[ RadSafe ] FINAL- Ludlum probes on radium

Geo>K0FF GEOelectronics at netscape.com
Fri Aug 29 13:56:31 CDT 2008

Talked some more with Ludlum prior to calibrating my first probes for radium, got things straight and nailed down a little better. .

The Model 44-10 is normally set so that the meter reads 900 CPM per MICRO-R/H for Cs-137, now we are supposed to set it between 975 and 990 CPM per MICRO-R/H for radium. The cables should all be he same length and the HV set for plateau. Input is run at about 26 mV if settable, so that it matches the input on meters that are not settable- like a model 3.

This should keep things on the same sheet of music.

The setting for the 44-2 is 200 cpm per uR/H for radium instead of 175 cpm for Cs.

If the HV is not adjusted for plateau, and instead run at a standard 900V, the probe *may* be a little more sensitive than it should be, but in this case, it will never report a reading LOWER than it actually is. 

To really tweak the probe+meter, the high voltage should be set for that pair and that pair alone, but this would not allow other probes to be used.

Instead there is a trick Ludlum uses, which makes a small modification inside the probe, bringing its individual normal operating Voltage right to 900V. This is a one time thing and can be done inexpensively, once I get the chart from them.

Believe me, I don't think for a moment that there won't be pitfalls using this equipment for this purpose, but as long as we have the blessings from Ludlum, we should be fine. Any errors would be in favor of the consumer, and eventually I think we can get all the rest of the uncertainties address. 

In an ideal world, we would marry up the probe and meter as a pair, plateau check each individual probe, set the meter high voltage to that figure, set the input sensitivity of the meters all the same, and keep the cable type/length all the same.

George Dowell
New London Nucleonics Lab

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