|The ____ of an element have different numbers of neutrons.
|Radioactive carbon-14 is used to study organic reaction ____.
|Boron and cadmium are used in ____ to absorb neutrons.
|U-233, U-235, and Pu-239 are used as ____ in fission reactors.
|Unlike electrons, protons and neutrons are ____.
|Alpha particles are helium ____ formed by radioactive decay.
|Graphite and heavy water are ____ that slow down neutrons.
|Water, heavy water, air, and molten sodium are used as ____.