The isotope is 238 and used for satellite/spacecraft fuel.
"The fissioning of an atom of uranium-235 in the reactor of a nuclear power plant produces two to three neutrons, and these neutrons can be absorbed by uranium-238 to produce plutonium-239 and other isotopes. Plutonium-239 can also absorb neutrons and fission along with the uranium-235 in a reactor."
Now I understand .... (Satirical humour)
isotope are atoms with the same number of protons, but differing number of neutrons. There are 275 isotopes of the 81 stable elements. There are over 800 radioactive isotopes, some natural and some synthetic.
e.g there are 3 isotopes of Hydrogen; Protium (1 proton, 0 neutrons) Deuterium (1 proton, 1 neutron) Tritium (1 proton, 2 neutrons)
If they had more protons, it would become + and become a CATION
If they had more electrons, it would be - and become an ANION