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Join Date: Feb 2008
Location: Texas
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Radiation Detection

04/09/2008 5:09 PM

As the RSO (Radiation Safety Officer) of my company I need a digital survey meter that accurately detects small amount of radiation (less than 1 m/r per hour) to determine the annual dose of members to the general public (which in Texas is 100 mrem). I have searched the web and found many digital meters but the "penny pinchers" wants quotes from different companies and so far the accuracy has been in question. This meter needs to be able to measure such low levels in a format like 0.00 m/r per hour. I might be able able to get away with a meter that measures in micro curies but would prefer a meter that measures in m/r per hr. Any help from someone that has experience in this or knows the make and model number of a very sensitive meter and knows where to get one would be helpful.

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#1

Re: Radiation Detection

04/09/2008 5:41 PM

You dont mention what type of radiation you want to measure. For Gamma the Ludlum 193 is pretty popular. http://www.ludlums.com/product/m193.htm

If this doesn't fit the bill they have a large selection of other instruments. http://www.ludlums.com/product.htm#MicroR%20Meters

Another manufacturer is Thermo Scientific, the ASP2 may be for you. http://www.thermo.com/com/cda/product/detail/1,,13457,00.html

Once again there are many possibilities here. http://www.thermo.com/com/cda/landingpage/0,10255,796,00.html

If you wouldlike to find a lot more try typing radiation survey meter in to your favorite search engine.

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#2

Re: Radiation Detection

04/09/2008 5:51 PM

If you're looking at the dose to members of the public, I'd have thought you'd be into environmental monitoring. To do this effectively, you'd need to continuously monitor at several strategic points around the site.

I'd suggest looking for a service who could provide you with monthly TLDs (Thermo-Luminescent Dosimeters) which they'd take back for processing & replace on a continuous cycle.

I'm not an RPA (Radiation Protection Advisor) or RSO, but I've been working (indirectly) in and around the nuclear industry for about 30 years.

(BTW μCi is a unit of activity, not doserate).

Regards, John.

[Edit - having read Ace's reply, I'd agree that something from Thermo may suit you - though you'd have to be going around checking at your strategic points & logging the results on a regular basis. If you could get away from having to have a digital unit, something from the Mini 7-10 range is cheap 'n' cheerful, very reliable and very sensitive.]

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#3
In reply to #2

Re: Radiation Detection

04/09/2008 6:13 PM

Another BTW - a very useful tool for doserate calculations and units conversions (and an awful lot more) is the Rad-Pro Calculator, available as a free download.

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#4

Re: Radiation Detection

04/09/2008 6:24 PM

Thanks Ace and John for your timely response. Ace, the type of radiation is x-ray machines. John, I have placed film badges(TLD) in certin areas surrounding the machines. The exposure rate is well below the 2 mr/hr as Texas requires. The problem is in addition to my three xray machines, I now have contractors in various locations running their own machines. Now in Texas, as radiographers, we cant expose the general public to more than 100 milli rem per year. Now, the hours that we are now running...6 days a week, 12 hours a day, 50 weeks a year will expose the general public to more than allowable. (The last survey done by the state a reading of 0.25 mr/hr calculated with our number of exposures per hour and our exposure time per shot put the general worker to 2500 milirem per year). Now that additional shielding has been placed I need to recalculate but I need a digital meter to get accurate reading. My "needle" type meters isn't accurate enough. Thanks again

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#5

Re: Radiation Detection

04/10/2008 11:22 PM

HI,

Check with Radcal Corporation, USA. Typically the Ion Chamber, converter and doseimeter combined together can give you the spec/resolution you are looking at. You can definetely select from the wide range available with them. We use something alike.

Mr.Idiotalways.

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#6

Re: Radiation Detection

04/11/2008 11:56 AM

I am not going to tell you how to suck an egg as you seem pretty clued up about it anyway. Just a remark as left over experience when I worked as a NDT engineer for an independent inspection company in the Netherlands all those years ago.

Some 20 years ago we only had analogue machines. they were incredibly sensitive and like all analogue machines, could be set to a specific range. Bad news is they were big, heavy and I have forgotten who made them but Siemens springs to mind for some funny reason.

Secondly, if the contract testers are doing on site testing work, they could be doing 2 types of work. Fixed equipment or loose mfg'd parts. In the case of the fixed stuff you are depending on the situation as to where you can aim the beam. In the case of the loose stuff we were always obliged to attempt an upward facing beam which would result in an almost zero outward radiation. The pre-assessment would subscribe our plan and if not possible it would have to be reported and the zone beaconed off at a good distance.

Thirdly, if your target area has already been exposed to a fair portion of your annual allowance, you can always provide the NDT team with lead panels to obstruct the path closest to your outside environment. When measured then, the total will have come down considerably and might help you to remain in your legal amount. We always shielded as extra protection as a matter of fact. Even after our area had been beaconed off at the right distance so the exposure would be ok, we still shielded as an additional protection. Safe from little mishaps as well that way.

Are you doing electrical X-ray only or also radioactive elements like iridium or cobalt? We used both as we did not always have electricity handy.

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#7
In reply to #6

Re: Radiation Detection

04/11/2008 5:12 PM

At this current time we are using electrical machines only.As far as my equipment, I have two 320 kv tubes. We normally shoot at 10 ma and about 240/250 kv. On my third machine,the fluoroscope, it normally runs 7 or 8 ma and the kv will vary on the thickness of the pipe being x-rayed. I am not to concerned about my equipment as we are a manufacturer of large diameter steel pipe and the mill was built to accommodate such radiation levels.(ie:distance and shielding).As far as the contractors, 300 kv tube (not sure of the ma...I think 8ma), they are shooting panoramic shots that join two of my pipes together. (meaning they shoot in all directions 360 degrees) with very little shielding. I have instructed them where to place the shielding and I "think" they are in compliance now. The problem is the word "think". I want to be sure before anyone of "importance" comes around. That is why I am looking for a very accurate digital meter to determine the long term exposure at these contract locations. The distance of the 2mr/hr barricade cannot be increased as they are inside a building. So the other option is a lot of lead/steel shielding. As I stated I "think" they are ok now,I just want to be sure. Thank You all your help is greatly appreciated.

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#8
In reply to #7

Re: Radiation Detection

04/11/2008 5:38 PM

Hmmm...seems to me that any good subcontractor who wants to continue work, or get invited back, would want to work WITH you there...if the TDEQ (or whomever) gets their undies in a bunch, they'll suffer along with you!

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#9
In reply to #7

Re: Radiation Detection

04/11/2008 7:14 PM

Going back to my earlier thoughts about using TLDs/films or whatever, if you're looking way down at the low levels (not too much above natural background), you're going to be looking for changes in the region of a few counts per minute - you won't spot this with a doserate meter. You need to measure the integrated dose over the time you're running the X-ray generator(s), and work from there.

You'd have to take that figure & multiply by the maximum number of shots per year to be able to compare with the total dose limit. I agree that an analog instrument won't really do here, you need an integrating dosemeter (electronic equivalent of TLD or film).

[BTW - have you followed up the links from the Texas Department of State Health Services? - you should be able to get some advice there relevant to your local regulations.]

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#10
In reply to #7

Re: Radiation Detection

04/12/2008 5:54 AM

My immediate first thought, yes I know that is one of those double whammy expressions I don't know the name of but hey, is that contractors have an obligation themselves to comply with local, and national laws if applicable, and are supposed to be able to deliver, upon request, a detailed radiation report with values. We always had to take measurements while we were on anybodies site and if we were on an oil refinery, they knew we had to do this, we were always asked for the reports with the films.

The reports were sketches of the area with measurement points and values and intervals.

Is this not your local requirement?

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#11

Re: Radiation Detection

06/01/2008 4:48 AM

Natural background of cosmic radiation on earth on an average value is about 5uR/hour. There are some hot spot where it can be as high as 200mR/hour.

All measurement for calibration need to be done in near radiation free zone with little radiation from soil and wall embedded radioactive sources. Perhaps house roof is most ideal place and keep the measurement device and source 1m above ground on some kind of elevated table or tool.

Inverse square function is pretty good one if your source is small and you are 1m away. Lead shielded container to be used and if you have an electronic shutter then it is great to open source from remote.

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#12

Re: Radiation Detection

01/19/2024 7:24 AM

<...0.00 m/r per hour...>

Measuring zero is by its very nature extraordinarily difficult.

"Oh, look! There goes a Plutonium atom!"

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