http://www.ck12.org Chapter 25. Nuclear Physics
Physicists realized that a strong force (or interaction) would be necessary to hold the quarks together and produced
a theoretical framework for this calledquantum chromodynamics.
In the 1960s, it was shown that the nuclear weak force and electromagnetism were aspects of the same force,
now called theelectroweak force. By the 1970’s physicists had worked out a model of particle physics called
theStandard Model. The model combined everything that was known about the myriad of subatomic particles
of the time. It did not incorporate gravity (general relativity) but did combine the electroweak force and quantum
chromodynamics.
Einstein’s dream was to find a single force from which the four fundamental forces of nature would arise. The goal
today is to extend the standard model into a grand unified theory (affectionately known as GUT) by incorporating
into it the strong nuclear force and gravity. String theory, the notion that all forces and particles can be attributed to
fundamental structures called strings, was thought to be able to provide such a theory. However, after 20 years of
work with very little progress, more and more physicists are beginning to suspect that string theory may not hold the
promise it once did.
In the summer of 2012, a very important discovery was made concerning a subatomic particle called the Higgs boson
particle. The standard model has predicted the existence of a particle which conveys mass to particles. It is called
the Higgs boson and physicists believe they have confirmation of its existence due to the high energy experiments
conducted with the CERN (Conseil Europeen pour la Recherche Nucleaire) particle accelerator located near Geneva,
Switzerland.
To learn more about the Higgs boson particle follow the link below.
http://en.wikipedia.org/wiki/Higgs_boson
- Atoms are always neutral; that is, they have the same number of protons in the nucleus as electrons about the
nucleus. - Neutrons and protons are callednucleonssince they form the atomic nucleus.
- Theatomic numberof an atom is the number of protons in its nucleus. It is expressed symbolically asZ.
- The total number of nucleons in the nucleus is called theatomic mass number. It is expressed symbolically as
A. - The nuclei that contain the same number of protons but a different number of neutrons are calledisotopes. All
chemical elements have multiple isotopes. - The nucleus is often represented symbolically asAZX.
- Experimental evidence shows that the total mass of astablenucleus is smaller than the sum of the masses of
its components. The energy equivalent of this mass difference∆m, ormass deficit, can be used to findthe
binding energyof the nucleus. - The binding energy is found from the Einstein equationE=∆mc^2.
- The half-life is the amount of time required for half of the radioactive parent atoms to transform into the
daughter atoms. - The amount of a sampleNoof radioactive material remaining afterndoublings of its half-life isN, given by
the equationN=
( 1
2)n
No.- The splitting of an atom with a large atomic mass into at least two relatively equal parts, with an accompanying
release of energy, is called nuclearfission. - The process in which the nuclei of lighter elements combine and form heavier elements, with an accompanying
release of energy, is called nuclearfusion.