The glow coming from a tritium (H-3) exit sign demonstrates a characteristic associated with a radioactive cascade. Rutherford and his associate studied three such cascades. Each produced evidence of a disintegration, one that yields a number of breakdown products. All of the products in each cascade have come from the same original element.
Each breakdown product represents a slightly different version of the original element. Rutherford and his associates chose to refer to such products and isotopes. The chemical nature of each isotope caused it to fall into a particular position within the overall cascade.
Rutherford and other chemists first learned about the disintegration of isotopes by studying larger radioactive molecules, such as radium. Only later did chemists discover that even hydrogen, the smallest of all elements had isotopes. Tritium was one such isotope.
The small size of hydrogen does not keep it from displaying a characteristic associated with all atoms. Its electrons travel continuously around a nucleus. Each electron travels at a fantastic speed, as it circles round that collection of protons and neutrons. If any single electron moves from one spin level to another, one closer to the nucleus, then it releases a quantum of energy.
Because the H-3 isotope has only one extra electron, just one more than the normal hydrogen molecule, a change to the spin level of that one electron does not yield much energy. Only a small amount of energy can contribute to production of a distinctive glow. That fact must be mentioned in any comparison that focuses on the H-3 exit sign.
Because only a small quantum of energy has been released, following disintegration of a tritium isotope, that substance does not produce a markedly visible glow. In fact, its glow remains undetectable until the lights go out. Only then can the human eye detect the glow coming from an H-3 exit sign.
That fact underlines a key difference between radioactive tritium and larger radioactive substances. Any comparison should highlight that difference. The level of radiation that comes from a tritium exit sign is nowhere near the level of radiation that comes from a functioning X-ray machine.
A human cannot be harmed by infrequent and brief exposure to the radiation from a standard X-ray machine. By the same token, a human cannot be harmed by exposure to the minimal level of radiation that comes from any of the H-3 signs. Neither occurrence can do real damage to any part of a living human. In fact physicians use radioactive substances that are even more powerful that tritium, when trying to diagnose certain conditions. At times, a patient must swallow or be injected with a radioactive substance, in order to permit the capturing of an organ’s or a blood vessel’s outline.
While that exposure is shorter than the time that a person might spend in a theater, it entails exposure to a larger amount, although an acceptable amount, of radiation. Such comparisons should not alarm the reader. Each is meant to drive home the acceptable level of quantum-powered rays that come from a tritium exit sign. Each such ray ensures the presence of glowing letters during an emergency.