FEATURE NEUTRINOS
Savannah River, South Carolina,
14 June 1956. Frederick Reines
had spent much of the 1950s
exploding nuclear bombs in the
Pacific Ocean. One, with 700 times
the destructive power of the
Hiroshima bomb, had vaporised
an entire island, creating a
radioactive mushroom cloud 150
kilometres across and gouging
a hole in the ocean floor more
than two kilometres wide and
as a deep as a 16-storey building.
But Reines was sick to death of it.
He persuaded the leader of the
theoretical division at the bomb
lab in Los Alamos, New Mexico,
to give him time off from testing
weapons to think about physics.
For several months, he sat in
a bare office staring at a blank
piece of paper, asking himself the
question: “What do you want to do
with your life?”
Reines flew to a conference in
Princeton, New Jersey, and the
plane developed engine trouble,
forcing a stopover in Kansas City.
On the plane was another bomb
scientist called Clyde Cowan, who
Reines had met but never talked
to properly. In Kansas City, the pair
hit it off. When their conversation
turned to fundamental physics,
the question that came up was:
“What is the hardest experiment
in the world?” Both instantly
agreed: detecting the neutrino.
There and then, they decided
to use their ‘can do’ attitude,
developed during the bomb
programme, to try and bag
nature’s most elusive particle.
Their first idea was to
place a neutrino detector 50
metres from Ground Zero of a
nuclear explosion. They had a
50-metre-deep vertical shaft dug
at the Nevada bomb testing site.
If, at the instant of detonation, the
detector were dropped into the
shaft, it would be in freefall andisolated from the shockwaves
thundering through the ground.
At the bottom of the shaft, the
detector’s fall would be cushioned
by a thick bed of foam rubber
and feathers. Reines and Cowan
intended to retrieve the detector
several days later when radiation
levels were deemed low enough to
risk a quick in-and-out foray.
Fortunately, it never came to
this. Reines and Cowan decided
to use a nuclear reactor rather
than a bomb. Although a nuclear
reactor was a source of neutrinos
1,000 times weaker than a nuclear
bomb, it had the advantage that a
detector might soak up neutrinos
for months or even years, rather
than the few seconds available
at a bomb blast. Reines and
Cowan eventually found an ideal
reactor at the Savannah River
Plant, a facility used to make
the tritium and plutonium for
nuclear bombs. As a tribute to the
local cuisine of South Carolina,
they even planned to shield their
experiment from stray neutrons
with sacks of black-eyed peas.
Sadly, wet sawdust was easier and
cheaper to obtain in the required
quantities. It was at P Reactor at
the Savannah River Plant that, on
14 June 1956, Reines and Cowan
finally bagged neutrinos (strictly
speaking, antineutrinos).
Their telegram to Wolfgang
Pauli read: “We are happy to
inform you that we have definitely
detected neutrinos from fission
fragments by observing the
inverse beta decay of protons...
Frederick Reines, Clyde Cowan.”
The next day, Pauli sent a reply
from ETH Zürich, the Swiss Federal
Institute of Technology: “Frederick
REINES, and Clyde COWAN,
Box 1663, LOS ALAMOS, New
Mexico. Thanks for the message.
Everything comes to him who
knows how to wait. Pauli.”DISCOVERING THE NEUTRINO
ABOVE Nearly a mile
beneath the Gran Sasso
mountain and 60 miles
outside of Rome, this
stainless steel sphere is
part of the neutrino
detector used to detect
geoneutrinosBELOW The US flag hangs
proudly on the P Reactor
at Savannah River Site,
used to detect the
neutrino in 1956, one of
the most significant
experiments in modern
physics