[ RadSafe ] Question re survey meters

Ivor Surveyor isurveyor at vianet.net.au
Wed Mar 16 21:40:08 CDT 2011

I have a question about radiation survey 
instruments.   My understanding is that an air 
ionisation chamber for instance collects the 
charge released by an ionisation event (about 34 
ev/ion pair in air or air like material lining 
the chamber); the resulting current is measured 
by a sensitive electrometer and converted into 
Roentgen.  Now I understand the Roentgen is 
defined as 2.58E-4 Coulomb/ kg dry air at 0° C and 760 mm atmospheric pressure.

My question is that instruments read as R/ h or 
rem/h on the assumption that there is a rough 
equivalent between an exposure of IR and an 
absorbed dose of I rad (10mSV) to tissue.  Am I 
correct that the instruments electronics sample 
the ionisation currents over a time interval?  If 
this is correct is there a “standard time” 
sampling interval?  Can the operator vary the time sampling interval?

Ivor Surveyor
isurveyor at vianet.net.au 

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