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Re: FIDDLER

The FIDLER (an acronym for Field Instrment for Detection of Low Energy 
Radiation) consists of a thin window, large diameter (usually 5 inch) by 
thin (usually 1 or 2 mm) NaI crystal connected to a ratemeter/scaler, 
usually one with capability of at least one energy discrimination 
window.  I have also seen 5 in diameter by 1 inch thick crystals used as 
FIDLERs.  A handle allowed easy carrying of the probe a few inches above 
the ground to look for Plutonium (mostly) or Uranium on the ground 
surface, or at most a few inches deep - 17 keV x-rays (from Pu-239) 
don't penetrate far.  One could also calibrate the devices to the Am-241 
emission at 60 keV (or to any other low energy gamma/x-ray emission). 

The ones I have used were all made by Eberline Instruments.  There is 
nothing "magic" about the Eberline instrument.  Any NaI detector with a 
suitable characteristics can be used as a "FIDLER".

A new and improved version, using modern integrated circuits, was tripod 
mounted and gave direct reading of soil concentration of the isotope of 
interest.  

Ed Tupin
RSO, Center for Devices and Radiological Health
EAT@fdadr.cdrh.fda.gov
(301) 827-1230
Fax:  (301) 594-4760