44
5 How Radiological Weapons Work
contaminated; for this reason it is reasonable to assume that injured persons more
likely to have internal radioactivity than the uninjured. Even more importantly, those
who are most seriously injured are likely to be the most heavily contaminated and
to have the highest levels of internal radioactivity owing to their proximity to the
explosion.
What size area can be affected by an RDD?
In the United States, a former regulatory guidance document [20] limited
radioactive contamination in an uncontrolled area to 1000 dpm/100 cm
2 if the
contamination is removable and 5000 dpm/100 cm
2 (50 dpm/cm
2 ) for fixed
plus removable contamination. *So how large an area will be contaminated by
a 10 GBq radioactive source?
10 GBq = 10
10 dps = 6 × 10
11 dpm
6 × 10
11 dpm
50dpm/cm 2 = 1.2 × 10
10 cm
2
There are 10,000 cm
2 in one square meter, and 10,000 m
2 per ha, so the area
that this source can contaminate to levels requiring regulatory access control
would be 120 ha, or about 1.2 km
2 .
It is worth noting that this level of contamination does not necessarily pose
a risk to persons on the contaminated area. According to Federal Guidance
Report #12 [22] Co-60 contamination produces a radiation dose rate of 2.35 ×
10
−15 Sv/s for contamination levels of 1 Bq/m
2 . For simplicity, we can round
off 50 dpm/cm
2 to be 1 dps/cm
2 , which is 1 Bq/cm
2 because 1 Bq = 1 dps =
60 dpm. Thus, this level of contamination is about 1 Bq/cm
2 or 10,000 Bq/m
2
and will produce a radiation dose rate of 2.35 × 10
–11 Sv/s. Bearing in mind
that there are 3600 s in one hour, this is a dose rate of about 8.5 × 10
–8 Sv/hr, or
0.085 µSv/hr. This is very similar to normal background radiation dose rates
in most parts of the world and is not harmful.
*While this document was withdrawn in 2016, the contamination limits
are well-entrenched in the US and are published in a number of US state
regulations. They are used here for illustrative purposes.
5.2.2.2 Covert
In a December 19, 2006 New York Times opinion column, physicist Peter
Zimmerman suggested that a terrorist attack involving radioactive materials might
not be announced with an explosion. Using the term “smoky bomb” Zimmerman
5 How Radiological Weapons Work
contaminated; for this reason it is reasonable to assume that injured persons more
likely to have internal radioactivity than the uninjured. Even more importantly, those
who are most seriously injured are likely to be the most heavily contaminated and
to have the highest levels of internal radioactivity owing to their proximity to the
explosion.
What size area can be affected by an RDD?
In the United States, a former regulatory guidance document [20] limited
radioactive contamination in an uncontrolled area to 1000 dpm/100 cm
2 if the
contamination is removable and 5000 dpm/100 cm
2 (50 dpm/cm
2 ) for fixed
plus removable contamination. *So how large an area will be contaminated by
a 10 GBq radioactive source?
10 GBq = 10
10 dps = 6 × 10
11 dpm
6 × 10
11 dpm
50dpm/cm 2 = 1.2 × 10
10 cm
2
There are 10,000 cm
2 in one square meter, and 10,000 m
2 per ha, so the area
that this source can contaminate to levels requiring regulatory access control
would be 120 ha, or about 1.2 km
2 .
It is worth noting that this level of contamination does not necessarily pose
a risk to persons on the contaminated area. According to Federal Guidance
Report #12 [22] Co-60 contamination produces a radiation dose rate of 2.35 ×
10
−15 Sv/s for contamination levels of 1 Bq/m
2 . For simplicity, we can round
off 50 dpm/cm
2 to be 1 dps/cm
2 , which is 1 Bq/cm
2 because 1 Bq = 1 dps =
60 dpm. Thus, this level of contamination is about 1 Bq/cm
2 or 10,000 Bq/m
2
and will produce a radiation dose rate of 2.35 × 10
–11 Sv/s. Bearing in mind
that there are 3600 s in one hour, this is a dose rate of about 8.5 × 10
–8 Sv/hr, or
0.085 µSv/hr. This is very similar to normal background radiation dose rates
in most parts of the world and is not harmful.
*While this document was withdrawn in 2016, the contamination limits
are well-entrenched in the US and are published in a number of US state
regulations. They are used here for illustrative purposes.
5.2.2.2 Covert
In a December 19, 2006 New York Times opinion column, physicist Peter
Zimmerman suggested that a terrorist attack involving radioactive materials might
not be announced with an explosion. Using the term “smoky bomb” Zimmerman