64
R. N. Mohapatra
he worked with Frederic and Irene Curie in Paris., He left for the USA when
World War II broke out. He became a fervent communist under the influence
of his brother and defected to the Soviet Union in 1950. He did not return to
the west for a long time. He was a legendary figure in neutrino physics. He is
one of the physicists after whom the neutrino mixing matrix is named, as we
will see below.
Pontecorvo’s suggestion was to use a nuclear reactor as the source of antineutrinos, which will produce a positron by inverse beta decay. By the same
token, one can use the neutrinos coming from the sun to produce an electron
by a different inverse beta decay. Both processes must keep the lepton number
unchanged between the initial and final states. This principle later was used in
the 1960s by Ray Davis to discover the neutrinos from the sun. The general
principle of detecting a neutrino was thus laid out and has been used many
times since. The only catch is that since neutrinos are so weakly interacting,
the detector target must be large, i.e., the more neutrons and protons the
neutrinos and anti-neutrinos hit, the better the chance of a reaction happening.
The detector must also be underground in order to shield it from the large
number of atmospheric neutrinos produced by cosmic ray reactions. The
cosmic ray neutrinos also produce charged leptons which can be confused with
the neutrino inverse beta decay process. For a detector underground, the overlayer of material can shield from atmospheric charged leptons.
9.2 From Hanford to Savanna River
Fred Reines was born in Paterson, New Jersey, in 1918, to Israel and Gaussie
Cohen, two immigrants from a small town in Russia. He received his Ph.D.
in theoretical physics from New York University, and was recruited by Richard
Feynman to work in the Manhattan Project in Los Alamos. After the war
ended, he was employed by the Los Alamos Laboratory. In 1951, he took a
sabbatical leave from Los Alamos to think about physics. That is when he
decided to search for the neutrino [86], and the neutrino remained his passion
for the rest of his career. He and Clyde Cowan teamed up to search for the
neutrino, which was still a mystery particle at that time. The first target in
their attempt to establish that neutrino was a real particle was to work near a
nuclear reactor. Reactors were known to have nuclear weak interactions going
on all the time and were assumed to produce neutrinos in vast numbers.
Nuclear reactors are used for electricity generation, using energy released
in a nuclear reaction that involves weak processes. Essentially, there are four
nuclei (
235 U,
238 U,
239 Pu,
241 Pu) in reactor fuel that undergo fission, and in the
R. N. Mohapatra
he worked with Frederic and Irene Curie in Paris., He left for the USA when
World War II broke out. He became a fervent communist under the influence
of his brother and defected to the Soviet Union in 1950. He did not return to
the west for a long time. He was a legendary figure in neutrino physics. He is
one of the physicists after whom the neutrino mixing matrix is named, as we
will see below.
Pontecorvo’s suggestion was to use a nuclear reactor as the source of antineutrinos, which will produce a positron by inverse beta decay. By the same
token, one can use the neutrinos coming from the sun to produce an electron
by a different inverse beta decay. Both processes must keep the lepton number
unchanged between the initial and final states. This principle later was used in
the 1960s by Ray Davis to discover the neutrinos from the sun. The general
principle of detecting a neutrino was thus laid out and has been used many
times since. The only catch is that since neutrinos are so weakly interacting,
the detector target must be large, i.e., the more neutrons and protons the
neutrinos and anti-neutrinos hit, the better the chance of a reaction happening.
The detector must also be underground in order to shield it from the large
number of atmospheric neutrinos produced by cosmic ray reactions. The
cosmic ray neutrinos also produce charged leptons which can be confused with
the neutrino inverse beta decay process. For a detector underground, the overlayer of material can shield from atmospheric charged leptons.
9.2 From Hanford to Savanna River
Fred Reines was born in Paterson, New Jersey, in 1918, to Israel and Gaussie
Cohen, two immigrants from a small town in Russia. He received his Ph.D.
in theoretical physics from New York University, and was recruited by Richard
Feynman to work in the Manhattan Project in Los Alamos. After the war
ended, he was employed by the Los Alamos Laboratory. In 1951, he took a
sabbatical leave from Los Alamos to think about physics. That is when he
decided to search for the neutrino [86], and the neutrino remained his passion
for the rest of his career. He and Clyde Cowan teamed up to search for the
neutrino, which was still a mystery particle at that time. The first target in
their attempt to establish that neutrino was a real particle was to work near a
nuclear reactor. Reactors were known to have nuclear weak interactions going
on all the time and were assumed to produce neutrinos in vast numbers.
Nuclear reactors are used for electricity generation, using energy released
in a nuclear reaction that involves weak processes. Essentially, there are four
nuclei (
235 U,
238 U,
239 Pu,
241 Pu) in reactor fuel that undergo fission, and in the