1. Nuclear Forces How do you keep a bunch of Protons together?

2. The Nucleus  Our present knowledge about the atomic nucleus:  1) Protons and Neutrons make up the nucleus  2) Protons and Neutrons are made up of smaller particles called quarks  3) Neutrons can split apart and become a proton and an electron

3. The Electrical Force  Protons have a positive electrical charge  Protons attract electrons because they have opposite charges  Protons repel protons because they all have the same charge  It is obvious that there must be some force that is stronger than the electrical force to hold the nucleus together.  Without this force the protons in the nucleus would fly apart

4. Atomic Glue  We have examined the relationship between protons and neutrons and have discovered that something about neutrons stabilizes the nucleus  In stable isotopes, neutrons must equal or slightly exceed the number of protons  Atomic Isotopes Atomic Isotopes Atomic Isotopes

5. The Strong Nuclear Force  As we read in Chapter 19, Radioactivity Results from an Imbalance between the Electrical Force and the Strong Nuclear Force  As the name implies, this force is stronger than the electrical force of repulsion between protons  Neutrons are fundamental in this process as they tend to attract protons and other neutrons instead of repelling

6. Atomic Stability and Distance  Elements are defined by the number of protons within the nucleus  Each additional proton (and the accompanying neutrons) increases the nuclear size  The strong nuclear force is only strong enough to exceed the electrical force over a very small distance  All elements beyond Bismuth are unstable due to the distance between nucleons (See pg 328 in the text)

7. Nuclear Instability Continued  So we have a conundrum:  1) The more protons in the nucleus, the more neutrons are needed to maintain stability  2) The more nucleons in the nucleus the larger the distance from side to side  3) The strong nuclear force is limited by distance  4) The electrical force begins to predominate  5) The nucleus becomes unstable

8. The Relationship between Fission and Radioactivity  Those elements that are radioactive are also more likely to break apart if impacted by a speeding neutron  Remember, 1 Neutron can make a nucleus unstable without an impact  Add tremendous speed to the neutron and instability becomes critical and fission occurs

9. Energy and Fission  It turns out that the mass of the protons and neutrons in different elements are slightly different.  Those elements that are prone to fission (large nuclei, greater than Atomic # 26) have increasingly more massive protons and neutrons.  This increasing mass seems to be a sort of energy storage for the nucleus

10. Energy Release during Fission  As the unstable nucleus breaks apart, a massive amount of energy is released  The particles that are produced by the fission event have less mass in each proton and neutron than before the fission  Einstein showed us how these relate in his famous equation E = mc 2

11. Using E = mc 2  Unless mass is converted to energy, the fission process is unimportant  Since mass is converted to energy in fission reactions, it is possible to use very small quantities of “fissionable” isotopes to create huge energy releases  Something like a teaspoon of U – 235 is capable of producing the same energy as several train loads of coal

12. E = mc 2 math  One Nanogram of mass (1 x 10 -12 g) multiplied by the speed of light (3 x 10 8 m/s) squared is the process so…  E = (1x10 -12 )x(3x10 8 ) 2  E = 90,000 joules of energy from one trillionth of a gram of mass!!!  Wow!