Nuclide
Sometimes referred to as a "nuclear species", a nuclide is a species of atom that has a particular number and arrangement of protons and neutrons in it's nucleus. A nuclide is also characterized by it's mass, atomic number (also called "Z", the number of protons), mass defect, and nuclear binding energy.
If two nuclides have the same number of protons but a different number of neutrons they are considered two different isotopes of the same chemical element. For this reason the term nuclide is often used interchangeably with isotope.
Nuclides can be stable or unstable. When unstable, one type of nuclide spontaneously transforms into another type according to a set statistical formula. This process emits radiation. The rate at which a radioactive nuclide decays is indicated by it's half-life.
Nuclides may decay by different types of nuclear radiation. Alpha decay occurs when the nucleus emits two protons and two neutrons (a 4Helium nucleus). The 238Uranium nuclide decays by alpha particle emission according to the scheme: 238U--->234Th + 4He where the energy released in the transformation is Q=4.25MeV.
Other types of nuclear emissions can be electrons and positrons, which are grouped together as beta decay, and high energy photon emission called gamma decay.