The neutrino is a subatomic particle first proposed by Wolfgang Pauli on December 4, 1930.
 The particle was required to resolve the problem of missing energy in observations of beta decay, when a neutron decays into a proton and an electron.
 The new hypothetical particle was required to preserve the fundamental law of conservation of energy.
Enrico Fermi renamed it the neutrino, Italian for "little neutral one", and in 1934, proposed his theory of beta decay by which  the electrons emitted from the nucleus were created by the decay of a neutron into a proton, an electron, and a neutrino:
n⁰
 → 
p⁺
 + 
e⁻
 + 
ν
ₑ
The neutrino accounted for the missing energy, but Fermi's theory described a particle with little mass and no electric charge that appeared to be impossible to observe directly.
In a 1934 paper, Rudolf Peierls and Hans Bethe calculated that neutrinos could easily pass through the Earth, and concluded "there is no practically possible way of observing the neutrino."

In 1951, Reines and his colleague Clyde Cowan decided to see if they could detect neutrinos and so prove their existence.
 At the conclusion of the Greenhouse test series, Reines had received permission from the head of T Division, J. Carson Mark, for a leave in residence to study fundamental physics.
  "So why did we want to detect the free neutrino?"
he later explained, "Because everybody said, you couldn't do it."

According to Fermi's theory, there was also a corresponding reverse reaction, in which a neutrino combines with a proton to create a neutron and a positron:
ν
ₑ + 
p⁺
 → 
n⁰
 + 
e⁺
The positron would soon be annihilated by an electron and produce two 0.51 MeV gamma rays, while the neutron would be captured by a proton and release a 2.2 MeV gamma ray.
This would produce a distinctive signature that could be detected.
They then realised that by adding cadmium salt to their liquid scintillator they would enhance the neutron capture reaction, resulting in a 9 MeV burst of gamma rays.
For a neutrino source, they proposed using an atomic bomb.
Permission for this was obtained from the laboratory director, Norris Bradbury.
 Work began on digging a shaft for the experiment when J. M. B. Kellogg convinced them to use a nuclear reactor instead of a bomb.
Although a less intense source of neutrinos, it had the advantage in allowing for multiple experiments to be carried out over a long period of time.

In 1953, they made their first attempts using one of the large reactors at the Hanford nuclear site in what is now known as the Cowan–Reines neutrino experiment.
Their detector now included 300 litres (66 imp gal; 79 US gal) of scintillating fluid and 90 photomultiplier tubes, but the effort was frustrated by background noise from cosmic rays.
With  encouragement from John A. Wheeler, they tried again in 1955, this time using one of the newer, larger 700 MW reactors at the Savannah River Site that emitted a high neutrino flux of 1.2 x 10¹² / cm² sec.
They also had a convenient, well-shielded location 11 metres (36 ft) from the reactor and 12 metres (39 ft) underground.
On June 14, 1956, they were able to send Pauli a telegram announcing that the neutrino had been found.
When Bethe was informed that he had been proven wrong, he said, "Well, you shouldn't believe everything you read in the papers."

From then on Reines dedicated the major part of his career to the study of the neutrino's properties and interactions, which work would influence study of the neutrino for future researchers to come.
Cowan left Los Alamos  in 1957 to teach at George Washington University, ending their collaboration.
On the basis of his work in first detecting the neutrino, Reines  became the head of the physics department of Case Western Reserve University from 1959 to 1966.
 At Case, he led a group that was the first to detect neutrinos created in the atmosphere by cosmic rays.
Reines had a booming voice, and had been a singer since childhood.
During this time, besides performing his duties as a research supervisor and chairman of the physics department, Reines sang in the
The neutrino is a subatomic particle first proposed by Wolfgang Pauli on December 4, 1930.  The particle was required to resolve the problem of missing energy in observations of beta decay, when a neutron decays into a proton and an electron.  The new hypothetical particle was required to preserve the fundamental law of conservation of energy. Enrico Fermi renamed it the neutrino, Italian for "little neutral one", and in 1934, proposed his theory of beta decay by which  the electrons emitted from the nucleus were created by the decay of a neutron into a proton, an electron, and a neutrino:
n⁰
 → 
p⁺
 + 
e⁻
 + 
ν
ₑ
The neutrino accounted for the missing energy, but Fermi's theory described a particle with little mass and no electric charge that appeared to be impossible to observe directly. In a 1934 paper, Rudolf Peierls and Hans Bethe calculated that neutrinos could easily pass through the Earth, and concluded "there is no practically possible way of observing the neutrino."
In 1951, Reines and his colleague Clyde Cowan decided to see if they could detect neutrinos and so prove their existence.  At the conclusion of the Greenhouse test series, Reines had received permission from the head of T Division, J. Carson Mark, for a leave in residence to study fundamental physics.   "So why did we want to detect the free neutrino?" he later explained, "Because everybody said, you couldn't do it."
According to Fermi's theory, there was also a corresponding reverse reaction, in which a neutrino combines with a proton to create a neutron and a positron:
ν
ₑ + 
p⁺
 → 
n⁰
 + 
e⁺
The positron would soon be annihilated by an electron and produce two 0.51 MeV gamma rays, while the neutron would be captured by a proton and release a 2.2 MeV gamma ray. This would produce a distinctive signature that could be detected. They then realised that by adding cadmium salt to their liquid scintillator they would enhance the neutron capture reaction, resulting in a 9 MeV burst of gamma rays. For a neutrino source, they proposed using an atomic bomb. Permission for this was obtained from the laboratory director, Norris Bradbury.  Work began on digging a shaft for the experiment when J. M. B. Kellogg convinced them to use a nuclear reactor instead of a bomb. Although a less intense source of neutrinos, it had the advantage in allowing for multiple experiments to be carried out over a long period of time.
In 1953, they made their first attempts using one of the large reactors at the Hanford nuclear site in what is now known as the Cowan–Reines neutrino experiment. Their detector now included 300 litres (66 imp gal; 79 US gal) of scintillating fluid and 90 photomultiplier tubes, but the effort was frustrated by background noise from cosmic rays. With  encouragement from John A. Wheeler, they tried again in 1955, this time using one of the newer, larger 700 MW reactors at the Savannah River Site that emitted a high neutrino flux of 1.2 x 10¹² / cm² sec. They also had a convenient, well-shielded location 11 metres (36 ft) from the reactor and 12 metres (39 ft) underground. On June 14, 1956, they were able to send Pauli a telegram announcing that the neutrino had been found. When Bethe was informed that he had been proven wrong, he said, "Well, you shouldn't believe everything you read in the papers."
From then on Reines dedicated the major part of his career to the study of the neutrino's properties and interactions, which work would influence study of the neutrino for future researchers to come. Cowan left Los Alamos  in 1957 to teach at George Washington University, ending their collaboration. On the basis of his work in first detecting the neutrino, Reines  became the head of the physics department of Case Western Reserve University from 1959 to 1966.  At Case, he led a group that was the first to detect neutrinos created in the atmosphere by cosmic rays. Reines had a booming voice, and had been a singer since childhood. During this time, besides performing his duties as a research supervisor and chairman of the physics department, Reines sang in the 
Frederick Reines