1.1 Theoretically Predicted Neutron Stars
3
it was not investigated further by Bothe and Becker. Two years later, Irène JoliotCurie (1897−1956) and Frédéric Joliot (1900−1958) in Paris showed their new
experimental results: if this unknown radiation fell on paraffin wax or any other
hydrogen-containing compound, it ejected protons of very high energy. Paraffin wax
is a hydrocarbon high in hydrogen content, hence offers a target dense with protons.
On hearing of the Joliot–Curie couples’ results, Chadwick at the Cavendish Laboratory did not believe the gamma-ray hypothesis. Chadwick and his colleagues had
already conducted experiments on disintegrating light elements using alpha particles
emitted from polonium, and also developed more accurate and efficient methods for
detecting, counting and recording the ejected protons. Chadwick quickly performed
repeatedly the Joliot–Curie couples’ experiment: the hydrogen and helium atoms
were respectively disintegrated by using the ray produced from alpha particles falling
on the beryllium atoms, and as a result, the hydrogen and helium nuclei were ejected.
Since a gamma ray had to have impossibly high energy and momentum to scatter the
massive protons, the gamma-ray hypothesis was untenable. If it was assumed that the
new rays were the neutral particles without charges and their mass almost equal to the
mass of protons, the experimental results could be interpreted reasonably. Chadwick
performed a series of experiments to measure the range of these protons, the velocity
of hydrogen and helium nuclei, and the mass of the new particles. Meanwhile, he
also measured how the new particles impacted the atoms of various gasses. He finally
concluded that the new particles are not composed of gamma rays, but uncharged
particles with about the same mass as the protons. So, these uncharged particles were
named neutrons . In 1932, Chadwick published a classic paper in Nature, “Possible
Existence of a Neutron”, and thereby declared the neutrons were discovered [1].
Therefore, Chadwick won the Nobel Prize in Physics for the discovery in 1935.
Currently, it is measured more accurately by the experiments that the neutron’s
mass is 1.674927211 × 10
−27 kg, the proton’s mass 1.672621637 × 10
−27 kg and
the electron’s mass 9.10938215 × 10
−31 kg. Obviously, neutrons and protons have
almost equal mass, and the mass of electrons is only 1/1836 of the protons. The
atomic diameter is about the order of 10
−10 m, and the atomic nucleus only has 10
–4
of the atomic size. Nevertheless, the mass of the entire atom almost concentrates on
the atomic nucleus, and hence its density is very high, up to the order of 10
12 kg/cm
3 .
1.1.2 Neutron Stars in the Universe
From the atomic structure size, it can be shown that the vast majority of the interior
of the atom is empty. Hydrogen is the lightest element on the periodic table and
has one proton and no neutron. The elements except for hydrogen on the periodic
table contain the neutrons. For example, helium-4 located in the second period has
two protons and two neutrons. If the electrons and protons inside the atoms can
be combined to become neutrons, the substance consists of neutrons. And thus, the
atomic sizes would be compressed into very small nuclei. It needs enough high
pressure which the electrons are compressed into the atomic nuclei and bounded
3
it was not investigated further by Bothe and Becker. Two years later, Irène JoliotCurie (1897−1956) and Frédéric Joliot (1900−1958) in Paris showed their new
experimental results: if this unknown radiation fell on paraffin wax or any other
hydrogen-containing compound, it ejected protons of very high energy. Paraffin wax
is a hydrocarbon high in hydrogen content, hence offers a target dense with protons.
On hearing of the Joliot–Curie couples’ results, Chadwick at the Cavendish Laboratory did not believe the gamma-ray hypothesis. Chadwick and his colleagues had
already conducted experiments on disintegrating light elements using alpha particles
emitted from polonium, and also developed more accurate and efficient methods for
detecting, counting and recording the ejected protons. Chadwick quickly performed
repeatedly the Joliot–Curie couples’ experiment: the hydrogen and helium atoms
were respectively disintegrated by using the ray produced from alpha particles falling
on the beryllium atoms, and as a result, the hydrogen and helium nuclei were ejected.
Since a gamma ray had to have impossibly high energy and momentum to scatter the
massive protons, the gamma-ray hypothesis was untenable. If it was assumed that the
new rays were the neutral particles without charges and their mass almost equal to the
mass of protons, the experimental results could be interpreted reasonably. Chadwick
performed a series of experiments to measure the range of these protons, the velocity
of hydrogen and helium nuclei, and the mass of the new particles. Meanwhile, he
also measured how the new particles impacted the atoms of various gasses. He finally
concluded that the new particles are not composed of gamma rays, but uncharged
particles with about the same mass as the protons. So, these uncharged particles were
named neutrons . In 1932, Chadwick published a classic paper in Nature, “Possible
Existence of a Neutron”, and thereby declared the neutrons were discovered [1].
Therefore, Chadwick won the Nobel Prize in Physics for the discovery in 1935.
Currently, it is measured more accurately by the experiments that the neutron’s
mass is 1.674927211 × 10
−27 kg, the proton’s mass 1.672621637 × 10
−27 kg and
the electron’s mass 9.10938215 × 10
−31 kg. Obviously, neutrons and protons have
almost equal mass, and the mass of electrons is only 1/1836 of the protons. The
atomic diameter is about the order of 10
−10 m, and the atomic nucleus only has 10
–4
of the atomic size. Nevertheless, the mass of the entire atom almost concentrates on
the atomic nucleus, and hence its density is very high, up to the order of 10
12 kg/cm
3 .
1.1.2 Neutron Stars in the Universe
From the atomic structure size, it can be shown that the vast majority of the interior
of the atom is empty. Hydrogen is the lightest element on the periodic table and
has one proton and no neutron. The elements except for hydrogen on the periodic
table contain the neutrons. For example, helium-4 located in the second period has
two protons and two neutrons. If the electrons and protons inside the atoms can
be combined to become neutrons, the substance consists of neutrons. And thus, the
atomic sizes would be compressed into very small nuclei. It needs enough high
pressure which the electrons are compressed into the atomic nuclei and bounded