Nuclear physics and radioactive decay are probably among
the most misunderstood scientific topics by the general public. People have been terrified of nuclear energy
since the creation of the nuclear bomb, fear which has only been enhanced both
by legitimate disasters such as Chernobyl and the Fukishima Power Plant along
with a 60+ year history of films that exaggerate the dangers and misrepresent
the science. Nuclear power plants have a
better safety record than the fossil fuel plants that most of our energy currently
comes from, while also being more environmentally-friendly. Many scientists believe that worldwide energy
problems could be improved by nuclear power, without the need for investing in
newer less efficient technologies, if only they would be accepted by the
public. This post will explain the
science behind nuclear power, atomic bombs and radioactive decay, including how
they are so often misunderstood by society and the media.
Radioactive Decay
Radioactive decay
is the random breakdown of an atom with an unstable nucleus into a more stable
form, releasing energy in the process. Every
radioactive substance has a predictable rate of decay, known as a half
life. The half-life of a radioactive
substance is the time that it will take for half of its atoms to decay. Radioactive decay releases energy, and it is
the released energy that is known as radiation.
There are three
major types of radiation released from decay: alpha decay, beta decay and
gamma decay. Alpha decay releases an
alpha particle, which is essentially a Helium nucleus containing 2 protons and
2 neutrons. It cannot penetrate
materials very deep but is extremely damaging.
Beta decay releases an electron and in
contrast to alpha decay, it has greater penetrance but is less harmful. Gamma decay expels a high-energy photon,
which is extremely penetrating while also able to cause DNA damage. Radioactive decay occurs in all elements of
atomic number (number of protons) 83 (bismuth) or greater. Additionally, radioactive isotopes (varying
number of neutrons) naturally exist for many elements under atomic number 83 at
a specified ratio in nature. By
utilizing knowledge of the known ratio of these isotopes in nature and their
half-life, they are useful for a multitude of processes
including archaeological dating, medical imaging, and tracing of biological
processes.
Nuclear Fission
Nuclear fission
is very often confused with radioactive decay.
While both involve the release of energy due to nuclear degradation, the
two processes are unrelated. Nuclear
fission is usually instigated by bombardment with neutrons and results in the
release of two large fragments of somewhat unpredictable size along with neutrons
and massive amounts of energy. Unlike radioactive decay which is a controlled
spontaneous process occurring at regular intervals that releases defined
smaller particles (alpha, beta), nuclear fission only occurs spontaneously at
extremely low rates in certain heavy elements (can theoretically occur in
elements above atomic number 92, but only realistically observed above atomic
number 231), and is typically induced through man-made reactions in only a
select group of isotopes. Isotopes
that are able to undergo fission upon bombardment with a high energy neutron
(even at low probability) are fissionable, while isotopes that can easily
fission with lower-energy neutrons are fissile. Nuclear fuel for energy reactors or bombs
typically utilizes Uranium (U)-235, U-233, Plutonium (Pu)-239 and Pu-241. These nuclides are all fissile isotopes that
are capable of sustaining a chain reaction of neutron release and capture, are
relatively abundant and are radioactively stable.
