Stripping Radon From Air Samples

[Robert Augdahl <augie@macconnect.com>]

I need help, I have been looking for a way to strip Radon (and daughters) 
from air samples that I need to count in a relatively quick time frame.

Here's my situation; we are doing soil clean-up activities, the soil 
contains primarily Pu-239 and Am-241, we're running air samplers in the 
area to check for airborne concentrations. We would like to only have the 
personnel in the immediate area wear respirators. In the past we have 
always done air sampling but waited 24hrs to allow for decay before 
counting the sample. This could be a serious delay time if we found we 
had exceeded a 10th of a DAC the previous day.

I have found in Cember 'Intro to Heath Physics' a calculation to strip 
the Rn and Th counts out, but it requires a 20hr delay in counting. Not 
much help. I have been told by some of the old hands that they used to 
have a calculation for doing this but no one remembers it. I don't mind 
if it is a quick and dirty method, I can always count the filter again at 
a later date and get a final number for the records, I just need 
something to show with some certainty that the work area was below a 10th 
of a DAC. Also all the workers will be wearing BZA samplers for dose 
estimations, which are counted after a 24hr decay.

My plan is to run a sampler pulling approx. 5 CFM, start it at the 
beginning of the shift. Change the filter at lunch (about 4hrs) and stop 
(change) at end of shift. The filter changed at lunch I would like to 
count after 2hrs decay, and again after 2 hrs. Using those two counts, 
can I strip the Rn and Th counts out with any degree of certainty?  Would 
some other time frame (that would fit in a single day) work better? The 
filter I change at end of shift could be counted at the start of the next 
day before work began. That should give me enough of a decay time to show 
a count below 10% DAC.

I'm open to any ideas, and would like to hear how its done other places.

On a related note, I have a copy of a program by K. Skrable and C. French 
for a HP-42S calculator that allows the user to count the sample a couple 
of times, enter the info and leave you with only the long lived nuclides. 
The problem I have is I can't for the life of me find how to enter one of 
the program instructions.

The instruction is    J+   it will increment the column pointer in an 
indexed matrix. I can't find anywhere in the owner's manual how to enter 
that command. Anyone familiar with it?

Bob Augdahl
RRPT
augie@macconnect.com
Las Vegas, NV