Download Chapter 32 Nuclear Physics

Chapter 32 Nuclear Physics
Chapter Introduction
The nucleus of an atom is incredibly small.
The diameter of the nucleus is about 100,000
times smaller than the diameter of the atom.
Although small, the nucleus contains more
than 99.9% of the mass of an atom, because
each of its constitutes (protons and
neutrons) is about 1800 times more massive
than an electron. We will see that many
nuclei, particularly those of the heavier
elements, are unstable and spontaneous break
apart, or disintegrate, into other nuclei.
This spontaneous disintegration is called
radioactive decay, and it is accompanied by
the emission of certain types of particles
and high-energy photons. While these
particles and photons can be very dangerous
to individuals and to the environment,
radioactive decay also has many beneficial
uses. In this chapter, we will study the
common types of radioactive decay and what
they imply about nuclear structure.
Basic Terms
Nucleus
The nucleus of an atom consists of protons
and neutrons, which are collectively
referred to as nucleons.
Proton
A proton has a positive electrical charge
which, in magnitude, is equal to the charge
carried by an electron (e = 1.602 177 33 ×
10-19 C). Its mass mp = 1.672 6231×10-27 kg.
Neutron
A neutron is an electrically neutral
particle whose mass is slightly larger than
that of a proton, mn = 1.674 9286 × 10-27 kg.
Atomic number
The atomic number Z is the number of protons
in the nucleus.
Atomic mass number (nucleon number)
The atomic mass number (or nucleon number) A
is the total number of protons and neutrons
in the nucleus: A = Z + N, where N is the
number of neutrons.
Isotopes
Nuclei that contains the same number of
protons, but a different number of neutrons,
are called isotopes.
Strong nuclear force
The strong nuclear force is the force of
attraction between nucleons and is one of
the fundamental forces of nature. This force
balances the electrostatic force of
repulsion between protons and holds the
nucleus together. The strong nuclear force
has a very short range of action and is
almost independent of electric charge.
Binding energy
The binding energy of a nucleus is the
energy required to separate the nucleus into
its constitute protons and neutrons. The
binding energy is equal to (∆m)c2, where c
is the speed of light in a vacuum and Delta
m is the mass defect of the nucleus.
Mass defect
The mass defect is the amount by which the
sum of the individual masses of the protons
and neutrons exceeds the mass of the parent
nucleus.
Atomic mass unit
When specifying nuclear masses, it is
customary to use the atomic mass unit (u),
which is one-twelfth of the mass of a 12C
atom.
Radioactivity
The Radioactivity is a process in which
unstable nuclei spontaneously decay by
breaking apart or rearranging their internal
structures. Naturally occurring
radioactivity produces alpha rays, beta
rays, and gamma rays.
Alpha particle
Alpha rays consist of positively charged
particles, each particle being the 42He
nucleus of helium.
Beta particle
There are two kinds of beta rays. One
consists of negatively charged particles
which are electrons, the other consists of
positively charged particles which are
positrons that have the same mass as
electrons but carry a charge of +e.
Gamma ray
Gamma rays are high-energy photons.
Transmutation
If a radioactivity parent nucleus
disintegrates into a daughter nucleus that
has a different atomic number, one element
has been converted into another element, the
conversion being referred to as a
transmutation.
Neutrino
The Neutrino is an electrically neutral
particle that has near zero or zero mass.
The neutrino travels near or at the speed of
light and is emitted along beta particles.