RADIOGRAPHY - CORDON OFF DISTANCE CALCULATION
Part 1 of 2
Radiography is always a safety concern but it is an unavoidable NDT process.
The safe method to
execute the radiography is to avoid the public reaching the radiography area
This is done by hard/soft barricading, bringing warning lights, warning
signs, Hooters etc.
How far the public to
be blocked from the radiography process, in the case of industrial
radiography is cleared by the concept called corden-off distance.
How cordon off is
calculated.
I am not going in to
the basic concept of the radiography units and other related concepts.
The activity of 1 curie source at a distance of 1 meter in one hour is called Dose Rate and differs to different industrial radiography isotopes.
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
The radiography work may or may not happen in an area on regular basis. The work load on an area is calculated as follows.
Work Load, W = Dose Rate x Present Activity of your Source x Working hours in a week.
Occupancy factor around the site = T
The activity of 1 curie source at a distance of 1 meter in one hour is called Dose Rate and differs to different industrial radiography isotopes.
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
The radiography work may or may not happen in an area on regular basis. The work load on an area is calculated as follows.
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/hr = 0.002R/hr
Cordon-Off distance : d=√(W x T / P), meter
Example for the same will be discussed in the next blog.
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What is prescribed radiation level?
ReplyDeleteDoes the value remain 2mR/hr at all instance?
Thank you for reading my blog.
ReplyDeleteThe radiation level allowed on the unrestricted areas (for general public) are defined by governing organisation of the country/area/province (Eg: AERB in India). That radiation level is called the prescribed radiation level.
The radiation level will not be same for all distances. As distance increases attenuation increases and the value get reduced. If there are shielding materials (like concrete, steel, lead etc) the radiation gets absorbed and the value will be reduced. The concept of collimator, Half value layer (HVL) and Tenth Value Layer (TVL) are based on the absorption of radiation.
Nice.can you give me formula...
ReplyDeleteThe formulae is in this blog. Please read
Delete