Re: start up calibration facility

[tdc@ehssun.lbl.gov (Ted M. de Castro)]

>>Ok... Why can't a properly calibrated MDH serve as a reference for a
>>calibration range?

an MDH - even properly calibrated - does not meet the ANSI STANDARD criteria 
as a "standard instrument".  This is required if the source is to be 
calibrated in a manner which the standard considers to be  "traceble".

"Traceble" includes a specification to the number of steps removed the 
reference is from a "primary source" or a "standard instrument"

Besides that - the MDH was designed to simply be a survey instrument to fit 
a BRH test stand.  It was never designed to be a "calibration" device.

In my personal/professional opinion I do not consider it to be quality 
instrument and consider its use in the BRH test stand to be poor geometry 
and therefore bad health physics.

When I do x-ray machines - as I have for many many years - I use a keithley 
chamber and my own test stand which gives a great deal of consideration to 
scatter and "good geometry".

Also - since the MDH has a low rate cut off - which is undocumented - it can 
give misleading results at low levels.  It is this low level cut-off that 
makes the MDH - "appear" to have a very low and very stable background 
response - especially considering the small chamber volume.

Anyhow - I digress!!

Bottom line is: for source calibration it does not meet ANSI requirements.

Ted de Castro
UC LBL