help!!! chem q's please!?

Question

why does the U-238 disintegration series end w/ nuclide Pb-206?


2)nuclear decay of the radioisotope used to study red blood cells equation?
59/26 Fe --> ______+______
24 na halflife = 15hrs
59 Fe halflife - 44.5 days
131I halflife = 8.1 days
all are betas

Answer 1

1) Because Pb-206 is stable.

2) 59/26 Fe ===> 59/27 Co + e-