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RE: irradiated mail
Classic depth dose curve. Where are all of the medical physicists? Dose
increases with depth up to a certain point.
dmax (depth of maximum dose) occurs at a depth in the material that is based
upon the incident energy and the density (physical and electron) of the
material irradiated. As the material density goes up (or the incident energy
goes down) the dmax gets closer to the beam entrance surface. For 4-20 MeV
electron beams used in therapy, the dmax varies from about 1.2 to 2.0 cm in
water. For gamma beams of 4 MV to 10 MV, dmax varies from about 1.3 to 2.4
cm. The percent depth dose at greater distances is higher with gamma. The
depth dose curve is much deeper and broader for gamma than for electron. At
a depth of 10 cm in water, the electron beam is almost completely
attenuated. For gamma at 10 MV, you are still at about 80% of the dose at
the location of dmax. The electron beam option would appear to be difficult
to deliver a uniform dose across a bundle of mail. Gamma would be a much
better choice.
Rex Ayers, CHP
Cyclotron Products Team Leader
Tyco Healthcare/Mallinckrodt
-----Original Message-----
From: William V Lipton [mailto:liptonw@DTEENERGY.COM]
Sent: Thursday, August 29, 2002 9:10 AM
To: Franta, Jaroslav
Cc: Radsafe (E-mail)
Subject: Re: irradiated mail
I agree that we need an expert answer. However, I doubt that the electron
beam used would produce most of the dose near the surface, since the LET of
electrons increases as they lose energy. Since the energy used would have
to be high enough for the electrons to completely penetrate the item being
irradiated, the dose may actually increase with depth.
The opinions expressed are strictly mine.
It's not about dose, it's about trust.
Curies forever.
Bill Lipton
liptonw@dteenergy.com
"Franta, Jaroslav" wrote:
I hope an expert answers your question.
In the mean time, the common sense answer is that, in thicker pieces of
mail, the gammas deposit their energy evenly throughout, whereas the e-beam
will deposit it mostly near the surface.
In technical lingo, we say that the "Bragg peak" is close to the surface.
Jaro
-----Original Message-----
From: William V Lipton [ mailto:liptonw@DTEENERGY.COM
<mailto:liptonw@DTEENERGY.COM> ]
Sent: Thursday August 29, 2002 7:17 AM
To: Muckerheide
Cc: Jim Hardeman; radsafe@list.vanderbilt.edu
Subject: Re: irradiated mail
My understanding is that virtually all of the dose from gamma irradiation is
produced by the secondary electrons. In that case, how would gamma
irradiation
produce different effects than beta or electron beam irradiation?
The opinions expressed are strictly mine.
It's not about dose, it's about trust.
Curies forever.
Bill Lipton
liptonw@dteenergy.com
Muckerheide wrote:
> Jim,
>
> As noted, e-beams, not gammas. E-beams are "politically-correct" vs.
> radioisotopes/radioactivity.
>
> Another fool's errand pushed by ignorance by "authorities" and "marketing"
> playing on anti-radiation perceptions.
>
> Regards, Jim
>
> on 8/28/02 6:00 PM, Jim Hardeman at Jim_Hardeman@dnr.state.ga.us wrote:
>
> > Ruth -
> >
> > Based on what I saw about the "irradiation machines", I think you're
probably
> > looking at electron beams rather than gamma or X-rays. I would suspect
the
> > reaction of electrons w/ the organic sulfides would be similar to that
of
> > alphas.
> >
> > I've heard stories (that's the best I can characterize them) of the
clear
> > plastic windows on irradiated envelopes being browned / charred, other
> > plastics (floppy disks, CD's, etc.) being "melted" or deformed. To my
mind the
> > chemical reactions in irradiated plastics are as likely, if not more
likely,
> > to be responsible for the production of "irritants" as the irradiation
of
> > paper ... assuming for the sake of argument, of course, that some sort
of
> > irritants are actually produced by the irradiation process.
> >
> > For what it's worth, when I was working on the Radiation Sterilizers,
Inc.
> > (RSI) cleanup here in Decatur, GA seemingly a lifetime ago (it was only
1988),
> > we were working with paper products, predominantly cardboard boxes, that
had
> > been sterilized with gamma doses in the megarad range ... and we handled
those
> > products with no ill effects. Now granted, we were surveying them for
> > contamination, so we did have latex gloves, etc. ... so that may not be
a
> > valid data point ... but in the thousands of person-hours that we worked
with
> > these products, I don't recall anybody saying anything about any sort of
> > irritant.
> >
> > My $0.02 worth ...
> >
> > Jim Hardeman
> > Jim_Hardeman@dnr.state.ga.us
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