Tritium gas light source

Tritium gas light sources (also GTLS , from the English " Gaseous tritium light source "), known under the trade names trigalight , Betalight and nite glowring , are light sources that shine visibly for several decades without any external energy supply . A tritium gas light source consists of a small glass tube made of borosilicate glass , which is coated on the inside with a light source (" phosphor ") and filled with tritium . Tritium gas light sources were invented in the 1960s; they shine much more strongly than the previously known tritiated luminous colors .

use

Tritium gas light sources are used as emergency lighting for signs and for clock faces and hands. Other uses include key rings and similar “ glow-in-the-dark ” products. Since, in addition to their lifespan, they also have the advantage of being independent of external energy supply, they are also used by the military, but also by some hunters to mark paths. They can also replace the glow stick when fishing .

Dials of a wrist watch
Tritium light element on a key fob
Three-point sight of an FN Five-Seven
self-luminous escape sign

functionality

A tritium gas light source consists of a section of mostly tubular borosilicate glass that is coated on the inside with a layer of a fluorescent substance ( phosphor ). In the tube, the tritium emits beta radiation relatively constantly . When exposed to beta radiation, the fluorescent material emits photons in a light color typical of the fluorescent material, which is what defines the weak luminaire, which only decreases in strength after years. Since the tritium emits beta radiation due to the beta decay and transforms itself into the stable helium isotopic ³ He, the luminosity decreases with the half-life of tritium (approx. 12.3 years), since the amount of tritium also decreases.

During production, a glass capillary is filled with radioactive tritium (a natural isotope of hydrogen ). Then small sections (a few millimeters up to 10 centimeters) of the capillary are sealed and cut off with the help of a laser .

Theoretically it is possible to fill any beta emitter into the tube to achieve this function. However, tritium is particularly suitable for this because it and its decay product are non-toxic and the energy of the beta rays is very low (maximum 18.6 keV ).

Alternatives

In China, so-called nano-tritium atom batteries are also available; these generate light by converting beta radiation into electrical current in a semiconductor similar to a photodiode, see also: Betavoltaics

hazards

Intact tritium gas light sources completely shield the beta radiation from the radioactive tritium. However, braking the electrons creates bremsstrahlung in the X-ray range , which penetrates to the outside. Gas light sources with a high tritium content can increase radiation exposure .

If the glass tube is damaged and tritium escapes, there is little danger to humans and the environment because the body ingests it when it is inhaled and it continues to emit beta radiation. The particular danger of tritium is its biological activity, that is, like hydrogen, it can enter the natural cycle of materials and, for example, cause damage as a component of then radioactive drinking water. However, because of the small amount of tritium that tritium gas light sources contain and the relatively low distribution of tritium gas light sources, this does not pose a great danger.

In the event of the destruction of a tritium gas light source in the form of a key fob and the assumed complete inhalation of the gas, a single intake of approx. 350 µSv can be expected (based on an equivalent dose of 20 µSv specified by the Federal Office for Radiation Protection when the gas is absorbed from a tritium-containing watch with an activity of 1 GBq ). This corresponds to about a seventh of the natural radioactivity absorbed annually. For more realistic scenarios such as B. Breaking in a room with insufficient air exchange and very poor air quality (high carbon dioxide content of 3000 ppm due to breathing in the oxygen in the air), and staying in this room until this state is reached, one comes to about five hundredth of the annual natural radioactivity absorbed .

legality

Tritium gas light sources are legal in most of the world, but only with special requirements, especially for the civil market.

The following applies to the civil sector in Germany :

An activity of 1 GBq must not be exceeded.
From an activity of 0.5 Bq / g, the manufacturer must take back light sources free of charge.
Manufacturing and importing require a permit.

The total activity of tritium gas light sources used in watches and small key fobs starts below a GBq (trigalight marker) and goes up to 17.5 GBq (trigalight Glowring, similar to NITE GlowRing). The light source of the torch "Betalight Torch", which is mainly used in the military sector, has an activity of 70 GBq.

The possession of tritium gas light sources with a total activity of over 1 GBq is subject to approval in Germany. Possession without a corresponding permit is an administrative offense and can be punished with a fine of up to € 50,000.

Web links

http://www.pro-physik.de/details/articlePdf/4802561/issue.html

Individual evidence

↑ A Review of Consumer Products Containing Radioactive Substances in the European Union: Chapter 3.2.6 (PDF file; 452 kB)

↑ Radiation Protection Ordinance Section 107, Paragraph 1. a)

↑ Trigalight Marker product description ( Memento of the original dated December 2, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.8 MB) @1@ 2