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Re: [MW:11871] Ir92 with 32 Curie-What is the safe distance?

By Materials & Welding
Please fnd below te equaton for cacuating th safe distace
 
 
 
Calculating Intensity with the Inverse Square Law

I1/ I2 = D22/ D12

Where:
I1 = Intensity 1 at D1
I2 = Intensity 2 at D2
D1 = Distance 1 from source
D2 = Distance 2 from source

Example Calculation 1
The intensity of radiation is 530 R/h at 5 feet away from a source. What is the intensity of the radiation at 10 feet?

Rework the equation to solve for the intensity at distance 2
            I2 = I1 x D12 / D22

Plug in the known values
           I2 = 530R/h x (5ft)2 / (10ft)2

Solve for I 2
           I2 = 132.5 R/h

In this instance the distance has been doubled and the intensity at that point has decreased by a factor of four.

Example Calculation 2
A source is producing an intensity of 456 R/h at one foot from the source. What would be the distance in feet to the 100, 5, and 2 mR/h boundaries.

Convert R/hour to mR/hour

       456R/h x 1000 = 456,000 mR/h

Rework the equation to solve for D2

      

Plug in the known values and solve

       

         D2= 67.5 feet

Using this equation the 100mR/h boundary would be at 68 feet, the 5mR/h boundary would be at 301.99 feet, and the 2mR/h boundary would be at 477.5 feet. Sources are seldom operated for an entire hour, and collimators are often used which reduce these distances considerably.

Best Regards,

Mumtaz Ali Khan
Works Manager - AMW
Mob: 00971-50-4131684

DESCON ENGINEERING
P.O Box 46821, Abu Dhabi - UAE
Off. Direct: 02-8760422
Off. : 02-8761287 Ext. 202, F: 02-8760423
email: mumtaz.khan@descon.com
web site: www.descon.com


On Tue, Jul 19, 2011 at 4:23 PM, Jean Staton <Jean.Staton@metco-ndt.com> wrote:

Your distance depends if you want an actual 2 mR/hr boundary or a calculated one, What are they shooting,etc.

 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of limesh M
Sent: Monday, July 18, 2011 10:47 PM
To: Materials & Welding
Subject: [MW:11816] Ir92 with 32 Curie-What is the safe distance?

 

Dear All,

In one fabrication yard,IR192(Iridium192) Isotope being used to take radiography of welded joints to ensure it's integrity after visual inspection.NDT crew usually brings radiation source with a strength of 32 Curie(NDT contractor claiming that they are using 32 curie only but I don't know the exact strength.This is due to client pressure otherwise they are ready to bang with higher curies!!).I would like to know what would be the safe distance when IR92 with 32 curie strength operates without collimator.How can I calculate the safe distance from above parameters?I need this calculation urgently due to non availability of completely covered (except roof) concrete bunker or natural sand wall.For NDT crew protection during RT, two pieces of concrete wall provided to cover their body.Moreover, people like skilled/unskilled workers are staying very close(20Mtr to 35 Mtr range) to radiography area and nobody aware of the seriousness of the activity including the world famous client!!!

It will be highly appreciated if someone could provide an excel spread sheet to calculate the safe distance for different source strength.

Thanks in advance



Regards,


Limesh

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