Radiation Survey Monitors

Why haven't you consulted the manufacture?

True, but will the sensor respond that way? It might saturate the sensor. You don't know.

Contact the manufacture, but why would he listen to them when you get a whole spectrum of conflicting opinions from the internet?

I established the procedure that if saturation is questioned then back away from the suspect slab , slowly, until the meter starts to read (inverse square law) then evaluate from a distance. This has not happened , yet, but we did find some old cooler units that were hot. Still don't know what the radioactive element was.

That doesn't tell you what the sensor's linear range is.

A telephone call probably would.

However, if the device is specified to a limit there just may be a reason for that published limit.

We establish the linear range from the Cs-137 by movement of the GM tube using a 24" caliper. This is performed monthly and records kept. Really don't need to make a call, i have been doing this for over 40 years and my procedures work.

When i was younger it was part of my job to retrieve disconnected sources, mainly Ir 192 and Co 60. I have yet to have or had an overexposure. My current life exposure is slightly over 23 Rems, which considering the above is a good record.

If the monitor is saturated, then all you know is 'off the scale,' but not how FAR off the scale.

If I had a radiation monitor that was saturated, I would be backing away QUICKLY, if not turning and running until I could be sure I was out of any potential 'death zones.'

At least here you demonstrate exceptionally good common sense!

I would be backing away QUICKLY, if not turning and running until I could be sure I was out of any potential 'death zones.'
There is a safety issue involved. As the radiation monitoring is being done in a steel slab yard by moving slower and going behind a stack of slabs the tech is shielded(time,distance shielding). Running in a slab yard is not safe and the tiny amount of radiation that would be received is allowable rather than slip, trip,fall. These techs are radiation trained and allowed up to 5R/yr. But still the minimum is the goal.

Do the radiation techs carry scissors while running? Walk, don't run. Hey good on you for the work you do, stay safe out there.

The setting was not stated, so I took the most logical result to finding out mid-job that I am in an area with more radiation than I can measure: "Screw this, I'm not paid to die, I'm outa here."

With steel slabs to move behind for protection, my response would be much different:

1. Confirm from radiation monitor than where I am is safe.
2. Extend sensor end of radiation monitor past side of shield, confirm path to next shield is safe.
1. If safe, move to safe zone behind next slab.
2. If reading are not safe, or off the chart, do NOT enter area and report findings to supervisor.
3. Repeat until all measurements are taken, or until monitor cannot provide accurate readings.
   

Yes, one can extrapolate higher dose rates if one knows a lot more information. Depending on the nature of the unknown radiation sensor the reference rate and the higher rate may both reside in a linear range of the detector. In this case a simple linear extrapolation can be performed. If the higher rate causes the sensor or the electronics reading the sensor to non-linearly saturate then one cannot extrapolate an accurate number.

Then there's the different measurements of ionizing radiation that gets very confusing to many laymen.

Meter accuracy is optimized if the readings taken lie within 80% of maximum scale. Based on this I would not use the meter to measure anything out of it's calibrated range.

Generally that is a strongly recommended practice for nearly any measurement.

This I don't think can be generally stated as it would depend on the unit itself....but generally speaking, no....

http://122.physics.ucdavis.edu/sites/default/files/files/Gamma%20Spec/Guide.pdf

https://en.wikipedia.org/wiki/Survey_meter

A general rule for any calibrated sensor/instrument is that you calibrate as near to the full scale reading as possible. There are two aspects to calibration, zero and span. For the zero reading you need to know your local background radiation figure. To get a true zero, cancel out the background radiation by setting the zero on your instrument at minus the background radiation figure. Assuming the scale is linear, a 1% calibration error when setting the span at 5% of full scale will produce progressively higher errors further up the scale reaching approximately a 20% error at full scale. But a 1% calibration error when setting the span at 95% of full scale produces progressively lower errors as you move down the scale reaching approximately 0.02% at zero reading. Your span calibration error, as described in detail above has to be added to your zero calibration error to arrive at your total calibration error. This may also need to be amended for temperature variations.

Thank you and the responding bloggers for this thread. I found the units link most helpful, along with the discussion. There are indeed certain principles of measuring any radiation (including light), that depend on known facts about the source of the radiation.

(1) Is the source considered a point source, distributed source, or coherent source? It makes a world of difference...

(2) What is the known linear response range of the detection instrument for the source at hand? The source must not be far different in energy (wavelength) from any calibration source. The detector if used in particle (or photon) counting mode must truly be set up for that (obviously), and has to have a fairly sophisticated discrimination circuit built-in as part of detection of bona-fide events.

(3) How does the intensity of the detected source change with distance upon approach?

(4) If the source is radioactivity, can discrimination between alpha, beta, and gamma radiation be readily made by the operator? Hint: if the detector could possibly detect all three, there are simple tests with attenuating materials, such as paper for beta, aluminum foil for alpha, and lead for gamma. What to do if the source is not ionized as such or ionizing, but represents perhaps neutrons, or other particles (will leave this to someone's imagination)? Obviously then one must begin to delve into the black arts of neutron detection, etc.

In answer to #4.

http://www.goldmine-elec-products.com/prodinfo.asp?number=G19153