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GALEN W. EWING Professor Emeritus Seton Hall University Address: P.O. Box 2573 Las Vegas. NM 87701
CI. Thermoluminescence Part I: Principles Emanuel P. Manche, Department of Natural Sciences, York College of the City University of New York, Jamaica, New York 11451
INTRODUCTION
certain types of prior incident radiations is generally termed luminescence. Specialized names are used t o classify this phenomenon according to the type of excitation. Table 1 summarizes this classification. The luminescence is further classified on the basis of the time elapsed between the application of excitation and the photon emission. For delays shorter than about 10-%ec, the process is generally regarded as fluorescence; in other cases i t is generally called phosphorescence. Thermoluminescence falls under the latter category where it can be considered as an extremely delayed phosphorescence. Thermoluminescenee (TL) is the photon energy (henceforth referred to simply as light) that is released when a crystalline substance is heated from a convenient low temperature, usually room temperature, ta a higher value but below the temperature of "incipient" incandescence (400-SOOT). The thermolumineseent energy is produced and stored when the crystalline material is irradiated with some kind of ionizing radiation any time prior to the heating. Among the most effective sources of ionizing energies are those originating from nuclear emissions such as a J , y as well as X-rays, cosmic rays, electron beams, and other fast particles. The total
light emission is proportional to the overall radiation dosage the material has received, regardless of the dose rate. What is generally referred to as the thermoluminescence "glow curve" is, in effect, the sum of all the measured lieht ouanta emitted bv a substance as
erasure of the previous radiation history. Upon cooling and reheating, no further TL light will be obtained until the sample receives an additional dose of ionizing radiation. The emission measured at the higher temperatures, after the reheating cycle, is due solely to thermal (blackbody) radiation.
HISTORICAL Thermoluminescence must have been obsewed as far back as the Stone Age, as certain limestones, when heated, give off a glow. Luminescence phenomena have been known and actually recorded as far backas 1500 B.C. when glowworms were mentioned in the Chinese "Shih Ching" or "Book of Odes," and in the first half century of the Christian Era when Pliny the Elder, in his "Historio Naturalis," catalogued, along with the glowworms, a host of other phenomena, including the lantern fish, as well as luminous mollusc, woad, and fungus. However, it was not until 1603 that the first investigation
Emanuel P. Manche received his BS and MS degrees from the City College of New York and Brooklyn College, respectively. In 1965, he received his PhD degree from Rutgers University, after which he joined the luminescence group of the research laboratories of General Telephone and Electronics Corporation as an Advanced Research Engineer. Dr. Manche joined York College of the City University of New York in 1968 where he is presently an Associate Professor of Chemistry. His teaching, consulting and research interests are in the area of chemical instrumentation, with particular emphasis on thermoanalytical techniques, solid state reactions and thermoluminescence.
began with a synthetic material. Vincenzo Cascariolo, a cobbler and alchemist in Bologna, Italy, heated a mixture of barium sulfate (in the form of barite) and coal. Aftet.cooling, the synthetic powder exhibited a bluish ghw a t night which could be restored by exposing it to sunlight. It was named "lapis solaris" or sunstone, which alchemists hoped would transform baser metals into gold, the symbol for gold being the sun ( I ) . In 1663, Sir Robert Boyle reported to the Royal Society, in London, (2) the light emission from a diamond heated in the dark. Today we know that his experimental findings were, in fact, examples ~~fthermoluminescence and the basis for the modern science of solid-state dosimetrv. I he f i r d pr~,lx~.:,Ii,r ! I N t4.e ad'~hwttt~,. l u m i n t . * r r ~ ttlfr ~ r ~r .~h n r ~ o nd ~ l ~ , l w l r hy .d ever, wm m.xh l>y l ) . n d s L J I m l Y 3 1 . Stnw ~ h tame n ~ thrrmdum~ntnenrcduitmetr) h,.; ~wnw d d c npplmrlun ,n -Ivnrwt) UI v #en! ~ I I c ~ s I ! ~Inwrhi $ . ~ i r l dOI medi
