9
The Neutrino is Discovered
The search for the intriguing particle, the neutrino, caught the imagination
of physicists in the 1940s, even though they were aware that it was going
to be a difficult task. The first nuclear explosion was carried out on July 16,
1945. It was already known that if Pauli’s hypothesis was correct, the nuclear
explosion should produce plenty of neutrinos, since a nuclear decay process
was involved in both nuclear explosion and neutrino production. Fermi and
Hans Bethe thought the nuclear explosion might be a good place to catch one
of the neutrinos emitted.
9.1 How to Detect a Neutrino
The neutrino is an electrically neutral particle. Therefore unlike an electron
or proton, if a neutrino flies through a medium, it will not “tear” off charged
particles from the atoms in the medium and leave a track. So how does one
detect a neutrino? In 1946, Bruno Pontecorvo, an early assistant of Enrico
Fermi, who was then in Canada working in the Chalk River reactor, suggested
that it may be possible to discover the neutrino using an inverse beta decay
reaction. In such a reaction, an anti-neutrino hitting a chlorine nucleus
converts it into an argon nucleus, and at the same time emits a positron.
The positron would then annihilate with electrons in the detector to produce
gamma rays, which can be detected.
Pontecorvo had a complex life. Born to an Italian Jewish family, he spent his
early research career with Enrico Fermi, working on neutrons. Subsequently,
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_9
63
The Neutrino is Discovered
The search for the intriguing particle, the neutrino, caught the imagination
of physicists in the 1940s, even though they were aware that it was going
to be a difficult task. The first nuclear explosion was carried out on July 16,
1945. It was already known that if Pauli’s hypothesis was correct, the nuclear
explosion should produce plenty of neutrinos, since a nuclear decay process
was involved in both nuclear explosion and neutrino production. Fermi and
Hans Bethe thought the nuclear explosion might be a good place to catch one
of the neutrinos emitted.
9.1 How to Detect a Neutrino
The neutrino is an electrically neutral particle. Therefore unlike an electron
or proton, if a neutrino flies through a medium, it will not “tear” off charged
particles from the atoms in the medium and leave a track. So how does one
detect a neutrino? In 1946, Bruno Pontecorvo, an early assistant of Enrico
Fermi, who was then in Canada working in the Chalk River reactor, suggested
that it may be possible to discover the neutrino using an inverse beta decay
reaction. In such a reaction, an anti-neutrino hitting a chlorine nucleus
converts it into an argon nucleus, and at the same time emits a positron.
The positron would then annihilate with electrons in the detector to produce
gamma rays, which can be detected.
Pontecorvo had a complex life. Born to an Italian Jewish family, he spent his
early research career with Enrico Fermi, working on neutrons. Subsequently,
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_9
63