How to calculate the thickness of lead used for shielding of gamma rays 2

[ting123]

Dear's,

I am looking for a movable shield that I can use for radiography of pressure vessels using gamma rays. After making a search I was able to get few information. The material that I can use are concrete blocks, steel plates and steel plates lined with lead.

My query is what is the best method for making a movable radiography shield that can be used on the shop floor with out disturbing the other processes going on the shop floor. I cannot use a dedicated space as the vessels are extremely big in size nearly 10m in diameters. So i have to radiogaph the vessel in its own position.

Could you please help me in getting the optimized solution on this. If someone has such thing in practical please guide me so that I can follow the same methods.

Many thanks in Advance.

 

[IRstuff]

The stuff used in medical x-rays are like this:

http://www.universalmedicalinc.com/Mobile-Lead-Porta-Shield-p/2424mb-umi.htm

http://marshield.com/wp-content/uploads/2013/08/Radiation_Barrier_Website.pdf

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[btrueblood]

ting,

I get really nervous about people, apparently tasked with such a risky job as radiography, asking such basic questions. Have you had training in radiographic inspection? I'd have hoped that the laws of physics regarding radiation shielding would be one of the first chapters studied in such a course.

Please see

http://www-pub.iaea.org/MTCD/publications/PDF/Pub1466_web.pdf

as a starter.

 

[EdStainless]

Hire a health physics professional. Pay the consulting fee, follow their recommendations.
Otherwise there is no upper limit to your liability.


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[arunmrao]

You have not checked the thickness of the plate and the strength of the source that will be needed. Also,if you are to use Ir192 or Co60, must be decided. The wall thickness of the shield will vary with the source. Also, check your local area safety guidelines for carrying out such tests.

How do you plan to store the camera, during any stoppage is also important. A pit must be dug deep enough for the camera to be kept.

Googling/public forums is not an answer for such risky jobs.

(Sorry, please bear with me for an interesting but frightening experience. A reputed engineering contractor was carrying out pipeline work and a small Ir192 camera was being used to test the weld joints. One day a few disgruntled employees stole the camera and threw it into a nearby canal. There was a serious public scare ,and it took over 15 days to recover the camera.)

 

[FiatfLux]

Is this based in the United States? If so, how is the NRC not all over your project?

We used a beta source to track glass level/flow, and the spare was kept in a safe that would trigger an alarm at an NRC office. That's beta, electron radiation, no big deal.

The hoops to jump through to use gamma radiation in the U.S. have got to be a lot higher, and smaller.

Is this a school project, a thought experiment?

 

[FiatfLux]

Trueblood, thanks for that document, very interesting.

In the magnetics business, the condition of thin walls, such as pipelines, are measured by flux leakage. I wonder how/whether the methods overlap.

 

[JR97]

Ting,

A few suggestions: If possible do the set-up with the source inside the vessel and the film outside. The vessel itself will provide some shielding. To minimize the size of the shielding, get it as close to the source as possible - use a heavy collimator with a tight angle window. That should attenuate the majority of the radiation in directions other than toward the film. As far as shielding the balance of the radiation, there is a definite trade off in materials. Concrete blocks (use solid not hollow ones) are lighter and easier to handle, but you will need significant thickness of concrete to do the same job as a thin amount of lead. However, the lead is more cumbersome to position where you need it.

I agree with the others making posts. This is not something you want to try without having someone experienced involved.

JR97

 

[SnTMan]

What I am used to seeing is really large blocks of concrete, big panels, 2 ft or thicker. Don't know if there is another material, like lead for example, encapsulated or not.

Regards,

Mike

 

[arunmrao]

SnTman, you are right, it is 2 ft thick wall with lead cladding.

 

[ting123]

Dear's,

Thanks for such a good help. But my query is still unanswered. As seen from the replies i would like to clarify that most of them had not got my query correctly...Let me rephrase..I am just in a need to know ways to shield radiography...and the arrangement shall be movable. We had definitely made calculations at our end. To share we will be using a combination of steel with concrete. The total thickness comes to around 150mm. But what I would like to know is are there any arrangement that can be moved. For Eg. As everybody know that pressure vessel had longitudinal and circumferential seams.So if the vessel is 10 meters in diameter. I cannot move the vessel every time for radiography of each seam. I shall have a movable shielding arrangement to cover the seam that is being radiography. I have contacted most of the consultants at our end but none of them have done this. It looks like we the first one local who are trying to make such an arrangement.

I hope have made myself clear this time. Thanks in advance for such a good support.

 

[racookpe1978]

No.

The costs of calling in a certified RT company for the few hours needed for the few welds needed FAR FAR outweigh the risks of your workers trying to do it yourself. Clearly, neither you nor your boss nor the company president see the risks involved, nor can we (over here) convince you of the dangers of trying to use mobile, very heavy, very complex shields around a pressure vessel at many different configurations and locations.


Loose Steel and concrete blocks are poor gamma ray shields when used incorrectly and especially when they are deliberately temporary and not assembled as a permanent structure such as a seismically braced wall.

The weight of the shields themselves is a complex structural engineering job for the frame, lifts, mounts, and braces alone! And, since the shield units are themselves heavy, portable, and flexible as separate blocks, THEY pose a weight and center-of-gravity problem as they are stacked and unstacked for each xray shot.

Now, .... If you do NOT use a certified X-Ray company hired in to do the xray shots and their associated radiation exposure control, who is going to recover, develop, print, read and process those xray exposures? You do understand that an "uncertified" reader looking at any "uncertified" and uncalibrated xray will NOT be acceptable to the certifying agency or customer, right?

 

[arunmrao]

Well said racookpe 1978 . A pink star for you.