The atomic mass of nitrogen isotopes ranges from 10 to 24. Of these, two isotopes -- N14 and N15 -- are stable. The N14 isotope has seven protons and seven neutrons and the N15 isotope has seven protons and eight neutrons. N14 and N15 are found naturally in the atmosphere and soil. In fact, N14 is the most abundant nitrogen isotope and makes up about 99.6 percent of the total natural nitrogen, according to the website Chemicool.com. Nitrogen isotopes can be formed naturally or can be made by man. However, making isotopes isn't easy; it requires sophisticated equipment and specialized training.
Synthetic or artificial nitrogen isotopes are less stable than the natural ones. They are made by scientists in special machines such as nuclear reactors and accelerators. The reactors bombard the nitrogen atoms with alpha particles which contain two protons and two neutrons. These particles interact with the stable isotopes and convert them into heavier isotopes.
A cyclotron is a particle accelerator that moves the particles around a circular tract with periodic pushes from an electric field. These charged particles bombard the nitrogen atoms and convert them into isotopes. A cyclotron can produce a continuous stream of particles at the target atom, and hence, is highly effective. It is also less expensive than a nuclear reactor.
Natural nitrogen isotopes were formed millions of years ago when cosmic radiation in space interacted with the nitrogen atoms in the upper atmosphere. These isotopes are commonly known as cosmogenic isotopes. Most natural nitrogen isotopes are found in very low concentration and are usually detected using techniques such as accelerator mass spectrometry, which detects the mass to charge ratio of the atoms.