13.3 Instrument Operators
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is given the most basic instruments. A Tier 3 emergency responder will be given a
simple PRD that measures only radiation dose rate, and they will be trained on how
to distinguish between, say, a car carrying a nuclear medicine patient versus a car
carrying a radiological device. To adjudicate such an alarm they will rely on what
police term “the totality of circumstances,” using a combination of their instrument
readings, the person’s age and demeanor, the location where the stop was made,
response to questions (including consistency of answers and the agreement of these
answers with other observations), and so forth.
If the totality of circumstances indicate that the person is a harmless nuclear
medicine patient then the alarm would be considered adjudicated; if not then the
officer might call for a Tier 2 responder to help collect additional information.
Consider for example, a person claiming to be a nuclear medicine patient who is
carrying a backpack; when separated from the backpack by a few meters, radiation
dose rates near the “patient” drop to background while the backpack remains “hot.”
This would suggest that the radioactivity is contained within the backpack, not within
the “patient” as one would expect. This would call for follow-up.
A Tier 2 responder might be equipped with a radioisotope identifier (RIID) to
identify the radionuclide(s) present. If, for example, the nuclide in the backpack was
found to be I-131 then it is possible that the person really is a nuclear medicine patient
and that the backpack was contaminated at the hospital. If the backpack contained
Ra-226 then it might contain an RDD…or it might contain the person’s radioactive
rock or antique watch collection. If the backpack contains Cs-137 it might be a
“button” source for checking radiation instruments or it might be that the backpack
was contaminated as the person was building an RDD. Identifying the nuclide(s)
present, in conjunction with additional questions from a better-trained officer, can
help to determine if the person is free to go, or if they should be questioned and
investigated further.
There are times that even a Tier 2 responder will not be able to resolve a situation;
in these cases it might be necessary to call for a Tier 1 asset. In the US the Tier 1 assets
are the National Laboratories, who will carefully analyze the spectra sent to them
through a process called “reachback.” In the example above, a Cs-137 identification
would not call for reachback as the Cs-137 spectrum is unambiguous. On the other
hand, the Ra-226 gamma has an energy almost identical to that of U-235 (186 versus
185 keV) and it is not uncommon for a RIID to mistake one nuclide for the other.
Thus, if Ra-226 was identified, it would be prudent to send the spectrum to a Tier
1 asset for assessment, to confirm the nuclide identification and the material giving
rise to it.
Quantifying interdicted sources
During a three-state radiological interdiction exercise conducted in a large
American city in 2011 the scenario called for the “theft” of a high-activity
(about 90 TBq) Co-60 radioactive source from a facility in a neighboring state.
Over the course of the next two days, investigators determined that the source
133
is given the most basic instruments. A Tier 3 emergency responder will be given a
simple PRD that measures only radiation dose rate, and they will be trained on how
to distinguish between, say, a car carrying a nuclear medicine patient versus a car
carrying a radiological device. To adjudicate such an alarm they will rely on what
police term “the totality of circumstances,” using a combination of their instrument
readings, the person’s age and demeanor, the location where the stop was made,
response to questions (including consistency of answers and the agreement of these
answers with other observations), and so forth.
If the totality of circumstances indicate that the person is a harmless nuclear
medicine patient then the alarm would be considered adjudicated; if not then the
officer might call for a Tier 2 responder to help collect additional information.
Consider for example, a person claiming to be a nuclear medicine patient who is
carrying a backpack; when separated from the backpack by a few meters, radiation
dose rates near the “patient” drop to background while the backpack remains “hot.”
This would suggest that the radioactivity is contained within the backpack, not within
the “patient” as one would expect. This would call for follow-up.
A Tier 2 responder might be equipped with a radioisotope identifier (RIID) to
identify the radionuclide(s) present. If, for example, the nuclide in the backpack was
found to be I-131 then it is possible that the person really is a nuclear medicine patient
and that the backpack was contaminated at the hospital. If the backpack contained
Ra-226 then it might contain an RDD…or it might contain the person’s radioactive
rock or antique watch collection. If the backpack contains Cs-137 it might be a
“button” source for checking radiation instruments or it might be that the backpack
was contaminated as the person was building an RDD. Identifying the nuclide(s)
present, in conjunction with additional questions from a better-trained officer, can
help to determine if the person is free to go, or if they should be questioned and
investigated further.
There are times that even a Tier 2 responder will not be able to resolve a situation;
in these cases it might be necessary to call for a Tier 1 asset. In the US the Tier 1 assets
are the National Laboratories, who will carefully analyze the spectra sent to them
through a process called “reachback.” In the example above, a Cs-137 identification
would not call for reachback as the Cs-137 spectrum is unambiguous. On the other
hand, the Ra-226 gamma has an energy almost identical to that of U-235 (186 versus
185 keV) and it is not uncommon for a RIID to mistake one nuclide for the other.
Thus, if Ra-226 was identified, it would be prudent to send the spectrum to a Tier
1 asset for assessment, to confirm the nuclide identification and the material giving
rise to it.
Quantifying interdicted sources
During a three-state radiological interdiction exercise conducted in a large
American city in 2011 the scenario called for the “theft” of a high-activity
(about 90 TBq) Co-60 radioactive source from a facility in a neighboring state.
Over the course of the next two days, investigators determined that the source