<Li> Primary sources, used for startup of a fresh reactor core; conventional neutron sources are used . The primary sources are removed from the reactor after the first fuel campaign, usually after few months, as neutron capture resulting from the thermal neutron flux in an operating reactor changes the composition of the isotopes used, and thus reduces their useful lifetime as neutron sources . <Ul> <Li> Californium - 252 (spontaneous fission) </Li> <Li> Plutonium - 238 & beryllium, (α, n) reaction </Li> <Li> americium - 241 & beryllium, (α, n) reaction </Li> <Li> polonium - 210 & beryllium, (α, n) reaction </Li> <Li> radium - 226 & beryllium, (α, n) reaction </Li> </Ul> </Li> <Ul> <Li> Californium - 252 (spontaneous fission) </Li> <Li> Plutonium - 238 & beryllium, (α, n) reaction </Li> <Li> americium - 241 & beryllium, (α, n) reaction </Li> <Li> polonium - 210 & beryllium, (α, n) reaction </Li> <Li> radium - 226 & beryllium, (α, n) reaction </Li> </Ul> <Li> Californium - 252 (spontaneous fission) </Li> <Li> Plutonium - 238 & beryllium, (α, n) reaction </Li>

Where does the first neutron come from in nuclear fission