Re: inverse square law - limitations(3)

[Ted de Castro <tdc@xrayted.com>]

P van Rooyen wrote:
> 
> 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)?

If the either the source dimension or detector dimension are greater
than 1/3 this distance - then it is no longer a point source problem and
you need to use a formula for a more appropriate geometry.  (Assuming no
nearby scatterers)

> 2. which corrections should I use for bigger distances?

Attenuation by intervening materials such as air and buildings and
scatter - especially ground scatter.  Background AND ITS VARIABILITY is
also a factor as you get further away and levels get lower.

You also mention concern at 5% error.  Remember ONLY transfer standard
class instruments are rated to better than 5% accuracy (3% actually). 
Survey and monitoring instruments are more like 15% (or even maybe 25%
on analog readouts at the ends of the scale).  Their precision may of
course be better than that - but includes counting statistics.

So - some of this sounds like "hair splitting".
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