136
13 Developing a Radiological and Nuclear Interdiction Network
made it possible to perform all of the tasks listed above except for interdiction (due
to the location of the detectors), and changing their location from rooftop to street
level accomplished that. By this time, however, the grant under which the detectors
were being purchased had expired, leaving the city with a small network of detectors
that were unable to serve any useful function, and without any of the more capable
detectors.
The moral of this particular story is that, before selecting any radiation detectors,
one must know what it is that they are to be used for and to communicate this clearly
to the vendor(s) that manufacture and sell them. This is why it can be helpful to
consider what the city plans to do with the radiation detectors—the mission they are
trying to accomplish—as well as who will be operating them when trying to decide
which detectors to purchase (e.g. [4]).
Consider the potential uses noted above and the characteristics of a detector to
meet the particular needs of that city.
• Interdiction requires a high degree of sensitivity to detect even low-activity or
well-shielded radioactive sources. The ability to identify radionuclides is also very
useful. Detectors used for interdiction should be placed as close as possible to
the locations they are intended to survey to minimize attenuation due to distance.
Sodium iodide, cesium iodide, and other gamma scintillators are idea for this
purpose due to their relatively low cost, relative ease of operation and upkeep,
and the lack of need for liquid nitrogen.
• Health and safety monitoring requires the ability to accurately measure very high
radiation dose rates, in excess of 1 Gy hr
−1 so that emergency responders and those
supervising them are aware when they enter areas with dangerously high radiation
levels from one or more radionuclides. Thus, a detector for such a purpose should
be energy-independent. This purpose is best served by an ionization chamber
or energy-compensated GM detector. These devices should be placed at ground
level, where emergency responders will be working and through which members
of the public will be evacuating.
• Tracking fallout plumes also requires the ability accurately measure both relatively low and very high radiation dose rates from nuclides with a variety of
gamma energies. It does not require a high degree of accuracy, although accurate
readings are always better than readings that are inaccurate. Here, too, ion chambers and/or energy-compensated GM detectors are ideal, although it might be
necessary to use multiple detectors to provide reasonably accurate measurements
from dose rates that vary over several orders of magnitude, from a few tens of
µGy hr
−1 through a few tens of Gy hr
−1 . Tracking and mapping the footprint of
a fallout plume is best accomplished using detectors on the tops of buildings to
minimize the effects of shielding by high-rise buildings as well as to avoid local
effects caused by winds swirling around buildings and other structures at ground
level.
• Dose reconstruction and the later adjudication of radiation injury compensation claims calls for the ability to measure accumulated dose with a high degree
of accuracy, ideally from multiple energies of gamma radiation and (in the event
13 Developing a Radiological and Nuclear Interdiction Network
made it possible to perform all of the tasks listed above except for interdiction (due
to the location of the detectors), and changing their location from rooftop to street
level accomplished that. By this time, however, the grant under which the detectors
were being purchased had expired, leaving the city with a small network of detectors
that were unable to serve any useful function, and without any of the more capable
detectors.
The moral of this particular story is that, before selecting any radiation detectors,
one must know what it is that they are to be used for and to communicate this clearly
to the vendor(s) that manufacture and sell them. This is why it can be helpful to
consider what the city plans to do with the radiation detectors—the mission they are
trying to accomplish—as well as who will be operating them when trying to decide
which detectors to purchase (e.g. [4]).
Consider the potential uses noted above and the characteristics of a detector to
meet the particular needs of that city.
• Interdiction requires a high degree of sensitivity to detect even low-activity or
well-shielded radioactive sources. The ability to identify radionuclides is also very
useful. Detectors used for interdiction should be placed as close as possible to
the locations they are intended to survey to minimize attenuation due to distance.
Sodium iodide, cesium iodide, and other gamma scintillators are idea for this
purpose due to their relatively low cost, relative ease of operation and upkeep,
and the lack of need for liquid nitrogen.
• Health and safety monitoring requires the ability to accurately measure very high
radiation dose rates, in excess of 1 Gy hr
−1 so that emergency responders and those
supervising them are aware when they enter areas with dangerously high radiation
levels from one or more radionuclides. Thus, a detector for such a purpose should
be energy-independent. This purpose is best served by an ionization chamber
or energy-compensated GM detector. These devices should be placed at ground
level, where emergency responders will be working and through which members
of the public will be evacuating.
• Tracking fallout plumes also requires the ability accurately measure both relatively low and very high radiation dose rates from nuclides with a variety of
gamma energies. It does not require a high degree of accuracy, although accurate
readings are always better than readings that are inaccurate. Here, too, ion chambers and/or energy-compensated GM detectors are ideal, although it might be
necessary to use multiple detectors to provide reasonably accurate measurements
from dose rates that vary over several orders of magnitude, from a few tens of
µGy hr
−1 through a few tens of Gy hr
−1 . Tracking and mapping the footprint of
a fallout plume is best accomplished using detectors on the tops of buildings to
minimize the effects of shielding by high-rise buildings as well as to avoid local
effects caused by winds swirling around buildings and other structures at ground
level.
• Dose reconstruction and the later adjudication of radiation injury compensation claims calls for the ability to measure accumulated dose with a high degree
of accuracy, ideally from multiple energies of gamma radiation and (in the event