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Re: high vacuum -> prize topics



Hugh Haskell wrote:

If a
positron can be kept from colliding with any real matter for a period
of several days, I suspect that should qualify as a long enough mean
free path.

1) Several days???? In 1984, a positron named Priscilla was
kept for three months.

http://www.nobel.se/physics/laureates/1989/dehmelt-lecture.html
http://www.google.com/search?q=positron+priscilla

I imagine much longer times have been achieved since.

2) I have personally created vacuums where the density of
residual gas was, on average, much less than one particle
per cubic mile. And since the cell was only a few centimeters
in size, you could be pretty sure there was nothing in there
at all.

It's not even particularly hard. All you need is a dilution
refrigerator. Ones that will get you to 15mK are commercially
available. Calculate the equilibrium vapor pressure of anything
you like at that temperature.
http://www.oxinst.com/SCNPSN232.htm

3) As y'all may have noticed, on about 25 occasions I have
posted links to pages at the nobel.se site.

It's a hint.

Back when I was a sorcerer's apprentice, we were required to
know something about each of the Nobel prizes in physics
and chemistry. We weren't required to know a lot of detail,
but we were supposed to know, for instance, that there was
such a thing as a phase-contrast microscope, and there was
such a thing as zero-sound in liquid helium-3, and that
Dehmelt was the maestro of the single-electron traps.

I must admit I found the assignment a bit daunting at the
time. But since then, it has saved me from embarrassment
on a number of occasions.

Take the hint. Go to
http://www.nobel.se/physics/laureates/index.html
and read down the list. That way you've got at least some
idea what were the hot topics during the last 100 years.

And you can use this as an almost-endless supply of topics
if students are supposed to do a report and need ideas for
a topic.