Order Code RS21528
Updated October 29, 2003
CRS Report for Congress
Received through the CRS Web
Terrorist “Dirty Bombs”: A Brief Primer
Jonathan Medalia
Specialist in National Defense
Foreign Affairs, Defense, and Trade Division
Summary
Many, rightly or wrongly, fear a terrorist attack with a radiological dispersal device
(RDD).1 RDDs may scatter radioactive material with an explosive (a “dirty bomb”) or
other means. Radioactive atoms are unstable; as they decay, they emit electromagnetic
radiation or subatomic particles that can damage cells. Many legitimate activities
worldwide use radioactive material. Dealing with RDDs involves controlling sources,
detecting radiation, and preparing for and responding to an attack. This report will be
updated from time to time.
“Nuclear and Radiological Terrorism,” in the CRS
electronic briefing book on terrorism, tracks developments. This report does not address
nuclear power-related issues; see CRS Report RS21131, Nuclear Powerplants:
Vulnerability to Terrorist Attack.
Technical aspects
RDDs vs. nuclear weapons. In nuclear weapons, fission and fusion of certain
slightly radioactive materials release energy in a huge explosion. RDDs simply scatter
radioactive material; their main physical effect is contaminating an area. A terrorist group
could create an RDD much more easily than a nuclear weapon.
Radiation. Most atoms are stable: they remain in their current form indefinitely.
Unstable, or radioactive, atoms “disintegrate” or “decay” into other elements, mainly by
emitting an alpha particle (two neutrons and two protons) or a beta particle (an electron
1
Useful documents include Roger Eckhardt, “Ionizing Radiation — It’s Everywhere,” Los
Alamos Science, no. 23, 1995, a primer on radiation; Charles Ferguson et al., Commercial
Radioactive Sources: Surveying the Security Risks, Center for Nonproliferation Studies, January
2003; Charles Ferguson and Joel Lubenau, “Securing U.S. Radioactive Sources,” Issues in
Science and Technology, Fall 2003; American Nuclear Society, sessions on radiological
terrorism, November 2002, [http://eed.llnl.gov/ans]; U.S. Nuclear Regulatory Commission,
“ M e d i c a l ,
I n d u s t r i a l ,
a n d
A c a d e m i c
U s e s
o f
N u c l e a r
M a t e r i a l s , ”
[http://www.nrc.gov/materials/medical.html]; and Gregory Van Tuyle et al., “Reducing RDD
Concerns
Related
to
Large
Radiological
Source
Applications,”
September
2003
[http://www.nti.org/e_research/official_docs/labs/LAUR03-6%202.pdf].
Congressional Research Service ˜ The Library of Congress

---

CRS-2
or positron). Emission of photons (typically gamma rays, or high-energy x-rays) often
accompanies decay. The emitted particles and photons are radiation.
All elements have multiple isotopes, or forms with the same chemical properties but
different numbers of neutrons. Each radioactive isotope decays by steps to isotopes of
other elements, ending as a stable atom. While the instant when one atom will decay
cannot be predicted, each isotope has a “half-life,” the time for half the atoms in a mass
of that isotope to decay. The faster an isotope decays, the faster it releases, and exhausts,
its radiation. The radioactivity of a mass of material is measured in Curies (Ci; 1 Ci = 3.7
x1010 disintegrations per second). Cobalt-60 (the number is the number of neutrons plus
protons in the atom’s nucleus), with a half-life of 5.3 years, is highly radioactive;
uranium-235, with a half-life of over 700 million years, is not.2 Each isotope has a unique
decay fingerprint (e.g., gamma radiation energy) that can be used to identify it.
Biological effects. Radiation strikes people constantly, but most of it, like radio
waves and light, is not “ionizing”: it does not have enough energy to damage cells
significantly. The biological effects of ionizing radiation depend on the amount of energy
deposited in the body, called the absorbed dose. Higher doses produce direct clinical
effects including tissue damage, radiation sickness and, at very high levels, rapid death.
With chronic low-level exposure, no clinical effects are observed, but the exposed
individual may have an increased lifetime risk of developing cancer.
Absorbed dose depends on several factors. Some are straightforward, such as source
strength (Curies), distance, shielding, time of exposure, and amount of energy in each
particle or photon. Others are more complex. Type of radiation: A layer of dead skin or
a few inches of air stops alpha particles; more material is needed to stop beta particles,
which are lighter and faster. Substantial shielding is needed to block gamma rays, which
are more penetrating. Form of material: Alpha and beta emitters do little harm outside
the body because they are easily stopped. Inside the body, though, they can do much
damage. One can with few ill effects pick up a lump of plutonium-239, an alpha emitter,
because the dead skin layer stops alphas, but a speck of the same material deep in the
lungs bombards tissue with alphas and can cause lung cancer. An RDD thus poses a
greater health threat if its material is finely powdered — and thus more readily dispersed
and inhaled — rather than granular. Chemical behavior of the element in the body:
Certain organs concentrate particular elements.
Strontium concentrates in bone;
radioactive strontium-90 can cause bone cancer, breast cancer, and leukemia. The thyroid
gland concentrates iodine; radioactive iodine-131 can cause thyroid cancer.3
Sources of radioactive material. Millions of radioactive sources are used
worldwide because they have many beneficial uses. Sources with a tiny fraction of a
Curie, such as household smoke detectors, do not pose a terrorist threat. A source with
2
U.S. Department of Energy. Office of Environmental Management. “Characteristics of
Important Radionuclides.” [http://www.em.doe.gov/idb97/tabb1.html]
3
Potassium iodide protects against radioactive iodine by saturating the thyroid with stable
iodine-127; it offers no protection against other elements. Terrorists are unlikely to use iodine-
131 in an RDD because they could obtain it only from a nuclear reactor, its half-life (8 days) is
so short that much of it would decay before they could use it, and its intense radioactivity owing
to its short half-life makes it hazardous to handle.

---

CRS-3
even a few Curies, though, may be of use for an RDD. While hundreds of radioactive
isotopes exist, only a few isotopes, and in only a few forms, are of concern for RDDs; all
are produced in nuclear reactors, mainly in a few countries. Isotopes of particular concern,
typical sources, and Curies per source, include cesium-137 (half-life 30.2 years), used in
external beam radiation devices to treat cancers (13,500 Ci), equipment to monitor wells
for oil (0.027-2.7 Ci), and gauges (0.27-27 Ci); and cobalt-60 (half-life 5.3 years), used
in industrial radiography (3-250 Ci) and cancer therapy (0.0014-0.27 Ci). Such sources
often have little security because they are small, have modest amounts of shielding so they
can be used in the field, and do not have enough radiation to be self-protected. They are
sometimes abandoned. In contrast, terrorists would find isotopes with very short half-
lives (hours or less) of little use because the radiation could decay to low levels before the
material could be used, while those with long half-lives (millions of years) emit radiation
very slowly and would do little damage unless inhaled. There is legitimate global
commerce in radioactive materials of concern, but also potential for fraudulent purchases
and theft during shipment or use, and problems of disposing of sources no longer wanted.4
Radiological Dispersal Devices
Alternative designs. Perhaps because of the term “dirty bomb,” the public and
media have focused on radioactive material dispersed by an explosive device. A dirty
bomb could be made by surrounding TNT, C-4, or other chemical explosive with a
powdered radioisotope. Many terrorist groups would have the skill and materials needed
to make the explosive part of the device; it would be somewhat harder for them to obtain
the radioactive material and convert it to powdered form. Terrorists could also disperse
radioactive material without an explosive by spraying, scattering, or simply dumping it.
Effectiveness. An RDD’s effectiveness depends on many factors. (1) Some
isotopes do more harm than others, and some elements (including their radioisotopes),
such as cesium, bond strongly to concrete and asphalt. (2) Smaller particles disperse more
easily and are more readily inhaled, but may be harder to make. (3) Using more material
increases physical effects. (4) More explosive would disperse the material more widely.
(5) Weather would play a large role. Higher wind speed would disperse the material more
widely, and wind direction would determine where it would fall. Thermal currents, more
prevalent on a summer’s day than a winter’s night, would also disperse material. Rain or
snow would wash material out of the air but concentrate it in rivers, lakes, and seacoasts.
Greater dispersion would increase the number of people affected while reducing the effect
on each; less dispersion would inflict more effects but on fewer people.
Several estimates have appeared on radiation levels from dispersal of radioactive
material. For example, the Federation of American Scientists calculated that the cesium-
137 in a medical gauge, a small amount, detonated in an RDD at the National Gallery of
Art in Washington, would cover about 40 city blocks with radiation that would exceed
Environmental Protection Agency (EPA) contamination limits (a one in 10,000 chance
of getting cancer). This area might, depending on wind direction, include the Capitol,
Supreme Court, and Library of Congress. “If decontamination were not possible, these
4
Much of the material in this paragraph is from Ferguson et al., Commercial Radioactive
Sources, p. vi, 3, 12, 13, 43-44.

---

CRS-4
areas would have to be abandoned for decades,” by one estimate.5 Others feel that such
scenarios exaggerate the effectiveness of RDDs by assuming that material disperses well
and by downplaying the ability to decontaminate affected areas. EPA guidelines magnify
RDD effectiveness. Steven Koonin, Provost of California Institute of Technology, stated
that 3 curies of an appropriate isotope, a fraction of a gram, dispersed over a square mile
“would make the area uninhabitable, according to the maximum dose currently
recommended for the general population.”
However, “the health effects of such
contamination would be minimal. For every 100,000 people exposed to that level of
radiation, four lifetime cancers would be induced, which would take place on top of the
20,000 cancers already expected to arise from other causes.”6 Even such low-level effects
are debated; some argue that these effects are extrapolations from higher doses with no
conclusive evidence to support their existence.7
Terrorists could try to achieve several goals with RDDs in the following sequence.
Most depend on public fear of any radiation rather than actual levels of radiation. (1)
Deaths and injuries. Any prompt casualties would most likely come only from the
explosion of a dirty bomb; many experts believe these would be few in numbers.8 (2)
Panic. Small amounts of radioactive material might cause as much panic as larger
amounts. (3) Recruitment. The worldwide media coverage of an RDD attack would be
a powerful advertisement for a terrorist group claiming responsibility. (4) Asset denial.
Public concern over the presence of radioactive material might lead people to abandon a
subway system, building, or university for months to years. (5) Economic disruption. If
a port or the central area of a city were contaminated with radioactive material, commerce
there might be suspended. (6) Long-term casualties. Inhalation of radioactive material
or exposure to gamma sources could lead to such casualties, probably in small numbers.
Prevention and Response
Securing radioactive sources. Prior to September 11, 2001, safe handling of
sources was the chief concern. They were used worldwide in medical equipment, oil well
gauges, etc., with little or no security. Some were abandoned, becoming “orphan
sources.” After the attacks, attention shifted to securing them. Various measures seek to
control U.S. radioactive materials. The Nuclear Regulatory Commission (NRC) regulates
the use and transportation of most radioactive sources for nuclear power and research
reactors, related facilities like waste repositories, and for medical, industrial, and
5
U.S. Congress. Senate. Committee on Foreign Relations. Dirty Bombs and Basement
Nukes: The Terrorist Nuclear Threat. Senate Hearing 107-575, 107th Congress, 2nd Session,
Washington, U.S. Govt. Print. Off., 2002, p. 39-40. See also Michael Levi and Henry Kelly,
“Weapons of Mass Disruption, Scientific American, November 2002: 76-81.
6 Senate Foreign Relations Committee, Dirty Bombs and Basement Nukes, p. 17.
7 See U.S. General Accounting Office. Radiation Standards: Scientific Basis Inconclusive, and
EPA and NRC Disagreement Continues. RCED-00-152 June 30, 2000.
8 Richard Meserve, former Chairman, Nuclear Regulatory Commission, held that an RDD might
cause “deaths on the order of tens of people in most scenarios.” Senate Foreign Relations
Committee, Dirty Bombs and Basement Nukes, p. 8.

---

CRS-5
academic uses.9 Many states also share in this regulation. An NRC-Department of
Energy (DOE) working group to increase the security and regulatory oversight of high-
risk radioactive sources has proposed verifying the legitimacy of applicants for licenses,
preventing insiders from diverting sources, and controlling imports and exports of
sources.10 Several programs provide for the disposal of unwanted radioactive sources,
which can be difficult. The Off-Site Source Recovery Project, operated by Los Alamos
National Laboratory, gathers sources owned by, or the responsibility of, the Department
of Energy from around the United States, transports them to Los Alamos, and stores them
there.11 EPA’s Orphan Sources Initiative will establish a national system to retrieve
radioactive sources from non-nuclear facilities like scrap yards and dispose of them.12
There are modest international efforts to secure sources. These are important;
according to one expert, over 100 countries in 1999 were “known or thought to lack
effective control over radiation sources and radioactive materials.”13 In March 2003, the
International Atomic Energy Agency (IAEA) held an International Conference on Security
of Radioactive Sources.14 In June 2002, the G-8 committed itself to “six principles to
prevent terrorists or those that harbour them from acquiring or developing” radiological
and other weapons of mass destruction (WMD).15
The National Nuclear Security
Administration has identified 35 large radiological waste sites and over 1,000 orphan or
surplus radioactive sources in the former Soviet Union, and has initiated a cooperative
program with the IAEA and these republics to locate and secure these sites and sources.16
The IAEA has begun discussions with source manufacturers and suppliers to address
alternate sources, possible fraudulent purchases, and source disposal options.
Avoiding the use of radioactive sources. For some uses, radioactive material
is the only way to achieve the desired result. For others, alternatives exist, such as x-ray
machines or particle accelerators.
These machines use electric power to generate
radiation, have no radioactive material, and are not radioactive when the power is off.
9
U.S. Nuclear Regulatory Commission, “Medical, Industrial, and Academic Uses of Nuclear
Materials” [http://www.nrc.gov/materials/medical.html]; and “How We Regulate,”
[http://www.nrc.gov/what-we-do/regulatory.html#evaluating]. For legislation establishing and
governing NRC, see [http://www.nrc.gov/who-we-are/governing-laws.html].
10 Richard Meserve, Chairman, “Statement Submitted by the United States Nuclear Regulatory
Commission to the Subcommittee on Oversight and Investigations, Committee on Energy and
Commerce, United States House of Representatives Concerning Nuclear Security,”Mar. 18, 2003.
11 For further information on this program, see [http://osrp.lanl.gov].
12 U.S. Environmental Protection Agency. “Orphan Sources Initiative.”
http://www.epa.gov/radiation/cleanmetals/orphan.htm
13 Abel Gonzalez, “Strengthening the Safety of Radiation Sources & the Security of Radioactive
Materials: Timely Action,” IAEA Bulletin, 41/3/1999: 9.
14 See [http://www.iaea.org/worldatom/Press/Focus/RadSources/index.shtml].
15
G8, “The G8 Global Partnership Against the Spread of Weapons and Materials of Mass
Destruction,” June 27, 2002, [http://www.g7.utoronto.ca/summit/2002kananaskis/arms.html].
16 U.S. Department of Energy. Office of Management, Budget and Evaluation/CFO. FY 2004
Congressional Budget Request: National Nuclear Security Administration, DOE/ME-0016, vol.
1, February 2003, p. 649-651. [http://www.mbe.doe.gov/budget/04budget/content/defnn/nn.pdf]

---

CRS-6
Detection. RDDs are the least difficult WMD to detect. Chemical or biological
agents in sealed airtight containers have no signatures by which they could be detected.
RDD-suitable material is also more readily detectable than the highly enriched uranium
or plutonium-239 used in nuclear weapons because it is much more radioactive. Hiding
radioactive material would require much shielding, which could raise suspicions if seen
on an x-ray inspection machine, and infrared detectors can detect the heat generated by
large radioactive sources despite shielding. On the other hand, detecting RDDs is not
simple. Only a small fraction of cargo containers is physically inspected, and material
might be smuggled across unguarded stretches of coasts or borders. Further, since
material for an RDD might be obtained within the United States, a system to detect RDDs
inside this nation might be needed to complement detection efforts at borders. Many
sensors can detect radioactive material, such as pager-size radiation detectors used by U.S.
Customs Service agents, Geiger counters, and gamma-ray detectors. Some experts
recommend advancing R&D on detectors, and linking them into a national system to
detect radioactive materials. The difficulty of finding RDD material emphasizes the value
of eliminating or securing it.
Advance steps to minimize effects of an RDD attack. As noted earlier,
most such effects flow from fear of radiation. A large-scale public education program,
available for use in the event of attack, could help quell panic.17 Other steps might
include deploying radiation detectors in large cities, and developing and applying coatings
to prevent radioactive material from bonding to streets and buildings, though it is not clear
that the benefit of coatings would merit the cost.
Response to an attack. The initial response would likely involve detecting an
attack, evacuating areas that might receive radiation or keeping people indoors until
respirable material had dispersed, treating people who might be exposed, and sheltering
evacuees. The Federal Radiological Emergency Response Plan18 would come into play.
DOE’s Nuclear Emergency Support Teams, among others, could assist.19 Harry Vantine,
of Lawrence Livermore National Laboratory, suggests having the prompt ability to predict
dose to the population from an RDD attack, and exercising decontamination procedures.20
A public education program could be implemented promptly. Longer-term responses
would include monitoring radiation levels, defining and decontaminating affected areas,
and decontaminating or demolishing affected buildings. Promulgating standards that
permitted exposure to somewhat higher levels of radiation while having few adverse
health effects, as noted above, would greatly reduce the area to be abandoned and the
decontamination required. Public acceptance of such standards would be uncertain.
17
For information on coping with RDD attack and other emergencies, see U.S. Federal
Emergency Management Agency, Are You Ready?: A Guide to Citizen Preparedness, revised
September 2002, 101 p. [http://www.fema.gov/areyouready/]; National Council on Radiation
Protection and Measurements, “Management of Terrorist Events Involving Radioactive
Material,” 2001, 232 p., NCRP report 138, [http://www.ncrp.com/ncrprpts.html]; and RAND,
Individual Preparedness and Response to Chemical, Radiological, Nuclear, and Biological
Terrorist Attacks, 2003, 232 p. [http://www.rand.org/publications/MR/MR1731].
18 See [http://www.au.af.mil/au/awc/awcgate/frerp/frerp.htm].
19 See Jeffrey Richelson, “Defusing Nuclear Terror,” Bulletin of the Atomic Scientists, March-
April 2002: 39-43; and U.S. Department of Energy. Order DOE 5530.2, “Nuclear Emergency
Search Team,” Sept. 20, 1991, at [http://www.fas.org/nuke/guide/usa/doctrine/doe/o5530_2.htm].
20
Senate Foreign Relations Committee, Dirty Bombs and Basement Nukes, p. 55.

---