you
we have ignition and liftoff of Columbia
on an ambitious tims a international
research flight the critical fluid bite
scattering experiment isn't exciting
part of the second United States
microgravity payload that will fly
aboard the space shuttle Columbia this
precise experiment will challenge the
universal understanding of some physical
phenomena the experiment is named Zeno
in honor of an ancient Greek philosopher
Zeno evelia who first pondered the
concept of infinity Zeno's most famous
paradox of infinity demonstrates that an
infinite number of successively smaller
steps can be squeezed into the distance
between two points Zeno's paradox is
analogous to the modern-day Zeno
experiment where a series of minut steps
are made toward the critical temperature
of a fluid the critical temperature of a
fluid is the highest temperature at
which it's liquid and vapor phases can
coexist at low temperatures both the
liquid and its vapor can be observed and
exhibit on earth a visible meniscus or
boundary at temperatures above the
critical temperature only a single phase
exists the Zeno experiment will begin in
this supercritical single phase region
and will progress toward the critical
point to study fluid properties as the
fluid prepares to separate into two
phases this is an example of a second
order phase transition other examples of
second order phase transitions include
normal conductors superconductor
transitions and magnetic transitions at
the Curie point at the critical
temperatures of these second order phase
transitions the materials fluctuate
between different states it's these
fluctuations that scientists want to
study much progress has been made in
theory and measurement of these phase
transitions but the Earth's gravity
makes it impossible to do a careful
study of the secondary liquid vapor
phase change at the critical
temperature fortunately the space
environment now permits a new generation
of experiments to test the best theories
currently available zeno principal
investigator Robert gammon explains why
the gaseous elements xenon was chosen
for this experiment we believe that
xenon is an ideal fluid for studying the
liquid vapor critical point it's
available in very high purity it's a
simple monatomic spherical atomic fluid
and it has a convenient critical
temperature it's better than all the
other systems we could think of for very
precise studies close to the critical
point because it's not limited by purity
and not limited by crystal perfection
the xeno experiment is being done in the
microgravity environment of space
because on earth as you near the
critical temperature the Earth's gravity
causes the fluid to stratify or form
layers this distorts the sample but the
microgravity environment of space
permits a very close approach to the
critical temperature before the
stratification begins during this
experiment careful control of the sample
density and thermal environment enables
precise measurement to be made within a
few millions of a degree of the critical
temperature 100 to 1,000 times closer
than is possible on earth we might
compare the experiment to climbing a
mountain the goal is to analyze the area
closest to the peak the critical point
to do that the climber makes minut moves
toward that point as the climber gets
closer some unusual things happen it's
fascinating xenon near the critical
point is a billion times softer than
water the system doesn't know whether it
wants to be a liquid or a vapor and it
readily goes back and forth between the
two and has nearly an infinite heat
capacity in the process of this sloshing
back and forth it turns milky white it's
in this state that important
measurements will be made as the
temperature of the fluid sample and the
xeno experiment approaches the critical
temperature density fluctuations
increase dramatically a laser serves as
a
gentle probe that is sent into the
sample to measure those fluctuations the
sample becomes turbid or cloudy and
scatters light strongly this experiment
can be compared to the familiar
twinkling of stars we see in a clear
night sky the twinkle we see on earth is
due to fluctuations in the density of
the atmosphere during the experiment
laser light that is being scattered by
the sample actually twinkles here the
twinkling is due to density changes in
the fluid as it nears the critical
temperature the Zeno instrument will
measure and analyze the brightness and
frequency of the twinkle as the fluid
nears the critical temperature under the
direction of Professor gammon a team
from the University of Maryland defines
the science requirements for the
experiment and developed the flight
instrument the instrument was fabricated
and tested by Ball Aerospace the heart
of the experiment is a high pressure
sample sale located in the thermostat
the this sample is eliminated by a laser
which is brought around through the
apparatus with mirrors and a beam
splitter and in along the axis from
either end the sample is located close
to the center of this thermostat and
scatters light to this photo multiplier
at a small angle or through a bending
mirror to a second photo multiplier so
that we can see two angles at once the
other principle detectors in the
experiment are photo diodes which sample
the light behind this partially
transmitting mirror and there's one at
the other end as well the Zeno
instrument will fly aboard the space
shuttle Columbia as part of the second
United States microgravity payload this
series of payloads has been sponsored by
the NASA office of life and microgravity
Sciences and applications these payloads
include some of the most challenging
experiments to be conducted in space
during this decade Zeno will provide
data that is not observable on earth
theories will be challenged and
experience will be expanded improved
understanding of second-order
transitions will help in here
theories that may have an impact on many
scientific fields
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