2 Particles as Building Blocks of Matter
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particle collision had the same mass as proton. He called it the neutron. Thus
the picture of elementary particles changed from just protons and electrons
to protons, electrons, and neutrons, all of which were present in all atoms
except hydrogen. Chadwick was awarded the Nobel Prize for this fundamental
discovery in 1935. This pretty much established the roadmap of nuclear physics
for the coming decades.
Born in Manchester England, Chadwick was a shy child. While doing
research under Hans Geiger in Germany, he spent 4 years in a prison camp
for being a British citizen in Germany during the World War I (all British
citizens living in Germany were detained in prison camps in Germany during
World War I). His discovery of the neutron shaped the future of an important
field in physics with many implications for science and society.
Understanding as much about the neutron as possible was the next big task.
There was an urgency to this, since it was a big part of every atomic nucleus.
The neutron had no electric charge, but what else did it have? Soon after it was
discovered, it was found that it behaved like a tiny magnet and in the physics
language, it had a magnetic moment, like a bar magnet, but tiny in size. The
magnetic moment was much too large for an electrically neutral particle—
since electrically neutral particles are not supposed to have magnetic moment.
On the other hand, the neutron’s magnetic moment was almost as big as that
for the proton but was pointed in the opposite direction to that of the proton.
That was a strange feature. As we note later, it was explained by the quark
substructure of protons and neutrons.
2.3 Particle Spin
Particles are always characterized by how much they weigh and that is a
characteristic of their kind, i.e. all electrons have the same mass and so do
all protons. Is there any other property that is intrinsic to the particles of the
same kind? It turns out that each kind of particle has another intrinsic property
called spin. That is as if the particles are like soccer balls that are spinning,
except that the particle spin does not mean the body of the particle is actually
turning at a rapid rate—but only that the particle behaves like it is. Moreover,
just like the Bohr model had discrete orbits for the electron around the proton
in the hydrogen atom, the discreteness is also a property of spin, i.e. the spin
orientations go in steps rather than continuously. For example, electron spins
have only two possibilities, either up or down and nothing in between; so
do protons and neutrons. These particles are said to be carrying spin half.
The number of spin orientations is given by twice the value of spin plus one.
13
particle collision had the same mass as proton. He called it the neutron. Thus
the picture of elementary particles changed from just protons and electrons
to protons, electrons, and neutrons, all of which were present in all atoms
except hydrogen. Chadwick was awarded the Nobel Prize for this fundamental
discovery in 1935. This pretty much established the roadmap of nuclear physics
for the coming decades.
Born in Manchester England, Chadwick was a shy child. While doing
research under Hans Geiger in Germany, he spent 4 years in a prison camp
for being a British citizen in Germany during the World War I (all British
citizens living in Germany were detained in prison camps in Germany during
World War I). His discovery of the neutron shaped the future of an important
field in physics with many implications for science and society.
Understanding as much about the neutron as possible was the next big task.
There was an urgency to this, since it was a big part of every atomic nucleus.
The neutron had no electric charge, but what else did it have? Soon after it was
discovered, it was found that it behaved like a tiny magnet and in the physics
language, it had a magnetic moment, like a bar magnet, but tiny in size. The
magnetic moment was much too large for an electrically neutral particle—
since electrically neutral particles are not supposed to have magnetic moment.
On the other hand, the neutron’s magnetic moment was almost as big as that
for the proton but was pointed in the opposite direction to that of the proton.
That was a strange feature. As we note later, it was explained by the quark
substructure of protons and neutrons.
2.3 Particle Spin
Particles are always characterized by how much they weigh and that is a
characteristic of their kind, i.e. all electrons have the same mass and so do
all protons. Is there any other property that is intrinsic to the particles of the
same kind? It turns out that each kind of particle has another intrinsic property
called spin. That is as if the particles are like soccer balls that are spinning,
except that the particle spin does not mean the body of the particle is actually
turning at a rapid rate—but only that the particle behaves like it is. Moreover,
just like the Bohr model had discrete orbits for the electron around the proton
in the hydrogen atom, the discreteness is also a property of spin, i.e. the spin
orientations go in steps rather than continuously. For example, electron spins
have only two possibilities, either up or down and nothing in between; so
do protons and neutrons. These particles are said to be carrying spin half.
The number of spin orientations is given by twice the value of spin plus one.