Ir92 with 32 Curie-What is the safe distance?

[limesh M]

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

[Pablo J Acelajado]

 July 19, 2011

 

Hello,

 

You may find the attachment useful.

 

This is a copy distributed by norm in one of the presentations in ASNT  Saudi Arabian Section Technical Dinner Meeting in Al Khobar.

 

Thanks.

 

PJA

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[Julio Magalhães Jesus]

Dear Limesh,

I attached database of calculate the safe distance of Radiography (RT).


Kindest Regards.


Magalhães Júlio

Welding Around the world

2011/7/19 limesh M <lime...@gmail.com>

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[Ramakrishna]

Dear Friend,

It will be great if you can send the English one to understand fully.

Thank you very much for sharing.

Regards,

Ramakrishna.

 

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[Jean Staton]

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

 

From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of limesh M

Sent: Monday, July 18, 2011 10:47 PM
To: Materials & Welding

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[Sunil K. Mani]

Mr.Jean Staton,

I am looking for calculated safe distance for Ir192 isotope with 32 curie in open space.I don't think that the type of material and shooting have any role in my case as I mentioned clearly in my query that NDT crew shooting the joints without collimator in open space.So, as you know that the radiation coming out from isotopes must be scattered 360 degrees in X,Y&Z direction.The intensity of the Gamma rays will decrease once it penetrates the material wall and the rate of reduction will be based on the density and thickness of the material.In my case NDT crew following DWSI(Double Wall Single Image) and obviously intensity reduction should be only in one direction and not in all direction like what we expect in panoramic(SWSI) shot.

Regards,

Limesh 

[Mumtaz Ali Khan]

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
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