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Offline JasonConner

Geiger-Muller
« on: Jan 02, 2013, 09:50 »
Greetings,

     I am rather new to this industry and I have a question relating to pancake and side-window detectors.  I realize pancakes are for contamination, but I wonder if it's acceptable to use a pancake to quickly locate the hottest spot on a package and then use the side-window to actually pull the dose rate, or would I be totally out of line?  I ask only because the pancake seems to respond much faster than my side-window, and I would like to survey the package as quickly as possible while still maintaining accuracy. 

Chimera

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Re: Geiger-Muller
« Reply #1 on: Jan 02, 2013, 10:15 »
It is a technique that works albeit highly unofficial and not supported by procedures.

Offline GLW

Re: Geiger-Muller
« Reply #2 on: Jan 02, 2013, 10:31 »
It is a technique that works albeit highly unofficial and not supported by procedures.

In short, if you screw up, you cannot defend your methodology.

been there, dun that,... the doormat to hell does not read "welcome", the doormat to hell reads "it's just business"

Offline Laning

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Re: Geiger-Muller
« Reply #3 on: Jan 02, 2013, 10:52 »
Nothing at all wrong with using a pancake probe as a tool to quickly locate areas of elevated activity, then quantifying with a calibrated exposure rate instrument.
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Offline SloGlo

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Re: Geiger-Muller
« Reply #4 on: Jan 02, 2013, 11:58 »
Nothing at all wrong with using a pancake probe as a tool to quickly locate areas of elevated activity, then quantifying with a calibrated exposure rate instrument.
yeah, watt he sayed.  butt, you need to take care that your energies are equally detected by each instrument, otherwise you may need to resurvey the package entirely with the calibrated dose instrument and sew not save any time nor exposure.
Iffen eye remember a thumb rule along these lines, it was that a frisker pancake probe would yield 1 microR/hr per 30 cpm to a cesium 137 source.
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Offline JasonConner

Re: Geiger-Muller
« Reply #5 on: Jan 02, 2013, 12:27 »
Thanks a lot, guys.  You all have been extremely helpful.

Offline OldHP

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Re: Geiger-Muller
« Reply #6 on: Jan 04, 2013, 10:38 »
Greetings, I am rather new to this industry and I have a question relating to pancake and side-window detectors.  I realize pancakes are for contamination, but I wonder if it's acceptable to use a pancake to quickly locate the hottest spot on a package and then use the side-window to actually pull the dose rate, or would I be totally out of line?  I ask only because the pancake seems to respond much faster than my side-window, and I would like to survey the package as quickly as possible while still maintaining accuracy. 

Nothing at all wrong with using a pancake probe as a tool to quickly locate areas of elevated activity, then quantifying with a calibrated exposure rate instrument. 

As long as you know the isotopes of interest it is a quick and acceptable method of identifying the first areas you need to get a direct dose rate survey on.

You might want to consider (since you said 'side window I assume G-M) an open/closed window IC since it sounds like you are trying to deside if it goes out as BSFR or LLW (and use 40 uR/hr vs 50 as your cut off) since the receiver is probably basing on a GM.
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Re: Geiger-Muller
« Reply #7 on: Feb 12, 2013, 10:34 »
When you refer to the term hotspot,are you looking for dose rates or contamination levels? the pancake probe is good for finding loose or fixed contamination levels.And if something inside the box in which you are surveying has a contaminated object inside of it,then the pancake probe will detect it fast.But as far as dose rates its not as practical as a telepole or a ion chamber,remember too the ALARA concept should apply for checking a unknown source..time=distance=shielding...which in this case time,and distance from the source should be of concern.

Offline retired nuke

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Re: Geiger-Muller
« Reply #8 on: Feb 12, 2013, 12:57 »
When you refer to the term hotspot,are you looking for dose rates or contamination levels? the pancake probe is good for finding loose or fixed contamination levels.And if something inside the box in which you are surveying has a contaminated object inside of it,then the pancake probe will detect it fast.But as far as dose rates its not as practical as a telepole or a ion chamber,remember too the ALARA concept should apply for checking a unknown source..time=distance=shielding...which in this case time,and distance from the source should be of concern.
Regardless of the instrument, you are detecting RADIATION.
The pancake probe is pretty efficient (15%-20%) for beta. That is why it is used for detecting the radiation from surface contamination. It is pretty low effieciency (1%-2%) for gamma, due to the shallow detector depth. What you are detecting from the contaminated object inside the box is gamma radiation. The pancake probe can still quickly give an indication of radiation, as any interaction of radiation with the probe produces a pulse (for the most part, won't get into threshold, etc here), but it will not quantify it.


Quote from: JasonConner on January 02, 2013, 04:50:40

Greetings, I am rather new to this industry and I have a question relating to pancake and side-window detectors.  I realize pancakes are for contamination, but I wonder if it's acceptable to use a pancake to quickly locate the hottest spot on a package and then use the side-window to actually pull the dose rate, or would I be totally out of line?  I ask only because the pancake seems to respond much faster than my side-window, and I would like to survey the package as quickly as possible while still maintaining accuracy. 


The pancake will indicate higher levels of radiation quickly. But not accurately, it's not designed / calibrated for that use. The side window will (when calibrated properly) quantify the radiation levels. It is generally used because it is similar to what most regulatory agencies use. Side / end window G-M probes / meters / Telepole often read a bit higher than an Ion Chamber, but if the people that are checking you are using G-M, then you use G-M

The biggest problem I have with using the improper instrument for a task, is that if the actual theory behind the meter choice isn't understood, eventually, someone lazier than you will use the wrong instrument without followup with the correct one. Then you end up with Tech A, excessive rad levels on a package, and regulatory agency involvement.

This has some interesting info that may be helpful.
http://www.nukeworker.com/study/hp/rct/lanl_p2_pdf/217_sg_1999.PDF
http://www.nukeworker.com/study/hp/rct/pdf/2_16_Radiation_Survey_Instrumentation_sg.pdf
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Offline navynukedoc

Re: Geiger-Muller
« Reply #9 on: Mar 16, 2013, 06:06 »
Iffen eye remember a thumb rule along these lines, it was that a frisker pancake probe would yield 1 microR/hr per 30 cpm to a cesium 137 source.

On contact, at 30cm ???

The biggest problem I have with using the improper instrument for a task, is that if the actual theory behind the meter choice isn't understood, eventually, someone lazier than you will use the wrong instrument without followup with the correct one. Then you end up with Tech A, excessive rad levels on a package, and regulatory agency involvement.

Agreed!!! [train]
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Offline spentfuel

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Re: Geiger-Muller
« Reply #10 on: Mar 20, 2013, 12:10 »
Quote
but I wonder if it's acceptable to use a pancake to quickly locate the hottest spot on a package and then use the side-window to actually pull the dose rate,


Short answer is yes.  If your dealing with standard "stuff" from a nuke plant efficiencies and energies don't matter.  I have done this for many years for shipping RAM and or just for yellow tagging trash etc.  Does save a lot of time.

My two cents

sf

 


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