Energy Scale of Nuclear Reactions
The 12C standard makes it useful to think about nuclear mass in atomic mass units for the definition of the mass excess. However, its usefulness arises in the calculation of nuclear reaction kinematics or decay. From Einstein's work on mass-energy equivalence (E=mc2), it is well known that nuclear reactions transform energy into mass and vice versa. However, most of the energy remains in the mass of the nuclei involved, and only a small fraction of the total energy, on the order of 0.01 to 0.1% of the total mass, may be absorbed or liberated. Thus by working in terms of the mass excess, one has effectively removed much of the mass changes which arise from the mere transfer or release of nucleons, making more obvious the scale of the net energy difference.
Nuclear reaction kinematics are customarily performed in units involving the electron volt, a consequence of accelerator technology. The combination of this practical point with the theoretical relation E=mc2 makes units of mega electron volts over the speed of light squared (MeV/c2) a convenient form to express nuclear mass. However, the numerical values of nuclear masses in MeV/c2 are quite large (even the proton mass is ~938.27 MeV/c2), while mass excesses range in the tens of MeV/c2. This makes tabulated mass excess less cumbersome for use in calculations. One trivial point worth noting that the 1/c2 term is typically omitted when quoting mass excess values in MeV, since the interest is more often energy and not mass; if one wanted units of mass, one would simply change the units from MeV to MeV/c2 without altering the numerical value.
Read more about this topic: Mass Excess
Famous quotes containing the words energy, scale, nuclear and/or reactions:
“His eloquence was of every kind, and he excelled in the argumentative as well as in the declamatory way. But his invectives were terrible, and uttered with such energy of diction, and stern dignity of action and countenance, that he intimidated those who were the most willing and the best able to encounter him. Their arms fell out of their hands, and they shrunk under the ascendant which his genius gained over theirs.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“That age will be rich indeed when those relics which we call Classics, and the still older and more than classic but even less known Scriptures of the nations, shall have still further accumulated, when the Vaticans shall be filled with Vedas and Zendavestas and Bibles, with Homers and Dantes and Shakespeares, and all the centuries to come shall have successively deposited their trophies in the forum of the world. By such a pile we may hope to scale heaven at last.”
—Henry David Thoreau (1817–1862)
“The reduction of nuclear arsenals and the removal of the threat of worldwide nuclear destruction is a measure, in my judgment, of the power and strength of a great nation.”
—Jimmy Carter (James Earl Carter, Jr.)
“Prolonged, indiscriminate reviewing of books is a quite exceptionally thankless, irritating and exhausting job. It not only involves praising trash but constantly inventing reactions towards books about which one has no spontaneous feeling whatever.”
—George Orwell (1903–1950)