Relative Thermoluminescence Efficiency Research Articles

Thermoluminescence efficiency and glow curves of Cr-doped Al2O3 ceramic TLD for a wide linear energy transfer range

We investigated the thermoluminescence (TL) efficiency and the glow curve of Cr-doped alumina (Al2O3) ceramic thermoluminescent dosimeters (TLDs) for heavy charged particles. The TLDs were irradiated with beams of protons, helium, and carbon ions. A 6-MV X-ray was used as the reference radiation for investigating the relative TL efficiency. The relative TL efficiency reaches its peak when the linear energy transfer (LET) is approximately 6 keV/μm and decreases with increasing LET. Moreover, the relative TL efficiency was 1.09 for the helium beam (LET: 11.5 keV/μm) and 1.22 for the carbon beam (LET: 13.3 keV/μm). This indicates that the relative TL efficiency of a Cr-doped Al2O3 ceramic TLD varies not only with the LET but also with the particle species. In order to investigate the relationship between the trap center of the Cr-doped Al2O3 ceramic TLD and the LET, the glow curve for each irradiation condition was also measured. As a result, the shape of the glow curve remained the same for a wide LET range, between 0.5 keV/μm and 128 keV/μm.

Thermoluminescent response of differently doped lithium magnesium phosphate (LiMgPO4, LMP) crystals to protons, neutrons and alpha particles

Differently doped lithium magnesium phosphate crystals have been investigated with respect to their thermoluminescent properties. The LiMgPO4 crystals with Tb, B, Eu, Er, Tm, Y rare-earths elements were grown by the micro pulling down method. Different radiation qualities, such as protons of different energies, neutrons and alpha particles, have been used for samples irradiation. Thermoluminescent sensitivity to ionizing radiation, dose-response characteristics and relative thermoluminescence efficiency have been evaluated for all radiation qualities and compared for all analyzed crystal samples. It was found that the radio-sensitivity of the studied compound varies within several orders of magnitude depending on the applied doping ion and its concentration. The highest response was measured for the samples doped with thulium ions. In this case, the signal amplitude was about 3 times higher as compared to the standard LiF:Mg,Ti samples in the form of cold-pressed and sintered pellets. The dose-response of the studied LiMgPO4 crystals was found to be linear up to kGy range, regardless of the applied dopant and its concentration. An interesting behavior was observed in case of relative efficiency vs. linear energy transfer dependence. For protons of different energies the analyzed samples show a similar behavior as the reference LiF:Mg,Ti samples, showing a maximum efficiency evaluated for 20 MeV particles. The response of LiF-based samples for alpha particles decreases significantly to the value of around 0.08. The response of the analyzed lithium magnesium phosphate samples also decreases, but the decrease is not so significant in this case. This probably corresponds to the wide linear dose-response range and also indicates that the local signal saturation effects occur in this material in the range of much higher doses as compared to the reference LiF-based samples.

Comparative investigations of the relative thermoluminescent efficiency of LiF detectors to protons at different proton therapy facilities

Radiotherapy with proton beam is one of the most modern methods of cancer treatment. The basic dosimetric tools in proton therapy are ionization chambers. However, thermoluminescent detectors (TLDs) are also widely applied, being unrivalled in phantom measurements of spatial dose distribution. The relative thermoluminescent efficiency of LiF detectors for protons, which is important for radiotherapy and space dosimetry, have been studied several times, but the available experimental data concerning this subject are not straightforward. Some researchers show that the efficiency of LiF:Mg, Ti to protons with respect to gamma-rays, may significantly exceed unity (even more than 30%), however, many others show the efficiency close to unity or lower.In relation to this issue a research investigation concerning the efficiency of two commonly used TLDs: LiF:Mg, Ti and LiF:Mg,Cu,P, were started at the Institute of Nuclear Physics (IFJ PAN).The measurements were realized exploiting three separate proton beam accelerators normally used for cancer treatment. Two of them at the IFJ PAN Kraków using the 60 MeV and 230 MeV proton beams and another at the Helmholtz-Zentrum Berlin using the 68 MeV proton beam. The relative TL efficiency was determined for protons with energy ranging from 12 to 218 MeV. The results confirmed general energy dependence of two used TLDs. For LiF:Mg, Ti it was found that efficiency increases with decreasing proton energy and shows a maximum of 1.15 at about 20–25 MeV. For LiF:Mg,Cu,P the relative efficiency decreases systematically with decreasing proton energy and is below unity even for the highest studied proton energy.

Thermoluminescence of sol–gel derived Y2O3:Nd3+ nanophosphor exposed to 100 MeV Si8+ ions and gamma rays

Nanocrystalline Nd3+ doped Y2O3 was synthesized by sol–gel technique. Crystallite size calculated by Scherrer relation was found to be in the range 28–30nm. Fourier transform infrared spectroscopy (FTIR) revealed YO, OH stretching and CO bending bonds. Pellets of Y2O3:Nd3+ were irradiated with 100MeV swift Si8+ ions and γ-rays for the fluence/dose in the range 3×1011–3×1013ionscm−2 and 1.0_14kGy respectively. A prominent thermoluminescence (TL) glow with peak at 527K and a weak one with peak at 600K were observed in Si8+ ion irradiated samples while, a prominent TL glow with peak at 393K besides a shoulder at 434K and a weak one with peak at 581K were observed in γ-irradiated phosphors. The relative TL efficiency of Y2O3:Nd3+ of 100MeV Si ion beam to γ-rays of 60Co and is found to be 0.059. The TL kinetic parameters were calculated using Chen’s peak shape method and the results obtained are discussed. Y2O3:Nd3+ was observed for its use in space dosimetry application.

Evaluation of the relative TL efficiency of the thermoluminescent detectors to heavy charged particles.

The relative thermoluminescence efficiency, η, is in general not constant but depends on ionisation density. Evaluation of the η is therefore important especially for correct interpretation of measurements of densely ionising radiation doses in proton radiotherapy or in space dosimetry. The correct determination of the η is not always straightforward especially when more strongly ionising radiation is to be measured. In the present work, the process of calculation of the η based on two kinds of heavy charged particles was studied. Several factors which may influence the value of the η and their significance for the final result were discussed. These include for example non-uniform deposition of the dose within the detector volume, self-attenuation of thermoluminescent light, choice of the reference radiation, etc. The presented approach was applied to the experimental results of η of LiF:Mg,Ti detectors irradiated with two kinds of heavy charged particles, protons and alpha particles.

Thermoluminescent responses of Li3B7O12:Cu to proton beam.

A thermoluminescent (TL) phosphor Li3B7O12:Cu was irradiated by a proton beam at NIRS-HIMAC in Japan. Irradiation was performed at different water-equivalent depths using range shifters made of polymethyl methacrylate. The thermoluminescent responses of Li3B7O12:Cu were analysed, focusing on the TL efficiency and glow curve. The irradiated samples were heated from room temperature to 200°C at 0.16°C s(-1). The high-temperature area of the glow curve under proton irradiation changed in comparison with that under (60)Co gamma-ray irradiation. The relative TL efficiency of the main peak slightly varied between 0.8 and 1.1. The relationship between the relative TL efficiency of the main peak and the high-temperature area ratio (HTR) value, the relative TL ratio of the main peak to the high-temperature area, showed approximate linearity for proton dosimetry. Using correction based on the HTR method, the TL phosphor Li3B7O12:Cu can become a useful dosimetric tool for therapeutic proton beams.

Relative TL and OSL efficiency to protons of various dosimetric materials

Thermoluminescence (TL) and optically stimulated luminescence (OSL) are the well-known phenomena used for passive methods of dose measurements. TL and OSL detectors are frequently used in the dosimetry of cosmic radiation in space and of particle radiotherapy beams. However, the relative TL/OSL efficiency, which is defined as a ratio of the emitted light intensity per unit dose for a given radiation type, to the same quantity for the reference gamma radiation is not constant and depends on radiation type and energy. In the present work several types of TL and OSL dosimetric materials, including lithium fluoride (LiF), aluminium oxide, beryllium oxide and lithium aluminate, were tested with protons. The measurements were realised exploiting the 60-MeV proton beam of the AIC-144 cyclotron in the Proton Eye Radiotherapy Facility at Institute of Nuclear Physics (IFJ PAN). The influence of proton energy on the relative efficiency and other TL/OSL characteristics of the studied detector types was presented.

Evaluation of the relative thermoluminescence efficiency of LiF:Mg,Ti and LiF:Mg,Cu,P TL detectors to low-energy heavy ions

Abstract The most popular types of LiF-based thermoluminescent (TL) detectors, LiF:Mg,Ti (MTS-N) and LiF:Mg,Cu,P (MCP-N), have been investigated, with respect to their dose (fluence) response and relative TL efficiency to different ion species. The detectors were irradiated using the nitrogen, iron, krypton and xenon ion beams, at energies ranging from 5.0 to 9.3 MeV/n. Supra- and sublinear response was found, for the MTS-N and MCP-N, respectively, similarly as observed for γ-rays. However, the level of nonlinearity of response of studied detectors is strongly reduced by increasing values of the ion ionization density (no supralinearity for Xe ions, for MTS-N, within calculated uncertainties). The growth of high-temperature TL peaks, with increasing ionization density, was observed for MCP-N, what was not previously reported. At the whole range of applied energies higher efficiencies were noted for MTS-N, for all ion species. A decrease of the efficiency with decrease of the ion energy was confirmed, for both types of studied detectors. At a given energy, higher efficiency was observed for lighter ions, because of the lower ionization density. Significantly higher decrease of the efficiency was measured for MCP-N. The obtained results remain in a general agreement with other theoretical and experimental data. The data collected for the highest doses (fluences) of Xe ions will be used for testing a recently proposed method of experimental verification of radial dose distribution models.

Relative thermoluminescent efficiency of LiF detectors for proton radiation: Batch variability and energy dependence

The available experimental data on the relative thermoluminescent efficiency of the LiF:Mg,Ti dosimetric peaks for protons are contradictory. There are several reports showing that the efficiency exceeds unity by even more than 30%, however, many others show the efficiency close to unity or even lower. These contradictory data might be a result of the real variability of TLD properties or of not perfectly reproduced experimental conditions. In an attempt to resolve this issue, the efficiency of 16 batches of LiF:Mg,Ti (MTS) detectors for 60 MeV protons produced at the IFJ Kraków over the last 20 years was measured. All values of the relative TL efficiency were found to exceed unity significantly, with an average of 1.09. Dispersion between different batches was very low, all data were within 4% of the mean value. In second part of experiment the dependence of the relative efficiency of LiF:Mg,Ti and LiF:Mg,Cu,P detectors on proton energy was determined. The efficiency for LiF:Mg,Ti dosimetric peaks was found to have a maximum of 1.20 at about 20 MeV. For LiF:Mg,Cu,P the relative efficiency decreases systematically with decreasing proton energy, from 0.96 at 56 MeV, to 0.61 at 11 MeV.

Calculation of the relative efficiency of thermoluminescent detectors to space radiation

Abstract Thermoluminescent (TL) detectors are often used for measurements of radiation doses in space. While space radiation is composed of a mixture of heavy charged particles, the relative TL efficiency depends on ionization density. The question therefore arises: what is the relative efficiency of TLDs to the radiation present in space? In the attempt to answer this question, the relative TL efficiency of two types of lithium fluoride detectors for space radiation has been calculated, based on the theoretical space spectra and the experimental values of TL efficiency to ion beams. The TL efficiency of LiF:Mg,Ti detectors for radiation encountered at typical low-Earth’s orbit was found to be close to unity, justifying a common application of these TLDs to space dosimetry. The TL efficiency of LiF:Mg,Cu,P detectors is significantly lower. It was found that a shielding may have a significant influence on the relative response of TLDs, due to changes caused in the radiation spectrum. In case of application of TLDs outside the Earth’s magnetosphere, one should expect lower relative efficiency than at the low-Earth’s orbit.

Thermoluminescence of BaSO4 : Eu irradiated with 48 MeV Li3+ and 150 MeV Ag12+ ions

The effects of irradiation by 48 MeV Li3+ and 150 MeV Ag12+ ion beams on the thermoluminescence (TL) of BaSO4 : Eu phosphor are studied. Samples in the form of pellets were exposed to different fluences in the range 1 × 109–5 × 1011 ions cm−2. The modifications in TL glow curves of the materials irradiated by lithium (Li) and silver (Ag) beams are essentially similar to those induced by γ-ray irradiation. There is a significant variation in the relative intensity between the main glow peak at 497 K and the small shoulder at 465 K. This variation is more dominant in the samples irradiated by Ag ions. This has been attributed to the change in the population of the luminescent/trapping centres (LCs/TCs) during the bombardment by high-energy heavy ions. The relative TL efficiency values of BaSO4 : Eu to 48 MeV Li and 150 MeV Ag ion beams have been measured relative to 0.662 MeV γ-rays of 137Cs and are found to be 0.374 and 0.0017, respectively. It is found that BaSO4 : Eu phosphor is suitable for recording irradiation from light ions (Li) as well as heavy ions (Ag) as it shows linearity in its TL responses over wide ranges of fluences of ion beams. It is linear in the ranges 1 × 109–1 × 1011 and 1 × 109–1 × 1010 ions cm−2 for Li and Ag ion beams, respectively. This property along with its low fading make BaSO4 : Eu phosphor a good candidate to be used as a dosimeter for cosmic rays and medical applications.

Environmental dosimetry using high-sensitivity TL detectors

Two highly sensitive thermoluminescent (TL) materials (Al 2O 3:C and CaSO 4:Tm) were investigated for environmental monitoring. We compared their response to low and to high linear energy transfer (LET) radiations in order to develop a two-element TL system. The relative TL efficiency for α-particle irradiation as compared to γ-exposure was about 0.04 and 0.5 for Al 2O 3:C and CaSO 4:Tm, respectively. Measurements of external environmental radiation doses in an international balloon experiment were performed with our highly-sensitive TL system having various sensitivities to low and to high LET radiations.

Determination of LiF:Mg,Ti and LiF:Mg,Cu,P TL efficiency for X-rays and their application to Monte Carlo simulations of dosemeter response

The simulation of response of a new passive area dosemeter for measuring ambient dose equivalent H*(10) for photons has been performed using the Monte Carlo code MCNP and experimentally determined responses of LiF:Mg,Ti and LiF:Mg,Cu,P thermoluminescent (TL) detectors for hard-filtered X-ray spectra from 20 to 300 keV and for 137Cs and 60Co gamma radiation. Relative TL efficiency for both types of detectors, determined in experiments with bare detectors and similar Monte Carlo simulations, compared favourably with prediction of microdosimetric models for proposed microdosimetric target sizes in the range of 20-40 nm. The concluding verification experiment showed small deviations between measured and simulated dosemeter energy response values in the range of a few percent.

On the use of LiF:Mg,Ti thermoluminescence dosemeters in space--a critical review.

The use of LiF:Mg,Ti thermoluminescence dosemeters (TLDs) in space radiation fields is reviewed. It is demonstrated in the context of modified track structure theory and microdosimetric track structure theory that there is no unique correlation between the relative thermoluminescence (TL) efficiency of heavy charged particles, neutrons of all energies and linear energy transfer (LET). Many experimental measurements dating back more than two decades also demonstrate the multivalued, non-universal, relationship between relative TL efficiency and LET. It is further demonstrated that the relative intensities of the dosimetric peaks and especially the high-temperature structure are dependent on a large number of variables, some controllable, some not. It is concluded that TL techniques employing the concept of LET (e.g. measurement of total dose, the high-temperature ratio (HTR) methods and other combinations of the relative TL efficiency of the various peaks used to estimate average Q or simulate Q-LET relationships) should be regarded as lacking a sound theoretical basis, highly prone to error and, as well, lack of reproducibility/universality due to the absence of a standardised experimental protocol essential to reliable experimental methodology.

LET Dependence of High Sensitivity TL Dosemeters

LET dependence of highly sensitive Al 2 O 3 :C and CaF 2 :Mn thermoluminescence (TL) dosemeters was investigated using glow curve analysis to determine the efficiencies of TL light production for alpha particle and neutron irradiation relative to gamma exposure. No high temperature peak, nor significant change of glow curve shape were found after irradiation by high LET (alpha and neutron) radiation. Gamma sensitivity of Al 2 O 3 :C as compared to CaF 2 :Mn was 6:1. However the relative TL efficiency for alpha particle irradiation of Al 2 O 3 :C was a factor of ten lower as compared to that of CaF 2 :Mn. Neutron sensitivity was found to be similar for the two materials.

Study of the energy deposition in LiF by heavy charged particleirradiation and its relation to the thermoluminescent efficiency of thematerial

The initial energy deposition stage of the thermoluminescent (TL) process is investigated. A coupled ion-electron Monte Carlo (MC) transport code developed for LiF considering its solid-state nature is used to obtain radial dose distributions for incident proton and helium ions at several energies. Models which relate the initial energy deposition to the final TL light emission are used to predict TL efficiencies. Track structure theory (TST) efficiency calculations using the MC radial dose distributions and target sizes of 50, 100 and 150 Å were performed for the total signal of LiF. Comparison with recent high linear energy transfer (LET) efficiency measurements suggests a value for the target size within the interval 50-100 Å. Modified TST (MTST) proton-to-gamma and helium-to-gamma relative TL efficiency calculations were performed with the MC radial dose distributions and 8.1 keV x-rays as test radiation. It is found that both theories show good agreement with the data, though both predict an energy dependence stronger than observed. A `core radius' for a given ion may be found by applying MTST. The importance of the cut-off energy for secondary electron generation in the MC code is discussed. The fraction of ion energy deposited by the secondary electrons around the heavy charged particle (HCP) path obtained from the MC simulation is in accordance with known values. This work includes solid-state effects in the calculated radial dose distributions in LiF providing dose profiles which are necessary for the calculation of efficiency values and may prove to be essential for further understanding of HCP induced thermoluminescence in LiF.

Track Interaction Theory for Heavy Charged Particle TL Supralinearity

Abstract Microdosimetric phenomena, not addressed by conventional kinetic calculations in the framework of 'conduction band/valence band' atomic models, play an important role in the thermoluminescence (TL) dose response and the relative TL efficiency of various types of radiation fields of different microscopic patterns of ionisation density. In this paper we discuss the contribution of higher order nearest neighbour interactions in track interaction theory applied to heavy charged particle (HCP) induced TL linearity and supralinearity in LiF:Mg,Ti. For example, at a fluence of 1010 particles.cm-2 and for an average charge carrier migration distance of 3700 Å, the relative contribution to the measured supralinearity factor of 1.65 for peak 8 in LiF:Mg,Ti from first, second and third nearest neighbour interactions is 70%, 24% and 6% respectively. Even higher order track interactions contribute less than 1% to the supralinearity. The track interaction model should be viewed as the model providing the microdosimetric framework which, when coupled with other appropriate physical mechanisms (spatial localisation of traps and recombination centres, competing centres in the recombination stage, variation in the capture cross section with temperature) can be used to describe all the dominant features of the linear/supralinear behaviour of LiF:Mg,Ti.

The role of microdosimetry in heavy charged particle induced thermoluminescence dose response

Microdosimetric phenomenae, not addressed by conventional kinetic calculations in the framework of “conduction band/valence band” atomic models, play an important role in the thermoluminescence (TL) dose response and the relative TL efficiency of various types of radiation fields of different microscopic patterns of ionization density (1). In this paper we discuss Track Interaction Model (TIM) calculations of the heavy charged particle (HCP) induced TL linearity and supralinearity of the various glow peaks of LiF:Mg,Ti,OH.

Efficiency of various ionizing particles (beta, p, d, alpha) in causing the “pre-dose effect” in SiO2

Abstract The pre-dose effect has been investigated in Si02 for various ionizing particles and specifically p, d, α., e− and X-rays. The general features are qualitatively similar; the effect intensity is however rather different for particles with different specific ionization and changes monotonically with s/p. At the same time data on the relative thermoluminescence efficiency (K factor) have been obtained. A microdosimetric approach to the energy release along the track has been considered and the interpretation of the phenomenology in terms of those concepts is discussed.