Text 6649, 100 rader
Skriven 2008-05-07 17:52:00 av JOAN MACDIARMID (1:123/140)
     Kommentar till en text av GLEN JAMIESON
Ärende: IRRADIATED FOODS   80503
================================
 Hi, Glen,

 JM> I was supposing high-intensity UV for three
 JM> reasons. First, that's what's used to keep the
 JM> labs used for cell-culture at the Uni sterile when
 JM> they are not occupied. And second, the cider, though
 JM> a bit murky as pressed, is not opaque, so a thin layer
 JM> passed under a high-intensity source should be
 JM> adequately treated. Third, I suspect high-intensity
 JM> UV is way cheaper than gamma or X-ray irradiation, and
 JM> several separate orchards represented at my Farmers
 JM> Market are offering this irradiated cider,
 GJ> UV sterilisers are cheap,
 GJ> UV treatment leaves no taste or odor. Murky water
 GJ> (eg apple juice or treated waste water) has to be
 GJ> spread to a thin layer to ensure the radiation
 GJ> penetrates effectively.

 Note I did specify thin layers, i.e., I knew that!

 GJ> Gamma radiation, usually obtained from a radio-active isotope, easily

 I think it HAS to come from a radioactive isotope.
 Although my dictionary mentions the energy range of
 gamma rays overlaps that of high-energy X-rays. It's
 been ages since I studied nuclear chemistry, and my
 physical chemistry book is in a place hard to reach.
 You might know this, but in answer to some of Dale's
 worries, gamma rays are purely electromagnetic, and
 I don't think they can initiate fission of other atoms.
 Beta rays are actually particulate, being highly
 energized electrons or positrons. I don't think they
 can initiate fission either, because even if they
 do have mass, they are very small. Alpha rays are also
 particulate, being highly energized and charged particles
 almost the same as a helium atom (2 protons and two
 neutrons, no electrons) for an effective "atomic weight"
 of about 4. These alpha rays might be able to destabilize
 an already unstable heavy atom, as they are hefty little
 bowling balls moving fast. But they would not be able
 to destabilize a stable isotope. So how do you get
 useful gamma rays without too much alpha or beta stuff?
 For one thing, you know the breakdown path favored by
 the unstable isotope you are using! Each isotope has a
 usual pattern of breakdown into (usually) 2 smaller
 atoms plus "change" in the form of alpha and beta
 particles, maybe free neutrons, and gamma radiation
 to shoot off the excess energy. Some isotopes might
 have beakdown paths which involve no more "change"
 than the gamma rays, so you use that as the source
 isotope. Alternatively, there may be shields which
 selectively block alpha and beta particles while
 being invisible to gamma radiation, so you would
 "filter" the radiation to get just the gamma rays.

 GJ> penetrates packets of meat or similar. It requires a much more
 GJ> expensive installation, with lots of lead to protect passers-by, and
 GJ> every few years, as the isotope loses its "kick", it has to be
 GJ> replaced by a fresh source.

 JM> I have tried
 JM> the "irradiated" ground beef Wegman's sells at
 JM> a somewhat higher price, and it is definitely
 JM> better to my taste.
 GJ> I suggest that the irradiated meat tastes better than the usual minced
 GJ> (ground) meat because it doesn't have any nitrate or other
 GJ> preservatives added to give it an acceptable shelf life.

 JM> I don't think our ground meat includes extra
 JM> "ingredients", as that would have to be in
 JM> the labeling. (Inadvertent contamination is
 JM> not a deliberate ingredient.) I think the

 GJ> Is there anything on the normal ground meat packages just given as
 GJ> "preservative" or "colouring"?

 No.

 JM> meat is prepackaged, then irradiated to
 JM> sterility, and little more can happen to it
 JM> as long as it is sealed and refrigerated. This
 JM> includes no more exposure to oxygen after the
 JM> packaging, which probably has its own
 JM> degradative effect. Anyway, I did like the
 JM> product, though am less willing to pay the
 JM> higher price for it.

 GJ> Does it have a longer storage life, as shown by a later "use by" date?

 I don't know. I'll try to check that next
 shopping trip, if I can remember that long.
 I suspect so, though. Of course, once the
 consumer opens the packet, the clock has
 started ticking, as bacteria and oxygen
 will have been introduced.

 Joan MacDiarmid
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