5.2 Types of Radiological Weapons
43
(RDD)—popularly known as a “dirty bomb,” although there has also been speculation
that disseminating radioactivity less obviously (a “smoky bomb”) might also be a
subject of concern [24].
5.2.2.1 Overt
An overt radiological attack is one that announces itself, classically as an explosion
laced with radioactivity. In this sort of an RDD it is assumed that the radioactive
materials would be placed on top of an explosive device and the force of the explosion
would spread the radioactive materials—directly by the force of the explosion as well
as smaller particles that would be carried by whatever wind or breeze might exist [7].
The materials carried by the force of the explosion would fly outwards on largely
ballistic trajectories; the dispersal radius would depend on the force of the explosion,
particle and fragment size, and related factors. For a large bomb (a few to several
tons of TNT equivalent), fragments can be dispersed to a distance of a few to several
hundred meters or more from the site of the explosion, carrying radioactivity to that
distance. In addition, smaller particles (a few to several microns in size) will be lofted
into the air and can be carried to a distance of several kilometers by the wind, breezes,
and air currents. For a high-activity radioactive source (tens of TBq), radiation dose
rates can be in the tens of mSv/hr over an area of a few hectares, while contamination
carried by the breeze can form a plume that will deposit sufficient radioactivity to
generate dose rates of up to a few tens of µSv/hr to a distance of three or four km
downwind. Thus, it might be necessary to establish an extensive safety and security
perimeter around the contaminated areas as well as those exposed to elevated levels
of radiation by the radioactive source and source fragments.
The amount of contamination and its extent will depend on the source activity,
the magnitude of the explosion, and the physical form of the source. Of these, the
first two are self-explanatory but the last warrants discussion.
Liquids and powders are rather easily dispersible and will be relatively easily
spread by a bomb. Some sources, however, are in the form of ceramic (e.g. Sr-90) or
solid metal (e.g. Co-60, Ir-192)—such sources might flake or be broken into pieces
(spalling) but are not likely to break into pieces small enough to be carried by the
wind in the same manner as a powder or liquid. Thus, if solid sources are used
in an RDD it seems reasonable to assume that radioactivity will not spread much
beyond a few hundred meters, that the source fragments will contain higher levels of
radioactivity (causing higher levels of radiation) than contamination from powdered
or liquid sources, and that the resulting radiation dose rates will be somewhat patchy,
with high dose rates in the vicinity of source fragments or shards and lower dose
rates elsewhere.
Radiation exposure to members of the public will come from direct exposure to
radiation from contamination and/or source fragments as well as exposure due to
internal radioactivity from inhaled, ingested, or embedded radioactivity.
An overt attack is likely to cause injuries in the same manner as any other explosive device, with the added concern that these injuries may also be radioactively
43
(RDD)—popularly known as a “dirty bomb,” although there has also been speculation
that disseminating radioactivity less obviously (a “smoky bomb”) might also be a
subject of concern [24].
5.2.2.1 Overt
An overt radiological attack is one that announces itself, classically as an explosion
laced with radioactivity. In this sort of an RDD it is assumed that the radioactive
materials would be placed on top of an explosive device and the force of the explosion
would spread the radioactive materials—directly by the force of the explosion as well
as smaller particles that would be carried by whatever wind or breeze might exist [7].
The materials carried by the force of the explosion would fly outwards on largely
ballistic trajectories; the dispersal radius would depend on the force of the explosion,
particle and fragment size, and related factors. For a large bomb (a few to several
tons of TNT equivalent), fragments can be dispersed to a distance of a few to several
hundred meters or more from the site of the explosion, carrying radioactivity to that
distance. In addition, smaller particles (a few to several microns in size) will be lofted
into the air and can be carried to a distance of several kilometers by the wind, breezes,
and air currents. For a high-activity radioactive source (tens of TBq), radiation dose
rates can be in the tens of mSv/hr over an area of a few hectares, while contamination
carried by the breeze can form a plume that will deposit sufficient radioactivity to
generate dose rates of up to a few tens of µSv/hr to a distance of three or four km
downwind. Thus, it might be necessary to establish an extensive safety and security
perimeter around the contaminated areas as well as those exposed to elevated levels
of radiation by the radioactive source and source fragments.
The amount of contamination and its extent will depend on the source activity,
the magnitude of the explosion, and the physical form of the source. Of these, the
first two are self-explanatory but the last warrants discussion.
Liquids and powders are rather easily dispersible and will be relatively easily
spread by a bomb. Some sources, however, are in the form of ceramic (e.g. Sr-90) or
solid metal (e.g. Co-60, Ir-192)—such sources might flake or be broken into pieces
(spalling) but are not likely to break into pieces small enough to be carried by the
wind in the same manner as a powder or liquid. Thus, if solid sources are used
in an RDD it seems reasonable to assume that radioactivity will not spread much
beyond a few hundred meters, that the source fragments will contain higher levels of
radioactivity (causing higher levels of radiation) than contamination from powdered
or liquid sources, and that the resulting radiation dose rates will be somewhat patchy,
with high dose rates in the vicinity of source fragments or shards and lower dose
rates elsewhere.
Radiation exposure to members of the public will come from direct exposure to
radiation from contamination and/or source fragments as well as exposure due to
internal radioactivity from inhaled, ingested, or embedded radioactivity.
An overt attack is likely to cause injuries in the same manner as any other explosive device, with the added concern that these injuries may also be radioactively