Box Calibation Source & Scatter

[Josh Mancheiwitz <hptech99@YAHOO.COM>]

Comrades,

If anyone has information concerning scattered photons

produced within Sheperd Model 89 Calibrators please

reply. My laboratory owns and operates three of these

units and we recognized that the calibration charts do

not reflect the actual dose rates at lower level

geometries (1 - 10 mR/hr points). One of the

calibrators has an approximately 15 mCi Cs-137 source

for lower dose rate calibrations, the other two are

equipped with 130 mCi sources which can also be

attenuated (per the cal chart) to acheive lower dose

rates. However, the actual dose rates are not equal at

these low levels. When verified with Eberline Ion

Chamber dose rate instruments, and Eberline GM dose

rate instruments, the higher curie (130 mCi) sources

produce dose rates 10 to 40 % higher than expected.

The calibrators are verified yearly using MDH and

electrometer readings down to approx 60 mR/hr and fall

within +-5%. My theory is that the higher curie

content sources produce enough scattered photons

within the box calibrator to affect the instrument

response at the low range. 

If anyone knows of a positive way to prove or disprove

the scatter theory, please respond. 



PS: Please hold all criticisms and respond with

helpful anecdotes only.



Thanks,

Josh Mancheiwitz

HPTECH99@yahoo.com



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