Question

In a nuclear reactor, the excess neutrons produced from fission are absorbed by elements, preferably in solid form, which will not undergo further reaction when they absorb a neutron.

From the table below, choose the best material to absorb neutrons in a nuclear reactor, and then explain your choice.

Half-lives of isotopes

Isotope	Half-Life (if unstable)
1H	stable
2H	stable
3H	12.3 years
12C	stable
13C	stable
14C	5730 years
27Al	stable
28Al	2.25 minutes
209Bi	stable
210Bi	5.01 days

Answer 1

The best material to absorb the neutrons is those which will not undergo fission on the absorption of neutrons. In a nuclear reactor, graphite is used for this purpose. The most efficient material is C¹² because, on the absorption of a neutron, it produces the most stable C¹³ .

H¹ can also be considered since it will form stable isotope H² on the absorption of a neutron; however, in this case, there is the possibility of a nuclear fusion reaction combining four hydrogens to form helium ion.

So the best material is C¹².