RE: Spectral Analysis

["Perrero, Daren" <Perrero@IDNS.STATE.IL.US>]

To all of you who provided clues and advice, THANK YOU VERY MUCH!  Late

Friday additional measurements determined the source to be an Am-Be source.

It took an extra day to get a neutron meter to the site.  But when used,

there was no doubt.  Calculations of fluence rate ratio with gamma dose

rates at prescribed distances, and absence of gamma ray peaks discounted

Pu-Be and Ra-Be leaving only Am-Be as the culprit.  The size of the source

capsule (1 inch long by 1/8 of an inch in diameter) was deceiving.  I never

thought Americium in something that small could be mixed with enough

material to produce sufficient fluence to be a practical neutron source.

Guess that was my take home lesson from this.  I was holding out for a pure

beta source myself.



As way of information, the original spectra was taken at a distance of about

8 feet, dead time was 12% in an ambient field of about 0.25 mr/h.  Many of

you suggested these may have been problems with the initial measurements

from my limited posting.



Mystery Solved. (Unless you want to participate is trying to determine where

it was from or would otherwise like to own the source.)  Again, thanks to

all who assisted.



The thoughts expressed are mine, mine, all mine!

I'm with the government, I'm here to help........

Daren Perrero, Health Physicist

perrero@idns.state.il.us





-----Original Message-----

From: Perrero, Daren [mailto:perrero@idns.state.il.us]

Sent: Thursday, November 01, 2001 12:08 PM

To: 'RADSAFE'

Subject: Spectral Analysis





This is definitely not my strong suite so any help here is appreciated.  The

situation involves a field test using a portable MCA.  Field readings give

dose rates of approximately 100 mr/h near contact and 10 mr/h at a foot from

a discrete source with no markings.  However a limited time (approx  5 min)

NaI spectra out to 2.5 MeV does not show a discernible peak.   What type of

nuclide could be producing these readings?  If a beta emitter was here

wouldn't there at least be an x-ray peak produced from the capsule material?





Eventually a lab quality spectra will be obtained and the mystery solved but

it would be nice to have some idea (or at least a couple of good guesses) of

what's being transported before it gets to the lab.



Daren Perrero

Health Physicist

Illinois Department of Nuclear Safety

(217) 785-9929

perrero@idns.state.il.us

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