Walrus pups are able to swim at birth and weigh between 100 and 150 pounds. Most are only children (twin births are rare), and they stay with their mothers for two years. Eventually, their small young tusks will grow up to three feet long.
Definition of nuclear for Students. 1  1 : of, relating to, or being a nucleus (as of a cell) 2  2 : of or relating to the nucleus of the atom Fission is a nuclear reaction. 3  3 : produced by a nuclear reaction nuclear energy.  4 : of, relating to, or being a weapon whose destructive power comes from an uncontrolled nuclear reaction.
isotope. a chemical element having the same atomic number as another (i.e. the same number of nuclear protons), but having a different atomic mass (i.e. a different number of nuclear neutrons). radioactive isotope. one having an unstable nucleus and which emits characteristic radiation during its decay to a stable form.