NukeWorker Forum
Reference, Questions and Help => Nuke Q&A => Lessons Learned => Topic started by: duke99301 on Apr 04, 2006, 05:03
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I had an x-ray crew come on site they have a source Iridium192 '61 'cuires. since I do not have a book with me to figure out what they got. would some one tell me what the dose would be at contact and at 15 feet.
and what would be the dose through a pipe at contact . the pipe has a 1 inch wall 2 inchs ID. what would the dose be at 15 feet from the pipe?
I was having a good night until I was told two Iron workers came up an un protected scaffold and was standing in front of the camra. yikes...
thanks for your help.
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Our thumb rule on site is 5.5 for Ir-192. This is not exact, but I believe it fails on the conservative side. I have heard other numbers recently in conversations, but for now I think 5.5 would work for your constant at 1 foot. So 61,000 mCi and a constant of 5.5 yields 335500 mR/hr at one foot (Dose Rate= k * Activity(mCi)/distance^2). Divide this by 15^2 to get 1491.1 mR/hr at 15 feet unshielded. I dont know what the half value layers for Ir-192 are for steel so I will have to defer until I can find it or someone else does. BTW find the site RSO for the radiography company. He should have all the appropriate thumbrules......hopefully. Good luck with this however.
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6CE
E = ~ .8 mEv for Ir192
6 x 61 x .8 = ~ 300R/hr @ 30cm
Remember - Radiographers are the industry leaders in overexposures -
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The new version of my freeware, Rad Pro Calculator will be able to give you a quick visit with this question. I am currently programming in buildup factors and am weeks away from release of version 2.0. It does now, however, calculate your answer without buildup factors. The linear coefficient, mu, tends to overestimate the effects of shielding. The mass absorption coefficient, mu sub en, tends to underestimate the effects of shielding. Since the pipe is so small, I would tend to use mu sub en and overestimate to take in account scatter and sky shine.
My current software is in good agreement with cincinnatinuke's rule of thumb answer for unshielded Ir-192.
At 15 feet, unshielded, 1438 mR/hr. At 2 inches, 1.16E4 R/hr.
If the source is inside of the pipe, passing through 1" of steel, using mu sub en, at 15 feet, 764 mR/hr, at 2 inches, 6186 R/hr.
If the source is behind the pipe, passing through 2" of steel, at 15 feet, 406 mR/hr, at 2 inches, 3292 R/hr.
Using the linear coefficient (overestimating the effectiveness of the shield and not accounting for any Compton scatter or sky shine over the pipe).
At 15 feet through 2" of steel, 33 mR/hr, at 2 inches 264 R/hr. Through 1" of steel: 209 mR/hr at 15 feet and 1694 R/hr at 2 inches.
I hope this helps. I think version 2.0 of my freeware will be of use to many and your question has inspired me to keep programming in all these buildup factors (painful to make it accurate). When you click "Use buildup factors" it will get you closer to predictable numbers, or that is my wish.
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Ray's calculator is found here:
http://www.radprocalculator.com/
However, the site seems to be down today.
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Rennhack, its like you read my mind. Thanks for the link.
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The Rad Pro Calculator site has been down for days. I think that the data center hosting RadProCalculator.com was hit by a tornado and the server ended up in the Atlantic Ocean, maybe in the Bermuda Triangle. I have no idea what happened. My normal email is down also. I do, however, have Yahoo mail. That is what I am using now. I was going to wait a few weeks to share version 2.0 as a beta version for people to test.
If anyone is interested in looking at what I have now (shielding without buildup factors), send me an email at my Yahoo address: raymcginnis_mit@yahoo.com. I'll make a special installation with the buildup checkbox turned off and email it to you.
Version 2.0 will require installing the .NET framework 2.0, so expect a 23 MEG upgrade download.
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THANK YOU all for your help.. just remeber QC is our friend and they are here to help us!
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The Rad Pro Calculator site has been down for days. I think that the data center hosting RadProCalculator.com was hit by a tornado and the server ended up in the Atlantic Ocean, maybe in the Bermuda Triangle. I have no idea what happened. My normal email is down also. I do, however, have Yahoo mail. That is what I am using now. I was going to wait a few weeks to share version 2.0 as a beta version for people to test.
If anyone is interested in looking at what I have now (shielding without buildup factors), send me an email at my Yahoo address: raymcginnis_mit@yahoo.com. I'll make a special installation with the buildup checkbox turned off and email it to you.
Version 2.0 will require installing the .NET framework 2.0, so expect a 23 MEG upgrade download.
Ray, send me what you would like to share, and I'll host it for you. (The download version).
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The website and the desktop calculator, including 2.0 beta is posted on the new server now. The old server went back to a version from a year ago, after their crash, so radprocalculator.com now points to an old version with old software downloads. Until DNS propagates, the new site can be reached by ip address. I have the beta version of 2.0 posted there now. To get to the download, click on this link:
http://67.59.155.21/Software.aspx
For the home page:
http://67.59.155.21/index.aspx
Everything should be back to normal soon.
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Thanks for all of your work on this Ray. I still get compliments on your calculator. Keep up the great work.