Neutrinos

Neutrino, very small particles with no electric charge and little or no mass.

Neutrinos are elementary particles—that is, they cannot be broken into

Smaller particles. Neutrinos are so small that they pass right through

most material. One important kind of neutrino is created in the nuclear

reactions that give the Sun its energy. The Sun produces so many neutrinos

that 70 billion neutrinos pass through every square centimetre (0.15 sq in)

of the surface of Earth every second. Scientists study neutrinos to learn more

about the reactions that give the Sun its energy. Similar reactions occur in

radioactive substances, or materials made up of atoms that spontaneously

change into other particles (Radioactivity). Neutrinos also help scientists

understand these radioactive reactions. Neutrinos play an important part

in the theory scientists have developed to explain the elementary particles

That make up all matter and energy.

Neutrinos are members of a group of elementary particles called

Leptons. Leptons differ from other elementary particles in a property

called spin. Spin is analogous to a measurement of a particle’s angular

Momentum. Scientists measure the spin of particles in units of a constant

Number. This constant is equal to a number called Planck’s constant (h)

divided by two times the constant pi (p). Leptons have spins of +y

(times the unit h/2p). All neutrinos have a spin of +y.

Leptons are part of a larger group of particles called fermions.

Fermions are defined as particles that obey a rule called the

Pauli exclusion principle (named after its developer, Austrian-

born Swiss physicist Wolfgang Pauli). The Pauli exclusion principle

states that two identical particles cannot occupy the same point in

space. The two main types of leptons are those with electric charge

and those without electric charge. Neutrinos are leptons without

electric charge.

Physicists know of three kinds of neutrinos and three...