inverse square law - limitations(3)

[P van Rooyen <rooyen@aib-vincotte.nl>]

Thanks Dave and Tad,
It was the FROM bug buzzing into this message. 
Part of the previous messages was lost on the way;  I try again
 
Dear radsafers,

The dose rate at a certain distance from a point source can be calculated
with the 'ambient dose rate constant H*10' for that nuclide and the inverse
square formulae.  This is an approximation as I understand based on the
difference in area, where the 4-pi is included in the constant. 

Field experiments in open air showed that the measured and calculated
values for iridium 192 were within 5 % until approximately 100 meters.
Above 100m we measured lower values than calculated values. This formulae
can be used for greater distances but I can imagine that the absorption and
scatter with the air layer in between should be included in the formulae. 

I have two specific questions:
1. which corrections should I use when I want to estimate dose rates at
very short distances (less than 10 cm)? 
2. which corrections should I use for bigger distances?

By the way: question 2 does not originate from a need to calculate dose
values; we need to know the influence of our sources on detectors used for
control instrumentation in a plant.

Thanks

Paul van Rooijen
Manager HSE
AIB-Vinçotte Nederland BV
Postbus 6869, 4802 HW Breda
The Netherlands

tel	++31 (0) 76 579 11 54
fax	++31 (0) 76 587 47 60 
e-mail	rooyen@aib-vincotte.nl


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