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What type of radiation detector is best for me?
#1
Horse Wrote: 

What detection devices are affordable to independent researchers and what can the device actually measure?  



Picking the appropriate tool is one of the most important parts of doing the job right.  I personally use a variety of instruments for different purposes, there isn’t really a universal radiation detector that does everything, so you have to know what you want to do and which detector will help you.

I will start by identifying my most frequently used equipment and talk about what I use it for, over the next day or two I will put up posts about my most utilized equipment one by one.  Then I can answer additional questions about specific tests or equipment for other purposes.  I am not advertising any of the detectors and am only relating my personal experiences and thoughts.  I’d be happy to speak with anyone considering buying a detector to find out what they want to do and share my thoughts on what type of equipment would best suit their needs.
"All models are flawed, some are useful."
George E. P. Box
 
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#2
Tools I always want on hand if I’m headed into the field.

GammaRAE II R by RAE Systems –  ONLY MEASURES GAMMA

This is quite a handy little device and essentially the same as the Polimaster PM1703MO-1.  These units are designed to give emergency responders a first alert when they come into close proximity with gamma-emitting sources.  Mine has a small, sensitive, CsI detector and a compensated PIN diode detector for high range gamma doses.  My favorite feature of these units is the way in which they alert the user – by logarithmic changes in the background.  So I can walk around my basement and the unit collects the average background and displays it on the screen (generally between 4 uR/hr and 9 uR/hr).  Anyone who has spent a lot of time with a detector knows that the longer you operate it, the more flux you will see in the measurements.  “Background radiation” is not static and you will see variations and as you get more familiar with your equipment and the timing and manner of these variations you will identify trends which will yield hints at why you might be seeing the variations.  So for me, to see the background count rate to bounce from between 4 uR/hr – 14 uR/hr is not unusual or unexpected, but I definitely want to know when the background levels go from 4-14 uR/hr to 30-45 uR/hr so I can try to figure out why.  This is what the Gamma Rae II does, notifies you by lights, vibrations, or a very loud buzzer, that the background radiation levels have changed.  It is generally the first detector that goes off.  

I know people that toss them in the front windshield of their cars and have identified trucks on the highway carrying various medical/industrial radio-transports.  On the more extreme side, I even know someone who uses a device like this to go to hospitals and find where people who have been administered some form of medical radiation treatment have sat, or drank out of, or even what urinal they used.  The point being, if you want to be informed when radiation levels are changing around you and want to investigate why, these devices will do that with much more sensitivity than a “Geiger counter”.  These units conveniently clip onto my belt or shirt and can collect over 30,000 data points (approx. 7 days at 1 data point per minute), which can later be downloaded onto your pc and graphed over time.  The batteries also last some 600 hours on 2 AA batteries, so a great set it and forget it type of tool.  

I took mine to Chernobyl, below is a photo - it was the device I carried around the most.

   
"All models are flawed, some are useful."
George E. P. Box
 
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#3
I can't make out the measurement scale - uSv/h? or?
Pia
Jitsi chat: enfo.pia@gmail.com
 
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#4
(09-24-2015, 05:10 PM)piajensen Wrote: I can't make out the measurement scale - uSv/h? or?

I prefer raw counts (either gross counts or cpm) over dose conversions for the research I do, but the device measures uR/hr (preferred) and uSv/h and what you see in the photo is uR/hr.
"All models are flawed, some are useful."
George E. P. Box
 
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#5
Tools I have handy for specific purposes

I’ll talk about GM detectors next, because that is what I hear the most questions about.  For me, GM detectors are only used for specific uses, but I don’t rely on them to tell me about minor variations in environmental radiation levels.  When in the environment, don’t expect to measure a lot (if any) alpha, unless there has been a significant radiation release or you know you are in a contaminated area.  That’s what these detectors are primarily used for, surveying for NORM materials, measuring external contamination, measuring radiation levels after a significant release of radiation (from a device, accident, etc..) These detectors just aren’t that efficient at detecting them, alpha particles only travel a few centimeters in air, so in normal background areas most of what you see will be gamma with a little beta contribution depending on how you are using it.  They also saturate in high radiation fields and are not able to measure high radiation levels efficiently.  The two primary designs are the long hot-dog shaped tube, or the rounded pancake with a mica window.  

   

The things to be aware of are that they are not sensitive to low-energy gamma photos, they over-respond at mid- range gamma photons (below 661 keV), and under-respond to high-energy photons (over 661 kEv).  They normalize the detector response typically to Cs137 (661.65 keV). 

I do use them at times in the lab, but for gross counting purposes – and generally only screening at that.
I did take an Inspector EXP+ to Chernobyl to use to measure alpha and beta radiation in contaminated areas (I took other devices that I used for gamma) and to frisk our clothes to make sure we weren’t carrying contamination.  
I will also use the Inspector USB+ to go trying to find radioactive consumer products or fiesta ware.

In the attached photo you can see some of the GM detectors that I use.  In the back row, you can see three Eberline shielded gm detectors (with the handles and resting on sample trays), a Ludlum Model 44-40 shielded gm detector, a Ludlum Model 44-9 pancake detector, my Inspector USB+, as well as the probe for my Inspector EXP+ which is still in the special airtight container (special thanks to Ludlum for giving it to me for my Chernobyl trip) that is used to make sure that the detector isn’t damaged by the pressure changes during air travel.  You can also see an Eberline "hot dog" tube style gm detector in the foreground.

   
"All models are flawed, some are useful."
George E. P. Box
 
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#6
LWH - I did take an Inspector EXP+ to Chernobyl to use to measure alpha and beta radiation in contaminated areas (I took other devices that I used for gamma) and to frisk our clothes to make sure we weren’t carrying contamination.
I will also use the Inspector USB+ to go trying to find radioactive consumer products or fiesta ware.

The Inspector is one I've seen recommended. The Inspector USB+ sounds useful. Quite the lab just to detect nuclear particles.
"The map is not the territory that it is a map of ... the word is not the thing being referred to."
 
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#7
(09-25-2015, 07:24 AM)Horse Wrote: LWH - I did take an Inspector EXP+ to Chernobyl to use to measure alpha and beta radiation in contaminated areas (I took other devices that I used for gamma) and to frisk our clothes to make sure we weren’t carrying contamination.  
I will also use the Inspector USB+ to go trying to find radioactive consumer products or fiesta ware.

The Inspector is one I've seen recommended.  The Inspector USB+ sounds useful.  Quite the lab just to detect nuclear particles.

The only real differences between the Inspector USB+ and the Inspector EXP+ are the probe and the connection to the computer.  

The Inspector USB+ obviously uses a USB port to communicate with the computer and the GM detector is housed inside of the casing.


The Inspector EXP+ uses a standard headphone jack to communicate data and the GM detector is separate from the casing and mounted on a wand.  (I brought this one instead of the USB+ because it is easier to measure in tight areas and for frisking clothes with the wand in one hand and still see the measurement on the screen in the other hand).
"All models are flawed, some are useful."
George E. P. Box
 
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#8
The majority of my work in the field involves detecting gamma-emitting sources or source materials.  I have a wide variety of NaI scintillation probes that I use for these investigations.  The reason why I prefer NaI is its sensitivity and because it is also a great crystal for gamma-emitting isotopic identification with gamma spectroscopy.  

We should also take a moment to talk about how scintillation crystals like NaI interact with gamma rays so you can understand its uses and applications more.  

   

The luminescent crystals used as scintillators interact directly with the gamma ray and absorb its energy (remember there is no mass) and that absorption of energy causes the crystal to scintillate.  The amount of light produced is directly related to the energy of the gamma photon that is absorbed by the crystal.  The scintillation of light is captured (collected) by a photomultiplying tube which converts light into an electronic signal that is also directly related to the amount of light and therefore also related to the energy of the gamma ray.  This is one way we can gather information about and identify the isotopic signature of a particular gamma ray to identify what materials are in a particular sample.

By picking NaI detectors with different crystal sizes, I can look for different gamma ray energies.  I have low-energy gamma detectors, which have very thin crystals that allow the high energy gamma photos to pass right through and only interacts with low-energy photons generally under 200 keV.  I also have a few “enrichment” probes which are only ½” thick.  Lastly, I have 15 or so assorted 1”x1” and 2”x2” NaI probes that I use for general survey purposes.

When connected to a survey meter, these probes are interchangeable as long as one knows the operating parameters of the probe.  Scintillation probes are generally more sensitive than GM detectors, but will also have a higher background count rate (The gm detector may generally operate between 20-40 cpm at normal background, but my NaI probes can have anywhere between 3,000 cpm to 7,500 cpm in the same environment.  This is easy to factor out and is an indicator of just how sensitive a scintillation detector is.

At Chernobyl they use 2x2 probes to measure changes in environmental gamma levels.

One can also use the probes to perform surveys of property or buildings to look for various radioactive materials.
Radiation detectors at airports and seaports use scintillation materials.

I use scintillation probes with many different types of meters and scalers both portable and desktop.

   

When I went to Chernobyl I took a Ludlum Model 2350 data-logger and a Scionix Holland 1”x1.5” NaI probe (see above), it was great for finding hotspots and operates even in high radiation fields unlike gm detectors. 

If I want to do some gross gamma counting I can hook up any of my NaI probes to Ludlum Model 1000 or Model 2000 scalers and do timed counts.

If I want to look just for one particular isotope (like Cs137) in one or more samples I could use a Single Channel Analyzer like the Ludlum Model 2221 or Model 2200 or Model 2500 or Model 2600 (my favorite).

   

If I want to look for information about all potential isotopes in a sample I can hook up a NaI probe to my multichannel analyzer (see above) and generate a spectra which will point me in the right direction.
"All models are flawed, some are useful."
George E. P. Box
 
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#9
Thanks so much for detailing your technical experience with radiation detectors, Lucas. That is very helpful.
Pia
Jitsi chat: enfo.pia@gmail.com
 
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#10
(09-25-2015, 07:25 PM)piajensen Wrote: Thanks so much for detailing your technical experience with radiation detectors, Lucas. That is very helpful.

My pleasure.  There are a handful other probes that I use, like alpha scintillators for alpha detection etc, but those listed above are the main ones I rely on.
"All models are flawed, some are useful."
George E. P. Box
 
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