ROOM
90
Space Science
light detectors. The maximum distance is governed
by ice properties such as scattering and attenuation.
As these properties determine how far away a signal
can be detected, they determine how far a detector
grid can be spaced and therefore how big a detector
can be, given a fixed budget. Even with technological
progress it seems unlikely that it will become feasible
to build a Cherenkov light detector that will be big
enough to measure interactions that only occur
about once every year in 100 km
3
of ice.
Using ice as a detector is advantageous for
a number of reasons, not least because it is
available in large quantities at high purity and
no cost, but also because scientists can turn
to other reaction products that result from a
neutrino interaction: radio signals. The charged
particles that are created after a neutrino
interaction not only create a flash of light but also
a short broadband radio pulse, mostly at MHz
frequencies. This is caused by something called
the charge-excess, which in basic terms relates
to how the interaction of a once neutral neutrino
will accumulate charge as it traverses a dense
medium like our atmosphere.
In doing so, the neutrino initiates an
electromagnetic shower as it collects electrons
from the surrounding medium and leaves positively
charged ions behind. In this charge separation,
a changing current is created along the shower
axis, which leads to an emissions of radio waves.
In contrast to light, radio emission travel longer
distances through ice before being attenuated
which therefore allows for larger volumes of ice to
act as instruments, with the same number of signal
detectors, thus reducing costs.
The tricky thing about radio emission, however,
is that it is not particularly unique. While it is highly
unlikely for anything but an elementary particle
to cause a flash of light in dark ice, every electrical
machine creates radio emission. Since radio waves
can travel larger distances, it is possible to confuse a
neutrino signal with something man-made, like the
signal from a spark plug. Thankfully, modern data-
processing technology has advanced so that it has
become feasible to pick-out distinct features of the
radio emission that make neutrino signals unique.
This technological advancement combined with
a place (on Earth) associated with minimal human
activity, has subsequently lead to the development of
the ARIANNA project situated on the Ross ice-shelf.
ARIANNA
Currently, the ARIANNA detector is in its pilot-
phase. Located in a very specific corner on the
Ross ice-shelf with pure ice and shielded by
Cosmogenic neutrinos
are linked to ultra-high
energy cosmic rays - the
most energetically charged
elementary particles known in
the Universe today
Diagram of one
ARIANNA station and its
detection capabilities. The
autonomous stations are
sensitive to the radio
signals generated by
incoming neutrinos (Greek
letter ‘nu’, green) and
cosmic rays (CR, purple).
By studying the signals in
different antennas, it is
possible to distinguish the
signals and reconstruct
the arrival direction. The
full array will consists of
more than 1000 stations.
View at camp and the
transantarctic mountains.
The dot in the middle is a
station.
Neutrino > particle reaction > shower > radio signal
LPDA
antennas lie
just under
the surface
Solar
panel
and wind
turbine
Savannah Shively/ARIANNA
Chris Persichilli/ARIANNA
