Thermoluminescence as a Research Tool to Investigate Luminescence Mechanisms

Thermally stimulated luminescence (TSL) is known as a technique used in radiation dosimetry and dating. However, since the luminescence is very sensitive to the defects in a solid, it can also be used in material research. In this review, it is shown how TSL can be used as a research tool to investigate luminescent characteristics and underlying luminescent mechanisms. First, some basic characteristics and a theoretical background of the phenomenon are given. Next, methods and difficulties in extracting trapping parameters are addressed. Then, the instrumentation needed to measure the luminescence, both as a function of temperature and wavelength, is described. Finally, a series of very diverse examples is given to illustrate how TSL has been used in the determination of energy levels of defects, in the research of persistent luminescence phosphors, and in phenomena like band gap engineering, tunnelling, photosynthesis, and thermal quenching. It is concluded that in the field of luminescence spectroscopy, thermally stimulated luminescence has proven to be an experimental technique with unique properties to study defects in solids.RST/Fundamental Aspects of Materials and Energ

Passive detectors for neutron personal dosimetry: State of the art

Passive, solid-state detectors still dominate the field of neutron personal dosimetry, mainly thanks to their low cost, high reliability and elevated throughput. However, the recent appearance in the market of several electronic personal dosemeters for neutrons presents a challenge to the exclusive use of passive systems for primary or official dosimetry. This scenario drives research and development activities on passive dosemeters towards systems offering greater accuracy of response and lower detection limits. In addition, further applications and properties of the passive detectors, which are not met by the electronic devices, are also being explored. In particular, extensive investigations are in progress on the use of solid-state detectors for aviation and space dosimetry, where high-energy neutron fields are encountered. The present situation is also stimulating an acceleration in the development of international standards on performance and test requirements for passive dosimetry systems, which can expedite significantly the implementation of techniques in commercial personal dosimetry services. Upcoming standards will cover thermoluminescence albedo dosemeters, etched-track detectors, superheated emulsions and direct ion storage chambers, attesting to the level of maturity reached by these techniques. This work reviews the developments in the field of passive neutron dosimetry emerged since the previous Neutron Dosimetry Symposium, reporting on the current status of the subject and indicating the direction of ongoing research

Some developments in neutron and charged particle dosimetry

There is an increasing need for dosimetry of neutrons and charged particles. Increasing exposure levels are reported in the nuclear industry, deriving from more frequent in-service entries at commercial nuclear power plants, and from increased plant decommissioning and refurbishment activities. Another need stems from the compliance with requirements of the regulations and standards. The European Council directive 96/29 requires dosimetric precautions if the effective dose exceeds 1 mSv a-1. On average, aircrew members exceed this value. Further, there is a trend of increasing use of charged particles in radiotherapy. The present situation is that we have reasonably good photon dosemeters, but neutron and charged particle dosemeters are still in need of improvements. This work highlights some of the developments in this field. It is mainly concentrated on some developments in passive dosimetry, in particular thermally and optically stimulated luminescent detectors, indicating the direction of ongoing research. It shows that passive dosemeters are still a very active field. Active dosemeters will not be discussed with the exception of new developments in microdosimetric measurements [new types of tissue equivalent proportional counters (TEPCs)]. The TEPC is unique in its ability to provide a simultaneous determination of neutron/charged particle/ gamma ray doses, or dose equivalents using a single detector

Integrating detector for measuring low levels of gamma rays

Abstract of NL 1001913 (C2) The integrating detector (1) for measuring low levels of ~c-rays, added (9) to the natural background radiation, is provided with a screen (4) placed between at least two thermo-luminescent dosimeters (5-7). It is covered with a housing. Also claimed is the measurement of low ~c-ray levels using the apparatus above. The first dosimeter (6,7) is protected from the radiation source to measure the natural background, while the second (5,7) measures both background and source. Differences in the light quanta generated indicate the level of radiation from the source

On energy storage of Lu2O3:Tb,M (M=Hf, Ti, Nb) sintered ceramics: Glow curves, dose-response dependence, radiation hardness and self-dose effect

Thermoluminescent properties and energy storage characteristics of Lu2O3:Tb,M (M = Hf, Ti, Nb) sintered ceramics induced by ionizing radiation are presented and discussed. Dose-response dependence, radiation hardness and fading are studied. A linearity of the former exceeding seven orders of magnitude is confirmed for Lu2O3:Tb,Hf and Lu2O3:Tb,Nb ceramics. Lu2O3:Tb,Hf shows the best TL performance and also its fading is the lowest reaching 15% over 7 h and shows tendency to saturate. During the same period of time the Lu2O3:Tb,Ti, despite having TL at higher temperatures, losses about 25% of the stored energy and the TL signal of Lu2O3:Tb,Nb fades by almost 40% over 7 h. First order TL kinetics is confirmed for all three compositions. A self-dose effect in Lu2O3:Tb,Hf due to a natural content of the radioactive isotope (2.6%) is proved to be important for long-time reading of low doses.Accepted Author ManuscriptRST/Luminescence Material

Synthesis optimization and charge carrier transfer mechanism in LiLuSiO₄:Ce, Tm storage phosphor

LiLuSiO4:Ce and LiLuSiO4:Ce, Tm show very efficient charge carrier storage properties upon beta irradiation after samples have received treatment in vacuum. They outperform the commercial storage phosphor BaFBr(I):Eu2+ in many aspects. The influence of the synthesis conditions, Ce and Tm concentration, nonstoichiometry and codoping with Ca, Hf, Al and Ge are reported. Based on the results of the synthesis optimization, thermoluminescence (TL) emission and TL excitation spectra a mechanism of charge carrier transfer, storage, and recombination during irradiation and thermal or optical readout is proposed.Accepted Author ManuscriptRST/Fundamental Aspects of Materials and EnergyRST/Luminescence Material

The effect of temperature and excitation energy of the high- and low-spin 4f→5d transitions on charging of traps in Lu₂O₃:Tb,M (M = Ti, Hf)

This work presents a fresh insight into the excited charges trapping in the Lu2O3:Tb,M (M= Ti, Hf) ceramics and their characteristics as storage and/or persistent luminescence phosphors. The results were obtained by applying an exceedingly versatile set of experiments based on thermoluminescence and thermoluminescence excitation spectroscopy and exposed a dual-nature of these materials. In the contrary to the previous research, here we found that at least some of these materials can generate efficient persistent luminescence due to the presence of shallow traps which can be charged only upon specific irradiation conditions – by the spin-forbidden 4f→5d transition of Tb3+ around 360 nm and, possibly, the 7F6→5D3 intra-configurational transition of the activator at just slightly longer wavelengths. Besides that, changing the sample charging temperature the efficiency of filling the traps – both deep and shallow – with the 360 nm radiation varied greatly and exposed a very broad distribution of trap energies. Charging with 360 nm radiation at room temperature fills only the shallow traps giving, never reported in Lu2O3:Tb,Ti and Lu2O3:Tb,Hf, intense persistent luminescence, while at higher temperatures the deep traps are filled. At any temperature, radiation of wavelengths < 320 nm fills almost exclusively deep traps responsible for TL at high temperatures, 230 °C in Lu2O3:Tb,Hf and 355 °C in Lu2O3:Tb,Ti.RST/Fundamental Aspects of Materials and Energ