X-Message-Number: 25345
Date: Thu, 16 Dec 2004 13:16:05 -0500
From: Henry R Hirsch <>
Subject: Cryonic cooling by adiabatic demagnetization

The magnetic resonance method discussed by Leo in message #25294 appears to 
work by adiabatic demagnetization of a paramagnetic substance. I agree with 
Leo that it is very promising and should be studied by CI, Alcor, and 
others doing cryonic research. I too discussed this topic two years ago in 
message #18924. Because of its importance, I would like to expand a bit on 
the comments I made at that time.

The most difficult part of cooling a cryonic patient is that the 
surface-to-volume ratio is small. If the patient, or in the case of a neuro 
suspension, the brain, is submerged in a cold fluid, heat is removed slowly 
because the surface through which the heat passes is small relative to the 
volume which must be cooled. If the interior could be cooled directly, the 
process would be much more rapid, perhaps fast enough to achieve 
vitrification and avoid freezing.

In principle, interior cooling can be achieved by adiabatic demagnetization 
of a paramagnetic substance. The molecules of such a substance are, in 
effect, minute magnets - "nanomagnets" in today's terminology. When an 
external magnetic field is applied, the nanomagents are aligned parallel to 
the field. When the external field is switched off, the nanomagnets become 
disoriented, with the use of heat drawn from their surroundings. They cool 
their environment. This is the process of adiabatic demagnetization.

There are practical problems in using this process for cryonic cooling. The 
molecules of the body, for the most part, are not paramagnetic, although 
the iron atoms in hemoglobin in the blood and myoglobin in muscle, are 
strongly so. It would probably be necessary to perfuse the blood vessels 
with a water solution of a paramagnetic salt or a slurry of a paramagnetic 
substance in a liquid fluorocarbon carrier. It might even be necessary to 
drain the perfusate, cool it, remagnetize it, and repeat the process one or 
more times.

Initial experiments need not be expensive, since small tissue samples, such 
as the brain of a rat, could be used. I am not in a position to do such 
experiments myself, but I urge those who are to do so.

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