Key Questions We Want to Answer:
helium-4 atoms can be mixed together and cooled into a liquid. When they
are cooled to very low temperature, they become a superfluid. However,
when this mixture is further cooled there is a point where helium-3
and helium-4 act like oil and water and separate into two phases. The
tricritical point is where a combination of precise mixture, pressure,
and temperature levels bring these atoms to a remarkable spot where
the transitions between the superfluid state and the two-phase state meet.
We Already Know:
The mission Experiments Along Co-existence near Tricriticality (EXACT)
will perform rigorous tests at the tricritical point, to further test
the Renormalization Group theory-for which the Nobel prize was
awarded in 1982. The theory allows predictions to be made of the
critical properties of the mixture near the tricritical point.
this experiment already has been conducted on Earth, it is expected
to provide far more accurate data in the microgravity of space.
When testing this phenomenon on the ground, gravity causes stratification
of the mixture. This gradient in density makes it difficult to study
the properties of the mixture because they vary through the sample.
What We Hope to Find Out:
By conducting this experiment in the absence of gravity, the separation
of these atoms can be more easily studied, since they will not have
gravity pulling the heavier atoms to the bottom. Observing this
phase transition in a microgravity environment provides greater
details to this phenomenon because the sample will remain uniform.
We'll Conduct Our Experiment:
The experiment will be quite small, the size of a postage stamp.
The purpose for the petite sample size is that, even in microgravity,
a larger sample would tend to
form layers, i.e., surface forces in nonuniform samples.
understanding this phenomenon will add a new facet to the investigation
of current theories.