PROBLEM SET 6, QUESTION 3:

The atomic number of zirconium is 40 according to the Element Tables. The atomic number of uranium is 92. So the second nucleus on the right must have atomic number 52 (92 - 40).

(The general principle is that all the protons are in the two fission fragments. Only extra neutrons are left outside the two nuclei.)

The Element Table shows that element number 52 is tellurium (Te).

To find the number of free neutrons, just subtract the mass numbers: 236 on the left; 92 + 130 on the right, or 222. The difference is 14; there are 14 free neutrons.

A check: The second isotope is ¹³⁰Te, which has 78 neutrons (78 = 130 - 52). So the number of neutrons in the nuclei are:

uranium, 144
zirconium, 52 (92 - 40)
tellurium, 78

A total of 130 neutrons on the right (52 + 78), 144 neutrons in the uranium, so there are 14 neutrons left over.

The equation is:

²³⁶₉₂U --> ⁹²₄₀Zr + ¹³⁰₅₂Te + 14n.

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