How does u-235 become u-236?

he fissile isotope uranium-235 fuels most nuclear reactors. U-235 that absorbs a thermal neutron may go one of two ways. About 82% of the time, it will fission. About 18% of the time it will not fission, instead emitting gamma radiation and yielding U-236. Thus, the yield of U-236 per U-235+n reaction is about 18%, and the yield of fissile decay products is about 82%. In comparison, the yields of the most abundant individual fission products like Cs-137, Sr-90, Tc-99 are between 6% and 7%, and the combined yield of medium-lived (10 years and up) and long-lived fission products is about 32%, or a few percent less as some are destroyed by neutron capture.