18
2 Types of Radiation and Their Properties
Table 2.7 Half value layer (HVL) and tenth value layer (TVL) thicknesses for several radionuclides.
Values calculated using the RadPro Calculator [6]
Nuclide
Water
Concrete
Lead
HVL (cm)
TVL (cm)
HVL (cm)
TVL (cm)
HVL (cm)
TVL (cm)
Co-60
26.4
64.7
11.8
28.1
1.8
4.5
Cs-137
19.9
54.3
8.8
23.9
0.7
2.2
Ir-192
24.9
49.9
9.2
21.2
0.3
1.1
Am-241
15.4
32.6
2.4
5.3
< 0.1
< 0.1
2.3.3 Example
Now let’s put all of this together in an example.
Suppose you are in the role of a radiological Subject Matter Expert and you receive
a report that some police performing routine patrols are measuring a radiation dose
rate of 2 μGy hr
−1 at a distance of about 50 m from a storage locker.
Using the inverse square law, you can tell the Incident Commander that she should
establish a Hot Zone boundary at a dose rate of 20 μGy hr
−1 —this should be at
a distance of about 16 m from the storage locker.
50 m
20
2
∼ 16 m
You further calculate that the dose rate at a distance of 1 m would be 5 mGy hr
−1
(5000 μGy hr
−1 )
2μ
Gy
h
×
50 m
1 m
2
= 5000 μ Gy hr
−1
One of the responding police officers uses a RIID (radio-isotope identifier) and
finds that the radionuclide in the storage area is Co-60.
Using a gamma constant of 3.045 × 10
−04 mGy hr
−1 for 1 MBq for Co-60, you
calculate that the activity of the source (assuming it is unshielded) is about 16,400
MBq
5 mGy/hr
3.045×10 −4 m Gy
hr
per MBq
= 16, 400 MBq
You secure the area and obtain a warrant to search the storage area. You find
that the highest dose rates appear to come from a box that is about 30 cm × 30 cm
× 30 cm in size. The Bomb Squad is reluctant to handle the box because it might
2 Types of Radiation and Their Properties
Table 2.7 Half value layer (HVL) and tenth value layer (TVL) thicknesses for several radionuclides.
Values calculated using the RadPro Calculator [6]
Nuclide
Water
Concrete
Lead
HVL (cm)
TVL (cm)
HVL (cm)
TVL (cm)
HVL (cm)
TVL (cm)
Co-60
26.4
64.7
11.8
28.1
1.8
4.5
Cs-137
19.9
54.3
8.8
23.9
0.7
2.2
Ir-192
24.9
49.9
9.2
21.2
0.3
1.1
Am-241
15.4
32.6
2.4
5.3
< 0.1
< 0.1
2.3.3 Example
Now let’s put all of this together in an example.
Suppose you are in the role of a radiological Subject Matter Expert and you receive
a report that some police performing routine patrols are measuring a radiation dose
rate of 2 μGy hr
−1 at a distance of about 50 m from a storage locker.
Using the inverse square law, you can tell the Incident Commander that she should
establish a Hot Zone boundary at a dose rate of 20 μGy hr
−1 —this should be at
a distance of about 16 m from the storage locker.
50 m
20
2
∼ 16 m
You further calculate that the dose rate at a distance of 1 m would be 5 mGy hr
−1
(5000 μGy hr
−1 )
2μ
Gy
h
×
50 m
1 m
2
= 5000 μ Gy hr
−1
One of the responding police officers uses a RIID (radio-isotope identifier) and
finds that the radionuclide in the storage area is Co-60.
Using a gamma constant of 3.045 × 10
−04 mGy hr
−1 for 1 MBq for Co-60, you
calculate that the activity of the source (assuming it is unshielded) is about 16,400
MBq
5 mGy/hr
3.045×10 −4 m Gy
hr
per MBq
= 16, 400 MBq
You secure the area and obtain a warrant to search the storage area. You find
that the highest dose rates appear to come from a box that is about 30 cm × 30 cm
× 30 cm in size. The Bomb Squad is reluctant to handle the box because it might