Page 13 - EUREKA! Fall 2017

it’s the largest cavern at this depth in the world.) SNO was
operated as a cleanroom lab: scientists, technicians and
visitors had to shower and put on clean coveralls, shoes and
hairnets before entering the facility, eliminating the trace
levels of radiation that are emitted from the everyday dirt
on our clothing, skin and hair. The 10 or so neutrinos that
interacted with the detector every day would be stopped
or scattered by the heavy water, Sinclair and his colleagues
hypothesized, producing flashes of light called Cheren-
kov radiation. This light would be detected by an array of
9,600 photomultiplier tubes (PMTs) mounted on a geodesic
support structure surrounding the heavy water vessel. The
flashes would be recorded and analyzed, allowing scien-
tists to extract information about the neutrinos that caused
them. The lab included electronics and computer facilities, a
control room, and water purification systems for both heavy
Mil mossus. Ro elliquis qui volessitaes doluptaquas expernatum si
destrum sit omnimus and regular water. A trailer near the mine shaft on the sur-
face would function as its office.
As often occurs with experiments of this scale and com-
lenge due to the originality of the design and the difficulty plexity, there was a hiccup when the SNO detector was
in estimating costs for things being done for the first time. turned on for the first time in 1999. PMTs are a widely used
Sinclair — who was born in Montreal and grew up in Ot- technology in particle physics experiments but are not
tawa before doing a BSc and PhD in physics at Queen’s and normally submerged in water. The PMTs for SNO were water
then a post-doc at the Niels Bohr Institute in Copenhagen tested at Carleton and seemed to work fine, but in the detec-
— lived in Sudbury with his family during construction and tor, running at about 2,000 volts, they started to spark. “It
commissioning of the SNO experiment. An avid fisherman was a dark day for the SNO experiment,” recalls Sinclair, who
who frequently goes casting in Quebec and northern Can- was approached by McDonald and asked to find a solution.
ada, he brought a rod and reel and occasionally dropped a Sinclair had designed SNO’s innovative water purification
line into local lakes and nearby Georgian Bay. But the real system — the experiment required water with about a million
prize he was seeking was not so simple. times less radioactivity than drinking water — and had the
The neutrino was first postulated by theoretical physicist technical experience (and engineering and chemistry knowl-
Wolfgang Pauli in 1930 to explain why energy did not ap- edge) to address the problem. Eventually, he realized that
pear to be conserved in certain types of radioactive decay, because the PMTs were immersed in water from which all
which is defined as “the spontaneous transformation of an the standard dissolved gasses had been extracted, the gas
unstable atomic nucleus into a lighter one.” The missing permeable seal in the PMTs allowed gas in the tubes to dif-
energy, Pauli suggested, was carried off by a tiny subatomic fuse into the water. This was creating a vacuum at the base of
particle with zero electrical charge (neutrino is Italian for the PMTs, and as the pressure dropped, the voltage capability
“little neutral one”). Thought to be amongst the most abun- also dropped. Sinclair came up with a way to introduce very
dant particles in the universe, they were exceedingly difficult clean nitrogen into the water, and the sparking stopped.
to detect. “About 100 billion neutrinos from the Sun pass With the detector functioning properly, data collection
through your thumbnail every second,” according to the No- and analysis could begin. In 2001, the SNO team released its
bel Prize website, “but you do not feel them because they first results — and, right out of the gate, solved a 30-year-
interact so rarely and so weakly with matter.” old mystery.
Mil mossus. Ro elliquis qui volessitaes doluptaquas The Sudbury Neutrino Observatory consisted of 1,000 Since the early 1970s, scientists have known that electron-
expernatum si destrum sit omnimuscia iusdae. Am nos tonnes of heavy water (acquired from Atomic Energy of neutrinos — one of three types of the particle, along with
aut ma voloribus et optatia denderro berit facimag Canada Limited) inside a spherical acrylic vessel with a the muon-neutrino and the tau-neutrino — are emitted in
niminci liquae nonsequ atemperspit exerruntenis quid
quam qui abor minctor eperfero eseniaesti 12-metre diameter. This vessel was immersed in normal wa- vast numbers by the nuclear reactions that fuel the sun. But
ter in a barrel-shaped cavern 2,070 metres below the Earth’s experiments that detected neutrinos reaching Earth “found
surface. (Thirty metres tall, with a diameter of 22 metres, only a fraction of the number expected from detailed theo-

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