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Technical Discussions
Dr. Yossi Shoef
NDT Inspector
Gabi Shoef Ltd, Israel, Joined Dec 2005, 19

Dr. Yossi Shoef

NDT Inspector
Gabi Shoef Ltd,
Israel,
Joined Dec 2005
19
16:17 Jul-05-2016
Edge scatter in radiography

The iso 17636 states in its para. 7.5.1
"With Ir 192 and Co 60 radiation sources or in the case of edge scatter, a sheet of lead can be used as a lower energy scattered radiation filter between the object and the cassette. The thickness of this sheet shall be between 0,5 mm and 2 mm in accordance with the penetrated thickness."
Can someone explain what is this scatter and if the standard means really to put 2 mm lead sheet between the object and the film so that it will be radiographed together with the object?

 
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Arunprakash
NDT Inspector,
Caterpillar India, India, Joined Apr 2009, 30

Arunprakash

NDT Inspector,
Caterpillar India,
India,
Joined Apr 2009
30
10:57 Jul-07-2016
Re: Edge scatter in radiography
In Reply to Dr. Yossi Shoef at 16:17 Jul-05-2016 (Opening).

Scattering reduces Signal to Noise Ratio of your radiographic image. Lead sheet recommended to mask the scattered low energy radiation.

You have to use the lead sheet at the end of section thickness change or edge of the part where your radiograph quality may be affected because of scattering.

Depends upon the material/geometry and exposure time the amount of scattering varies. You can do experiment and find out the required thickness of lead sheet as a scattered radiation filter. The thickness can be varied from 0.5 to 2 mm. In case you need 2 mm lead sheet as a masking cover you can use 2 no's of 1 mm sheet also (should be kept close and one over another). Since lead sheet is highly ductile (bending is ease with hands) and easy to cut, you can do this very easily.

All the best.

 
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Arunprakash
NDT Inspector,
Caterpillar India, India, Joined Apr 2009, 30

Arunprakash

NDT Inspector,
Caterpillar India,
India,
Joined Apr 2009
30
11:39 Jul-07-2016
Re: Edge scatter in radiography
In Reply to Dr. Yossi Shoef at 16:17 Jul-05-2016 (Opening).




In continuation to your question, the lead sheet shall be placed in different place depends upon the part geometry, attached picture helps you to understand better.
 
 Reply 
 
Uwe Z.
Director,
BAM Berlin, Germany, Joined Jan 2010, 82

Uwe Z.

Director,
BAM Berlin,
Germany,
Joined Jan 2010
82
08:40 Jul-12-2016
Re: Edge scatter in radiography
In Reply to Arunprakash at 11:39 Jul-07-2016 .

Daer Arunprakash,
your sketch is nice but unfortunately not correct. We wrote this text at BAM because the lead should shield the scattered radiation out of the object just before the detector. This is always the problem when the detector is in dierct contact with the object, especially at higher energies. Your suggestion is to reduce the primary radiation BEFORE the object, but in my experinece this will generate unwanted artifacts in your image. A plain lead screen just in front of the detector will not generate artifacts to your image.
Best regards
Uwe Z.

 
 Reply 
 
Arunprakash
NDT Inspector,
Caterpillar India, India, Joined Apr 2009, 30

Arunprakash

NDT Inspector,
Caterpillar India,
India,
Joined Apr 2009
30
09:34 Jul-12-2016
Re: Edge scatter in radiography
In Reply to Uwe Z. at 08:40 Jul-12-2016 .

Thanks for highlighting the error in the picture, I was intended to keep the lead sheet close to film to filter the scatter radiation, by mistake it was shown at the top as a cover for the primary radiation. We have experimented with Ir-192 source similar geometry and got good result.
Now, I understand from your statement that entire film needs coverage of lead screen as a scatter radiation filter.

Thank again.

Arunprakash

 
 Reply 
 
Arunprakash
NDT Inspector,
Caterpillar India, India, Joined Apr 2009, 30

Arunprakash

NDT Inspector,
Caterpillar India,
India,
Joined Apr 2009
30
15:18 Jul-12-2016
Re: Edge scatter in radiography
In Reply to Uwe Z. at 08:40 Jul-12-2016 .


Back scatter filter for high thickness low thickness change region

Now I have corrected the masking position for better clarity. For the high thick zone soundness this method is suitable.

Generally the lead shall be placed between object and film cassette. (Film cassette contains intensifying lead screen, film & Back scatter filter lead screen as usual.
 
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