X-Message-Number: 3332
From: Brian Wowk <>
Date: Sat, 22 Oct 94 17:46:54 CDT
Subject: SCI.CRYONICS Brain scanning, reply to Yvan Bozzonetti

From: yvan Bozzonetti <>
>       I am happy we agree on the holographic method, at least on small 
>samples. Now, how to get to larger objects? The smallest element to look at 
>is near 100nm, so to have a "light" able to give a classical refraction 
>effect, the wavelength must be at least one order (ten times) smaller: 10 
>nm or a photon energy near 100 eV. Any radiation with energy near or above 
>100 eV will fits the bill, 1 kev is very good.
>        Now Brian, why do you say such waves are absorbed? Because you have 
>read about experiments on the subject to be sure! Well, but these 
>experiments was done with X rays generated by electrons colliding with a 
>metal plate at high energy in a tube. Such rays have a very broad band 
>spectrum. What absorb them is a forest of very narrow inner atomic energy 
>levels. With a very narrow band generator, it becomes possible to choose a 
>transparency window where there is very few absorbtion. Think of a large 
>mesh grid: it will stop a lion as surely as a concrete wall, but the lion's 
>fleas will no even see the grid if they want to jump to another lion on the 
>other side.
        This is not correct.  The physics of x-ray interactions is
well understood both theoretically using QED and experimentally using
monochromatic x-rays produced by Bragg scattering.  Photoelectric  
absorption will occur at *any* energy above the ionization energy
for an electron, although it is most intense when the x-ray energy
is close to the ionization energy.  In fact, for biological elements
like carbon and oxygen, all ionization energies are less than 1keV, yet
photoelectric absorption is intense at 1keV-- dominant over all other
interactions, including coherent scattering.  (For further information 
on the interactions of x-rays with matter, consult a standard reference 
such as Johns and Cunningham, Physics of Radiology.)
        The only thing that makes x-ray holography marginally possible
at 1keV is the low energy per photon.  However if you want to image  
anything larger than an insect, higher energies are required.  As energy
is increased, the cross section for coherent scattering drops, and the
energy per absorbed photon increases, escalating the required dose to
ridiculous (vaporizing) levels for something as large as a brain.
        I reiterate: Nobody is ever going to use ionizing radiation to
"read out" the memories of an intact whole brain.
--- Brian Wowk

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