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.     

Energy response of different types of RADOS personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) TL detectors

The photon energy response of different RADOS (Mirion Technologies) personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) thermoluminescence (TL) detectors was investigated. Three types of badges were applied. The irradiation with reference photon radiation qualities N (the narrow spectrum series), and S-Cs and S-Co nuclide radiation qualities, specified in ISO 4037 [International Organization for Standardization (ISO). X and gamma reference radiations for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy. ISO 4037. Part 1-4 (1999)], in the energy range of 16-1250 keV, were performed at the Dosimetry Laboratory Seibersdorf. The results demonstrated that a readout of a single MTS-N or MCP-N detector under the Al filter can be used to determine Hp(10) according to requirements of IEC 61066 [International Electrotechnical Commission (IEC). Thermoluminescence dosimetry systems for personal and environmental monitoring. International Standard IEC 61066 (2006)] for TL systems for personal dosimetry. The new RADOS badge with the experimental type of a holder (i.e. Cu/Al filters) is a very good tool for identifying the radiation quality (photon energy).     

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.     

Dosimetric properties of new cards with high-sensitivity MCP-N (LiF:Mg,Cu,P) detectors for Harshaw automatic reader

A new configuration for a thermoluminescent dosimetric card has been developed through collaboration between the Institute of Nuclear Physics in Kraków and several commercial dosimetric companies. The card is based on high-sensitivity LiF:Mg,Cu,P circular pellets (MCP-N) welded inside synthetic foils. The basic configuration consists of two pellets of 3.6 mm diameter and thicknesses from 0.25 up to 0.38 mm. The cards can be processed in a standard 6600 or 8800 Harshaw automatic TLD reader. The dosemeters demonstrate very high sensitivity, low background and good stability. This article presents results of the performance tests of the new dosimetric cards in the automatic TLD readers and a comparison of their properties.     

Batch homogeneity of LiF(Mg,Cu,P)-GR200 and LiF(Mg,Cu,P)-MCP-NS TL detectors for use as extremity dosemeters at ENEA personal dosimetry service

The results of a study of two commercially available LiF(Mg,Cu,P) TL materials, a GR200 detector and a MCP-Ns thin detector, are described in order to use these phosphors for individual monitoring for the extremities. After a dosimetry system has been type tested, the implementation routine is not straightforward. Additional tests and software modification are needed to make the routine system work comply with the type test results. Not often can literature be found on the steps required to implement the results in a routine study. This paper reports the results of the individual calibration of about 15 000 extremity dosemeters, 12 000 containing a GR200 detector and 3000 an MCP-Ns thin detector. It describes the experimental procedure followed in order to assure reproducibility and stability of the results with proper accuracy and reliability. In particular, this is the first time that results on homogeneity of such a large batch of MCP-Ns detectors are reported.     

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.     

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.     

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.     

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.     

Comparative study of LiF:Mg,Cu,Na,Si and Li2B4O7:Cu,Ag,P TL detectors

Recently, two new types of 'tissue equivalent' thermoluminescent detectors (TLDs) have aroused attention: LiF:Mg,Cu,Na,Si and Li2B4O7:Cu,Ag,P. In this work the characteristics of both detectors were compared with the characteristics of the well-known type LiF:Mg,Ti detector, TLD-100. The following properties were investigated: the glow curve structures, relative sensitivity, batch homogeneity and uniformity, detection threshold, reproducibility of the response, linearity in the wide dose range and fading. Also, the energy dependence for medium and low energy X rays was determined in the range of mean energies between 33 and 116 keV. The results confirmed 'tissue equivalency' of both new types in the investigated range of photon energies. LiF:Mg,Cu,Na,Si detector has very high sensitivity (approximately 75 times higher than that of TLD-100) and is convenient for use in a very low range of doses. Li2B4O7:Cu,Ag,P detector shows some improvements in comparison with the previously prepared types of lithium borate. The most important is the five times higher sensitivity than that of TLD-100. This detector is also very promising, especially in medical dosimetry.     

Comparison of two extremity dosemeters based on LiF:Mg,Cu,P thin detectors for mixed beta-gamma fields

Two types of thin LiF:Mg,Cu,P detectors, GR-200F and MCP-Ns, have been characterised for use in the design of an extremity dosemeter for mixed beta-photon radiation fields. Both detectors consist of an extremely thin layer of sensitive material with effective thicknesses of 5 and 8 mg cm(-2), respectively, held in a 5 mg cm(-2) PVC ring holder. Dosimetric performance was analysed according to the ISO 12794 standard and compared with 240 mg cm(-2) TLD-100 measurements. In particular, the energy response was obtained for ISO narrow X-ray spectra, (137)Cs, (60)Co, (204)Tl and (90)Sr/(90)Y. From these measurements a mean calibration factor was calculated to estimate H(p)(0.07). Subsequently, the performance of the dosemeters was checked for a set of 10 different mixed photon and beta-photon fields. The study shows that the proposed dosemeters can estimate H(p)(0.07) in a wide range of mixed beta-photon fields with a maximum deviation from the given dose of 30% and an overall uncertainty of the order of 25% (k = 1). However, the results also highlight a large variability among the different thin detectors and, thus, the standard TLD-100 material is recommended whenever the workplace does not include low-energy beta radiation.     

Evaluation of the performance of two LiF:Mg,Ti and LiF:Mg,Cu,P dosemeters for extremity monitoring

In this paper, the results aimed at assessing the performance of two varieties of LiF detectors (LiF:Mg,Ti and LiF:Mg,Cu,P) in photon fields relatively to reproducibility, detection threshold and angular dependence as defined in the ISO 12794 standard are presented. The fading properties and the limit of detection were also investigated for both materials. The results suggest that both LiF varieties are well suited for extremity monitoring. However, better fading properties of LiF:Mg,Cu,P when compared with LiF:Mg,Ti, combined with previous results relatively to energy dependence suggests that LiF:Mg,Cu,P dosemeters are better suited for extremity monitoring.     

Pre- and post-irradiation fading effect for LiF:Mg,Ti and LiF:Mg,Cu,P materials used in routine monitoring

LiF is a well-known thermoluminescent (TL) material used in individual monitoring, and its fading characteristics have been studied for years. In the present study, the fading characteristics (for a period of 150 d) of various commercial LiF materials with different dopants have been evaluated. The materials used in the study are those used in routine procedures by the Personal Dosimetry Department of Greek Atomic Energy Commission and in particular, LiF:Mg,Ti (MTS-N, TL Poland), LiF:Mg,Cu,P (MCP-N, TL Poland), LiF:Mg,Cu,P (MCP-Ns, thin active layer detector, TL Poland) and LiF:Mg,Cu,P (TLD100H, Harshaw). The study showed that there is a sensitivity loss in signal of up to 20 % for the MTS-N material for a 150-d period in the pre-irradiation fading phase. The MCP-N has a stable behaviour in the pre-irradiation fading phase, but this also depends on the readout system. As far as the post-irradiation fading effect is concerned, a decrease of up to 20 % for the MTS-N material is observed for the same time period. On the other hand, the LiF:Mg,Cu,P material presents a stable behaviour within ± 5 %. These results show that the fading effect is different for each material and should be taken into account when estimating doses from dosemeters that are in use for >2 months.     

Energy response of a two-dimensional sheet-type LiF:Mg,Cu,P TL dosemeter to photons

A 2-D tissue-equivalent sheet-type dosemeter (NTL sheet) was developed using thermoluminescent material of LiF:Mg,Cu,P (NTL-250). The energy responses of the NTL sheet and NTL-250 powder were measured with 10-150 keV monoenergetic photons from synchrotron radiation at SPring-8. The sample was irradiated by a rotational method for the uniform irradiation with the narrow beam. Linearity of the NTL-250 was confirmed up to 2 Gy. Energy responses of the NTL sheet and NTL-250 powder were close to that of soft tissue. On the other hand, the BaSO(4) sheet, which has been used practically, showed the response that the sensitivity approximately 60 keV was 100 times higher than that for (60)Co gamma rays. Therefore the NTL sheet can be said to have excellent properties for dose measurements.