241-Americium with a Beryllium moderator is probably used as a source for epithermal neutrons.
3-H Tritium is a beta emitter, and was in the radioactive methane flared after Operation Gasbuggy.
60-Cobalt and 137-Cesium are positron/gamma emitters.
It is counter-intuitive why one would use 238-U “depleted Uranium” sinker bars anywhere near a neutron source, since epithermal neutrons turn 238-U into 239-Pu.
Arrays of radionucleotides are released in accidents like Chernobyl, Fukushima, and Three Mile Island.
Of all radioisotopes, elements and chemicals, 239-Pu is probably the most toxic and carcinogenic.