Thank you for the reply,
wiki said fast neutrons required for U-238 to capture and become U-239, which then decays into Pu-239.
my confusion is: Won't fast neutrons more likely to cause fission than transform 238 to 239?
Wikipedia said U-238 is better with capturing fast neutrons than slow neutrons. shouldn't it be the other way round? I thought U-238 is not fissile but is fissionble by neutrons with high enough K.E, and doens't fast neutrons have higher K.E.??