Betalight: battery-free light provides 20 years of light
Lamps that shine forever don’t just appear in Tolkien’s stories. A betalight is pretty close.
How does a beta light work?
A beta light is named after the radiation that causes it to give light, namely beta radiation. Beta radiation is no different from the well-known electrons that are also found in an electrical wire, for example. These electrons collide with a sensitive layer on the inside of a glass tube, which starts to emit light. The beta radiation released during the decay of tritium is quite weak and therefore not dangerous, as long as the gas remains in the tube. The wall of this tube is usually very thick.
These electrons, of course, come from somewhere. They are formed when the radioactive tritium decomposes into an electron and helium-3. Indeed, the secret of a betalight is tritium. The tube is filled with this gas, which slowly disintegrates. Its energy is enough to make the light shine.
Tritium is the only radioactive form of hydrogen. It is an atom with an atomic nucleus made up of three particles, one proton and two neutrons. Normal hydrogen, protium, has only a proton, heavy water or deuterium has a proton and a neutron.
Always working emergency lighting or for dials
Because betalights are so reliable and do not rely on batteries, they are very popular as emergency lighting. Anglers know them as “isotopes”. Betalights always provide light, day and night, all year round. However, they are slowly weakening as an increasing percentage of the tritium has disintegrated.
Tritium has a half-life of 12.3 years. That is, if you have 100 tritium atoms, after 12 years and four months, only 50 of them will be left in your betalight.
Where does the beta light tritium come from?
Tritium is one of the most expensive substances we know because it hardly occurs in nature and does not last very long. For a gram of tritium you quickly pay € 30,000. It is formed when deuterium absorbs a neutron. This mainly happens in a type of Canadian nuclear reactor, the CANDU.
Heavy water, deuterium, is used here as a coolant and reaction inhibitor and because a lot of neutrons are always released in nuclear reactors, part of the deuterium changes into tritium. Because the mass difference between deuterium and tritium is very large, because tritium is one and a half times as heavy, it is easy to separate the two. So make it a beta light.
