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DEFENCE IN DEPTH
Defence in depth: sources

HOW BIG?

 

In the overview module we mentioned that the maximum consequences were related to the source category. The source category can be calculated from the activity of the source and the D value for the isotope.

Source category is determined by A/D ratio,
where A = activity of the source and D = D value

Category A/D ratio Common practices (examples)

1

A/D > 1000 Radioisotope thermoelectric generators
Irradiators
Teletherapy
Fixed multi-beam teletherapy
2 10 ≤ A/D < 1000 Industrial gamma radiography
High/medium dose rate brachytherapy
3 1 ≤ A/D < 10 Fixed industrial gauges
Well logging gauges
4 0.01 ≤ A/D < 1 Low dose rate brachytherapy
Thickness gauges
Portable gauges
Bone densitometers
Static eliminators

 

e.g. for a 4 TBq Ir-192 source (D value 0.08 TBq)
A/D = 4/0.08 = 50
Category is 2.

Examples of sources and their category are shown above. D values for a range of isotopes are provided in Table 22, appendix III. The next three pages give some further details on D values.

TABLE 22. D VALUES FOR A RANGE OF ISOTOPES

Radionuclide

D(TBq)

Am-241

6.E-02

Am-241/Be

6.E-02

Au-198

2.E-01

Cd-109

2.E+01

Cf-252

2.E-02

Cm-244

5.E-02

Co-57

7.E-01

Co-60

3.E-02

Cs-137

1.E-01

Fe-55

8.E+02

Gd-153

1.E+00

Ge-68

7.E-01

H-3

2.E+03

I-125

2.E-01

I-131

2.E-01

Ir-192

8.E-02

Kr-85

3.E+01

Mo-99

3.E-01

Ni-63

6.E+01

P-32

1.E+01

Pd-103

9.E+01

Pm-147

4.E+01

Po-210

6.E-02

Pu-238

6.E-02

Pu-239/Be

6.E-02