RE: AW: Xenolite Protective clothing

["Wright, Will \(DHS-PSB\)" <WWright2@DHS.CA.GOV>]

as far as the haz waste issue is concerned. the toxicity characteristic for lead is about 5ppm and that for barium is 100 ppm. these would present the same disposal problem even given the soluble threshold limit concentration are 20x different but easily attainable or the difference is irrelevant if the metal is small enough individual pellets or something.



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

From: owner-radsafe@list.vanderbilt.edu

[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of Peter Thomas

Sent: Sunday, December 05, 2004 3:09 PM

To: radsafe

Subject: RE: AW: Xenolite Protective clothing





I guess this thread has gone quiet but I thought I'd add my AUD$0.02 ...



Sam Iverstine was pointing out the differences in attenuation properties

and referring to "the diagnostic range" as "<300kVp".  Particularly in

diagnostic projection radiography (and in computed tomography), tube

potentials tend to be less than 150kV and the peak of the resulting

spectrum tends to be about one third of this, so as a rule diagnostic

spectra peak at around 30 to 50 keV, maybe a bit higher for CT.  This is

below the K-edge for Pb (88keV) with the result that other materials can

have higher mass attenuation co-efficients.  Barium for example has a

K-edge at 38keV and thus between 38keV and 88keV has a mass attenuation

co-efficient about 1.5 times that of lead (or 50% higher if you prefer).

Try the NIST database

http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html if you're

interested in plotting some curves against each other.  (I saved the

data as text and then imported into a spreadsheet to plot curves of

different elements or compounds on the same graph)



Other elements that have been used include: tin, aluminium and tungsten.

For a while there I understand that there were "light-weight lead"

formulations combining tin, lead and aluminium, but more recently there

seem to have been a number of "lead free" formulations marketed.  (Well

the formulations themselves have tended to be jealously guarded as far

as promotional material is concerned, but the "lead free" tag and the

weight savings have been trumpeted).  The makers of Xenolite state that

they use barium and tungsten, others talk cryptically about "ionized

salts" or "mimicking the electronic properties".



The reduced weight of the apron is quite helpful, particularly in long

fluoroscopic procedures.  However the other components are all less

effective than lead above 88keV so the aprons shouldn't be used in

nuclear medicine.



Peter Thomas

Medical Physics Section

ARPANSA

 





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