[ RadSafe ] Build-up in Microshield

[Kai Kaletsch]

Hi Mattias,

You may want to try JavaShield. (It's free!) Go to 
http://members.shaw.ca/eic/Tools/index.htm , scroll to the bottom and click 
on JavaShield. Make sure you look at the documentation ( 
http://members.shaw.ca/eic/Tools/JavaShield/Documentation/Documentation.htm  
) before you try it.

This is a program we mainly wrote for our own use for calculating shielding 
requirements in uranium mines. So, the user interface is a little rough, 
there are not a lot of geometries, and it is built to make it easy to work 
with uranium ore or slurries. However, you can also enter other sources, on 
the right side of the screen.

The program handles the buildup factor for mixtures and layers differently 
than MicroShield, if you let the program calculate the buildup factor. For 
layers, the program calculates the probability that the photon's last 
interaction (before arriving at the dose point) was in any given layer. The 
buildup factors of the different layers are then combined, according to 
those probabilities. So, if you are behind 2 thick layers of shielding, the 
last layer dominates, since the photon would have probably interacted last 
with the last layer of shielding. If you are behind 2 thin layers of 
shielding, they will both contribute to the buildup factor.

For a comparison between JavaShield and MicroShield results, please see:
http://members.shaw.ca/eic/Tools/JavaShield/Validation/JavaShield Validation 
Report.doc .
In particular, have a look at the graph "JavaShield Benchmark Pb". It shows 
that MicroShield produces very different results, depending on whether you 
choose the buildup factor for the source or the shield, for a uranium ore 
source behind a lead shield. JavaShield gives more reasonable results.

Even if you don't end up using JavaShield (because it does not contain the 
geometry that you need), you could justify your choice of buildup factor 
with it, using a simple geometry.

Cheers,
Kai Kaletsch
Environmental Instruments Canada Inc.


----- Original Message ----- 
From: "Olsson Mattias :MSO" <mso at forsmark.vattenfall.se>
To: <radsafe at agni.phys.iit.edu>
Sent: Monday, May 24, 2010 5:41 AM
Subject: [ RadSafe ] Build-up in Microshield


Hi all,

I sometimes use the simple Microshield (v. 7) software for not too complex 
activity to dose calculations. The one thing I have some trouble grasping is 
the implementation of build-up correction. When there are several layers in 
the shielding you can tell Microshield to assess build-up from for example 
the material of the outermost shield. I usually go with the outermost layer 
if it's thick enough to provide reasonable effect but I would have some 
difficulty arguing for it. Does anyone have a well tested way of setting up 
the build-up assessment in Microshield - with a reasoning behind it? Also, 
do you play around with the Change Energy function, and if so, how and why 
in that way? The manual recommendation about this detail is rather vague, I 
think.

Any shared experiences are welcome! Except for "You must use Monte Carlo or 
it's all crap". :)

All the best,
Mattias Olsson

-- 
Mattias Olsson

Vattenfall AB
Forsmarks Kraftgrupp AB
Kemi och Radiokemi
SE-742 03  Östhammar
Sweden

Phone: +46(0)173-810 00, +46(0)173-819 52
Mobile:  +46(0)70-580 19 52

mso at forsmark.vattenfall.se
www.vattenfall.se/forsmark

The opinions expressed in this e-mail are personal and do not represent 
Vattenfall AB or its subsidiaries.
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