The resulting element has the same atomic mass and the atomic number has increased by 1. This means that a neutron has been converted into a proton, and an electron has been emmitted; this happens in beta decay.

Beta decay:

 This is the standard isotopic notation.  is the mass number which is equal to the number of protons plus neutrons, and  is equal to the atomic number. Thus,  is a sodium atom with 12 neutrons.

 This is the standard isotopic notation.  is the mass number which is equal to the number of protons plus neutrons, and  is equal to the atomic number. Sometimes, the atomic number is left out since it can be easily found using the atomic symbol and the periodic table. Thus,  is a carbon atom (all of which have 6 protons) with 8 neutrons, giving us a mass number of 14.

Isotopes of elements have different numbers of neutrons, and different atomic weights, but must have the same number of protons. For example, carbon exists as isotopes of C12, C13, and C14, but these are all carbon atoms and have exactly 6 protons. The number of neutrons, and thus atomic weight varies between isotopes. Also, different isotopes may have different chemical properties, such as half-life and type of radioactive decay.

The element is either found by looking at the symbol "C" and identifying it on the periodic table as carbon, or by looking at the atomic number. The isotopic notation given is in the form of

Where X is the symbol for the element, Z is the atomic number (number of protons) and A is the atomic mass number (number of protons plus number of neutrons).

Since the atomic number is 6 we can also find this on the periodic table to be carbon. The isotope now can be written as 

To find the number of neutrons we take 

Radioactive decay is the result of an unstable nucleus in an atom. When an atom contains more neutrons than the nucleus can handle it will undergo radioactive decay, leading to emission of different particles such as alpha particles or beta electrons. This can occur in ground state elemental atoms, but is most commonly seen in radioactive isotopes. Isotopes contain the same number of protons as any other atom of a given element, but often contain a greater number of neutrons, leading to instability. These neutrons will be lost via radioactive decay in order for the atom to reach the ground state, the most stable isotope.

Ionization results in a charged particle via electron transfer, but does not contribute to radioactivity.

Gamma radiation is the only form of radioactive decay that does not emit a physical particle from the atomic nucleus. It is simply the release of energy in the form of high energy gamma rays, which do not carry any mass. These rays are more powerful than any other electromagnetic wave known to man.

Alpha decay results in the release of a helium nucleus. Beta decay results in the release of an electron or a positron. Electron capture results in the emission of a neutron.

A half life is the amount of time it takes a radioactive sample to decay by 50%. To reach 25% of the initial dose would take two half lives.

It will take 220 minutes, or 3 hours and 40 minutes, for there to be 25% of the sample remaining. Since the sample was administered at 9am, this means that there will be less than 25% remaining at 1pm.

Alpha decay, beta decay, and positron emission are all commonly recognized forms of radioactive decay. Electron capture is another form of nuclear alteration via radioactivity. The nucleolus is a biological structure found in cells, and has no relation to the atomic nuclei described in chemistry.

This is the definition of gamma radiation.