resulting in dangerously high radiation levels near the radiation source. Police and fire departments evacuated the building and closed off nearby streets. The DOHMH response included conducting extensive environmental surveys outside and throughout the building, assisting with shielding the source, conducting press conferences, providing approximately 2,000 copies of fact sheets to residents in nearby buildings, and conducting dose estimates for the contractor and postal service employees. It took over 24 hours to remove the radiation source safely. The public's maximal risk for exposure was less than that received from a single chest radiograph because of their distance from the radiation source. "
On Sept 13, 1987, two scavengers looked in building, an abandoned radiotherapy center, for scrap metal that could be sold to a junkyard. Unknown to them, they 1400 Curie cesium-137 radiation source, which, under the shield, was in pellets the size of rice grains (that glowed in the dark). It found its way to a junkyard operator in Goiania, Brazil. He pried it open, and was fascinating by the glowing objects. 
Public health authorities recognized the incident on September 28. By then, approximately 250 people had been contaminated, out of 113,000 who were monitored. There were 4 deaths. 85 homes were contaminated, 41 evacuated, and 4 demolished.
New Delhi incident
A recent event, still not completely understood, took place in New Delhi in April 2010. Seven workers in a scrap metal business were exposed to cobalt-60, the source of which is not yet known. A hospital recognized acute radiation syndrome in the sickest victim, and alerted authorities. Radiological response teams appeared to have been put together on an ad hoc basis, and there is concern India is not prepared for future
Eight radiation sources were identified and put into shielded storage. They do not match hospital radiation sources used in the area, and experts speculate it was imported industrial waste. Sources with these characteristics might come from gamma radiographs used for metal inspection, or possibly food irradiation systems. They generated between 20 and 1000 rem/hour, the latter delivering a potentially fatal dose in an hour  Part of the proposed response involves radiation monitors at Indian ports that receive scrap.
Terrorist threats and attempts
Chechen terrorists have been the most visible in working with real radioactive materials. They placed a detectable amount oc cesium-137 in a Moscow park in November 1995, and created a media event by giving its location to newsmen. The cesium was believed to have come from Chechnya. In December 1998, the Russian-dominated Chechen Security Service announced they had found a land mine with radioactive material next to a railway line used by Russian troops. A September 1999 incident differed, in that the terrorists were incapacitated while carrying highly radioactive material without adequate protection.
The hazard to the users is one of the basic challenges in deploying radiological weapons: even those willing to die require shielding from the most radioactive materials, or may be disabled in hours or even minutes, interfering with the final placement. Shielding, however, is heavy and makes the material harder to transport clandestinely. Unshielded material could also set off radiation detectors near protected targets.
Jose Padilla was originally charged in a "dirty bomb" plot, although he was not eventually tried for that accusation. It does not appear he came close to constructing a device, or had the skills to do so.
- Joint Chiefs of Staff (2 October 2006), Chemical, Biological, Radiological, Nuclear, and High-Yield Explosives Consequence Management, Joint Publication 3-41
- Archer, Daniel E. (October 28, 2006), Nuclear Security in the 21st Century, American Physical Society. Division of Nuclear Physics
- Scott Stewart (22 April 2010), Dirty Bombs Revisited: Combating the Hype
- Jonathan Medalia (4 June 2010), Detection of Nuclear Weapons and Materials: Science, Technologies, Observations, Congressional Research Service, R40154
- S Deitchman, C Miller, RL Jones, RC Whitcomb Jr, JB Nemhauser, J Halpin, D Sosin, T Popovic, K Uranek, MD (8 October 2010), "CDC Grand Rounds: Radiological and Nuclear Preparedness", Morbidity & Mortality Weekly Report 2010 (59(36)): 1178-1181
- Booth, Mason (13 May 2003), Mock Dirty Bomb “Detonated” in Seattle as Homeland Security Drill Begins
- Bell CR, Eyestone S, Moore a (May 21, 2003), Disaster Management Interoperability Services (DMIS) at TOPOFF 2: Supporting Operations & Advancing Technology, EIIP Virtual Forum Presentation
- "CSIS Analysts comment on TOPOFF2, CSIS Conducted 2001, 2002 Wargames on Bioterrorism, Dirty Bomb", Center for Strategic and International Studies, 12 May 2003
- "Brazil Deadly Glitter", Time, 19 October 1987
- Neetu Chandra (17 April 2010), "Cobalt 60 waste not from city hospitals", India Today