Fission fragments beta decay

Fig, 2 Level scheme of HPd determined from (t, pYY) studies Previous studies are beta decay (circles), fission fragment decay (squares), and (t,p) triangles. 

The prompt neutrons emitted in fission are available for fission in other nuclei - hence the chain reaction. The fission fragments formed initially are rich in neutrons. For example the heaviest stable isotopes of krypton and barium are 86Kr and 138Ba. Excess neutrons are emitted from the fission fragments as delayed neutrons or converted to protons by beta decays. For example... 

Figure 8.3 Fission processes. The uranium nucleus can split in many ways, of which two are shown here. Since fission fragments tend to be heavier with neutrons than stable isotopes of the same element, they each begin a sequence of beta decays, forming elements from virtually every group across the periodic table, including transition elements.

SF = spontaneous fission. Fission fragments are rich in neutrons and decay toward beta stability from the neutron-rich side. Fission produces... 

More than 300 different nuclides have been observed as the primary products of fission. The term fission products usually refers to the primary fission products, i.e., the fission fragments and their daughters resulting from radioactive decay and neutron absorption. Only a few of the primary fission products are stable, the rest being beta-emitting radionuclides. As a fission-product radionuclide undergoes beta decay, its atomic number increases whereas its mass number remains constant. The direct yield of a fission-product nuclide is the fraction of the total fissions that yield this nuclide, essentially as a direct-fission fragment. The cumulative... 

Figure 3.19 The fission fragments FFi and FFj from fission are neutron-rich. They reduce their neutron number either by beta decay or by neutron emission.

Consequently, in a nuclear reactor, fission products as well as isotopes of heavier elements are produced. These heavy elements are formed by the neutron capture followed by beta decay and are often referred to as the transuranic elements. Because the fission process is asymmetric, the products of the fission reaction tend to distribute themselves around mass 83-105 (light fragment) and mass 129-149 (heavy fragment). Some of the more common light fragments are Kr, Sr, Zr, Tc, and the corresponding heavy fragments are Cs, Ce, and Nd. 

---