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Technical Discussions
mahmoud Mohamed
mahmoud Mohamed
00:27 Aug-28-2002
Gamma ray using Ir192 for pipes with heavy wall thickness

I am NDT engineer and need to know the exposure time when use gamma ray Ir192 for pipes 10" and 40mm or 30mm thickness.

DJ Kallhof
DJ Kallhof
05:12 Aug-28-2002
Re: Gamma ray using Ir192 for pipes with heavy wall thickness
: I am NDT engineer and need to know the exposure time when use gamma ray Ir192 for pipes 10" and 40mm or 30mm thickness.
.
You will need to give a little more information for an informed answer. Source strength, film speed and processing facilities are all important factors.

Guido Crapels
Guido Crapels
06:21 Aug-28-2002
Re: Gamma ray using Ir192 for pipes with heavy wall thickness
: : I am NDT engineer and need to know the exposure time when use gamma ray Ir192 for pipes 10" and 40mm or 30mm thickness.
: .
: You will need to give a little more information for an informed answer. Source strength, film speed and processing facilities are all important factors.
.

At RTD we used the "plain old" nomograms and a calculus ruler to assess the exposure time as a function of Film-Focus-Distance, thickness and film sensitivity. From that, I had derived an algebraic equation, which holds for Agfa-D4 film sensitivity (D7 will be about 3/5 times faster). I hope I remember it correctly:

time[s]*Act[Ci] = 0.0424*(FFD [cm])^2 * 2^(t[mm]/17.78)

The ^ character denotes a power-of-symbol. The source activitity is expressed in Curies (sorry for that, I know it should be Bq). The FFD is the distance between the source and the film, expressed in cm's. The irradiated wallthickness t is expressed in mm's and is divided in this equation by the value 17.78 mm, which is the effective 1/2-value-decay-thickness of steel (I know the common literature always mentions about 13 mm, but I derived it from the calculus ruler we used a lot and really holds valid).
In any case, you can easily assess the necessary exposure time with Ir192 on steel items for any setup with this equation.

- Guido Crapels,
gcrapels@nuson.nl

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