Thermoluminescence dosimeters

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. 

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). 

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. 

Chapter 17 deals with special detectors and spectrometers that have found applications in many different fields but do not fit in any of the previous chapters. Examples are the self-powered detectors, which may be gamma or neutron detectors, fission track detectors, thermoluminescent dosimeters, photographic emulsions, and others. 

The second edition follows the same guidelines as the first—namely simplicity in writing and use of many examples. The main structural change is the elimination of Chap. 17 (Special Detectors and Spectrometers) and the relocation of the material in appropriate chapters. For example, rate meters and gas-filled detectors are now discussed in Chap. 5. Self-powered detectors are now included in Chap. 14 along with other neutron detectors. Chapter 16 deals with solid-state track recorders and thermoluminescent dosimeters. 

In a study from eight centers in Belgium (Monsieurs et al., 1998), the measured doses in 94 relatives of thyrotoxicosis and thyroid cancer patients are presented. The relatives wore thermoluminescence dosimeters (TLD) on the wrist for at least 7 days. The authors propose the implementation of a nonrigid dose constraint for people who knowingly and willingly help patients treated with 1311. 

Barrington et al., (1999) Hyperthyroidism 195-800 For 3-6 weeks use of thermoluminescence dosimeters on wrists of family members. Avoid close contact with other individuals following standard procedures from five hospitals in the United Kingdom advice A and B differed according to administered activities advice B was also dependent on the age of the child. 

Cappelen etal., (2006) Hyperthyroidism 260-600 For 2 weeks use of thermoluminescence dosimeters on wrists of family members. Detailed behavior restrictions according to the European Commission (1998) duration 14 days for children aged 0-10 years, 7 days for children aged 11-17 years, 3-7 days for persons aged 18-59 years, 1 -3 days for persons 60 years or older instructions were not dependent on administered activities. 

Azorin J., Furetta C. and Gutierrez A. 1989. Evaluation of the kinetic parameters of CaF2 Tm(TLD-300) thermoluminescence dosimeters, J. Phys. D Appl. Phys. 22 458-464. 

McKeever S. W. S. 1985. Thermoluminescence of Solids. Cambridge, U.K. Cambridge University Press, p. 75. McKeever S. W. S., Markey. B.G. and Lewandowski, A. C. 1993. Fundamental processes in the produchon of thermally stimulated luminescence. Nuclear Trackes and Radiation Measurements, 21(1) 57-64. Nakajima T, Murayama Y, Matazawa T. and Koyano A. 1978. Development of a new highly sensitive LiF thermoluminescent dosimeter and its applications, Nucl. Instrum. Methods 157 155—162. 

Dosimeters are the primary means of assessing external exposures. When required by a technical work document, personnel are required to wear dosimeters. Dosimeters are issued and monitored on a monthly or a quarterly basis, dependent on work requirements. Thermoluminescent Dosimeters (TLD s) are used at SNL as the basis for personnel dose exposure records. Self-reading dosimeters are used on an as-needed basis for specific jobs. Dosimeters are routinely maintained and calibrated by the SNL radiation protection organization In the ES H Center.. ... 

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