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.     

Microprocessor controlled portable TLD system

An up-to-date microprocessor controlled thermoluminescence dosemeter (TLD) system for environmental and space dose measurements has been developed. The earlier version of the portable TLD system, Pille, was successfully used on Soviet orbital stations as well as on the US Space Shuttle, and for environmental monitoring. The new portable TLD system, Pille'95, consists of a reader and TL bulb dosemeters, and each dosemeter is provided with an EEPROM chip for automatic identification. The glow curve data are digitised and analysed by the program of the reader. The measured data and the identification number appear on the LED display of the reader. Up to several thousand measured data together with the glow curves can be stored on a removable flash memory card. The whole system is supplied either from built-in rechargeable batteries or from the mains of the space station.     

Study of real heating profiles in routine TLD readout: influences of temperature lags and non-linearities in the heating profiles on the glow curve shape

This paper reports on the results of a heating profile analysis using a commercial routine read-out system with non-contact hot nitrogen heating, using linear heating gas profiles. Glow curves of TLD-100 were analysed for different linear heating gas rates from 1 degree C x s(-1) to 30 degrees C x s(-1). The analysis of the individual peak maxima (Peak 2-5) leads to an approximation of the real heating profile in the TL detector. It was found that the real heating profile deviates strongly from linearity, and that the temperature lag between the heating gas and the detector reaches values up to some tens of degrees C. The consequences of this non-linearity, with respect to the resulting glow curves, are discussed in this paper. These results lead to a better understanding of the shape of routine TL glow curves and help to improve the use of glow curves analysis in routine services. In addition, a simple procedure is described which allows calculation of the real heating profile based on the heating gas temperature profile. This model shows a very good match between experimental data and calculated values.     

Non-radiation induced signals in TL dosimetry

One source of background signals, which are non-radiation related, is the reader system and it includes dark current, external contaminants and electronic spikes. These factors can induce signals equivalent to several hundredths of mSv. Mostly, the effects are minimised by proper design of the TLD reader, but some effects are dependent on proper operation of the system. The other main group of background signals originates in the TL crystal and is due to tribothermoluminescence, dirt, chemical reactions and stimulation by visible or UV light. These factors can have a significant contribution, equivalent to over several mSv, depending on whether the crystal is bare or protected by PTFE. Working in clean environments, monitoring continuously the glow curves and performing glow curve deconvolution are suggested to minimise non-radiation induced spurious signals.     

Intercomparison exercise within a distributed-dosimetry network

The results of an intercomparison exercise within the US Navy dosimetric network (USN-DN) are presented and discussed. The USN-DN uses a commercially available LiF:Mg,Cu,P thermoluminescent dosemeter (TLD) model Harshaw 8840/8841 and TLD reader model Harshaw 8800 manufactured by Thermo Fisher Scientific. The USN-DN consists of a single calibration facility and 16 satellite dosimetry reading facilities throughout the world with ～ 40 model 8800 TLD readers and in excess of 350 000 TLD cards in circulation. The Naval Dosimetry Center (NDC) is the primary calibration site responsible for the distribution and calibration of all TLD cards and their associated holders. In turn, each satellite facility is assigned a subpopulation of cards, which are utilised for servicing their local customers. Consistency of the NDC calibration of 150 dosemeters (calibrated at NDC) and 27 locally calibrated remote readers was evaluated in the framework of this intercomparison. Accuracy of TLDs' calibration, performed at the NDC, was found to be <3 % throughout the entire network. Accuracy of the readers' calibration, performed with the NDC issued calibration dosemeters at remote sites, was found to be better than 4 % for most readers. The worst performance was found for reader Channel 3, which is calibrated using the thinnest chip of the Harshaw 8840/8841 dosemeter. The loss of sensitivity of this chip may be caused by time-temperature profile that has been designed for all four chips without consideration of chip thickness.     

Thermoluminescence glow curves and optical stimulated luminescence of undoped alpha-Al2O3 crystals

The characteristics of thermoluminescence (TL) and optical stimulated luminescence (OSL) in undoped alpha-Al2O3 single crystals were studied. The TL glow curves of the crystal samples irradiated at various dose levels were measured by Ris? TL/OSL-DA-15B/C reader with U-340 or 7-59 filters at different heating rates. The glow peaks measured with U-340 at approximately 210 degrees C of the undoped alpha-Al2O3 can be well fitted by first-order kinetic equation whereas the glow peaks measured with 7-59 filters are a composite of two first-order glow peaks. It indicates that the TL glow curves are dependent upon the filter used in the reader that is related to the emission spectra of luminescence materials. The OSL were also measured and fitted by two exponential functions to get the luminescence intensities. The TL and OSL dose responses of the undoped alpha-Al2O3 crystal were obtained in the dose range of 0.12-248 Gy and fitted by the composite action dose-response function to get nonlinear characteristic parameters. The TL and OSL dose responses are linear-sublinear.     

The implementation in routine of the ENEA new personal photon dosemeter

The ENEA photon dosemeter, introduced in 1995, consisting of two differently filtrated LiF(Mg,Cu,P) detectors, has been modified recently. The ABS (acrylonitrile butadiene styrene) plastic support has been replaced by a new aluminium card supporting the same two detectors (LiF(Mg,Cu,P) GR200). The new card, fully developed at the ENEA-Radiation Protection Institute (which is going to be patented), can now be processed through a Harshaw Model 6600 Automated TLD Reader, a hot gas reader. This paper reports the results of the individual calibration of approximately 60,000 LiF(Mg,Cu,P) GR200 detectors inserted on the new aluminium cards. Before the implementation in routine of the new cards, the reader has been characterised. Steps and tests to be made to use the card in routine (i.e. reader stability, linearity, reproducibility, etc.) are reported. The whole dosimetric system now combines the very good performances of the Harshaw Model 6600 reader and that of LiF(Mg,Cu,P) thermoluminescent material.     

Gepulstes Pirani‐Vakuummeter: Berechnung von Aufheizung und Abkühlung. Pulsed Pirani vacuum gauge: calculation of heating and cooling

The pulsed operation of the hot filament gauge according to Pirani offers several advantages: extension of the measuring range towards larger pressures, reduced influence of the gas species, and smaller power consumption. The heating and cooling of the wire has already been experimentally investigated. However, the observed characteristics in its details can not be easily understood. In the present paper, we report on theoretical calculations of the heating and cooling processes of the sensor system consisting of wire and surrounding gas. The processes can be modelled by the Fourier differential equation of heat transport. Calculations can be performed more easily by dividing the interior of the sensor into discrete annular elements and applying the finite‐element‐method under the given boundary conditions. The results provide a quantitative and illustrative presentation of the radial temperature profile of the gas and of its time‐evolution.     

Frost retardation of an air-source heat pump by the hot gas bypass method

This study is concerned with a hot gas (refrigerant) bypass method to retard the formation and propagation of frost in an air-source heat pump. The feasibility of the hot gas bypass method was investigated experimentally and the method's performance is compared with that of a normal, 1.12 kW capacity air-source heat pump system with no defrost equipment such as an electric resistance heater. Results indicate that the hot gas bypass method is useful for retarding the formation and growth of frost at the outdoor coil. The best performance is shown under a bypass refrigerant flow rate of 0.2 kg/min (20% of the whole system refrigerant flow rate). During 210 min of heat pump operation, the hot gas bypass method improved COP and heating capacity at an average of 8.5% and 5.7%, respectively, relative to the normal system.     

Effect of heating rate on the responses of CaF2:Cu,CaF2:Tm,CaF2:Dy and CaF2:Mn

Recent development of CaF2:Cu (the most sensitive material for radiation dosimetry) exhibiting a TL glow peak around 270 degrees C similar to that of CaF2:Mn has made it attractive to study the influence of heating rate on the response of CaF2 based TLDs. Influence of heating rate on CaF2:Mn (known to reduce the response with increasing heating rate) was confirmed in view of the reported controversy about other TLDs. Responses of TL glow peaks around 270 degrees C in CaF2:Cu, CaF2:Tm, CaF2:Dy and CaF2:Mn were studied. Except CaF2:Mn, no other CaF2 based TLD exhibited a reduction in response with increasing heating rate. On the contrary, in some cases a small increase (10-15%) was noted with increasing heating rate from 1 degrees Cs(-1) to 50 degrees Cs(-1). The shape and the position of the glow peak and the parameters derived from the shape of the glow curve appear to have no relation to reduction of TL efficiency at higher heating rates. Apart from the increased probability of non-radiative transitions at higher temperatures, the observed effects have been assigned to the effect of heating rate on the migration of charge carriers released during the TL readout.     

Study of the glow curves of TLD exposed to thermal neutrons

The glow curves of thermoluminescent dosimeters (TLD600, TLD700 and MCP), exposed to a mixed field of thermal neutrons and gamma photons are analysed. The fluence values of thermal neutrons used, comparable with those used in radiotherapy, allow one to define the reliability of the TLDs, in particular the most sensitive MCP, in this radiation field and to get information on the dose absorbed values. The glow curves obtained have been deconvoluted using general order kinetics and the observed differences for the different LET components have been analysed. In particular, the ratio of the n(0) parameter of two different peaks seems to allow to discriminate the different contributions of neutrons and gamma photons in the beam.     

Thermoluminescence properties of LiF:Mg,Cu,Na,Si pellets in radiation dosimetry

Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets have been developed for application in radiation dosimetry. LiF:M,Cu,Na,Si TL pellets were made from TL powders using a sintering process, that is, pressing and heat treatment. These pellets have a diameter of 4.5 mm, and a thickness of 0.8 mm are blue in colour and have a mass of 28 mg each. After 400 pellets had been produced they were irradiated with 137Cs gamma radiation and samples having a sensitivity within a +/-5% standard deviation were selected for experimental use. In the present study, the physical and dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets were investigated for their emission spectrum, dose response, energy response and fading characteristics. Photon irradiation for the experiments was carried out using X ray beams and a 137Cs gamma source at the Korea Atomic Energy Research Institute (KAERI). The average energies and the dose were in the range of 20-662 keV and 10(-6) - 10(2) Gy respectively. The glow curves were measured with a manual type thermoluminescence dosimetry reader (system 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of 5 degrees C.s(-1). the main dosimetric peak of the glow curve appeared at 234 degrees C, its activation energy was 2.34 eV and the frequency factor was 1.00 x 10(23). The TL emission spectrum appeared at the blue region centred at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to the 137Cs response were within +/-20% in the overall photon energy region. No fading of the TL sensitivity of the pellets stored at room temperature was found over the course of a year. Therefore LiF:Mg,Cu,Na,Si TL pellets can be used for personal dosimetry, but more research is needed to improve the characteristics for repeated use.     

Residential CO2 heat pump system for combined space heating and hot water heating

A theoretical and experimental study has been carried out for a residential brine-to-water CO₂ heat pump system for combined space heating and hot water heating. A 6.5 kW prototype heat pump unit was constructed and extensively tested in order to document the performance and to study component and system behaviour over a wide range of operating conditions. The CO₂ heat pump was equipped with a unique counter-flow tripartite gas cooler for preheating of domestic hot water (DHW), low-temperature space heating and reheating of DHW.

The CO₂ heat pump was tested in three different modes: space heating only, DHW heating only and simultaneous space heating and DHW heating. The heat pump unit gave off heat to a floor heating system at supply/return temperatures of 33/28, 35/30 or 40/35 °C, and the set-point temperature for the DHW was 60, 70 or 80 °C. Most tests were carried out at an evaporation temperature of −5 °C, and the average city water temperature was 6.5 °C. The experimental results proved that a brine-to-water CO₂ heat pump system may achieve the same or higher seasonal performance factor (SPF) than the most energy efficient state-of-the-art brine-to-water heat pump systems as long as: (1) the heating demand for hot water production constitutes at least 25% of the total annual heating demand of the residence, (2) the return temperature in the space heating system is about 30 °C or lower, (3) the city water temperature is about 10 °C or lower and (4) the exergy losses in the DHW tank are small.     

A comparative study on the susceptibility of LiF:Mg,Ti (TLD-100) and LiF:Mg,Cu,P (TLD-100H) to spurious signals in thermoluminescence dosimetry

It is well known that spurious signals can occur in thermoluminescence dosimetry (TLD) whenever contaminants (i.e. dirt, oil, dust) are present on the surface of the TLD card or crystal during the read-out process. For TLD cards, the Teflon material can also contribute to the background noise and this contribution has been found to depend on the material's light absorption. These non-radiation-induced signals contribute to the total light output during TLD read-out and can lead to incorrect dosimetry especially for low-dose measurements such as personal dosimetry. However, these spurious signals are generally in the low-temperature channels and are mostly accompanied by abnormal glow curves. Most of the published reports dealing with this type of spurious TL signal are on the LiF:Mg,Ti (TLD-100) material. The relatively new TLD material, LiF:Mg,Cu,P, is more sensitive and has higher signal-to-noise ratio than the traditional LiF:Mg,Ti. In this study, the effects of disturbing signals to the LiF:Mg,Cu,P (TLD-100H) cards used in personal dosimetry are investigated and compared with those of LiF:Mg,Ti (TLD-100).     

冷凝式壁挂炉在地面辐射供暖中的应用及其节能环保性分析

介绍了低温热水地面辐射供暖系统构成,分析了该系统的舒适性和节能性。本文对普通壁挂炉和冷凝式壁挂炉进行了系统介绍,并以一住宅为例分析计算了两种壁挂炉的性能及能耗费用,发现冷凝式壁挂炉比普通壁挂炉更稳定、更节能、更环保,是地面辐射供暖系统更理想的热源。     

Discrimination of photon from proton irradiation using glow curve feature extraction and vector analysis

Two types of thermoluminescence dosemeters (TLDs), the Harshaw LiF:Mg,Ti (TLD-100) and CaF(2):Tm (TLD-300) were investigated for their glow curve response to separate photon and proton irradiations. The TLDs were exposed to gamma irradiation from a (137)Cs source and proton irradiation using a positive ion accelerator. The glow curve peak structure for each individual TLD exposure was deconvolved to obtain peak height, width, and position. Simulated mixed-field glow curves were obtained by superposition of the experimentally obtained single field exposures. Feature vectors were composed of two kinds of features: those from deconvolution and those taken in the neighbourhood of several glow curve peaks. The inner product of the feature vectors was used to discriminate among the pure photon, pure proton and simulated mixed-field irradiations. In the pure cases, identification of radiation types is both straightforward and effective. Mixed-field discrimination did not succeed using deconvolution features, but the peak-neighbourhood features proved to discriminate reliably.     

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.     

生活浊水热泵热水器性能的试验研究

针对目前生活、洗浴热水的需求不断上涨以及生活洗浴热水废水热存在巨大浪费的现状,介绍了一套新型的回收废水热的热泵热水器及其主要的设备构成.通过对该试验机组进行相关的试验研究,得到组合分离式热管蒸发器废热回收热量与污水质量流量、污水进口温度的变化关系;热泵平均制热量与污水质量流量、污水进口温度变化关系;压缩机吸排气压力及其功率随出热水温度的变化曲线;出热水温度与时间的变化曲线;系统能效比随出热水温度的变化,其平均能效比达到了3.01.与传统的电热水器、燃气热水器以及电辅助加热的热水器产品相比更节能环保.     

Modelling the performance of a transcritical CO2 heat pump for high temperature heating

A prototype transcritical CO₂ heat pump was constructed for heating water to temperatures greater than 65°C while providing refrigeration at less than 2°C. The heating capacity was 115 kW at an evaporation temperature of +0.3°C and a hot water temperature of 77.5°C, with a heating coefficient of performance (COP) of 3.4. Performance data is presented for each of the compressor, the gas cooler, and the recuperator as well as for the overall heat pump system. Equipment performance data was incorporated into a computer model to enable parametric investigations of heat pump performance. Model predictions showed that the hot water temperature could be increased from 65 to 120°C with a relatively small reduction in heating capacity and heating COP of 33 and 21%, respectively. Model predictions also highlight the potential for significant capacity improvements by eliminating the recuperator in favour of a larger gas cooler.     

工业废热在地面辐射供暖中的利用

讨论了南方供暖成为业内热门话题的原因和当前南方地区实施集中供暖的难点,分析总结了当前常见供暖系统的优缺点,发现热水地面辐射供暖系统优势明显。对炼钢厂的废热特点进行了深入总结,分析结果表明炼钢厂可以作为热水地面辐射供暖系统的很好的热源。结合某实际工程,详细介绍了利用炼钢厂废热作为工厂生活辅助区地面辐射供暖系统的设计方案,并对其进行了技术经济性分析,发现该方案技术上可行、节能效果显著、经济优势明显,该设计方案充实了集中供暖的设计思路,对以后类似工程的设计具有一定的参考价值。