Measurement uncertainty of home radiation monitors

[mark.hogue@SRS.GOV]

There have been a number of links posted to hobby-level radiation monitors on the web. 


Most of the sites are equipped with inexpensive G-M radiation monitors on personal computers. They apparently have no calibration program other than the vendor's (http://www.aw-el.com/index.htm) original calibration. They use G-M tubes with mica windows, so they can be influenced by beta and alpha if that's an issue due to radon, e.g.


Examples of links recently posted in the "Colorado radiation" and related threads and others I found:

http://home.att.net/~robertson_family/radmonitor/ - Longmont, CO

http://www.metafire.com/radmonitor/index.html - Pittsburgh, PA

http://www.geocities.com/Athens/1555/backrad1.html - links

http://digistar.com/boston/ 

http://www.aw-el.com/nyc/


How much confidence can we have in these monitors? I'd like to think that the monitors will work fine until the tube fails and that failure will be obvious. But if that's true, why do we have to do so many calibrations and source checks on monitors in industry? (I have seen a monitor failure at a nuclear facility result in a steady 300 cpm and that was not an obvious failure. That was a G-M tube with a count rate meter and I think the fault was in the tube.) 


More to the point, is the original calibration valid in the range of 5 to 20 microR/hr that is the normal reported reading? The vendor claims (below) an accuracy of +/-5%, but is imprecise in what that means (e.g. range of the monitor?). Or, should we believe that a reading of 5 microR/hr is accurate to +/- 0.25 microR/hr?!


I think that having all these monitors on-line is an interesting development, especially for the educational value. Eventually, the HPS might want to take an authoritative position on what kind of accuracy and reliability can be expected from these monitors and maybe provide links to them. It might be worthwhile to provide links to sites that reciprocate a link back to HPS. That would provide people the opportunity to give the readings the right level of credibility. It could prevent scares resulting from someone  playing with lantern mantles on his home radiation monitor.


Just some thoughts, see disclaimer below.


----- Forwarded by Mark Hogue/WSRC/Srs on 03/11/02 06:15 AM -----

"Bryan Boardman/Aware Electronics Corp." <boardmanb@aw-el.com> 03/07/02 05:29 PM Please respond to "Bryan Boardman/Aware Electronics Corp."

To:        <mark.hogue@srs.gov>         cc:                 Subject:        Re: Information Request

Dear Mark,

 

Our RM units are digital in nature. All electronics and software are digitally locked to the tube.  The statinless steel tubes are very percise and accurate. They are rated at +- 5% and are halogen quenched hence self-regenerating.  RMs we manufactured 14 years ago provide the exact same results as our new units.

 

One can purchase a check source or a small bag of Uranium ore for checking response.  Approx. 80% of our sales are to professionals and they all seem very pleased.  See: http://www.aw-el.com/jnm/jnm.htm for an example.

 

Best Regards / Bryan Boardman / Manager / Aware Electronics Corp

 

Web Site:

http://www.aw-el.com

E-Mail:

boardmanb@aw-el.com

----- Original Message ----- 

From: mark.hogue@srs.gov 

To: Bryan Boardman/Aware Electronics Corp. 

Cc: radsafe@list.vanderbilt.edu 

Sent: Thursday, March 07, 2002 8:14 AM

Subject: Re: Information Request




Thanks for the links. I've spent some time looking for the standards you list, but without a lot of luck. I'd continue to hunt for the standards, but I suspect they would not really answer my questions anyway. Could you please tell me specifically: 

1.        What is the measurement uncertainty at 5 to 20 microR/hr of your monitors when new? 

2.        What would be the expected drift in the calibration after shipping, storage and time in use? 

3.        When a monitor is failing to measure accurately due to component failure, how would this be indicated? 


I see a lot of potential for your monitors and I don't want to give the impression that I'm just being critical. I would like to know how accurate the readings are that we are beginning to see from hobby radiation monitors around the country. I think the Health Physics Society should be ready to answer questions about what these readings mean and I would like to head off a panic due to someone's hobby monitor reading high. 


Mark Hogue

mark.hogue@srs.gov

"But we surely overrate the usefulness of what we like to call "stimulation" and underrate the need for time, peace of mind, mature reflection." -  Susan Haack


"DISCLAIMER: The opinions expressed are mine and do not necessarily represent Westinghouse Savannah River Co. or the United States Department of Energy."

"Bryan Boardman/Aware Electronics Corp." <boardmanb@aw-el.com> 03/06/02 04:42 PM Please respond to "Bryan Boardman/Aware Electronics Corp."

To:        <mark.hogue@srs.gov>        cc:                Subject:        Re: Information Request

Mark,


See

http://www.aw-el.com/specs.htm


http://www.aw-el.com/win.htm


Best Regards / Bryan Boardman / Manager / Aware Electronics Corp


Web Site:

http://www.aw-el.com

E-Mail:

boardmanb@aw-el.com


----- Original Message -----

From: <mark.hogue@srs.gov>

To: <aware@aw-el.com>

Sent: Wednesday, March 06, 2002 10:10 AM

Subject: Information Request



> Name:    Mark Hogue

> E-mail:  mark.hogue@srs.gov

> Phone:   (803) 208-7153

> Fax:     *803) 208-6158

> Contact: email

>

> Message:

> I am interested in calibration methods and frequencies, (if any), and how

much error should be expected.

>

> WSRC

> M.L. 704-26S

> Aiken, SC 29808