The Sudbury Neutrino Observatory (SNO)
What is the SNO?
The Sudbury Neutrino Observatory is an underground laboratory
that began operating in 1999 to study and detect solar neutrinos which are
particles that do not have an electric charge and nearly no mass. These
invisible particles are produced in the suns core as byproduct of nuclear
fusion and pass through the earth nearly at the speed of light. Due to the lack
of mass and electric charge, they are extremely difficult to study which is why
the Sudbury Neutrino Observatory was built for. The purpose of the SNO is to
help scientists and astronomers understand the processes that take place in the
sun. It is operated by around 130 Canadian,
American and British scientists.
Development began in 1990 and was completed in
1998. It cost a total of $73,000,000 and was supported and funded by the
Natural Sciences and Engineering Research Council of Canada, the Northern
Ontario Heritage Foundation, United States Department of Energy, Ontario Power
Generation and several more.
In the image above, you can see what the detector looks like along with the 9000 light sensors. Below is a diagram that displays the structures design and depth
Construction:
The Sudbury Netrino Observatory was built 2km underneath a
mine in Sudbury called Creighton Nickel Mine. The detector is made up of a
large acrylic ball that spans 12 m in diameter. The sphere hangs with the
support of 10 ropes made of synthetic fiber. There are over 9000 photo
multiplier tubes (or light sensors) right along the outside of the sphere that faces
towards it. To detect the presence of neutrinos, these sensors observe how the
neutrinos react with the water. When neutrinos interact with heavy water, it
creates Cherenkov radiation, in other words, flashes of light emitted from the
tank due to the interaction between neutrino and heavy water.
There were many
precautions taken in order to prevent unwanted signals from other sources and elements.
The main one is the depth of the detector. SNO was built deep underground to
shield the detector from noise of cosmic rays. Another is that the lab is kept
extremely clean to prevent signals from the dust of the mine from interfering with
the sensors.
This image shows just how deep the SNO is built.
Contribution:
The SNO has accomplished a lot in the field of neutrinos and
has made important discoveries about their production along with information
about the core of the sun. According to Astro-Canada, in the early 80s, “it was
realized that the number of solar neutrinos detected by various laboratories
were less than predicted by theoretical calculations”. This caused a debate
about the suns production of neutrinos. Scientists could not confirm whether we
simply did not understand our sun properly or if these neutrinos were changing
form as they reached earth causing the amount to lower. The SNO discovered that
neutrinos have some mass and can change form when they pass through the earth.
Although its primary goal has already been met, scientists
continue using its data in order to learn as much about neutrinos as possible.
Today,
the Sudbury Neutrino Observatory has been expanded and is being operated under
a new name, SNOLAB. The new observatory perform the same experiments and
studies as SNO, however the laboratory has been expanded. A Queens University
press release states that the lab will be “expanded by nearly 150% “,
http://astro-canada.ca/_en/a2115.php
http://physics.carleton.ca/sno/about-sno-project/sno-neutrino-detector
http://www.sno.phy.queensu.ca/sno/press_release/SNOBackgrounderNov15f.pdf
