7 The Neutrino Is Born as an Idea
53
understand as much as possible about these new rays. In 1902, Pierre and Marie
Curie showed that beta radiation was nothing more than electrons. Later, it
was determined that those electrons come out of the nucleus of the radioactive
atoms. Bacquerel was awarded Nobel Prize for that in 1903 (together with
Pierre and Marie Curie) for the discovery of radioactivity.
In 1914, James Chadwick, another student of Rutherford, was studying the
beta rays in the decay of nitrogen and lithium. These rays were supposed to
have discrete energy, since they were thought to emerge from a nucleus with
the nucleus breaking up into another nucleus and the beta rays. Energy conservation then predicts that beta rays should have a fixed energy corresponding to
the difference between the masses of the two nuclei; however, James Chadwick,
after many studies of this radiation with Lise Meitner, Otto Hahn, Wilson, and
von Baeyer, showed that this is not the case. Rather than being discrete, the
electron energy spectrum was continuous. Why it was continuous became a
puzzling observation since it flew in the face of the long believed principle
of energy conservation. If one particle at rest decays into two particles, then
its mass gets divided as two specific fixed energies and does not spread into
different energies, as was observed by Chadwick, for beta decaying nuclei.
Many people started worrying about this puzzle. Pauli too had been worrying
about Chadwick’s beta decay results. In fact, Bohr was arguing that perhaps
energy conservation was violated in beta decay but Pauli thought that was
too drastic. In his December night letter, he suggested another equally drastic
alternative, which he himself called “a desperate remedy” and suggested that
another particle not known then, the neutrino, might also be coming out of
the nucleus during their beta decay and carrying the missing part of the energy.
(Pauli actually called this particle a “neutron” but it was later dubbed as the
“neutrino” by Enrico Fermi (see Fig. 7.1)).
7.2 December Night Ball and Pauli Letter
It was a cold December night in 1930, in Zurich, Switzerland, when physicist
Wolfgang Pauli, a 30-year-old physicist, wrote a letter to a gathering of
physicists in Tubingen that he was unable to attend the conference due to a ball
that had must attend in Zurich. He wanted to let them know that he had found
a way to resolve the annoying missing energy puzzle in beta decay that has been
a crisis in nuclear physics for a long time. He wanted to propose a new particle
called the “neutron” (later known as “neutrino”), which has spin half, no mass
and resides inside the atomic nucleus. This particle is always emitted with the
electron in beta decay, taking away the missing energy, thereby resolving the
53
understand as much as possible about these new rays. In 1902, Pierre and Marie
Curie showed that beta radiation was nothing more than electrons. Later, it
was determined that those electrons come out of the nucleus of the radioactive
atoms. Bacquerel was awarded Nobel Prize for that in 1903 (together with
Pierre and Marie Curie) for the discovery of radioactivity.
In 1914, James Chadwick, another student of Rutherford, was studying the
beta rays in the decay of nitrogen and lithium. These rays were supposed to
have discrete energy, since they were thought to emerge from a nucleus with
the nucleus breaking up into another nucleus and the beta rays. Energy conservation then predicts that beta rays should have a fixed energy corresponding to
the difference between the masses of the two nuclei; however, James Chadwick,
after many studies of this radiation with Lise Meitner, Otto Hahn, Wilson, and
von Baeyer, showed that this is not the case. Rather than being discrete, the
electron energy spectrum was continuous. Why it was continuous became a
puzzling observation since it flew in the face of the long believed principle
of energy conservation. If one particle at rest decays into two particles, then
its mass gets divided as two specific fixed energies and does not spread into
different energies, as was observed by Chadwick, for beta decaying nuclei.
Many people started worrying about this puzzle. Pauli too had been worrying
about Chadwick’s beta decay results. In fact, Bohr was arguing that perhaps
energy conservation was violated in beta decay but Pauli thought that was
too drastic. In his December night letter, he suggested another equally drastic
alternative, which he himself called “a desperate remedy” and suggested that
another particle not known then, the neutrino, might also be coming out of
the nucleus during their beta decay and carrying the missing part of the energy.
(Pauli actually called this particle a “neutron” but it was later dubbed as the
“neutrino” by Enrico Fermi (see Fig. 7.1)).
7.2 December Night Ball and Pauli Letter
It was a cold December night in 1930, in Zurich, Switzerland, when physicist
Wolfgang Pauli, a 30-year-old physicist, wrote a letter to a gathering of
physicists in Tubingen that he was unable to attend the conference due to a ball
that had must attend in Zurich. He wanted to let them know that he had found
a way to resolve the annoying missing energy puzzle in beta decay that has been
a crisis in nuclear physics for a long time. He wanted to propose a new particle
called the “neutron” (later known as “neutrino”), which has spin half, no mass
and resides inside the atomic nucleus. This particle is always emitted with the
electron in beta decay, taking away the missing energy, thereby resolving the