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At least 685 records · Page 38Linked to original sources
PubMed2002

Influence of background exposure on detection and determination limits for a TL dosimetry system based on LiF:Mg,Cu,P(GR-200A).

Thermoluminescence dosemeters are widely used to monitor personal doses. For these low dose range applications, it is important to determine the detection limit L(D) and the determination limit L(Q) of the dosimetric system. The influence of background exposure on these limits for LiF:Mg,Cu,P(GR-200A) based TL dosimetry was investigated. Both the conventional analysis and the glow curve analysis methods were used to determinate these limits. The detection limit L(D) was compared with the recording level and the investigation level. A systematic error can occur in the occupational dose evaluation when the detection limit L(D) is more than the recording level. It was found that the L(D) of the dosimetric system-based LiF:Mg,Cu,P(GR-200A) was less than the recording level for exposure time tau > or = 10 days considering an annual dose limit of 1 mSv for the public recommended in ICRP Publication 60.

Air↗
PubMed2002

A system for rapid large-area monitoring of gamma dose rates in the environment based on MCP-N (LiF:Mg,Cu,P) TL detectors.

One lesson learned from the Chernobyl accident was that the spatial distribution of far-field contamination was strongly non-uniform due to local variation of atmospheric conditions, such as wind direction, rain etc. An environmental monitoring system using highly sensitive thermoluminescent LiF:Mg,Cu,P (MCP-N) detectors has been completed and field-tested. The system consists of 3000 MCP-N detectors in 1000 TLD cards (three TLDs per card), two Mikrolab automatic TL readers, heating ovens, and specially developed software which includes a database for rapid evaluation of results. The main dosimetric parameters of MCP-N dosemeters, such as thermally-induced fading, light sensitivity, minimum detectable dose, self-dose, zero-dose, energy response up to 6-7 MeV, influence of annealing and readout conditions on detector stability, have been tested. About 100 locations over an area of about 15,000 km2 in the south of Poland were selected for measurements lasting from 4 days to 3 months. The kerma rates measured over a 4 day screening period agree well with kerma rates determined over a 75 day monitoring period. Results from short- and long-term exposure periods agree well with those performed using MTS-N (LiF:Mg,Ti) over southern Poland in 1985, before the Chernobyl accident. Thus, using the system based on MCP-N detectors, one is able simultaneously to monitor environmental radiation kerma rates at a large number of locations over periods of four days or less. Provided natural background kerma rates at selected monitoring points are available prior to the accident, the system can be applied to assess kerma rates rapidly in the environment, following a nuclear accident.

Calcium↗
PubMed2002

Evaluating two extremity dosemeters based on LiF:Mg,Ti or LiF:Mg,Cu,P.

Evaluation of a new extremity dosemeter is presented. The dosemeter is a passive device that is easy to wear and features a permanent individual numerical ID with barcode, a watertight case, an automatic TLD reader and database management software. Two dosemeters were studied: the first consists of a 100 mg x cm(-2) 7LiF:Mg,Ti (TLD-700) chip and a 42 mg x cm(-2) cap, the other consists of a 7 mg x cm(-2) layer of 7LiF:Mg,Cu,P (TLD-700H) powder and a 5 mg x cm(-2) cap. Sensitivity, repeatability, lower limit detection, angular responses and energy responses for these dosemeters are studied and presented. The dose calculation algorithm is developed and its dosimetric performance accuracy is compared with the standard ANSI N13.32-1995, Performance Testing of Extremity Dosemeters.

Beta Particles↗
PubMed2002

The application of computerised analysis of glow curves to personal dosimetry in LiF:Mg,Cu,P.

In personnel monitoring services, it is important to omit the high-temperature annealing process so that large numbers of TL detectors can be produced economically. There are two efficient ways of reducing the residual signal of LiF:Mg,Cu,P. One is by increasing the maximum readout temperature and the other is by improving the preparation procedure (increasing the Cu concentration and the sintering temperature) but both reduce the TL sensitivity. In personal dosimetry the real dosimetric signals are separated from the residual signals by computerised analysis of glow curves. The adverse influence of the high residual signals of LiF:Mg.Cu.P TL material has been effectively eliminated and the sensitivity remains stable. A good dosimetric result using only reader measurement without pre-irradiation oven annealing is attained in a dose range of 50-80,000 microGy.

Computer Systems↗
PubMed2002

Experience gained from the Ciemat External Dosimetry Service participation in several environmental dosimetry intercomparisons.

This paper summarises the experience gained by the Ciemat External Dosimetry Service (EDS) in the environmental dosimetry intercomparisons organised by the US Department of Energy. During the three latest intercomparisons. important dosimetry aspects such as energy calibration, energy response, dosimetric quantities and signal stability have been tested by the Ciemat EDS on up to seven different thermoluminescent (TL) materials, including hypersensitive phosphors, and employing several dosimetric systems. In last year's intercomparison, in addition to TL dosemeters the Ciemat EDS sent a set of silicon diode active dosemeters, usually used as personal dosemeters, to be tested in environmental conditions without intervention for more than 3 months. All the results obtained from different dosemeters have undergone an exhaustive analysis process in order to find some conclusions that may help to increase the knowledge of field performance of these devices in real but controlled environmental conditions.

Equipment Design↗
PubMed2002

The influence of post-exposure heating on the stability of MCP-N (LiF:Mg,Cu,P) TL detectors.

Post-exposure annealing of highly sensitive LiF:Mg,Cu,P (MCP-N) detectors, at 100 degrees C over 10 or 20 min prior to readout, is usually recommended for routine dosimetry. The purpose of this anneal is to eliminate low-temperature peaks, especially peak 3, which fades at room temperature in about 3 months. However, as this annealing procedure does not entirely eliminate peak 3, 10% of its thermoluminescent (TL) signal still being readable, a fading correction must be applied. The aim of this work was to optimise the conditions of post-exposure treatment, i.e. its temperature and duration, in order to facilitate the use of MCP-N detectors in routine dosimetry. MCP-N detectors were annealed in standard conditions, i.e. at 240 degrees C over 10 min and exposed to a dose of 5 mGy (137Cs). For post-exposure annealing, six different temperatures between 100 degrees C and 150 degrees C and two time periods (10 and 20 min) were tested. TL glow curves were deconvoluted with the GCA code. A post-exposure anneal at 120 degrees C over 10 min was found to be optimal. Heating at this temperature eliminates 100% of the TL signal of peak 3, while maintaining the area and maximum intensity of the main peak 4 unchanged. In this case, no fading correction needs to be applied. Annealing at higher temperatures, up to 150 degrees C, results in a loss of peak 4 signal, and is therefore not recommended.

Copper↗
PubMed2002

Extremity and whole-body dosemeters for beta and beta gamma fields based on LiF:Mg,Cu,P thin detectors.

This study aims at proposing two TL dosemeters: one for the whole body and another for the extremities, for beta and gamma fields. Selected sensible material consists of 5 mg x cm(-2) LiF:Mg,Cu,P film (GR-200F) manufactured in China. Calibration was carried out according to ISO 4037-3, in terms of Hp(0.07), and dosimetric performance was analysed on the basis of IEC-1066 and ISO-12794 Standards. Experiments showed a satisfactory sensitivity of the proposed dosemeters for detecting beta radiation at protection levels and a very good energy response; thus, highly recommending their use for weakly penetrating radiation measurements. However, the homogeneity and the reproducibility of GR-200F are not found to be as reliable as in standard materials.

Arm↗
PubMed2002

MCP-N (LiF:Mg,Cu,P) TLDs for radon measurements with charcoal canisters.

A method of measurement of radon concentration in air was developed, based on high-sensitivity LiF:Mg,Cu,P (MCP-N, TLD Poland) thermoluminescent detectors installed in charcoal canisters. The canisters were exposed typically for 72 h in a calibration chamber with a radon concentration ranging from 100 Bq x m(-3) to 87 kBq x m(-3). It was found that in these conditions the signal registered by the TL detectors was proportional to the 222Rn concentration and the lowest limit of detection (LLD) was at a level of 100 Bq x m(-3). The proposed method can be used in large-scale, multi-site surveys aimed at screening for high levels of indoor radon concentration or for measuring ground radon exhalation rates.

Charcoal↗
PubMed2002

LiF:Mg,Cu,P 'pin worms': miniature detectors for brachytherapy dosimetry.

Dose measurements in brachytherapy 192Ir implants are often difficult due to large dose gradients and complex photon spectra. Therefore, tissue-equivalent detectors with a high spatial resolution, such as the highly promising LiF:Mg,Cu,P thermoluminescent detectors (TLDs) are required. It was the aim of the present work to ascertain if miniature LiF:Mg,Cu,P TLDs can effectively measure the dose distribution around 192Ir implants. 'Pin worm' TLDs (type MCP, diameter 0.6 mm, length 2 mm) were compared with GR-200R (SSDL, Beijing) rods cut in half. The TLDs were tested for reproducibility and energy dependence using high dose rate (HDR) and low dose rate (LDR) brachytherapy units. 192Ir measurements were performed in a tissue equivalent phantom accommodating hollow needles and catheters routinely used in brachytherapy. Pin worms had an average reproducibility of less than +/-2% (1 SD) and a detection limit of less than 10 microGy. The small dimensions of the pin worms allowed their placement within brachytherapy needles and catheters. The measured relative dose distribution was in good agreement with the predictions of a computerised treatment planning system (ADAC Pinnacle); however, limitations in the TLD energy correction did not allow for absolute dose comparison.

Brachytherapy↗
PubMed2002

Reproducibility of TL measurements in a mixed field of thermal neutrons and photons.

The reproducibility of measurements performed with GR-100 (LiF:Mg,Ti) from the Solid Dosimetric Detector and Method Laboratory (DML) China, GR-107 (7LiF:Mg,Ti, DML), TLD-700H (7LiF:Mg.Cu,P, Harshaw) and Al2O3:Mg,Y (Hungary) in photon and mixed photon-neutron fields was investigated. Mixed-field irradiations were performed in a thermal neutron field generated at a nuclear reactor. GR-100 sensitivity decreased after mixed-field irradiations, while no significant change was found for the other materials. Using GR-100 for the dosimetry of mixed and high-intensity fields requires careful procedures.

Aluminum Oxide↗
PubMed2002

CVD diamonds as thermoluminescent detectors for medical applications.

Diamond is believed to be a promising material for medical dosimetry due to its tissue equivalence, mechanical and radiation hardness, and lack of solubility in water or in disinfecting agents. A number of diamond samples, obtained under different growth conditions at Limburg University, using the chemical vapour deposition (CVD) technique, was tested as thermoluminescence dosemeters. Their TL glow curve, TL response after doses of gamma rays, fading, and so on were studied at dose levels and for radiation modalities typical for radiotherapy. The investigated CVD diamonds displayed sensitivity comparable with that of MTS-N (Li:Mg,Ti) detectors, signal stability (reproducibility after several readouts) below 10% (1 SD) and no fading was found four days after irradiation. A dedicated CVD diamond plate was grown, cut into 20 detector chips (3 x 3 x 0.5 mm) and used for measuring the dose-depth distribution at different depths in a water phantom, for 60Co and six MV X ray radiotherapy beams. Due to the sensitivity of diamond to ambient light, it was difficult to achieve reproducibility comparable with that of standard LiF detectors.

Diamond↗
PubMed2002

The zero signal and glow curves of bare LiF:Mg,Ti detectors in a hot gas TLD system.

The uncertainty in very low doses measured with TLDs is partly caused by the uncertainty in the zero signal of the detector. A mathematical model for the thermodynamics of TLD heating and the zero signal in a hot gas reader with constant gas temperature is presented. The major component of the heating is described as diffusion limited conductive heating, the major component of the zero signal is black body radiation from the hot TLD. The parameters in the model were determined from the glow curves recorded at five different gas temperatures. The model explains the shape and statistics of a zero signal glow curve and can be used in the quality control of non-irradiated TLDs before calibration irradiation and readout.

Fluorides↗
PubMed2002

Glow curve analysis of composite peak 5 in LiF:Mg,Ti (TLD-100) using optical bleaching, thermal annealing and computerised glow curve deconvolution.

The relative intensity of glow peak 5a in the composite glow peak 5 of LiF:Mg,Ti (TLD-100) is very weak following gamma irradiation, and has been estimated at approximately 0.1 of the intensity of peak 5. Typical glow curve analysis using computerised glow curve deconvolution with unconstrained variation of the peak shape parameters, yields values of the relative intensity of glow peak 5a varying from 0 to 15%. Due to the potential of peak 5a to fulfil the criteria of a quasi-tissue-equivalent nanodosemeter which estimates quality factor, considerable efforts have been invested in ancilliary techniques to improve the reliability of the estimation of the intensity of peak 5a. Optical bleaching and thermal annealing techniques were used to obtain single-peak glow curves consisting of peak 4 only and peak 5 only. A multi-stage CGCD protocol was then constructed using these peak shape parameters for peaks 4 and 5, which allows more accurate estimation of the relative intensity of peak 5a. Following 60Co irradiation of ten chips to a dose level of 1 Gy, the technique yields a relative intensity of 0.08 +/- 0.008 (1 SD).

Equipment Design↗
PubMed2002

Glow curve analysis applied to the discrimination of X ray versus proton irradiation.

Three types of thermoluminescence dosemeters (TLDs): LiF:Mg,Ti (TLD-100), CaF2:Tm (TLD-300), and alpha-Al2O3:C (TLD-500), were investigated for their glow curve response to separate X ray and proton irradiations. The glow curve structure for each individual TLD's exposure to the X ray and proton irradiations was analysed and compared. Distinguishable differences between the glow curve structure characteristic of each type of radiation were observed. The proton TLD-100 glow curve has revealed a complex high-temperature peak structure that was used for the proton/X ray discrimination algorithm. Proton irradiation of TLD-300 resulted in an apparent switch in the relative heights of peaks 3 and 5 as compared to X ray. In TLD-500, proton irradiation produced a more subtle difference in the glow curve with an increase in the ratio between high- and low-temperature peaks. Results demonstrate promising differences in glow curve structure present allowing for discrimination between X ray and proton radiation field exposures.

Calcium Fluoride↗
PubMed2002

The unified interaction model applied to LiF:Mg,Ti (TLD-100): properties of the luminescent and competitive centres during sensitisation.

An attempt is made to predict/interpret theoretically the experimentally measured values of f(D) and S(Ds)/So for composite peak 5 in TLD-100. using the Unified Interaction Model (UNIM) with identical values of the UNIM parameters for both sets of experimental data. Although an excellent fit can be obtained to the experimental f(D) data over the entire dose region where f(D) is greater than unity. i.e. from 5 Gy to several thousand Gy, a satisfactory fit to both sets of data is found to require different values for at least one of the parameters. The lack of success in fining f(D) and S(Ds)/So with the same values of all the parameters, suggests that the sensitisation anneal (particularly the duration of the anneal) may somehow change the structure (S(LC)) and/or the total number of available LCs in an unknown manner.

Fluorides↗
PubMed2002

Response components of LiF:Mg,Ti around a moderated Am-Be neutron source.

The responses of TLD-1010, TLD-700 and TLD-600 thermoluminescence dosemeters to the radiation field inside a water tank enclosing an isotopic 241Am-Be neutron source are analysed. Separate contributions coming from thermal neutrons, neutrons with energies above thermal and gamma rays to the total response of the three types of TLD are obtained. This is accomplished by assuming that the gamma responses for materials with different 6Li enrichments are identical and that the neutron response of TLD-700 is negligible compared to TLD-100 and TLD-600. The last assumption is tested by Monte Carlo simulations of the neutron energy spectrum at the points where the TLDs are irradiated.

Americium↗
PubMed2004

On fading corrections for LiF:Mg,Ti irradiated by thermal neutrons.

The phenomena of preirradiation and postirradiation fading of LiF:Mg,Ti phosphors are considered a significant practical problem in routine dosimetry because of the uncertainties introduced, especially for mixed neutron-gamma dosimetry, as different fading corrections may be necessary for the gamma and neutron contributions. We have investigated if the region of interest (ROI) method is applicable to minimizing the fading effect for thermal neutron irradiation as it is for gamma irradiation. By employing the ROI method, which consists of integration between channel 31 below the glow curve maximum and channel 16 above the glow curve maximum, a constant dose value was obtained for the period of 90 d. Thus, by employing the ROI method, a fading independent evaluation of the thermal neutron dose can be made.

Algorithms↗
PubMed2004

The effects of ionisation density on the thermoluminescence response (efficiency) of LiF:Mg,Ti and LiF:Mg,Cu,P.

In this paper, the various models dealing with the effects of ionisation density on the thermoluminescence (TL) response (efficiency) of TL LiF dosemeters are discussed. These include (i) the Unified Interaction Model (UNIM), which models photon/electron linear/supralinear dose response; (ii) the Extended Track Interaction Model (ETIM), which models heavy charged particle (HCP) TL fluence response; (iii) Modified Track Structure Theory (MTST), which models relative HCP TL efficiencies; and (iv) Microdosimetric Target Theory (MTT), which models both relative HCP efficiencies and photon energy response.

Copper↗