Study of paramagnetic and luminescence centers of microcline feldspar.

Microcline feldspar crystal has been analyzed in order to determine the centers suitable for use in ESR and luminescence dating. ESR measurements at RT showed the Fe3+ line, and at 77K the Si-O(-) ..X signal with g=2.0052, 2.0098 and 2.0128. TL glow peak at 157 and 300 degrees C in UV interval were observed and in the VIS range we noted peaks at 150, 280 and 340 degrees C. TL growth curve of the 340 degrees C peak could be fitted by a saturating exponential equation and can be used in TL dating. Emission curves showed band widths 1.95+/-0.09, 2.73+/-0.08 and 4.94+/-0.50 eV. Transitions from 4T1-->6A1)of Fe3+ can be associated with the 1.95 eV band and the transition from 4A1 4E(G)-->6A1(S) with 2.73 eV band.     

Thermoluminescence and electron spin resonance properties of some travertines from Turkey

For the sake of dating certain calcite geological samples, the TL and ESR properties of travertines from Denizli (in the southwestern part of Turkey) were studied and the effects of pre-heating temperature and pre-heating time on the sensitivity of the samples to radiation evaluated. Heat treatment above 350°C increases the sensitivity of all radiation-induced TL peaks except the 330°C glow peak. Results of gamma-ray dose calibration in travertine (CaCO₃ crystal of trigonal symmetry) indicate that the 180 and 280°C TL peak amplitudes increase exponentially with dose. We show that second-order kinetics characterizes the 180 and 280°C glow peaks reasonably well. The Mn²⁺ lines of the ESR spectra are used to investigate the thermal decomposition processes of travertine samples, showing very good agreement with those of thermogravimetry. Glow mechanisms of TL in travertine have also been studied using ESR analysis. The pre-heating and subsequent laboratory irradiation procedure is found to enhance the TL and ESR signals of CO₃³⁻ and CO₂⁻ centres. An isochronal thermal anneal sequence experiment showed that 180 and 280°C peaks in travertines are correlated with CO₃³⁻ and CO₂⁻ centres in the same way that the peak at 330°C is correlated with SO₂⁻ centres. A model for the recombination mechanism is suggested on the basis of the TL and ESR measurements.     

ESR dosimetry using inorganic materials: a case study of Li2CO3 and CaSO4:Dy as prospective dosimeters.

The CO2- radical ion, detected by ESR technique in bones and teeth enamel, was proved to be invaluable in high level and retrospective dosimetry. In these matrices, impurity carbonate (at phosphate sites) was the precursor to CO2-. With a view to investigate the possibility of using inorganic materials such as lithium carbonate as ESR dosimeters, studies were carried out on gamma-irradiated Li2CO3. The intensity of radiation-induced ESR signals of Li2CO3 at g = 2.0036 (CO3-) and g = 2.0006 (CO2-) was followed as a function of gamma dose in the low dose range of 1-1350 Gy. It was observed that the intensity of the ESR signal at g = 2.0036 (CO3-) was in a linear relation with the radiation dose in the dose range 10-800 Gy and the signal at g = 2.0006 (CO2-) showed linear response in the dose range 5-800 Gy. The lowest dose that could be detected in the present studies using the signal of CO2- in Li2CO3 powder samples (approximately 50 mg) is 3.2 Gy. ESR studies were also carried out on the widely used TL dosimetric material CaSO4:Dy and in pure CaSO4 after gamma irradiation. The TL materials were used in powder as well as pellet forms. The linearity of ESR response with dose for powder and pellet forms of CaSO4: Dy was also studied using the signals at g = 2.0030 (SO3-) and at g = 2.0139 (SO4-). It was observed that the range of linearity of dose response extended between 20 and 1200 Gy, for SO3- signals. The results of dosimetric study indicate that the ESR-Li2CO3 system could be used in dosimetric applications in radiotherapy. However, for the actual applications further advancement is needed to lower the detection limit. The TL phosphor, CaSO4:Dy in powder and pellet forms, could be used as ESR dosimeter in the dose range 20-600 Gy.     

Electron spin resonance age determination of a travertine sample from the southwestern part of Turkey

Travertine powdered samples collected from Denizli in the southwestern part of Turkey appear to be suitable for dating by ESR analysis due to presence of a g=2.0006 ESR signal. In general, ESR spectra of natural travertine show two absorption lines: g=2.0006 and g=2.0056. ⁶⁰Co gamma-ray irradiations enhance the g=2.0006 signal but not g=2.0056. The signal amplitude of the g=2.0056 line remains constant and shows no dose dependence after annealing at 150–180°C for periods from 15 min to 2 days. Line g=2.0056 disappears in turn after an annealing of 15 min at 400°C. Thermal annealing experiments at different temperatures for different annealing times show that the only travertine ESR signal stable enough for dating of ages over the past 10 Ma, is the one at g=2.0006. The present ESR dating result is 1.11±0.11 Ma. The g=2.0006 signal used for dating appears to correspond with the 280°C TL peak, but at elevated temperatures the mean life, accumulated dose and age of the latter is significantly less than that measured by post irradiation analysis using the ESR signal. This can be attributed to coming from other carbon-containing paramagnetic centers. In fact, gamma-ray absorbed dose rate dependence of the ESR signal has been studied, and no dependence was observed over a 12-fold change in dose rate.     

EPR spectrum deconvolution and dose assessment of fossil tooth enamel using maximum likelihood common factor analysis.

In order to determine the components which give rise to the EPR spectrum around g = 2 we have applied Maximum Likelihood Common Factor Analysis (MLCFA) on the EPR spectra of enamel sample 1126 which has previously been analysed by continuous wave and pulsed EPR as well as EPR microscopy. MLCFA yielded agreeing results on three sets of X-band spectra and the following components were identified: an orthorhombic component attributed to CO2-, an axial component (CO3(3-)), as well as four isotropic components, three of which could be attributed to SO2-, a tumbling CO2- and a central line of a dimethyl radical. The X-band results were confirmed by analysis of Q-band spectra where three additional isotropic lines were found, however, these three components could not be attributed to known radicals. The orthorhombic component was used to establish dose response curves for the assessment of the past radiation dose, D(E). The results appear to be more reliable than those based on conventional peak-to-peak EPR intensity measurements or simple Gaussian deconvolution methods.     

An investigation of ESR signals and their related TL emission in speleothem calcite

TL emission spectra were recorded using a sensitive Fourier transform spectrometer for 4 samples of speleothem calcite which had been selected to display a range of ESR signals. Two samples showed principal emissions at 610 nm for both the 160°C and 270°C TL peaks which are attributed to Mn-related luminescence centres, while the remaining two samples had their principal emissions at 480 and 580 nm, which is characteristic of Dy-related luminescence centres. The relative intensities of the TL emission and ESR signals within individual samples, and between those having the same luminescence centres, together with kinetic studies infer correlations between the g = 2.0036 ESR signal and TL emission at 220°C, and the 160°C TL peak and the g = 1.9975 ESR signal. The g = 2.0005 signal used for dating appears to correspond with the 270°C TL peak, but at elevated temperatures the mean life of the latter is significantly less than that of the ESR signal. This could be explained if the luminescence centres have a lower stability than the trap sites measured directly by ESR. All correlations should be treated with caution because charge may be lost from ESR traps via different routes in each calcite, giving wide variations in luminescence efficiency.     

Environmental studies on X- and gamma-irradiated LiCsSO4 crystals.

Thermoluminescence (TL) characteristics of LiCsSO4 crystal have been studied after exposure to different doses of X and gamma radiations. The glow curves showed TL response of three peaks at 75 degrees C, 125 degrees C and 250 degrees C. The structure of the glow peaks due to X-rays is quite different from that due to gamma-rays. UV exposure yields a regeneration of the TL peaks for the post-irradiated samples with X- or gamma-radiation with some changes in the peak structure especially the third peak. For the post-X-ray irradiated crystals, the area under the third glow peak (PK III) increased linearly with the integrated time of UV exposure till about 30 min after which no changes were observed; while, for the post-gamma-irradiated crystals, two linear regions were observed. The models of the TL response for the post-irradiated samples as a result of exposure to UV are discussed.     

Changes in the paramagnetic centres in irradiated and heated dental enamel studied using electron paramagnetic resonance.

The EPR signals in dental enamel produced by radiation and by heat were studied. The inherent background signal at g = 2.005, and a radiation-produced signal at g = 2.002 have different saturation behaviour with microwave power, and this affords a method of signal optimization. Heating enamel at temperatures from 100 degrees C to 450 degrees C produces a range of radical species from g = 2.002 to g = 2.005, which have been characterized by their g-values, line widths and saturation behaviour. Standard dental drilling produces a range of radicals which appear to be similar to those produced by heat.     

Linear transformation of EPR spectra as a method proposed for improving identification of paramagnetic species in ceramic.

In the present paper the paramagnetic centres in pottery generated after gamma-irradiation were investigated. The computer resolution enhancement method (CREM) was used to increase the electron paramagnetic resonance (EPR) spectra resolution. The measurements were performed at room and liquid nitrogen temperatures. The paper shows the results of non-irradiated and gamma-irradiated pottery before and after resolution enhancement. Each EPR spectrum showed a multiple structure after the CREM procedure application. An aluminium hole centre [AlO(4)](0) has been ascribed to these lines. The g factors are: g(1)=2.0602, g(2)=2.0079, and g(3)=2.0019 and hyperfine splitting is A(1)=5.5G and A(2) approximately A(3)=6.3G.     

Volumetric quantification of coronary artery calcifications using dual-slice spiral CT scanner: improved reproducibility of measurements with 180 degrees linear interpolation algorithm

PURPOSE: The purpose of this work was to determine the reproducibility of coronary total calcium score (TCS) with dual-slice helical CT and compare three acquisition protocols. METHOD: Fifty patients (59 +/- 10 years old) underwent dual-slice helical CT (collimation = 2 x 2.5 mm) and coronary angiography. Two successive scans were performed, resulting in three sets of images: pitch = 1, 360 degrees linear interpolation (LI) (A360); pitch = 1, 180 degrees LI (A180); and pitch = 1.5, 180 degrees LI (B180). TCS values, calculated using a volumetric method with a threshold of 90 HU, were compared, and the interscan variation was determined. Diagnostic performances were compared with receiver operating characteristic curves. RESULTS: Protocol A360 provided significantly lower TCS than protocols A180 and B180 (p < 0.0001). No statistical difference was seen between A180 and B180, which provided the lowest interscan variation (40 +/- 58%). However, no significant clinical impact of the observed interscan variations was found. CONCLUSION: Reproducibility of TCS with dual-slice helical CT is improved by the 180 LI algorithm. However, dual-slice helical CT is not sufficiently reproducible to allow serial quantification of TCS over time.     

EPR dosimetry using commercial glasses for high gamma doses.

Commercial transparent and colored (bronze, brown, and green) glasses were studied as possible dosimeters for high gamma doses using electronic paramagnetic resonance (EPR). All EPR spectra showed the characteristic Fe3+ signals, g=4.27 and 2.01. The signal at g=2.01 presented a more useable behavior for the calibration curve. All samples showed their usefulness as high dose dosimeters.     

Comparison of gamma- and UV-light-induced EPR spectra of enamel from deciduous molar teeth.

From previous work, it is known that CO2- radicals in tooth enamel are induced by gamma as well as by UV-light exposure. The parameters of the EPR signal of the CO2- radical were found to be independent of the source of exposure. However, it would be desirable for retrospective dosimetry to identify other characteristic features of the EPR spectrum of tooth enamel, which would allow differentiation between the two sources of exposure. In the present work, enamel of deciduous molars was exposed to gamma-radiation from a 60Co-source and 254 nm UV-light from a low-pressure mercury lamp. The resulting EPR spectra were deconvoluted, and the native spectrum simulated from spectra of the CO2- radical, and two further EPR lines. Both EPR signals of the native spectrum were located at g=2.0046, but were different in line shape and width. One was a 1 mT wide isotropic signal of Gaussian line shape while the other was a 0.7 mT wide axial signal of Lorentzian line shape. A comparable study of the amplitudes of the native and CO2- signals was done before and after gamma- and UV-light exposure. While the native signals were found to be only slightly sensitive to gamma-radiation, their amplitude increased significantly on UV-light exposure. Feasibilities are discussed to distinguish different radiation sources by exposure-induced alterations of the native EPR spectrum.     

Effect of environmental temperature on shock absorption properties of running shoes.

OBJECTIVE: To determine the effect of temperature changes on the shock attenuation of 4 running shoe shock absorption systems. DESIGN: Prospective. SETTING: Motion analysis laboratory. INTERVENTIONS: The shock attenuation of 4 different running shoes representing common shock absorption systems (Nike Air Triax, Asics Gel Nimbus IV, Adidas a3 cushioning, Adidas Supernova cushion) was measured at ambient temperatures of -20 degrees C, -10 degrees C, 0 degrees C, +10 degrees C, +20 degrees C, +30 degrees C, +40 degrees C, and +50 degrees C. Repeated-measures analysis of variance was used to determine differences between shoes. OUTCOME MEASURES: Shock attenuation as indicated by peak deceleration (g) measured by a mechanical impactor following ASTM Standard F1614-99. RESULTS: Shock attenuation decreased significantly with reduced temperature for each shoe tested. The Adidas a3 shoe exhibited significantly higher peak decelerations (lower shock attenuation) at cold temperatures compared with the other shoes. CONCLUSIONS: Cold ambient temperatures significantly reduce the shock attenuation of commonly used running shoes. These findings have important clinical implications for individuals training in extreme weather environments, particularly those with a history of lower limb overuse injuries.     

Cardiovascular responses to facial cooling are age and fitness dependent.

PURPOSE: Aging of the cardiovascular system may be altered by differences in physical fitness. We investigated the cardiovascular responses to brief periods of facial cooling (5 degrees C) in 20 healthy men differing in age and aerobic fitness (VO2max). METHODS: Facial cooling was administered at rest in the supine position during 60-s quiet breathing to 6 fit young (FY; VO2max = 75.8 +/- 18 mL x kg(-1) x min(-1); 29 +/- 7 yr), 6 sedentary young (SY; VO2max = 36.0 +/- 2.2 mL x kg(-1) x min(-1); 27 +/- 3 yr), 6 fit old (FO; VO2max = 56.1 +/- 4.0 mL x kg(-1) x min(-1); 54 +/- 5 yr), and 6 sedentary old (SO; VO2max = 29.6 +/- 5.0 mL x kg(-1) x min(-1); 62 +/- 2 yr) volunteers. The following were measured before and after facial cooling: heart rate (HR), mean arterial blood pressure (MAP), pressure-rate product (PRP), and M-mode echocardiographically determined left ventricular internal dimensions, peak circumferential shortening (peak V(CF)), and ejection fraction (EF). RESULTS: Facial cooling produced a statistically significant bradycardia in all groups except for the SO whereas MAP was increased in the young groups but unchanged in the older groups. Pressure-rate product was significantly reduced in the FY, unchanged in the SY and FO, and significantly increased in the SO group. None of the groups showed a change in left ventricular dimensions, whereas only the SO group showed an increase in peak V(CF) (P < 0.05). CONCLUSIONS: These data suggest that endurance training and fitness level do not significantly alter cardiovascular responses to facial cooling in young men or physically fit older men. However, in older subjects, a sedentary lifestyle appears to be associated with an absent facial cooling reflex bradycardia, an increased PRP, and contractility (peak V(CF)).     

Ultraviolet difference spectral studies in the gamma-radiolysis of DNA and model compounds. II. Oxygen and temperature dependence in adenine radiation chemistry.

Ultraviolet difference spectra between gamma-irradiated and unirradiated aqueous solutions of oxygenated adenine reveal spectral maxima at 224, 286 and 360 nm, and suggest the existence of multiple radiation products. The presence of long-wavelength absorbing products implies the extension of the conjugation of the adenine ring. The product absorbing at 360 nm appears only in the presence of oxygen, with its yield dependent on both oxygen concentration and temperature. The absorbance peak at 360 nm in the UV difference spectra appears to demonstrate simple first-order decay kinetics, with a half-life of 50 min at 3 degrees C. At temperatures below 23 degrees C relative yields of the radiation products are approximately constant, suggesting a common mechanism. Higher temperatures apparently induce a mechanistic alteration. Since the temperature during and subsequent to irradiation, as well as the oxygen concentration of the solution, affects the absolute yields and distribution of the radiation products, great care must be exercised in controlling these variables.     

Characteristic association between K-ras gene mutation with loss of heterozygosity in X-ray-induced thymic lymphomas of the B6C3F1 mouse

PURPOSE: To elucidate the characteristics of radiation carcinogenesis, the spectra of K- and N-ras oncogene mutations, loss of heterozygosity (LOH) and their association in X-ray-induced thymic lymphomas (TL) were determined by comparing with those of N-ethyl-N-nitrosourea (ENU)-induced and spontaneously occurring TL. MATERIALS AND METHODS: TL that arose in untreated, X-ray-irradiated and ENU-treated B6C3F1 mice were examined both for K- and N-ras mutations by PCR-SSCP and DNA sequencing and for LOH by PCR with polymorphic microsatellite markers. RESULTS: (1) ras gene mutations were found in a proportion of TL from X-ray-exposed (approximately 20%) and ENU-treated (30-40%) mice while no ras gene mutations were found in spontaneous TL. N-ras mutations were rare. (2) The spectrum of ras gene mutations was diverse and seemed to differ little between X-ray-induced and ENU-induced TL, even though there was a higher frequency of ras mutations in ENU-induced TL that clustered to K-ras codon 12. (3) The X-ray-induced TL showing K-ras mutation were associated with LOH on chromosome 6, while those showing no K-ras mutation were associated with high frequency of LOH on chromosomes 4, 11 and 12. CONCLUSION: These results demonstrate that, in the B6C3F1 mouse TL, X-ray-induced lymphomagenesis showed both the co-expression, yet low occurrence of allelic imbalance on chromosome 6 and K-ras mutation, and exclusive expression of frequent allelic imbalance on chromosomes 4, 11 and 12 and K-ras mutation.     

用电子顺磁共振波谱拟合方法估算牙釉质辐射剂量

目的 探讨运用电子顺磁共振(electron paramagnetic resonance, EPR)波谱拟合技术估算牙釉质EPR辐射剂量的准确性。方法 编制多成分叠加型EPR粉末波谱拟合软件,分别拟合牙齿本底信号(background signal,BS)和辐照诱发信号(radiation-induced signal,RS)的EPR波谱模型,用波谱模型叠加计算方法拟合出实际辐照后牙釉质的EPR波谱,从复合谱中提取出RS成分并计算其相对强度,建立剂量响应曲线,估算样品剂量,并将剂量估算结果与传统的波谱强度测量方法进行比较。结果 拟合获得的BS信号为单峰高斯线形粉末谱,g=2.0035,线宽Hpp=0.650-1.100 mT; RS信号为轴对称多晶粉末谱线形,其g_⊥=2.0018,g_‖＝1.9965,线宽Hpp=0.335-0.400 mT;分离BS与RS后得到的RS相对强度与辐照剂量呈线性相关,剂量响应方程为:y=240.74x+76 724(R²=0.9947),剂量估算结果相对误差期望值为0.13。结论 EPR波谱拟合方法在一定程度上提高了牙釉质辐射剂量估计的准确性和可信度。     

Characteristic association between K- ras gene mutation with loss of heterozygosity in X-ray-induced thymic lymphomas of the B6C3F1 mouse

Purpose : To elucidate the characteristics of radiation carcinogenesis, the spectra of K- and N- ras oncogene mutations, loss of heterozygosity (LOH) and their association in X-ray-induced thymic lymphomas (TL) were determined by comparing with those of N -ethyl- N -nitrosourea (ENU)-induced and spontaneously occurring TL. Materials and methods : TL that arose in untreated, X-ray-irradiated and ENU-treated B6C3F1 mice were examined both for K- and N- ras mutations by PCR-SSCP and DNA sequencing and for LOH by PCR with polymorphic microsatellite markers. Results : (1) ras gene mutations were found in a proportion of TL from X-ray-exposed (~20%) and ENU-treated (30-40%) mice while no ras gene mutations were found in spontaneous TL. N- ras mutations were rare. (2) The spectrum of ras gene mutations was diverse and seemed to differ little between X-ray-induced and ENU-induced TL, even though there was a higher frequency of ras mutations in ENU-induced TL that clustered to K- ras codon 12. (3) The X-ray-induced TL showing K- ras mutation were associated with LOH on chromosome 6, while those showing no K- ras mutation were associated with high frequency of LOH on chromosomes 4, 11 and 12. Conclusion : These results demonstrate that, in the B6C3F1 mouse TL, X-ray-induced lymphomagenesis showed both the co-expression, yet low occurrence of allelic imbalance on chromosome 6 and K- ras mutation, and exclusive expression of frequent allelic imbalance on chromosomes 4, 11 and 12 and K- ras mutation.     

Features of EPR dosimetry with CaSO4:Dy phosphor.

The electron paramagnetic resonance(EPR) technique was used to study the paramagnetic centers induced by ionizing radiation in thermoluminescent CaSO4:Dy. Two different radiation induced centers, detectable in the (1-10(7)) Gy dose range and attributed to (SO3)- and Ca-vacancy center, (VCa)2-, respectively, can be used for dosimetry purpose. The (VCa)2- center is detectable only upon sample annealing at temperatures higher than about 180 degrees C. A reliable dose assessment can be performed in the (1-10(7)) Gy dose range and likely over 10(7) Gy. The sensitivity decreases with thermal cycles, while the yield of both centers increases with accumulated dose (pumping effect), at a greater extent for (VCa)2- center. (VCa)2- center is stable with time, while (SO3)- center shows a dose-dependent fading. Among the applications that can be imaged for this dosimeter, very high dose assessment capability is of particular importance.     

Role of alkali ions in limiting the capacity of the 110 degrees C peak of quartz to remember the firing temperature.

Establishment of a reliable thermoluminescence (TL) technique to record the firing temperature has not been possible so far. Attempts made so far have resulted in incoherent results. Recent studies involving thermal effects on TL properties of the 110 degrees C glow peak of quartz by various workers have demonstrated the crucial role of monovalent ions in the TL process. In the light of these results, an attempt is made to understand the mechanism which disables quartz to remember and manifest its firing temperature using its 110 degrees C peak.