RADIOGRAPHY - CORDON OFF DISTANCE CALCULATION
Part 2 of 2

Please refer the previous post 

https://hareeshkv.blogspot.com/2018/08/radiography-cordon-off-distance.html

Cordon-Off distance : d=√(W x T / P), meter

Work Load, W = Dose Rate x Present Activity of your Source x Working hours in a week.

Occupancy factor around the site = T

Prescribed radiation level along the cordon-off area, P = 2 mR/week = 0.002R/week

The dose rate of different some common radiography isotopes are as follows.

1. Ir-192: Dose rate = 0.5 R/Ci/m/hr
2. Se-75: Dose rate = 0.203 R/Ci/m/hr

3. Co-60: Dose rate = 1.3 R/Ci/m/hr

Example 1:

Source used: Ir-192 ; Strength of the source : 10 Ci ; Working Hours: 6 Hours per day and 5 days per week. Consider the occupancy as office.

Solution:

Work Load = 0.5 X 10 X (6 X 5) = 150

Cordon-Off distance : d=√(150 X 1 /0.336) = 273.86meter

Example 2:


Source used: Se-75 ; Strength of the source : 24.1 Ci ; Working Hours: 6 Hours per day and 6 days per week. Consider the occupancy as office.

Solution:

Work Load = 0.203 X 24.1 X (6 X 6) = 176.12

Cordon-Off distance : d=√(176.12 X 1 /0.002) = 296.75meter

Please note that these distances are for unshielded primary radiation direction open field radiation only. In a practical site there will be a lot of obstructions like, concrete pillar's, structures, other pipes and equipment's etc. So this distance will be measured using a calibrated survey meter and cordon off has to be done up to the point where it shows prescribed radiation level from the location of radiation source.

Collimator can also be used to reduce the cordon off distance.

There are a lot of advancements in the shielding process for radiation. SCAR radiography is one of such kind.

Note: The prescribed radiation limit along the cordon off may change according to the local / international rules and regulations. Please ensure the cordon off distance calculation process by consulting with the regulatory bodies of the state / country /region where the radiography examination is to take place.

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