Assessment of Occupational Radiation Exposure for Radiotherapy Healthcare Workers at Kenyatta National Hospital Using Thermoluminescence Dosimeter LiF:Mg,Ti

Kenyatta National Hospital (KNH) is the largest public referral hospital with a comprehensive cancer treatment facility in East and Central Africa. Occupational radiation monitoring is a significant technique for demonstrating compliance of radiation regulatory limits. The objective of the study was to carry out assessment of occupational radiation exposure among radiotherapy personnel at KNH using thermoluminescence dosimeter, TLD. KNH staff were monitored using dosimeter type TLD-100 made of LiF:Mg,Ti, on monthly basis. The reader system used for analysis was Harshaw 8800. The measurement established the average monthly accumulated occupational personnel dose for KNH to be 0.21 mSv and 0.29 mSv for Hp (10) and Hp (0.07) respectively. The accumulated dose results were within the maximum acceptable dose of 1.67 mSv/month and 41.6 mSv/month for Hp (10) and Hp (0.07) respectively. The investigation results were higher than the acceptable public limit of 0.08 mSv/month. Moreover, incidences were noted where the fetus dose limit 0.42 was also exceeded. Evaluation of statistical dose exposure among doctors, nurses and radiographers’ measurement results were within ±0.02 mSv. The study established the average KNH occupational radiation exposure levels for both Hp (10) and Hp (0.07) were within the ICRU recommendation, validating radiation protection safe practice. Data analysis of healthcare workers did not indicate exposure trend biased to any healthcare profession. Hence radiation risk cut across all professional categories. It is recommended that Radiation Monitoring program be reviewed to include non-clinical staff who access the facility. Radiation reporting should not be limited to one facility, but reflect cases where workers are involved in multiple multiple jobs.

Thermoluminescence studies on γ-irradiated CaF_2:Dy:Pb:Na single crystals

Therrnoluminescence （TL） glow, thermoluminescence emission （TLE） and thermal decay （TD） of optical absorption （OA） bands were studied on γ-irradiated CaF2：Dy （0.010at.%）：Pb （0.188at.%）：Na （0.026at.%） single crystals （hereafter called crystal-I）. The TL glow exhibited four glow peaks in the temperature region 300-500 K. The TL response with dose was studied up to -7.5 kGy. The total glow showed linear, supra linear and exponential growth with dose. The TLE showed bands characteristic of Dy^3＋ ions （around 1.65, 1.87, 2.18 and 2.63 eV） and sodium associated （SA） colour centres （CCs） such as MNa （around 1.67 eV） and XNa （a new SA CC, with an emission band around 2.63 eV）. The OA bands of MNa CC around 3.23 and 2.07 eV were found to decrease with temperature almost in accordance with the TL glow. The R＋A centre absorption around 2.48 eV was found to grow with temperature initially and then decayed. The formation/growth of the CCs R＋A and XNa might be from the conversion of the irradiation produced CC MNa. An attempt was made to explain the TL mechanism in the present system.

ALPHA THERMOLUMINESCENCE DOSIMETRY IN DATING OF POTTERY

This article describes the measurement of internal alpha dose-rate in pottery using ultrathin CaSO4: Tin thermoluminescence dosimeter. Among the advantages ofthe techllique are not only convenience, accuracy, lowcost, but also the beta dose--ratefrom pottery can be obtained at the same time.

Photoluminescence and thermoluminescence properties of dysprosium doped zinc metaborate phosphors

Polycrystalline powder samples of dysprosium doped Zn（BO2）2 phosphors were prepared by solid state reaction in air at high temperature and characterized by X-ray powder diffraction. The IR, Photoluminescence （PL）, diffuse reflectance and three-dimensional （3D） thermoluminescence （TL） emission spectrum after 60^Co gamma ray irradiation were investigated. The characteristic 3D TL emission bands at about 425, 481 and 573 um with a main emission band of around 573 um were attributed to the host emission, 4^F9/2→6H15/2 and F9/2→6^H13/2 f-f transitions of Dy^3＋ ions. No emission from Dy^2＋ ions was observed in the measurement wavelength range. The TL-dose response of the Zn（BO2）2：Dy polycrystalline powder sample to gamma ray radiation in the range from 1 to 100 Gy at clinical dose levels was almost linear. The experimental results showed that Zn（BO2）2：Dy had potential use as the materials of gamma-ray thermoluminescence dosimeter （TLD） for clinical dosimetry.

Natural thermoluminescence of fossil foraminiferals as a potential proxy for deep-sea temperature changes

Foraminiferal shells from two piston cores separately located at the Ninetyeast Ridge and the Bengal Fan of the Indian Ocean were selected and purified for measurements of natural thermoluminescence （NTL） intensity by a high precision thermoluminescence meter （RGD-3）. Variations of the NTL intensity along the two core sequences both spanning the last two glacial--interglacial cycles displayed a strong, identical signal of the global ice volume cycles, which matched well with their corresponding oxygen isotope data. As higher NTL intensity occurred within interglacial periods and changes in an NTL signal were most likely influenced by the temperature of ambient seawater in which the planktonic foraminiferal shells long existed, the NTL signal could be considered as a potential proxy for orbital scale temperature changes of bottom seawater in the tropical Indian Ocean.

A preliminary study on thermoluminescence characteristics of sediments from the North Pacific

Thirty-eight surficial deposit samples were collected from the equatorial North Pacific, and the natural thermoluminescence （TL） characteristics of both bulk and clay fraction samples （ 〈 2μm fractions） were studied by the FJ427 - AI automatic TL Dosimeter for the first time. With the measurements of clay mineral composition, element composition by XRD and ICP, the correlations between TL intensity and sedimentary environment proxies were analyzed, such as water depth, ratio of FeO to Fe2 O3 contents, LOI, and major clay mineral concentration, and it was found the bulk sample＇ s TL signal was stronger than the clay ones. Usually, increase in the clay components may result in the decrease of TL intensity. From the shape of TL curves, the pelagic sediments can be divided into two groups： the majority group has two glow peaks, in general, the first peak is broad and flat, but the second narrow and sharp; the minority group only has a single peak because the first is absent. The peak centers of TL curves are almost fixed, falling in the temperature sections 230 ~ 260 and 390 ~ 405℃ respectively. Lorentz model packed in the Origin 7.5 was chosen to deal with the TL curves. From the processing results, three parameters （H, C and A ） , corresponding to the height, center, and kurtosis of TL curve, were obtained to describe the curve characteristics. The correlations between TL curve parameters and sedimentary environment proxies were also calculated. On the basis of the above work, the relationship between TL characteristics and sediment type, mineral composition, sedimentary environment of surface sediments was discussed in the study area, and a conclusion is： sediments from the environment of shallower water, higher organic contents and weaker reductivity have stronger TL signals.

Thermoluminescence characteristics of NaSr_4(BO_3)_3:Ce^(3+) under β-ray irradiation

The thermoluminescence （TL） properties of Ce3＋ doped NaSr4（BO3）3 phosphor under the β-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr4（BO3）3：Ce3＋ phosphor was composed of only one peak. TL kinetic parameters of NaSr4（BO3）3：Ce3＋ were deduced by the peak shape method, the activation energy （E） was 0.590 eV and the frequency factor was 1.008×10^6S^-1. TL dose response was linear in the range of measurement. The 3-dimensional （3D） TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f^05d^1→2F（5/2,7/2） transitions of the Ce3＋ ion. The fading behavior of the NaSr4（BO3）3：Ce3＋ phosphor over a period of 15 d was also studied.

Thermoluminescence Characteristics of SrB_6O_(10)∶Tb

SrB6010：Tb phosphor was synthesized by high-temperature solid state reaction. The influences of Ce or Li as a co-dopant, Tb concentration and irradiation dose exposure on TL of SrB6010 ： Tb were investigated. Results show that Ce or Li as a co-dopant can not improve the sensitivity of SrB6010：Tb phosphor. TL response depends on Tb concentration and 0.02 is the optimum in the concentration range from 0.01 to 0.10. Using the optimum Tb concentration, we calculated the kinetic parameters of SrB6010：Tb employing the peak shape method, and suggested the phosphor obeying the second order kinetics. TL emission intensity is linearly dependent on the irradiation dose within the dose range of 50 - 200 Gy. The characteristic Tb^3＋ ion emission was observed in TL emission spectrum.

Thermoluminescence of BaFCl_xBr_（1－x）：Sm System and Assignment of Their Glow Peaks

Through the study of the thermoluminescence(TL) of BaFClxBr1-x: Sm(0<x<1) system, it is found that former assignment of the glow peaks of BaFX(X = Cl, Br) is plausible. Through detailed study by several methods and techniques, a correct assignment is given in this paper, i.e. the first, second, and third glow peaks of BaFClxBr1-xSm are assigned to F(F-), F(Cl-), F(Br-) centers respectively, and the first andsecond glow peaks of BaFX are assigned to F(F-) and F(X-) centers respectively. This results are confirmed by theoretical consideration. Possible reasons for former plausible assignment are also pointed out here.

Thermoluminescence and optically stimulated luminescence disadvantages of α-Al_2O_3:C crystal grown by the temperature gradient technique

Recently, α-Al2O3：C crystal with highly sensitive thermoluminescence （TL） and optically stimulated luminescence （OSL） has been successfully grown by the temperature gradient technique. This paper investigates the heating rate dependence of TL sensitivity, light-induced fading of TL signals and thermal stability of OSL of α-Al2O3：C crystals. As the heating rate increases, the integral TL response decreases and the dosimetric glow peak shifts to higher temperatures in α-Al2O3：C crystals. Light-induced fading of TL increases with the irradiation dose, and TL response decreases as the exposure time increases, especially in the first 15 minutes. With the increasing intensity of the exposure light, the TL fading of α-Al2O3：C crystal increases sharply. The OSL response of as-grown α-Al2O3：C crystal is quite stable below 373 K and decreases sharply for higher temperatures.

The fluorescence and thermoluminescence characteristics of α-Al_2O_3:C ceramics

This paper reports that polycrystalline （α-Al2O3：C ceramics are fabricated by conventional ceramics process. The excitation, emission spectra, thermoluminescence （TL） and optical stimulated luminescence （OSL） of α-Al2O3：C polycrystalline ceramics are investigated. There exists 410nm maximum emission peak which is caused by recombination of an electron with F＋ centre to produce an excited F centre. The samples show three clear TL glow peaks at 405, 493 and 610 K. The attenuation constant of exponentially decaying fast component （τ1） and slow component（τ2） of OSL curve are 8.43s and 41.73s, respectively. Those fluorescence and thermoluminescence characteristics are similar with α-Al2O3：C crystal.

Thermoluminescence Energy Response of Copper and Magnesium Oxide Doped Lithium Potassium Borate Using a Monte Carlo N-Particle Code Simulation

The energy absorption coefficient of Cu-doped lithium potassium borate (LKB) dosimeter and TLD 100 was reported theoretically and checked by simulation of Monte Carlo n-particle code version 5 (MCNP5). The response of LKB:Cu for various photon energies (20 keV to 10 MeV) were determined by calculation, experiment and simulation. The obtained results were discussed and compared with TLD 100. For more precise results, the geometry specification, the source information, the material information and tallies were identified and fully described. The results obtained by simulation were determined based on the tally F6, which exhibited the response as energy-dependant on heating function instead of flux. The current results showed that the prepared dosimeter has a greater response than TLD 100 in the lower energy range and a flat response in the higher energy ranges (≥100 keV).

Thermoluminescence Dating of Colluvial Deposits and Its Application to Chronological Study of Paleoearthquakes

On the basis of studies of lithofacies features of colluvial deposits, applicability of thermoluminescence dating of the colluvial deposits at different lithofacies positions, and reliability of the dating result, the thermoluminescent ages of colluvial deposit from different types of faults were determined. From the above, the ages of paleoseismic events and their recurrence intervals on the related fault were deduced.

TECTONOTHERMAL EVOLUTION OF ORDOS BASIN BY THERMOLUMINESCENCE, NW CHINA

Ordos Basin is a remnant cratonic basin undergone multiple tectonothermal cyles, by the comprehensive study of thermoluminescence combined with vitrinite reflectance,magmatism, metamorphism and tectonosedimentation in the basin. Highly geothermal field,strong crustal movement existed in the basin during Archean to Paleoproterozoic. Since Mesoproterozoic, the tectonothermal nature has been relatively stable in Ordos Basin, associating with constant subsidence or uplift sometimes,while heat flow has still been high in the vicinityof the basin with strong activation of graben structural system because of the upwarding mantle creep flow. Two tectonothermal evolution stages and four developing periods can be recongnized in Ordos Basin,i. e. Pre-Mesoproterozoic stage consisting of Archean much higher geothermal geodome period and Paleoproterozoic higher-Reothermal geosyncline period,Mesoproterozolc to present stage including Mesoproterozoic to early Triassic low-geothermal geodepression period and late Triassic to present lowugeothermal uplift-subsidence period. The tectonothermal event at middle Triassic caused the uplift of the basin and the formation of the central paleodome,indicating that the basin entered its residual developing period of the platform. During the residual stable developing period of plat form,the creeping of the mantle increased and the heat flow changed to be high,accompanied by wide spreading eruption of basalt, such as that in Yimeng Uplift area,while the tectonic activity has been quite strong in the surrounding of the basin and the surrounding obviously overthrusted over the basin. Since Triassic, the basin has been gradually uplifted and its tectonism has migrated westward. The tectonothermal event may predicted the breakup of ordos Basin.

Developing Suitable Sensitive Compound Semiconductor Materials Doped by Transition Metals for Occupational Thermoluminescence Dosimetry

The essential objective of radiation dosimetry is to develop suitable sensitive materials for different measurements in radiation fields. Our exploration is to find potentially suitable high gamma radiation dosimeters in the range from 0.5E4 to 1.5E4 Gy. Gamma rays source (60Co, 136 Gy/min) has been used. Many compound semiconductor materials were prepared and investigated. Thermoluminescence (TL) glow curve was analyzed into its component by analytical segregation program using computerized glow curve deconvolution (CGCD). Three zero dose readings for non-irradiated powders of the materials have been taken as lower limit of detection. The results indicated that some of the tested materials have exhibited TL linearly with respect to dose. In addition, dose response of these materials was found to be useful for high radiation dosimetry. Glow curve structures exhibited several peaks corresponding to the various energies of the emptied traps. Variation in the standard deviation for reusability cycles has been ten readout. The fading at ambient temperature was studied up to 60 days which reached a relative stability (~1.5% for all), 10 days after irradiation. A typical glow curve of CoPa which irradiated with 1.5E4 Gy was analyzed. Characterizations of tested materials indicated that crystals of ZnLa:Li, ZnLa:Cd, and ZnLa:Cr have stable and increasing thermoluminescent responses with high gamma radiation dose range. Special glow peaks can be used as estimators for absorbed doses as well as re-estimation for time elapsed exposures.

Thermoluminescence characterization of natural and synthetic irradiated Ce-monazites

The thermoluminescence(TL)emission of synthetic and natural Ce-monazites was characterized here to determine the potential application in the identification of microscopic defects from a qualitative point of view trying to link each TL peak to a chemical-physical process.The kinetic parameters that lead the luminescence processes were calculated by means of variable heating rate and computing glow curve deconvolution methods and allow identifying three groups of components at~90,130 and 290℃(for the mineral sample)and~90,170,220,270 and 320℃(for the synthetic CePO_(4):Nd_(0.20),La_(0.25)).The main differences appreciated in these complex TL curves are mainly due to(i)the content of impurities(natural sample contains lanthanides as well as U 0.60%and Th 5.22%)and(ii)the degree of crystallinity of the samples which is directly related to the type of impurities(synthetic monazite relies only on Nd and La).The behavior of the dose response in the range of 1-8 Gy is similar for both samples;the TL intensity increases linearly as the dose increases without changes in the position of the maxima,denoting first-order kinetic luminescence mechanism.Each peak could be mostly associated with structural defects(i.e.,phase transitions),chemical reactions(i.e.,Ce3+?Ce4+redox reaction,dehydration or dehydroxylation processes)or intrinsic defects(i.e.,Frenkel defects,ODCs or NBOHCs).

Thermoluminescence dating of the ancient Chinese porcelain using a regression method of saturation exponential in pre-dose technique

This paper studies the thermoluminescence (TL) dating of the ancient por- celain using a regression method of saturation exponential in the pre-dose technique. The experimental results show that the measured errors are 15% (±1σ) for the paleodose and 17% (±1σ) for the annual dose respectively, and the TL age error is 23% (±1σ) in this method. The larger Chinese porcelains from the museum and the nation-wide collectors have been dated by this method. The results show that the certainty about the authenticity testing is larger than 95%, and the measurable porcelains make up about 95% of the por- celain dated. It is very successful in discrimination for the imitations of ancient Chinese porcelains. This paper describes the measured principle and method for the paleodose of porcelains. The TL ages are dated by this method for the 39 shards and porcelains from past dynasties of China and the detailed data in the measurement are reported.

Spurious Thermoluminescence Characteristics of the Ediacaran Doushantuo Formation(ca. 635–551 Ma) and Its Implications for Marine Dissolved Organic Carbon Reservoir

The Ediacaran Doushantuo Formation（ca. 635–551 Ma） deposited immediately after the last Neoproterozoic glaciations and recorded the most prominent negative excursions of carbonate carbon isotopic composition（δ^（13）C（carb））. These excursions have been interpreted as a result of widespread remineralization of a large dissolved organic carbon（DOC） reservoir in the Ediacaran deep oceans. However, there is no direct evidence so far found in rocks for the proposed DOC reservoir, which devalues such an interpretation. Here, we conducted a detailed study on the glow-curves characteristics and signal origins of spurious thermoluminescence（TL） of the Doushantuo Formation at Jiulongwan in Yangtze Gorges area, South China, through sequential tests under CO2, N2 and air. Spurious TL intensities for test samples before and after removing soluble organic matter via accelerated solvent extraction（ASE） are nearly identical. Further, significant positive correlation between the spurious TL intensity and total inorganic carbon（TIC） content（R^2=0.7） indicate that the Doushantuo spurious TL with the characteristic peak at 393.5 °C from the sequential test is chemiluminescence（CL） which is derived from the oxidation of a type of non-volatile organic matter strongly associated with carbonate mineral lattice（termed as “X-OM”）. A most likely explanation is that the X-OM is a type of dissolved organic matter which co-precipitated with carbonate minerals into sediments in the Ediacaran Doushantuo Ocean. Furthermore, a significant exponential negative correlation（R^2=0.55） is observed between the CL data and the isotopic difference between carbonate and coexisting bulk organic matter（i.e., Δ^（13）C（carb-org）, a proxy for remineralization degree of DOC reservoir in proposed DOC hypothesis）, suggesting that the X-OM was derived from the oxidation of the DOC reservoir in the Ediacaran Ocean. We thus propose that the X-OM and its CL detected in our study may have recorded the evolution of the possible DOC reservoir in the Ediacaran Doushantuo Ocean. If this is correct, the stratigraphic variations of the CL intensity in the Doushantuo Formation at Jiulongwan support the pulsed oxidation of the DOC reservoir in the Ediacaran Ocean. Our findings indicate that the CL derived from the oxidation of non-volatile organic matter which is strongly associated with carbonate mineral lattices in rocks may provide a feasible approach for probing the evolution of DOC reservoir in the ancient oceans, thus likely provide direct geological evidence for the development of oceanic DOC reservoir in geological times.

Evaluation for the paleodose in thermoluminescence dating of porcelain

Sources, components and calibration of paleodose were studied for proper evalua- tion of the paleodose of porcelain in thermoluminescence (TL) dating. In the TL dating of porcelain using the pre-dose technique, the β dose from the internal natural radiation in the body of porcelain is the first, the environmental dose the second, and the α dose negligible. Sample thickness of 0.2―0.5 mm was used in the paleodose calibration. For a porcelain sample of such thickness, the distribu- tion of β dose inside the sample was nonlinear when the sample (aluminium re- places porcelain in this experiment) was irradiated by a laboratory 90Sr-90Y β source. Therefore, the β dose used was only an average value. A distribution curve of β dose and the calculation of average β dose in the sample were obtained, according to the build-up and attenuation effects of β dose in the sample. The results showed that a sample thickness of 200 μm resulted in an average dose increment of about 4% compared to the surface whereas for a sample with a thickness of 400 μm, the average dose reduced by the same percentage, and that for a sample of 300 μm in thickness the average dose is equal to surface dose approximately. The average β dose in samples with various thickness can be obtained by the provided equations.

Low temperature thermoluminescence behaviour of Y_2O_3 nanoparticles

Y_2O_3 nanoparticles were investigated using low temperature thermoluminescence (TL) experiments. TL glow curve recorded at constant heating rate of 0.4 K/s exhibits seven peaks around 19, 62, 91,115,162,196 and 215 K. Activation energies and characteristics of traps responsible for observed curves were revealed under the light of results of initial rise analyses and T_(max)-T_(stop) experimental methods. Analyses of TL curves obtained at different stopping temperatures resulted in presence of one quasi-continuously distributed trap with activation energies increasing from 18 to 24 meV and six single trapping centers at49, 117, 315, 409, 651 and 740 meV. Activation energies of all revealed centers were reported in the present paper. Structural characterization of Y_2O_3 nanoparticles was accomplished using X-ray diffraction and scanning electron microscopy measurements.