Skip to content Skip to navigation

2015 Nobel Prize In Physics Honors Advance In Neutrino

2015 Nobel Prize In Physics Honors Advance In Neutrino

2015 Laureates lift the veil on elusive particle.

Tuesday, October 6, 2015 - 13:45

Sara Rennekamp, Contributing Editor

(Inside Science Currents) -- This year's Nobel Prize in Physics forces the mind to ponder a spectacularly daunting realty: There are billions upon billions of particles dancing around and through us every second of every day that remain quite mysterious.

The 2015 Nobel Prize in Physics went to Takaaki Kajita and Arthur B. McDonald, and honors their research focused on one of the most common particles in the universe: the neutrino.

You can watch the announcement here:

What the heck is a neutrino?

The neutrino is a mystery. When Olga Botner, a member of the Nobel Committee was asked directly what neutrinos are, she replied: "I wish we knew!"

She went on to explain that no one has ever seen a neutrino. They are only detected when they interact with something else, which happens rarely for the ghostly particles. But, there are a few things that scientists have been able to discover about the neutrino.

What they do know is neutrinos are subatomic particles produced by the decay of radioactive elements. The prevailing theory is that most of the neutrinos that exist today were created about 15 billion years ago, shortly after the birth of the universe. Neutrinos are also produced during the birth, life, death and collision of stars, particularly during a supernovae. Technology produced by humans, such as nuclear power stations, particles accelerators and nuclear bombs, can also give birth to new neutrinos.

Physicist Wolfgang Pauli theorized the existence of the neutrino in the 1930s in a letter to the Physics Institute in Zurich that began "Dear Radioactive Ladies and Gentlemen."

The 1995 Nobel Prize in Physics went to US physicist Frederick Reines "for the detection of the neutrino," which happened in experiment he did in 1956 with Clyde L. Cowan using a nuclear reactor.

The 2002 Nobel Prize in Physics went in part to Raymond Davis Jr. and Masatoshi Koshiba for the detection of cosmic neutrinos.

The name

The name "neutrino" is a modification of the Italian word for neutron, "neutrone," which is another particle all together.  Neutrino was coined by physicist Enrico Fermi.

More to come…

UPDATE: 12:45p.m. EDT

Heavy water

During the press conference announcing the Nobel Prize, freshly minted laureate Arthur B. McDonald of Queen's University, who led the Sudbury Neutrino Observatory Collaboration, expressed his gratitude to his team of researchers and to something he called "heavy water." This water, he explained, allowed him to study solar neutrinos.

Heavy water is similar to regular water but, in each molecule the hydrogen atom is exchanged for a heavier isotope called deuterium.

Rather than H2O it is 2H2O or D­2O.  

The deuterium contains both a proton and a neutron. When the neutrinos collide with deuterium, the detector is able to count the neutrinos.

About 1,000 tons of this heavy water was poured into the Sudbury Neutrino Observatory – a 12-meter diameter sphere buried nearly 7,000 feet underground. This subterranean observatory is where McDonald and his team made their Nobel-winning discoveries.

The Super-Kamiokande

A similar feat of engineering supported the other half of the Nobel Prize this year. In Japan, Takaaki Kajita made his observations with the Super-Kamiokande. The Super-K, as it is nicknamed, is also a subterranean observatory located under Mount Kamioka near Hida, in Gifu Prefecture, Japan. It was designed to search for proton decay and study solar and atmospheric neutrinos. It also keeps a watchful eye out for supernovae in the Milky Way galaxy.

Super-K, which is filled with 50,000 tons of ultra-pure water (not heavy water) and monitored by 11,000 particle sensors, is what helped Kajita and his team detect neutrinos from particle showers from the atmosphere.

The sensors detected light produced by the rare interactions between a neutrino and an atom. This allowed the team to distinguish between two different varieties of neutrinos – electron- and muon-neutrinos. 

UPDATE: 3:07p.m. EDT

Reactions from the Laureates

One of my favorite parts of Nobel Day is listening to the interviews of the new laureates by Adam Smith, the chief science officer of Nobel Media.

Here is Arthur B. McDonald who was woken up with the news that he had won the Nobel Prize. The first thing he did was give his wife a hug.

Kajita was checking his e-mails in his office when he received the phone call and said that it was an unbelievable surprise to him.

Both of them were eager to talk about their research into neutrinos and expressed their debt to the massive team of scientists, including particle physicists, nuclear physicists who were able to understand the nuclear reactions that allowed the neutrinos to be detected at all. There were also chemists who helped the team understand the impurities in the water where the reactions took place that might affect the results of the experiments.

Reactions from the rest of us

Here's a cool video that interview several scientists about today's Nobel Prize. One of the scientists interviewed talked about her experience as a PhD student in 1998 when some of the work honored today was first announced.

What does it all mean?

A really great question was asked during the Nobel Press conference. Essentially, what are the practical applications of a discovery such as this?

The University of Hawaii's John Learned, who was part of the SuperKamiokande collaboration, mentioned that there are practical applications of neutrino detection that are being pursued. These include monitoring nuclear reactors and learning more about geophysical processes that occur in the Earth.

Olga Botner, a member of the Nobel committee stressed the importance of striving to understand the world around us.

"Humans have this urge to learn more about the universe we live in and fundamental science is one of the pillars of modern society…if we didn’t have this urge, we would still be living in caves and we would still be afraid of lightening," said Olga Botner, a member of the Nobel committee.

UPDATE: 3:50p.m. EDT

The prize

This is the 108th Nobel Prize in physics that has been awarded since 1901 when the prize was first awarded. No prize was awarded in 1916, 1931, 1934, 1940, 1941 and 1942.

Each Nobel Prize comes with an award of 8.0 million Swedish kronor, which is about $980,000 U.S. dollars. In the case that the Nobel goes to several people, the prize money is split among them.

The laureates also receive a medal, which is unique to each prize. The medal for physics and chemistry was designed by Erik Lindberg and has a depiction of the Greek goddess Isis emerging from the clouds holding a cornucopia in her arms. She is to represent nature. Another woman, who represents "The Genius of Science," holds a veil over Isis' face.

The inscription on the medal is taken from the Sixth Book of the Aeneid by Virgil:

Inventas vitam juvat excoluisse per artes
Inventions enhance life which is beautified through art


UPDATE: 10/8/15 2:15p.m. EDT

The enduring influence of Fred Reines

The late Nobel Laureate Frederick Reines, who first detected the neutrino with Clyde Cowan in 1956, influenced neutrino research in ways that could still be felt today, according to the University of Hawaii's John Learned, who was part of the Super-Kamiokande collaboration.

Reines worked at the University of California Irvine and helped to inspire subsequent neutrino detector projects. The late Herb Chen of the University of California at Irvine helped propose the SNO experiment in the 1980s. Learned worked at Irvine through 1981.

The Irvine-Michigan-Brookhaven (IMB) experiment, located in the Morton Salt mines near Cleveland, Ohio, performed a lot of important early research in neutrinos. In 1983, it found signs of a deficiency of muon neutrinos from the atmosphere. These and other experiments bore the influence of Reines and his collaborators, Learned said. 

Non-accelerator physics

The researchers in these experiments like to point out that they are making discoveries on the nature of matter without having to use particle accelerators, which can get expensive. In this realm of "non-accelerator physics" they are detecting neutrinos already in the environment without having to create new ones by speeding up or smashing particles.

Filed under


Authorized news sources may reproduce our content. Find out more about how that works. © American Institute of Physics

Author Bio & Story Archive