Final answer:
Strontium-90 undergoes positron capture to transform into Yttrium-90 while emitting a positron. The atomic number decreases by one, and the mass number stays the same during this decay process.
Step-by-step explanation:
When Strontium-90 undergoes positron capture, it transforms into a different element by converting a proton in its nucleus into a neutron. This process is accompanied by the emission of a positron. Since the atomic number decreases by one during this process, and given that Strontium has an atomic number of 38, the product of this radioactive decay by positron emission would be Yttrium-90 (Y-90), which has the atomic number 39. The nuclear equation for this decay process is: 9038Sr = 9039Y + e+ This equation indicates that the mass number remains the same during the transformation, but the atomic number reduces by one to form Yttrium-90 (Y-90), and a positron, designated as e+, is emitted.