Re: FW: Certification of "box" calibrators

[AndrewsJP@AOL.COM]

Glen, I believe that with the heavier attenuators you have a virtual source somewhat in front of the real source because of scattering from the attenuator.  I have always fit the data from Landsverk R meters to the curve with a polynomial function using as many terms as necessary to get the damn thing to fit.  


However, I have never had to calibrate a box calibrator.  I also have seen beaming in a box calibrator from the brass screws used to hold the attenuators to the mechanism.  The attenuation of the brass is significantly different so that there was a non-uniform field in the box with hot spots where the beam penetrated the screws better than the lead.  


If you want to be precise, you should compare the response of the specific instrument to the beam in the box calibrator and to the beam of a free air calibrator.  The calibration of the free air beam should be well known.  In this way all the scattering in the box calibrator is accounted for.  Once this is done, you should not have to "recalibrate" the box again unless you change something that changes the scattering for a particular detector.


Personally, I don't much care for box calibrators.




John Andrews

Knoxville, Tennessee