RE: Shielding Material

["Marco Caceci" <chemitech@chemitech.com>]

The ideal thing would be depleted U, but not politically correct.

Stopping power grows with atomic weight (more than linearly) and with

density, so the next maneageable heavy metals would be bismuth (blah),

gold (why not?), Pt (ditto), Os, Re (?), W.

There are machinable tungsten alloys there: I quote without promoting:

"tungsten heavy alloy is more than 50% denser than lead, yet can be

machined readily by conventional methods" 

specifically recommeded for radiation shielding.

so where is the problem?

You have cross section data for the elements vs gamma energy, right?

 

Marco



-----Mensaje original-----

De: owner-radsafe@list.vanderbilt.edu

[mailto:owner-radsafe@list.vanderbilt.edu] En nombre de Bob Westerdale

Enviado el: miércoles, 12 de mayo de 2004 18:07

Para: Radsafe@list.vanderbilt.edu

Asunto: Shielding Material







Greetings... 

I've been asked to recommend an alloy for use in the construction of a

port cover for a 400 kV Electron Microscope ( TEM).   I usually work

with low kV systems ( ie < 30 kV)  where material is much less a factor;

This high kV Instrument presents a challenge in that: 

1.        The part will be cut from a cube about 5" X 5" x 5",  with a

number of high precision machined features, so that  machinability is a

serious concern 



2.        I'd like to be able to plate the part ( Cu-Ni-Cr) for

aesthetics 



3.        I need an alloy with the best beam stopping capability I can

find.   



4.        I cannot make the whole part out of Pb,  as there are some

structural loads that would not be well served by a mushy material.  (

and plating would nearly impossible.) 



We've made similar parts in the past out of Leaded brass ( e.g. clock

brass or marine brass) and in some cases 303 or 304 Stainless,  I'm

hoping that there might be some more modern materials ( ie

tungsten/tantalum or ? alloys...)  that might allow for a less massive

solution.             Space is at a premium,   and I'd like to avoid a

prolonged search for ' Unobtanium '   



This component will be headed for Germany,  interesting to note that we

cannot allow any exposed Pb surfaces, for fear of toxicity, and the

Radiation leakage at 2" must be less than .1 mR/Hr.  (The end-user who

told me this was chain smoking unfiltered Rothmans in a tiny,

unventilated room.....  so much for risk perception!) 



If anyone has any suggestions/experience I'd be quite grateful! 



Thanks, 

        Bob Westerdale 

            EDAX Inc. 

        Mahwah, NJ.