Question 29.8: The Discovery of the Neutron Goal Balance a nuclear reaction...
The Discovery of the Neutron
Goal Balance a nuclear reaction to determine an unknown decay product.
Problem A nuclear reaction of significant note occurred in 1932 when Chadwick, in England, bombarded a beryllium target with alpha particles. Analysis of the experiment indicated that the following reaction occurred:
{ }_{2}^{4} \mathrm{He}+{ }_{4}^{9} \mathrm{Be} \rightarrow{ }_{6}^{12} \mathrm{C}+{ }_{Z}^{A} \mathrm{X}
What is { }_{Z}^{A} X in this reaction?
Strategy Balancing mass numbers and atomic numbers yields the answer.
Write an equation relating the atomic masses on either side:
4+9=12+A \rightarrow A=1
Write an equation relating the atomic numbers:
2+4=6+Z \rightarrow Z=0
Identify the particle:
{ }_{Z}^{A} X={ }_{0}^{1} \mathrm{n}(\text { a neutron) }
Remarks This experiment was the first to provide positive proof of the existence of neutrons.