Question 19.PS.1: Radioactive Series An intermediate species in the uranium-23......
Radioactive Series
An intermediate species in the uranium-238 decay series shown in Figure 19.1 is polonium-218. It emits an alpha particle, followed by emission of a beta particle, followed by the emission of a beta particle. Write the nuclear equations for these three reactions.
^{218}_{84}Po → ^{4}_{2}He + ^{214}_{82}Pb
^{214}_{82}Pb → ^{~~~0}_{-1}e + ^{214}_{83}Bi
^{214}_{83}Bi → ^{~~~0}_{-1}e + ^{214}_{84}Po
Strategy and Explanation The starting point of these linked reactions is polonium-218. When it emits an alpha particle, the atomic number decreases by two and the mass number decreases by four to produce lead-214.
^{218}_{84}Po → ^{4}_{2}He + ^{214}_{82}Pb
polonium-218 lead-214
When lead-214 emits a beta particle, the atomic number increases by one and the mass number remains constant to produce bismuth-214.
^{214}_{82}Pb → ^{~~~0}_{-1}e + ^{214}_{83}Bi
lead-214 bismuth-214
Bismuth-214 emits a beta particle, so the atomic number increases by one and the mass number remains constant to produce polonium-214.
^{214}_{83}Bi → ^{~~~0}_{-1}e + ^{214}_{84}Po
bismuth-214 polonium-214
Reasonable Answer Check An alpha emission decreases the atomic number by two and decreases the mass number by four. Each beta emission increases the atomic number by one and leaves the mass number unchanged. Therefore, one alpha and two beta emissions would leave the atomic number unchanged and decrease the mass number by four, which is what our systematic analysis found.