Thermoluminescent dosimeter

Because there are so many instruments available, only the use of the ion chamber dosimeter, thermoluminescent dosimeter (TLD), and the low-range beta-gamma radiation detector will be taught in this station. 

Lithium fluoride is an essential component of the fluorine cell electrolyte 1% LiF in the KF 2HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cells to depolarize (18). Thermoluminescent radiation dosimeters used in personnel and environmental monitoring and in radiation therapy contain lithium fluoride powder, extmded ribbons, or rods (19). 

A dosimeter is used to collect cumulative evidence of exposure to radiation and is worn as a badge. Dosimeters contain a thermoluminescent material such as lithium fluoride. Any incident radiation knocks electrons out of the flu-... 

These analyses require that the 10) values for normal incidence be modified for irradiation geometries where the field is incident other than perpendicular to the surface of the personal monitor. The methods used in developing these modifications to fl pdO) for nonnormal incidence included extensive Monte Carlo calculations of photon interactions in anthropomorphic phantoms (Xu, 1994) or in PMMA and tissue slabs and the ICRU sphere (Grosswendt, 1991 Grosswendt and Hohlfeld, 1982), and thermoluminescent dosimeter measurements in water cubes (Lakshmanan et al., 1991). Some of these modifications for /fp(lO) are presented in ICRU (1992). 

The current situation is exemplified by a study of clinical staff exposures in cardiac angiography at the Montreal Heart Institute (Renaud, 1992). Extensive measurements of staff exposures were made using thermoluminescent dosimeters (TLDs) for 15,000 procedures in three cardiac catheterization laboratories over a 5 y period (1984 to 1988). The TLDs were located under the protective apron at the waist and at the collar outside and above the apron. Readings were made at three-month intervals, with a minimum reportable value of 0.2 mSv. Average values (in mSv per y) for various groups of staff, based on measurements with TLDs worn at the collar, are given in Table 3.3. 

Sulfates. The basic lattice of sulfate phosphors absorbs very short wavelength UV radiation. On excitation with X rays or radiation from radioactive elements, a large proportion of the energy is stored in deep traps. For this reason, CaS04 Mn is used in solid-state dosimeters. Of the glowpeaks which can be selected by thermoluminescence, more than 50 % fail to appear at room temperature because of a self selection of the shallow traps. Other activators, such as lead or rare-earth ions (Dy3 +, Tm3 +, Sm3+), stabilize the trapped electrons [5.399]—[5.401]. 

Thermoluminescent phosphors are used industrially in dosimeters. They are produced by coprecipitation of CaF2 and an activator from a solution of the corresponding cations, or by the reaction of oxides or carbonates of the cations with hydrofluoric acid followed by firing. Moldings with high transparency for use in dosimeters can be produced by high-temperature pressing. 

A. Halperin, Activated thermoluminescence (TL) dosimeters and related radiation detectors 187... 

Thermoluminescence can be used to measure how much radiation a material has been subjected to. It is used for dosimeters by people working around x rays or radioactivity who need to know how much ionizing radiation they have been exposed to. Thermoluminescence is also used for radioactive dating of pottery shards and for finding radioactive minerals. 

Accident dosimetry using biological systems in which the quantification of chromosome aberrations or the ratios between different blood proteins can give an indication of exposure, is hampered by the individual characteristics of the victim (i.e. general health, diet etc.), and by the complexity of the techniques. These problems can be avoided by adopting a more physical approach, and both chemiluminescence and thermoluminescence of possible dosimeters, for example, have been found to be useful. The drawbacks here concern the solubility with chemiluminescence, the amount of sample required for thermoluminescence, and the impossibility of taking repeated measurements with either system. In contrast, electron spin resonance (ESR) spectroscopy is not subject to these constraints. Measurement is made directly on the sample, very small amounts of material can be used, and repeated measurements are possible... 

The thermoluminescent dosimeter is a special phosphor, such as CaS04 doped with Dy, with the ability to trap electrons between the conducting and the valence bands. These trapped electrons will return quickly to the valence band when the phosphor is heated, producing a light pulse that can be recorded with a photomultiplier tube. 

An important parameter, CT dose index (CTDI, defined as the cumulative dose along the patient s axis for a single tomographic image), should be evaluated at least semiannually at different values of kVp and mA. It is measured by using an ionization chamber or a thermoluminescent dosimeters placed in a tissue-equivalent acrylic phantom simulating head or body. ACR (2007) recommends maximum doses CTDI) of 6 rad (60 mGy) for brain, 3.5 rad (35 mGy) for adult abdomen and 2.5 rad (25 mGy) for pediatric (5-year-old) abdomen. The details of these measurements are available in standard CT physics books. 

A. Thermoluminescent dosimeter (TLD) badges used to provide a permanent record of the cumulative exposure to the whole body must be worn on the trunk (below the shoulders and above the hips) outside of clothing on the portion or area of the body nearest the radiation source. The dosimeter window must face out from the body. 

Whatever the source of radiation used, the dose delivered to the biological samples is determined by the time of exposure to radiations. Thus the dose delivered by the radiation source must be measured with precision. Dosimetry can be performed with a ferrous sulfate solution (Fricke and Morse, 1927), thermoluminescent dosimeters, bleaching of films (Hart and Fricke, 1967), Perspex dosimetry (Berry and Marshall, 1969), or calibration with standard enzymes (Beauregard et al., 1980 Beauregard and Potier, 1982 Lo et al., 1982). In many laboratories, control enzymes with known D37 are added to protein preparations as internal standards so that any variation between experiments could be corrected for. Because of the better precision of dose rate in Gammacell irradiators, this precaution is not necessary. 

When irradiating at low temperature, the temperature sensitivity of the various dosimeters must be taken into account to determine the dose rate. Thermoluminescent dosimeters are not affected by temperature, contrary to the other calibration methods (Kempner and Haigler, 1982 Jung, 1984). 

Figure 3 presents a typical y-ray calibration of LiF thermoluminescence using a dose rate of 0.90 rads/sec. The y-ray source was calibrated against the Fricke dosimeter. 

This chapter discusses in detail all the neutron detection methods mentioned above, as well as the Bragg crystal spectrometer, the time-of-flight method, compensated ion chambers, and self-powered neutron detectors (SPND). Other specialized neutron detectors, such as fission track recorders and thermoluminescent dosimeters, are described in Chap. 16. 

Thermoluminescent dosimeters (TLDs) are based on the property of thermoluminescence, which can be understood if one refers to the electronic energy-band diagram of crystals (see also Chap. 7). When ionizing radiation bombards a crystal, the energy given to the electrons may bring about several results (Fig. 

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