For elements with atomic numbers less than that of calcium, the most abundant isotope of each element with an even number of protons has Z=N, e.g. 4He, 12C, 16O, 40Ca, ... and those with odd proton numbers, N, Na, Al ... have Z nearly equal to N. When one goes to heavier nuclei however there is a surplus of neutrons in the most abundant isotopes; iron-56 has 26 protons and 30 neutrons. Explain both these trends why light nuclei have Z about equal to N while heavy nuclei have Z less than N.
Why is combination of a single neutron and a single proton stable but two protons is not?
Calculate the energy released in erg/g when a composition of pure helium burns to pure carbon-12 and to 50/50 carbon-12 and oxygen 16. What is the energy released when each of these mixtures is burned to Nickel-56? In both cases how much nickel has to be made to produce 1051 erg?
The neutron capture cross sections at 30 keV for the stable isotopes of barium are 130Ba, 715 mb 132Ba, 447mb, 134Ba, 221 mb 135Ba, 457 mb, 136Ba, 69 mb, 137Ba, 57 mb, and 138Ba, 3.9 mb. The s-only isotopes of barium are 134 and 136 and the nuclear charge is 56. a) Why is the cross section of 135Ba greater than that of 134Ba or 136Ba? Why is the cross section of 138Ba so small? What do you expect for the solar ratio of the abundance of 134Ba to that of 136Ba? Your discussion should at least mention why reactions with large releases of energy have large cross-sections.
