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Start a chain reaction, or introduce non-radioactive isotopes to prevent one. Control energy production in a nuclear reactor!
Why is the number of neutrons greater than the number of protons in stable nuclei having greater than about 40, and why is this effect more pronounced for the heaviest nuclei?
is a loosely bound isotope of hydrogen. Called deuterium or heavy hydrogen, it is stable but relatively rare—it is 0.015% of natural hydrogen. Note that deuterium has , which should tend to make it more tightly bound, but both are odd numbers. Calculate , the binding energy per nucleon, for and compare it with the approximate value obtained from the graph in [link] .
1.112 MeV, consistent with graph
is among the most tightly bound of all nuclides. It is more than 90% of natural iron. Note that has even numbers of both protons and neutrons. Calculate , the binding energy per nucleon, for and compare it with the approximate value obtained from the graph in [link] .
is the heaviest stable nuclide, and its is low compared with medium-mass nuclides. Calculate , the binding energy per nucleon, for and compare it with the approximate value obtained from the graph in [link] .
7.848 MeV, consistent with graph
(a) Calculate for , the rarer of the two most common uranium isotopes. (b) Calculate for . (Most of uranium is .) Note that has even numbers of both protons and neutrons. Is the of significantly different from that of ?
(a) Calculate for . Stable and relatively tightly bound, this nuclide is most of natural carbon. (b) Calculate for . Is the difference in between and significant? One is stable and common, and the other is unstable and rare.
(a) 7.680 MeV, consistent with graph
(b) 7.520 MeV, consistent with graph. Not significantly different from value for , but sufficiently lower to allow decay into another nuclide that is more tightly bound.
The fact that is greatest for near 60 implies that the range of the nuclear force is about the diameter of such nuclides. (a) Calculate the diameter of an nucleus. (b) Compare for and . The first is one of the most tightly bound nuclides, while the second is larger and less tightly bound.
The purpose of this problem is to show in three ways that the binding energy of the electron in a hydrogen atom is negligible compared with the masses of the proton and electron. (a) Calculate the mass equivalent in u of the 13.6-eV binding energy of an electron in a hydrogen atom, and compare this with the mass of the hydrogen atom obtained from Appendix A . (b) Subtract the mass of the proton given in [link] from the mass of the hydrogen atom given in Appendix A . You will find the difference is equal to the electron’s mass to three digits, implying the binding energy is small in comparison. (c) Take the ratio of the binding energy of the electron (13.6 eV) to the energy equivalent of the electron’s mass (0.511 MeV). (d) Discuss how your answers confirm the stated purpose of this problem.
(a) vs. 1.007825 u for
(b) 0.000549 u
(c)
Unreasonable Results
A particle physicist discovers a neutral particle with a mass of 2.02733 u that he assumes is two neutrons bound together. (a) Find the binding energy. (b) What is unreasonable about this result? (c) What assumptions are unreasonable or inconsistent?
(a)
(b) The negative binding energy implies an unbound system.
(c) This assumption that it is two bound neutrons is incorrect.
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