Student: Sheman Ip
Personal Tutor: Prof Mike Barlow
The Neutrino
Strontium 90 is a radioactive source, each Strontium 90 particle transmute itself over time into
another particle called Yttrium 90 by converting a portion of its own mass into an electron. Like
anything in the universe, the laws of physics says that energy must be conserved and can never
be destroyed, which means the energy Strontium 90 has must be the same as the energy of the
electron and Yttrium 90 added together, however this radioactive process is about to break the
law...[1]
Using Einstein's famous equation
, scientists can work out the energy of particles
if they know the mass of it. By finding out the difference in mass between Strontium 90 and
Yttrium 90, scientists predicted the energy of the emitted electron; they have worked it out to
be 0.546 mega electron volts (MeV).[1]
Diagram above shows the difference in mass, between Strontium 90 and Yttrium 90, is
converted into a beta particle or an electron.[1]
Following from this, scientists investigated whenever the emitted electron carried the energy
level of 0.546 MeV. However after many experiments, scientists came to the conclusion that
no electron had that amount of energy; these electrons had much less energy then predicted.
Where has the missing energy gone off to?[1]
Diagram above shows the range of energy of the emitted electrons. The majority of electrons
has energy levels much less than expected (0.546 MeV).[1]
After long hard research, physicists put forward the theory of the neutrino particle. As the
Strontium 90 emitted an electron, it also emits another particle called the anti-neutrino
carrying the ‘missing energy’. However the neutrino must be so small that it passes through
anything solid and it must travel very fast to carry the ‘missing energy.’ Physicists are
challenged to prove the existence of neutrinos, Nobel prize winner Raymond Davis Jr was one
of them.[1]
Inside the sun core, nuclear fusion occurs constantly and releases energy to heat the solar
system up; as a result extreme amounts of neutrinos are produced and this makes it a great
opportunity for Davis to detect neutrinos. In the mid 1960’s Davis was part of the Homestake
experiment; using a tank of 100,000 gallons of carbon tetrachloride a mile underground,
neutrinos from the sun will react with chlorine particles in the tank of carbon tetrachloride and
transmute it into argon gas. By counting the amount of argon gas particles, it is possible to work
out the number of neutrinos detected.[2]
Neutrinos were certainly detected however only a third of expected neutrinos were detected
from the sun. What went wrong? Is there something wrong with the sun or with Davis’
experiment? Davis quoted, “This was the genesis of the so-called "solar neutrino problem".”[2]
The solar neutrino problem was a hot debate between physicists for many years; Davis was
getting tried of it. The standard model of particle physics was challenged and a new theory
was put up, stating that neutrinos change to one of the three ‘favours’ as it travels: electron,
tau and mu. In 2001, the Sudbury Neutrino Observatory were able to detect the three types of
neutrinos using heavy water and the theory was confirmed.[2]
After many years of long research into problems, our understanding of the tiny neutrino
particle has developed over time.
Body text: 500 words
Image captions: 47 words
Bibliography
1. Jon Ogborn and Rick Marshall
2008 - IOP Publishing
Advancing Physics A2
2. Raymond Davis Jr.
Autobiography
http://nobelprize.org/nobel_prizes/physics/laureates/2002/davis-autobio.html