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By B. Alex Brown, National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University

* Number Of Pages: 290
* Publication Date: 2006-11
* Binding: pdf


excerpt:

1 NUCLEAR MASSES 6
1 Nuclear masses
1.1 Masses and binding energies
A basic quantity which can be measured for the ground states of nuclei is the atomic
mass M(N, Z) of the neutral atom with atomic mass number A and charge Z. Atomic
masses are usually tabulated in terms of the mass excess defined by
(N, Z) ≡ M(N, Z) − uA, (1.1)
where u is the Atomic Mass Unit defined by u = M(12C)/12 = 931.49386MeV/c2.
1 I will use the data from the 2003 compilation of Audi, Wapstra and Thibault [1].
Fig. (1.1) shows the position on the nuclear chart for these measured masses together
with the experimental error. There are 2127 nuclei measured with an accuracy of 0.2
MeV or better and 101 nuclei measured with an accuracy of greater than 0.2 MeV.
For heavy nuclei one observes several chains of nuclei with a constant N − Z value
whose masses are obtained from the alpha-decay Q values.
Nuclear binding energy is defined as the energy required to break up a given
nucleus into its constituent parts of N neutrons and Z protons. In terms of the
atomic masses M(N, Z) the binding energy B(N, Z) 2 is defined by:
B(N, Z) = ZMHc2 + NMnc2 −M(N, Z)c2, (1.2)
where MH is the mass of the hydrogen atom and Mn is the mass of the neutron.3 In
terms of the mass excess the binding energy is given by:
B(N, Z) = ZHc2 + Nnc2 − (N, Z)c2, (1.3)
where Hc2 = 7.2890 MeV and nc2 = 8.0713 MeV.


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