Two scientists share Physics Nobel for neutrino work - Takaaki Kajita of Japan and Arthur McDonald of Canada on Tuesday won the Physics Nobel for determining that neutrinos actually have mass.

"The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the Universe," the Royal Swedish Academy of Sciences said.

The findings challenge the so-called Standard Model, the conceptual model of fundamental particles and forces, it said.

Neutrinos are electrically neutral subatomic particles that are created as the result of nuclear reactions.

The existence of neutrino was first proposed in 1930, but its existence was only proved in the 1950s, when nuclear reactors started producing streams of the particles.

Earlier it was believed that neutrinos were massless, but experiments carried out by Kajita in Japan and McDonald in Canada showed that this was not the case.

The two scientists found that many neutrinos blasted out from the Sun "oscillated" en route to become cousin particles called muon-neutrinos and tau-neutrinos.

"It's ironic that in order to observe the Sun you have to go two kilometres underground. It's not what you would expect, that that's the best place to look into the core of the Sun, but low and behold it is," McDonald told the Nobel Foundation in an interview.

"You can chalk up yet another success for quantum mechanics because without it we would not be able to make sense of the experimental results that have led to this prize," said Robert Brown, head of the American Institute of Physics.

According to Nobel committee, the work challenged the concept of theoretical physics.

"The experiments have... revealed the first apparent crack in the Standard Model," the panel said.

"It has become obvious that the Standard Model cannot be the complete theory of how the fundamental constituents of the Universe function."