X-Message-Number: 3666
Date: Tue, 10 Jan 1995 22:28:40 -0500
From: "Keith F. Lynch" <>
Subject: Re: SCI.CRYONICS: Low Temperature Cryonics Replies

> Keith says that "the limiting factor in suspension time is radiation
> damage, which lower temperatures won't prevent." On this point I
> take the word of Brian Wowk, who has said that radiation damage is
> negligible because such damage in living systems is almost entirely
> due to the mobility of free radicals.

I'm not disagreeing with him.  He was answering in the context of
suspensions of several decades to several centuries.  I was saying
that radiation is the limiting (non-political & economic) factor in
suspension length, but that it's negligible until you're into the
thousands, or perhaps hundreds of thousands, of years.  And that
heat-related problems are even more negligible, at LN temperatures.

> Brian has told me that molecular mobility at liquid nitrogen
> temperature is so negligible that lead shielding for cryonics
> patients would be a waste of money.

Some radiation damage does not involve free radical mobility.  But
I agree that lead shielding is a bad idea.  For one thing, nobody
is planning on multi-thousand year suspensions.  For another, the
radiation that you *do* have to worry about won't be stopped by
reasonable amounts of lead.  For another, much of the radiation is
from atoms inside the patient.  And finally, lead itself is more
radioactive than the normal background!

> I think the contraction and viscosity-lowering between -130 C and -196
> C would be no different from these effects between -196 C and -246 C.

Molecular motion is already utterly negligible at liquid nitrogen
temperatures.  Ice, whether it's crystalline or vitreous, is held
together by hydrogen bonds.

A good measure of the mobility of water molecules in water or ice is the
vapor pressure, which is roughly proportional to the tendency for water
molecules at the surface to break free and float away.

Temperature (C)   Vapor pressure (mm of Hg)

    100             760 (1 atmosphere)

     20              18
     10               9
      0               4.6
    -10               1.9
    -20               0.78
    -30               0.29
    -40               0.097
    -50               0.030
    -60               0.0081
    -70               0.0019
    -80               0.00040
    -90               0.00007
   -100               0.00001

   -196 (LN)          very very small

Notice how it not only decreases rapidly, but does so at a rapidly
increasing rate.  At room temperature, pressure seems to halve with
each drop of 10 degrees.  By -100, it drops by about a factor of 7
with each 10 degrees.  That's as far down as my table goes.

It certainly isn't zero at -196, but I'm sure it's very very very
close to zero.

> I feel less confident about the difference between liquid helium and
> liquid neon because of superconductivity, superfluidity and other such
> low-temperature weirdness.

Not all liquid helium is superfluid.  It has to be at the right
combination of temperature and pressure for that.  Anyhow, superfluid
helium is just as good at cooling as any other kind of liquid helium.
The big problem with superfluid helium is that it is self-siphoning.
It will crawl out of any non-sealed container, and be wasted cooling
the surrounding room.  But if you seal the container, the pressure and
temperature will both increase as the helium boils, until the container
explodes.  Perhaps you could compromise by unsealing it for one second
every minute, if you can find a valve that's 100% reliable for decades
or centuries, and that operates at that temperature.

Of course liquid helium and liquid neon are both much more expensive
than liquid nitrogen.  Patient care funds would have to be in the
millions, rather than tens of thousands, of dollars.

> Keith repeats Hugh Hixon's assertion that there is no translational
> motion at liquid nitrogen temperature.

He doesn't say "none".  He says extremely little.  He's right.

> Water molecules in an ice crystal have vibrational, but not
> translational motion ...

No.  On the nano-scale, there's not much difference between cold water
and warm ice.  There's a threshold effect that's only noticable on the
macro-scale.  Cold water is slightly less than 90% hydrogen bonded.
Warm ice is slightly more than 90% hydrogen bonded.

It's roughly analogous to a huge rectangular grid of pipes with a valve
in every unit segment.  As you gradually increase the proportion of
valves that are open, the large-scale behavior of the fluid in the pipes
abruptly changes from near-total immobility to near-total mobility,
while the small-scale behavior is almost unchanged.  (It's a fun math
problem to try and figure out at exactly what proportion this happens.)

Glaciers do flow, even at polar temperatures.  But at liquid nitrogen
temperatures, they wouldn't, except under extreme pressures.  At least
not a noticable amount in a millions years.

The difference between crystalline and vitreous pure ice is also only
meaningful on the macro-scale.  The mobility is the same.

Of course vitreous pure ice is never used in cryonics.  Instead, it's
a mixture of water and cryoprotectants.  But that makes the mobility
even less, since the molecular weights are greater while still being
held together by hydrogen bonds.

> Dissolution and hydrolysis proceeds far more quickly than catalase.

I don't think so.  And even if they do, it's the slope of the curve
that's important.  I think Hugh chose catalase because it is slowed
down less by cold than any other known biological reaction is.

> Without knowledge of how much structural information can be lost
> without compromising identity, the most conservative approach is
> to store at the lowest temperature.

Not if doing so causes more damage of another type.  Not if it prices
over 99% of the customers out of the market.

> Molten silica (silicon dioxide, liquid glass), ...

Solid silica, or quartz, is normally crystalline.  Glass is not silica.
Glass is calcium silicate, and is normally vitreous.

> ... whereas for sugar the polymerization is assisted by weaker forces
> (van der Waals or hydrogen bonding). In neither case do these bonds
> have the defined bond-lengths and bond-angles of covalent bonds.
> Therefore, I say that molecules in these glasses have translational
> motion.

Hydrogen bonds aren't as strong as covalent or ionic bonds, but they
are just as real.  Molecules without sufficient kinetic energy to break
free are just as bound.  The hydrogen bond between two water molecules
is about 1/30th as strong as the covalent bonds within one water
molecule.  Not enormous, but not neglible either.

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