RE: AW: irradiated mail

["Langenegger, Armin" <alang@allsaintshealthcare.org>]

Zack is correct,



Medical sterilization is performed with either electrons or gamma/photons

depending on the thickness and material being irradiated.



Doses used are in the kilorad to megarad region to ensure that spores are

killed.



Letters and small packages only need a high intensity electron beam probably

around 20 MeV. This can be accomplished easily with a conveyer and an

industrial linear accelerator. The surface dose in water is about 90%-95% of

the dmax dose. The practical range is about Eo/2 cm, or in this case about

10 cm, but the dose delivered at this point is only about 5%-10% of the dmax

dose.



Practically, for a large field irradiation (medically 25 cm x 25 cm) at 100

cm source to object distance, and using the 90% dose line in water, the

maximum thickness that can be used would be around 6 cm.



A lot of paper have gloss coatings and am not sure but maybe related to

plastics. Most clear windows are plastic and will change optical properties

due to radiation exposure. In the medical industry we also use lucite trays

on which blocks are placed for shielding, and these do change color from

clear to yellow over some years with exposure to photons. Electrons deposit

dose better and any yellowing would be much quicker and more apparent with

electrons. The plastics also undergo radiation embrittlement, so would crack

and fall apart quickly.



My 2 cents, not endorsed by my employer.



Armin Langenegger

Medical Physicist



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

From: Zack Clayton [mailto:zack.clayton@EPA.STATE.OH.US]

Sent: Thursday, August 29, 2002 11:12 AM

To: franz.schoenhofer@CHELLO.AT; radsafe@list.vanderbilt.edu

Subject: Re: AW: irradiated mail





Franz,



The difference is that irradiation of food, spices, and med devices are

targeting active organisms.  The mail is being irradiated to eliminate

spores - inactive but still viable survival capsules for anthrax.  The rate

of metabolism and water content seems to be the determining factor.  The

spores require a much higher dose to destroy them than the active organisms.





I have seen the dose comparisons listed (I think on radsafe, someone

interested in the exact numbers could check the archives) but I do not

recall the exact numbers.  I think it is the difference between 10's of

KiloRads for food to MegaRads for spores.







Zack Clayton

Ohio EPA - DERR

email:  zack.clayton@epa.state.oh.us

voice:  614-644-3066

fax:       614-460-8249





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