2
1 Introduction to the Pulsars
As fundamental knowledge of understanding pulsars, the history from the discovery
of neutrons to the prediction of neutron stars is introduced briefly in this section.
1.1.1 A Brief Story of Discovering Neutron
Ernest Rutherford (1871−1937), a New Zealand-born British physicist, is known
as the father of nuclear physics. In 1907, he moved to the Victoria University of
Manchester (today the University of Manchester) in the United Kingdom and became
Director of the Department of Physics. He proved with Thomas Royds (1884−1955)
that alpha radiation is helium nuclei. In 1911, he thereby pioneered the Rutherford
model of the atom: the mass of the whole atom almost concentrates on the very small
core area that is called atomic nucleus ; the electrons orbit around the atomic nucleus;
the atomic nucleus is with positive charges and the electrons with negative charges.
However, the stability of in-orbit electrons could not be interpreted by Rutherford’s
model. At the time, Niels Henrik David Bohr (1885−1962) just received his doctorate
degree from the University of Copenhagen in Denmark. And then Bohr was invited
from Rutherford to conduct post-doctoral work at Victoria University of Manchester.
Bohr adopted Rutherford’s nuclear structure to Max Planck’s quantum theory and
hence created the Bohr model of the atom, in which he proposed that energy levels of
electrons are discrete and that the electrons revolve in stable orbits around the atomic
nucleus but can jump from one energy level (or orbit) to another. In 1913, Bohr
published a paper on the structure of atoms and molecules, in which the model of the
atomic structure was demonstrated completely. The issue on the stability of the atomic
structure could be interpreted perfectly by Bohr’s model, and thus the theory of the
atomic structure had been developed and enriched further. According to Rutherford’s
and Bohr’s models, it was commonly known at that time that the mass of the atomic
nucleus should equal the number of protons with positive charges. In fact, it was
shown by the experimental investigations that both are not equal unexpectedly. In
other words, the atomic nuclei should still contain other particles besides the protons
with positive charges. What were exactly “other particles”? It was a really puzzling
problem of physics at that time. The problem was then resolved by James Chadwick
(1891−1974) who had ever earned his master’s degree and doctorate degree under
Rutherford’s supervision, and had been Rutherford’s assistant director of research
at the Cavendish Laboratory of Cambridge University for over a decade. Chadwick
discovered that the “other particles” were exactly neutrons.
In 1930, two nuclear physicists from Germany, Walther Bothe and his student
Herbert Becker, found that an unusual penetrating radiation (or ray) was produced
if the energetic alpha particles emitted from polonium fell on certain light elements,
specifically like beryllium, boron or lithium. Alpha particle is identically a helium4 nucleus composed of two protons and two neutrons, together emitted from the
decay of some radioactive elements. Since the observed radiation was not influenced
by an electric field, it was thought to be gamma ray at that time. Consequently,
1 Introduction to the Pulsars
As fundamental knowledge of understanding pulsars, the history from the discovery
of neutrons to the prediction of neutron stars is introduced briefly in this section.
1.1.1 A Brief Story of Discovering Neutron
Ernest Rutherford (1871−1937), a New Zealand-born British physicist, is known
as the father of nuclear physics. In 1907, he moved to the Victoria University of
Manchester (today the University of Manchester) in the United Kingdom and became
Director of the Department of Physics. He proved with Thomas Royds (1884−1955)
that alpha radiation is helium nuclei. In 1911, he thereby pioneered the Rutherford
model of the atom: the mass of the whole atom almost concentrates on the very small
core area that is called atomic nucleus ; the electrons orbit around the atomic nucleus;
the atomic nucleus is with positive charges and the electrons with negative charges.
However, the stability of in-orbit electrons could not be interpreted by Rutherford’s
model. At the time, Niels Henrik David Bohr (1885−1962) just received his doctorate
degree from the University of Copenhagen in Denmark. And then Bohr was invited
from Rutherford to conduct post-doctoral work at Victoria University of Manchester.
Bohr adopted Rutherford’s nuclear structure to Max Planck’s quantum theory and
hence created the Bohr model of the atom, in which he proposed that energy levels of
electrons are discrete and that the electrons revolve in stable orbits around the atomic
nucleus but can jump from one energy level (or orbit) to another. In 1913, Bohr
published a paper on the structure of atoms and molecules, in which the model of the
atomic structure was demonstrated completely. The issue on the stability of the atomic
structure could be interpreted perfectly by Bohr’s model, and thus the theory of the
atomic structure had been developed and enriched further. According to Rutherford’s
and Bohr’s models, it was commonly known at that time that the mass of the atomic
nucleus should equal the number of protons with positive charges. In fact, it was
shown by the experimental investigations that both are not equal unexpectedly. In
other words, the atomic nuclei should still contain other particles besides the protons
with positive charges. What were exactly “other particles”? It was a really puzzling
problem of physics at that time. The problem was then resolved by James Chadwick
(1891−1974) who had ever earned his master’s degree and doctorate degree under
Rutherford’s supervision, and had been Rutherford’s assistant director of research
at the Cavendish Laboratory of Cambridge University for over a decade. Chadwick
discovered that the “other particles” were exactly neutrons.
In 1930, two nuclear physicists from Germany, Walther Bothe and his student
Herbert Becker, found that an unusual penetrating radiation (or ray) was produced
if the energetic alpha particles emitted from polonium fell on certain light elements,
specifically like beryllium, boron or lithium. Alpha particle is identically a helium4 nucleus composed of two protons and two neutrons, together emitted from the
decay of some radioactive elements. Since the observed radiation was not influenced
by an electric field, it was thought to be gamma ray at that time. Consequently,