X-Message-Number: 17208
From: 
Date: Sun, 5 Aug 2001 23:40:15 EDT
Subject: CO2 versus LN2

Louis Epstein poses a couple of questions/issues inspired by the Cryogenics 
Guide (previously posted on CryoNet).  My thoughts follow, but of course, as 
always, I reserve "retraction rights" based on new information/learning.  
First, in regards to long-term storage with solid CO2 versus LN2:

"So how is Trygve's grandpa doing in the
shed with the dry ice?"

At dry ice temperature bacterial action should be nonexistent, but the 
results of random thermal motions would accumulate (e.g., denaturation of 
proteins) over the years creating a much more significant nano-fix chore in 
the future.  Dry ice may be an underrated short-term solution but is probably 
insufficient for the multi-decade-long periods anticipated.

"What are the radiation-resistance properties
of extant dewars and cryostats?"

I believe cell culture dewars (like mine) have layers of reflective surface 
celephane-like layers or at least mirror-like coatings on the exterior 
surface of the inner wall of the vacuum chamber/envelope.  However, I believe 
this is intended more as a means to reduce radiant heat reaching the LN2 than 
to specifically prevent subatomic particle damage to the specimens.  We get 
that type of damage continuously but have very active cellular repair 
proteins constantly fixing "busted" organic cellular molecules such as DNA 
(forget inorganic cellular molecules which are tiny and cheap).  In short, I 
do not believe such ionizing radiation is significant over a few hundreds 
years (outer space would be a much different story).  It might be "ruinous" 
over several hundred thousand years.  Just my current thoughts.

Regards,

David C. Johnson

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