- Thermoluminescent Dosimeters. TLD's.They are used in industry to detect radiation and accumulate an absorbed dose reading over a period of time ( usually months, weeks ion the case of a pregnant worker).Pen dosimeters and film badges are some types. The TLD is another.Inside a ring, clip or badge are one or more small crystals for Lithium Fluoride (Mg Ti doped). Sometimes a large badge will have several crystals, each covered by a different absorber so that each will record a different parameter. Neutron chips are sometimes included, but they are CR39 plastic track recorders.After a predetermined time period, the TLD's are processed in a reader that heats them to a high temperature, in the 250C range. Upon heating, the crystal will put out light photons in proportion to the radiation absorbed, which is detected by a PMT. The heating reads and recharges the crystal at the same time.Electrons in most atoms will absorb energy from radiation or other external source, raising the electron's energy level, but it is released almost immediately as the electron falls back to it's ground state. LiF crystals are so stable that the electrons retain that extra energy for decades, up to about 80 years. When heated, this extra energy is released as light photons, and once those electrons have fallen back to their ground (stable) state, the crystal is ready again for use ( indefinitely).Readers are expensive, so many times an off-site service is employed to manage the rotating, reading and record keeping. If immediate reading is required, the individual company has it's own Health Physicist to do those chores.When I worked in the field, I was required to wear 2 rings, a film badge, a TLD clip and two pens! Pens were read every day, the film and TLD's were serial numbered to me and processed on a regular basis. Plus had get my thyroid scanned before going home.Shown in this link are some LiF Crystals (TLD-700) and LiF powder capsule.When I get hold of some ring and badge holders, I will make an article for that same link. Right now the only thing are the bare crystals. Oh yes,. check out Mat Hazard'sCosmic Ray Hat.Have funGeo.