A thermoluminescent dosimeter, abbreviated as TLD, is a passive radiation dosimeter that measures ionizing radiation exposure by measuring the intensity of visible light emitted from a sensitive crystal in the detector when the crystal is heated. The intensity of light emitted is measured by the TLD reader, depending on the radiation exposure. Thermoluminescent dosimeters were invented in 1954 by Professor Farrington Daniels of the University of Wisconsin-Madison. TLD dosimeters apply to situations where real-time information is not needed. Still, precise accumulated dose monitoring records are desired for comparison to field measurements or for assessing the potential for long-term health effects. In dosimetry, the quartz fiber and film badge types are superseded by TLDs and EPDs (Electronic Personal Dosimeter).
Thermoluminiscent Albedo Neutron Dosimeter
Albedo neutron dosimetry is based on the human body’s effect of moderation and backscattering of neutrons. Albedo, the Latin word for “whiteness,” is defined by Lambert as the fraction of the incident light reflected diffusely by a surface. Moderation and backscattering of neutrons by the human body create a neutron flux at the body surface in the thermal and intermediate energy range. These backscattered neutrons, called albedo neutrons, can be detected by a dosimeter (usually a LiF TLD chip) placed on the body, designed to detect thermal neutrons. Albedo dosimeters are the only dosimeters that can measure doses due to neutrons over the whole range of energies. Usually, two types of lithium fluoride are used to separate doses contributed by gamma-rays and neutrons. LiF chip enriched in lithium-6, which is very sensitive to thermal neutrons, and LiF chip containing very little lithium-6, which has a negligible neutron response.