Tuesday, August 5, 2014

The (Radioactive) Decay of Western Civilization: Nuclear Physics and the Safety of Nuclear Power

          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.