96
R. N. Mohapatra
information, how to quantify the number of neutrinos coming from the core.
Once emitted by the core, the neutrinos fly straight out and reach the detectors
on Earth since their interactions with matter is so weak.
In 1938, the challenge of quantifying the number of neutrinos coming from
the core of the Sun was taken up by Hans Bethe and Charles Critchfield, a
student of George Gamow. They analyzed the various fusion nuclear processes
(a subject on which Bethe was an expert) and ended up with a number, which
was too high compared to the known value of the solar luminosity. Bethe
was a bit disappointed and called it only an illustrative example. As it turned
out, however, the same year a higher solar core temperature measurement
was announced, giving a higher luminosity, making the Bethe–Critchfield
calculation agree better with observations. In 1967, Bethe was awarded the
Nobel Prize for his works on energy production in stars. Incidentally, it is
interesting that the Bethe–Critchfield paper makes no mention of the neutrino
as a by-product of the fusion reaction. Once the Fermi theory of neutrino
reactions was accepted by the community, it was clear that with every four–
proton fusion that gives helium, there would be two neutrinos. Since the
missing mass between four protons and the helium nucleus was known by that
time from solar luminosity measurements, one could calculate the number
of neutrinos being emitted by the Sun. It is 70 billion neutrinos per square
centimeter per second, passing through the Earth. These neutrinos have
different energies.
The question then was, could this neutrino emission be confirmed by
experimental measurement? A detailed calculation of number of neutrinos
from the Sun was needed together with an experiment to measure them. In
1962, Willy Fowler (whose research associate at Caltech was John Bahcall)
asked Bahcall, Icko Iben, and Dick Sears to do a detailed calculation of the
solar neutrino flux. So began the involvement of John Bahcall with the solar
neutrinos, a lifelong interest of his. He teamed up with experimental chemist
Ray Davis (Fig. 13.1) in a project to detect solar neutrinos, and history was
made with the measurement of the neutrino flux from the Sun. John Bahcall
and Ray Davis became the face of the solar neutrino puzzle. An account of their
solar neutrino journey can be found in the book written by John Bahcall [16].
Ray Davis was born in 1914 in Washington, D.C., and was trained as a
physicist and chemist, receiving his BS degree from the University of Maryland
in 1938. His fascination with neutrinos began when he was at the Brookhaven
National Laboratory, starting in 1948. He wrote about his getting interested
in neutrino research, “Thus began a long career of doing just what I wanted
to do and getting paid for it.” He started looking for solar neutrinos in 1965,
at a 4850 feet deep mine shaft in Homestake, South Dakota, using 100,000
R. N. Mohapatra
information, how to quantify the number of neutrinos coming from the core.
Once emitted by the core, the neutrinos fly straight out and reach the detectors
on Earth since their interactions with matter is so weak.
In 1938, the challenge of quantifying the number of neutrinos coming from
the core of the Sun was taken up by Hans Bethe and Charles Critchfield, a
student of George Gamow. They analyzed the various fusion nuclear processes
(a subject on which Bethe was an expert) and ended up with a number, which
was too high compared to the known value of the solar luminosity. Bethe
was a bit disappointed and called it only an illustrative example. As it turned
out, however, the same year a higher solar core temperature measurement
was announced, giving a higher luminosity, making the Bethe–Critchfield
calculation agree better with observations. In 1967, Bethe was awarded the
Nobel Prize for his works on energy production in stars. Incidentally, it is
interesting that the Bethe–Critchfield paper makes no mention of the neutrino
as a by-product of the fusion reaction. Once the Fermi theory of neutrino
reactions was accepted by the community, it was clear that with every four–
proton fusion that gives helium, there would be two neutrinos. Since the
missing mass between four protons and the helium nucleus was known by that
time from solar luminosity measurements, one could calculate the number
of neutrinos being emitted by the Sun. It is 70 billion neutrinos per square
centimeter per second, passing through the Earth. These neutrinos have
different energies.
The question then was, could this neutrino emission be confirmed by
experimental measurement? A detailed calculation of number of neutrinos
from the Sun was needed together with an experiment to measure them. In
1962, Willy Fowler (whose research associate at Caltech was John Bahcall)
asked Bahcall, Icko Iben, and Dick Sears to do a detailed calculation of the
solar neutrino flux. So began the involvement of John Bahcall with the solar
neutrinos, a lifelong interest of his. He teamed up with experimental chemist
Ray Davis (Fig. 13.1) in a project to detect solar neutrinos, and history was
made with the measurement of the neutrino flux from the Sun. John Bahcall
and Ray Davis became the face of the solar neutrino puzzle. An account of their
solar neutrino journey can be found in the book written by John Bahcall [16].
Ray Davis was born in 1914 in Washington, D.C., and was trained as a
physicist and chemist, receiving his BS degree from the University of Maryland
in 1938. His fascination with neutrinos began when he was at the Brookhaven
National Laboratory, starting in 1948. He wrote about his getting interested
in neutrino research, “Thus began a long career of doing just what I wanted
to do and getting paid for it.” He started looking for solar neutrinos in 1965,
at a 4850 feet deep mine shaft in Homestake, South Dakota, using 100,000