RE: Measuring Fe-55 & Pm-147 HOW?

[VERNIG.PETER@FORUM.VA.GOV]

{Original Msg: 'Measure Fe55, Pm147... HOW?' from <radsafe@romulus.ehs.uiuc.edu>
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{To: RADSAFE --INTERNET radsafe@romulus.eh
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{I am having a bit of trouble with an educated research person who is afraid
{ of radiation.  He wants a measurement of Fe 55, - to which I said "not possibl
{e" and he's concerned that his 7.4 GBq sealed source is generating bremstralung
{from the lead or stainless capsule - to which I said "it's probably beta".
{ This is not my area of expertise, can someone enlighten me on measuring these
{ things?
{
{Radiation Protection, Ministry of Health, British Columbia
{The opinions and material above are solely those of the author.
{Disclaimer for postings to bulletin boards, newsgroups, etc.
{rnross@bcsc02.gov.bc.ca
 
 
Mr. Ross,
Fe-55 is used in x-ray fluorescence as a standard for specifying peak
width resolution as it has an exceptionally "clean" emission in the right
energy range.  Decaying by elecron capture it produces K and L shell
characteristic x-rays and Auger electrons only.  The Auger electrons can
be discounted both for dose and detection as they are even weaker than
the betas from H-3, 5.2 keV and n even lower  energy one.   Likewise the
L shell x-rays are so weak as to be no factor. This leaves the K x-rays.
They can be detected and measured with a set up using a solid state
lithium drifted silicon Si[Li] detector usually using an MCA.  X-ray
fluorescence is used generally for elemental chemical analysis and the
softwarewas not designed to do radiological measurement.  Also the
equipment is expensive to buy and operate.  The Si[Li] detectors are 
liquid nitrogen cooled and a basic detector only would probably run 
about $2000 US.  In my experience they are only used with MCAs but it
would probably be possible to run one with an SCA.
 
Anyway, with respect to Fe-55 it can be detected but it is expensive.  I
would suggest trying to calm down the gentleman with an equation like
I = 0.156 n [10E+5] u, I = dose rate from a point source in mR/hr @ 1 m
n = fraction per disintegration, u = energy absorption coefficient in
air in E-1cm.  I'm sure the exposure would be fairly low even not
taking air attenuation which will be appreciable.  Oh, that I is per
mCi, I'm afraid.  Equation is from Radiological Health Handbook,1970
edition.
 
WRT Pm-147, I do not have the experience with it.  NCRP 58 shows it as
a nice clean beta emitter, 225 keV peak so air attenuation would take
care of it nicely.  Probably see it with 5-10% efficiency with a GM
and better with an SCA scintillation set up.  
 
Hope this helps,
Peter G. Vernig, VA Medical Center, Denver vernig.peter@forum.va.gov
 
 
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