 Atoms are held together by strong nuclear forces and electrical forces  The electrical force between positive protons and negative electrons keep electrons in their orbit.  Strong nuclear forces exist in the nucleus. While electrons are forcing the protons together in the nucleus, neutrons are keeping them from flying apart (this is strong nuclear force).

 The more protons there are in a nucleus, the more neutrons are needed to hold them together.  Ex: A typical helium atom has 2 protons and 2 neutrons. A typical uranium atom has 92 protons and 146 neutrons

 Neutrons, by themselves are not stable.  Any element above atomic number 83 has so many neutrons, that at some point the neutron will decay…. This makes that element radioactive.  When it decays, it emits α (alpha), β (beta), and γ (gamma) rays.

 An alpha ray is positively charged, a beta ray is negatively charged, and a gamma ray is neutral.  Alpha rays (light rays) can be stopped by a piece of paper; beta rays (X-rays) with a piece of aluminum; gamma rays are the strongest and have to be stopped with thick lead

 Isotopes are the same element with different number of neutrons.

 Different radioactive elements will decay at different rates. The time it takes half of the element to decay is that elements half-life.  Some elements have half-lives of a few seconds. Others, like U-238 have a half-life of 4.5 billion years.

 When a nucleus emits an alpha or beta particle, a different element is formed, this is transmutation.  U-238 will decay be emitting an alpha particle made up of 2 protons and 2 neutrons. This changes Uranium into Thorium.

 After U-238 decays into Thorium, Thorium will decay be emitting a beta particle (an electron).

 Carbon-12 is the most naturally occurring carbon atom. However, there is a very small percentage of Carbon-14 in the atmosphere.  Carbon-14 is less stable and will decay. We can use what we know about half-lives to date fossils and old trees  Carbon-14 has a half-life of 5730 years.

 Scientists can now make harmless elements radioactive by bombarding them with neutrons (thereby activating decay). They then insert the radioactive materials and can track them using radiation detectors  Fertilizer in plants  Used by doctors to study digestion and circulation

 Radiation is all around us in the form of earth minerals and cosmic rays. The human has evolved to withstand these natural does of radiation.  Prolonged exposure or exposure to radiation levels above 1000 times normal results in cancer and eventually death

 Nuclear Fission literally means the splitting of an atom. Normally, nuclear strong forces within the nucleus are too much to overcome.  However, in U-235 scientists found that if a neutron was fired into the atom, it would cause elongation and would eventually split.

 The energy released by the fission of one U- 235 atom is enormous… about seven million times the energy released by the explosion of one TNT molecule.  The energy is released as kinetic energy and gamma radiation

 This does not occur in nature because u-235 is mixed with the more stable U-238  U-235 must be at critical mass in order for an enormous explosion to occur.

 Nuclear Power Plants work much like a coal plant. They produce heat which powers a generator.  Nuclear Power Plants can use a lot less fuel and do not emit fossil fuels into the air  However, when elements have undergone fission, their waste products are highly radioactive.

 How Nuclear Plants work How Nuclear Plants work

 The next slide contains graphic images of mutations that may occur as a result of toxic exposure to radiation. Please skip the next slide if you have a sensitive stomach or have any doubts about whether or not you should see what is next.

 Instead of splitting an atom, nuclear fusion occurs when atoms combine. This requires a high temperature and a high velocity.  When atoms collide, radiant energy is released.

 Maintaining high temperatures  Energy required to maintain the high temps or produce products for fusion is much much higher than the energy output.

 No radioactive by-products  Fuel is basically unlimited (can be processed from water).