Re: HOT DUST

["USHINO, TOSH" <ushinot@songs.sce.com>]

Richard Richardson wrote;
     
>We are being asked to develop the capabilities and establish a procedure to 
>make retrospective particle size measurements on particles collected on filter 
>papers shown to be contaminated by alpha spectroscopy.

>This is a two part problem.  We need a method of locating the active particles 
>and determine their relative activity among the non-active particles, perhaps 
>using CR39.  Once the hot particles have been located it is important to know 
>the size because the size will have a significant impact on dose.   One 
>possibility being looked into is image analysis.
 <snip>
     
Sorry to send this out to entire RADSAFE.  I tried to send this response 
directly to Richard Richardson and Mike Wood but it kept coming back.
     
Of course the best approach to determine the particle size distribution at the 
work site is to use cascade air impactor.  Retrospective particle size 
determination is difficult, but you already know that.
     
Auto-radiograph, whether using CR-39 or other media, is certainly the easiest 
approach to find the hot spot.  But how would you tell hot particle from others 
if they are bunched up?  Do actinide dust particles to look different than 
non-radioactive dust particle?  Even if it is, if the work area is dusty, this 
could prove to be difficult.  If actinide particles look different, and it is 
not too dusty, then all you have to do is to examine the filter paper through a 
microscope.  Sounds like lots of work no matter how you look at it.
     
One suggestion I have for determining the particle size (assuming that the 
particles are in the form that don't dissolve easily) is to dissolve the filter 
paper and filter the residue through series of filters with progressively 
smaller pore size.  We use series of filter papers to determine particle size 
distribution in reactor coolant.
     
Keep us informed on any progress.
Good luck!
     
Tosh Ushino
ushinot@songs.sce.com