Radioactive Layer Research Articles

Tibetan Plateau insights into >1100 °C crustal melting in the Quaternary

AbstractPartial melting during high-temperature to ultrahigh-temperature (UHT) metamorphism facilitates crustal differentiation, element transfer, and the evolution of topography in orogens, however the mechanisms that drive heating of Earth’s crust remain controversial. We provide new evidence from ca. 2.3 Ma dacites in the Tibetan Plateau, representing the youngest known UHT metamorphic event. Our results show that these dacites were mainly generated by fluid-absent melting of metasedimentary rocks and minor mafic rocks at peak temperatures of 1100–1150 °C and pressures of 0.8–0.9 GPa. The dacites represent mixtures of UHT melts and granulite residues and are geochemically similar to A-type granites with extremely high heat-production values (5.33–5.99 μW m–3). Compared with the geological and geophysical observations, numerical modeling indicates that the key factor determining the thermal evolution of Tibet is the thickness of the radioactive layer. Orogens dominated by rocks of felsic composition, like Tibet, could easily reach UHT conditions within a short period of time (20–40 m.y.) after crustal thickening by radioactive heating, without the need for an additional tectonic mechanism.

X-ray fluorescence analysis of samples for beta spectrometry and its application to precise Monte Carlo simulations

Drop deposition is one of the techniques for the preparation of beta spectrometry samples. Its advantage is versatility and simplicity. On the contrary, the unsatisfactory repeatability of the sample quality is its drawback. The radioactive layer produced is not homogeneous, which causes the differences in absorption properties for low-energy beta radiation. This can be a problem in applications based on spectrum shape analysis, such as the determination of radionuclide impurities in pure beta emitter mixtures.The main objective of the paper is to investigate whether radioactive samples can be characterized in detail using X-ray fluorescence analysis. Furthermore, the application of this measurement for the accuracy improvement of beta spectra calculation in the MCNPX software package is demonstrated. Summing up the results obtained, it can be concluded that the high-resolution XRF 2D scanning of radiation sources can be used to reduce uncertainties in Monte Carlo simulations.

Effect of microemulsion formulation on biodistribution of 99mTc-Aprotinin in acute pancreatitis models induced rats

Background: Aprotinin is a monomeric globular polypeptide, which derived from bovine lung tissue and theoretically attractive molecule in ameliorating the effects of acute pancreatitis. Acute pancreatitis is an inflammatory condition of the pancreas that is painful and at times deadly. Over the following two decades Aprotinin therapeutic potential on pancreatitis is proven experimentally, its clinical therapeutic success is limited due to low targeting to pancreas.Objective: The aim of this study was to evaluate the biodistribution of Technetium-99m (99mTc)-Aprotinin solution (99mTc-Aprotinin-S) and 99mTc-Aprotinin loaded microemulsion, which was prepared for the aim of treatment for acute pancreatitis.Method: Aprotinin was radiolabeled with 99mTc. Radiochemical purity was determined with radioactive thin layer chromatography studies. 99mTc-Aprotinin-S and 99mTc-Aprotinin loaded microemulsion (99mTc-Aprotinin-M) was administered to acute edematous, severe necrotizing pancreatitis and air pouch model induced rats. Tissue distribution of Aprotinin was investigated with gamma scintigraphy and biodistribution studies.Results: Aprotinin was radiolabeled by 99mTc with high radiochemical purity (95.430 ± 0.946%). The complex was found to be stable at room temperature up to 6 h. Animal studies have shown that similar to that of other small proteins Aprotinin is accumulated primarily in the kidney. The scintigraphy and biodistribution studies showed that, while i.v. administration of 99mTc-Aprotinin-S distributed mostly in kidneys and bladder, 99mTc-Aprotinin-M, with droplet size of 64.550 ± 3.217 nm, has high uptake in liver, spleen and pancreas.Conclusion: This might be concluding that microemulsions may be suggested as promising formulations for selectively targeting Aprotinin to pancreas inflammation.

Physical parameters determination for gibbsite – bearing marl, Abu – Thor area, Southwestern, Sinai, Egypt

For the sake of determination of some physical factors for gibbsite – bearing marl, at the area under consideration, a cylindrical tube of length 60 cm and diameter 6 cm was used. This tube contains ten CR-39 detectors of area 1 cm*1 cm fixed on the inner side of the tube in mutual positions of fixed interval distance 5 cm for each. The measured radon gas concentrations ranged from 1027.87 ± 93.32 Bq/m3 to 1712.39 ± 126.19 Bq/m3, the exhalation rate ranged from 3.39E-5±3.08E-6 to 4.66E-5±3.00E-6 mBq/m2s−1. By using the measured value of porosity which is (49.19%), the measured diffusion coefficient was calculated, it ranged from 3.26 E-3 (m2 s−1) to 5.77E-8 (m2s−1) and the diffusion length ranged from 3.63 m to 56.19 m, these values were used to determine the depth of the top of radioactive layer, the obtained results was found to be 1.683 m.

SU‐E‐T‐338: Calculation of Dose Distributions From 106 Ruthenium COC‐Type Eye Applicator

Purpose: In the treatment of retinoblastoma, 106Ru brachytherapy is one of the important methods to control the tumor with preserving eye function. So far, we had some clinical experiences that the tumor on optic disc was effectively shrunk by using the COC‐type applicator (BEBIG), which has a notch. In this study, the dose distribution was evaluated by Monte Carlo simulation to investigate a dose to the notched area of COC applicator. Methods: The model of the COC‐type applicator was created and registered in EGS5 Monte Carlo simulation code. Here, the applicator thickness was 1mm including 0.1mm of the silver radiation window and 0.2 mm of radioactive layer. The notched area was also reproduced from the measurement of actual geometry. The dose to the notched area was represented with the polar coordinate, in which the two‐dimensional relative dose distributions of the spherical shells with 0.2 mm thickness at distances of 0.1, 1.3, and 2.5 mm from the surface were calculated. For comparison, the dose profile was also calculated by the Plaque simulator (BEBIG). Results: The Monte Carlo Result showed that the scattered electron largely contributed to the dose to the notched area. This contribution became dominant as the distance from the surface was larger. The calculation Result of the Plaque simulator was significantly different from that of the Monte Carlo simulation around the notched area of the applicator. Conclusion: The dose distribution with the COC‐type applicator could be quantified by the Monte Carlo Conclusion: The dose distribution with the COC‐type applicator could be quantified by the Monte Carlo calculation. It was found that the notched area of COC‐type applicator was irradiated sufficiently by the scattered electron. The Plaque simulator could not reproduce the dose distribution around the notched area.

CALCULATION OF ISODOSE CURVES FOR CCA AND CCB CONCAVE EYE APPLICATORS

BEBIG Ruthenium-106 ophthalmic plaques have been used for treatment of uveal melanoma, retinoblastoma, melanoma of the iris and other special applications for more than 30 years. The plaques consist of a thin film of Ru-106, a beta emitter encapsulated in pure silver. Simulations of small concave applicators CCA and CCB, manufactured by Bebig, were performed using Monte Carlo MCNP4C code which allows for description of the applicator (geometry and materials) in detail. Electrons are emitted from the 106 Ru nuclei isotropically with initial energy randomly sampled from the corresponding Fermi spectra and with initial positions uniformly distributed on the radioactive layer. In this work, relative doses were calculated in soft tissue phantom near the active layer. Isodose curves for CCA and CCB eye applicators were determined. Our calculated data agrees well with the measured phantom data reported in literature.

Heat sources and trigger mechanisms of exhumation of HP granulites in Variscan orogenic root

AbstractThe structure of the Moldanubian domain is marked by felsic granulites of Ordovician protolith age forming the cores of domes that are separated from mid‐crustal Neoproterozoic and Palaeozoic metasedimentary rocks that occur in synclines by a late Ordovician to Silurian metabasic unit. Reflection and refraction seismic sections combined with gravity inversion modelling suggest the presence of a low density layer at the bottom of the crust (interpreted as felsic granulite) overlain by a denser layer (interpreted as amphibolite) with layers of intermediate density at the top (interpreted as metasedimentary rocks). It is proposed that the granulite domes surrounded by middle crustal rocks reflect transposed horizontal layering originally similar to that preserved in the deep crust and imaged by the geophysical surveys. This geological and geophysical structure is considered to be a result of Viséan gravity redistribution initiated by radioactive heating of felsic crust tectonically emplaced at the bottom of a Palaeozoic orogenic root. The radioactive layer with heat production of 4 μW m−3 corresponds geochemically and isotopically to Ordovician felsic metaigneous rocks of the Saxothuringian domain that have been emplaced at Moho depth under thickened crust during late Devonian–early Carboniferous continental subduction. Part of the continental crust continued to be subducted and produced fluids/low‐volume melts which directly contaminated and enriched the local lithospheric mantle by lithophile elements, most notably Cs, Rb, Li, Pb, U, Th and K. Thermal incubation of 10–15 Myr was sufficient to heat and convert the underplated felsic layer into granulites via dehydration melting and melt segregation. The process of melt loss was responsible for the removal of radioactive elements and for switching off the heat at the beginning of the exhumation process. At the same time, the metasomatized underlying mantle was heated producing characteristic ultrapotassic magmas. Gravitational instability was then induced by the density contrast between the light granulites and the overlaying denser mafic lower crustal layer and a viscosity drop related to thermal weakening and partial melting of the latter.

Monte Carlo calculation of dose to water of a 106Ru COB-type ophthalmic plaque

The concave eye applicators with 106Ru/106Rh or 90Sr/90Y beta-ray sources are worldwide used in brachytherapy for treating intraocular tumors. It raises the need to know the exact dose delivered by beta radiation to tumors but measurement of the dose to water (or tissue) is very difficult due to short range of electrons. The Monte Carlo technique provides a powerful tool for calculation of the dose and dose distributions which helps to predict and determine the doses from different shapes of various types of eye applicators more accurately. The Monte Carlo code MCNPX has been used to calculate dose distributions from a COB-type 106Ru/106Rh ophthalmic applicator manufactured by Eckert & Ziegler BEBIG GmbH. This type of a concave eye applicator has a cut-out whose purpose is to protect the eye nerve which makes the dose distribution more complicated. Several calculations have been performed including depth dose along the applicator central axis and various dose distributions. The depth dose along the applicator central axis and the dose distribution on a spherical surface 1 mm above the plaque inner surface have been compared with measurement data provided by the manufacturer. For distances from 0.5 to 4 mm above the surface, the agreement was within 2.5 % and from 5 mm the difference increased from 6 % up to 25 % at 10 mm whereas the uncertainty on manufacturer data is 20 % (2s). It is assumed that the difference is caused by nonuniformly distributed radioactivity over the applicator radioactive layer.

Chernobyl nuclear accident revealed from the 7010 m Muztagata ice core record

The total activity variation with depth from a 41.6 m Muztagata ice core drilled at 7010 m, recorded not only the 1963 radioactive layer due to the thermonuclear test, but also clearly the radioactive peak released by the Chernobyl accident in 1986. This finding indicates that the Chernobyl nuclear accident was clearly recorded in alpine glaciers in the Pamirs of west China, and the layer can be potentially used for ice core dating in other high alpine glaciers in the surrounding regions.

A new ice-core record from Lomonosovfonna, Svalbard: viewing the 1920–97 data in relation to present climate and environmental conditions

AbstractIn 1997 a 121 m ice core was retrieved from Lomonosovfonna, the highest ice field in Spitsbergen, Svalbard (1250 m a.s.l.). Radar measurements indicate an ice depth of 126.5 m, and borehole temperature measurements show that the ice is below the melting point. High-resolution sampling of major ions, oxygen isotopes and deuterium has been performed on the core, and the results from the uppermost 36 m suggest that quasi-annual signals are preserved. The 1963 radioactive layer is situated at 18.5–18.95 m, giving a mean annual accumulation of 0.36 m w.e. for the period 1963–96. The upper 36 m of the ice core was dated back to 1920 by counting layers provided by the seasonal variations of the ions in addition to using a constant accumulation rate, with thinning by pure shear according to Nye (1963). The stratigraphy does not seem to have been obliterated by meltwater percolation, in contrast to most previous core sites on Svalbard. The anthropogenic influence on the Svalbard environment is illustrated by increased levels of sulphate, nitrate and acidity. Both nitrate and sulphate levels started to increase in the late 1940s, remained high until the late 1980s and have decreased during the last 15 years. The records of δ18O, MSA (methane-sulphonic acid), and melt features along the core agree with the temperature record from Longyearbyen and the sea-ice record from the Barents Sea at a multi-year resolution, suggesting that this ice core reflects local climatic conditions.

Monte Carlo calculation of the dose distributions of two 106Ru eye applicators

Background and purpose: Beta emitting 106Ru applicators are widely used to treat choroidal melanoma. In view of the importance of clinical applications of this radioisotope and the relative lack of knowledge of the dose distributions, three-dimensional dose maps of two concave applicators were calculated by means of Monte Carlo simulation. Materials and methods: Simulations of small CCA and CCB concave applicators manufactured by Bebig were performed using the Monte Carlo code PENELOPE, which allows the description of the structure (geometry and materials) of the applicator in detail. Electrons are emitted from the 106Ru nuclei isotropically, with initial energy randomly sampled from the corresponding Fermi spectra and with initial positions uniformly distributed on the radioactive layer. Primary electrons, as well as the produced δ-rays, are assumed to be absorbed in the medium when they slow down to an energy of 70 keV. Bremsstrahlung photons with energies larger than 7 keV are also simulated. The simulation code has been run on a 166 MHz PENTIUM PC. Results: Three-dimensional dose distributions produced by the CCA and CCB applicators in a water sphere, concentric with the applicator, were evaluated. To minimize the magnitude of statistical uncertainties, advantage has been taken of the cylindrical symmetry of the problem. The relative depth-dose (along the symmetry axis of the applicator) was also evaluated from the applicator surface up to distances larger than 1 cm, with statistical uncertainties of a few percent. Results compare well with data supplied by the manufacturer. Conclusions: We have performed accurate Monte Carlo calculations of three-dimensional dose distributions from CCA and CCB 106Ru applicators. The results, presented in the form of two-dimensional maps, depth-dose distributions along the symmetry axis and lateral dose profiles, provide a detailed description of the dose delivered in treatments of choroidal melanoma.

Determining the depth distribution of planar gamma-ray sources using the shape of the Compton continuum:: Experimental test

In single photon emission computed tomography, the spatial distribution of a gamma-emitting radionuclide is often determined without taking into account the shape of the continuum of the measured γ-ray spectrum. This text considers a previously published method for using the measured Compton scattered photons to determine the depth distribution. Least-squares fitting is employed instead of kernel matrix inversion and regularisation. The method is applied to experimental measurements of a radioactive layer of 2 MBq 51 Cr , using measurement times between 2 and 5 h. First, we describe the shape of the spectra, then the method used to reconstruct the depth distribution is described and tested for the almost noise free case. Furthermore, in order to assess the relation between statistical noise in the spectrum and the reliability of the reconstructed source distribution, we quantify these by defining two corresponding parameters and study their relationship. We do not consider generalisation beyond a single plane source oriented parallel to the detector face at an unknown depth, or multiples of such a source at different unknown depths.

Equilibrium line and mean annual mass balance of Finsterwalderbreen, Spitsbergen, determined by in situ and laboratory gamma-ray measurements of nuclear test deposits

In order to determine the equilibrium line (EL) and the annual net mass balance over the accumulation area of Finsterwalderbreen, Spitsbergen, Svalbard (by detection of the 1962–63 radioactive peak from the 1961–62 atmospheric nuclear tests), we collected 14 ice cores, at elevations of 445–730 m, in the springs of 1994 and 1995. The corresponding samples were melted and filtered for laboratory gamma spectrometry. In the accumulation area, the 1962–63 radioactive layer is found well below the surface. The mean annual accumulation is not invariably related to altitude. The EL, averaged to 545 in a.s.l., leads to an accumulation area ratio of 0.3 and indicates a strong negative balance. The 584 Bq m−2 mean137 Cs deposition rate (1954–74 nuclear tests) for eight ice cores in the accumulation area is nearly twice the 340 Bq m−2 mean Svalbard value obtained from six other glaciers (at time of deposition). An in situ gamma-ray detector was lowered down each borehole, and137 Cs levels were recorded. The counting rate is proportional to the apparent deposition rate and the specific activity. The laboratory measurements perfectly match the in situ determinations. In the ablation area, a dust layer and the associated nuclear test deposits are concentrated close to the bare ice surface of the glacier, under the winter snow layer and present maximum 137 Cs and 210 Pb contents. The dust layer acts like a filter for radioactive materials removed from the glacier and its basin by melting and water flow. The original specific activities and deposition rates at a given location are enhanced by adsorption of additional radioactivity on the dust particles. A linear relationship exists between 137 Cs and 210 Pb deposition rates. This process is almost constant for all studied ice cores. The apparent 137 Cs deposition rate for seven ice cores in the ablation area is 465 Bq m−2 (at date of measurement: 1 July 1995).

Equilibrium line and mean annual mass balance of Finsterwalderbreen, Spitsbergen, determined by in situ and laboratory gamma-ray measurements of nuclear test deposits

In order to determine the equilibrium line (EL) and the annual net mass balance over the accumulation area of Finsterwalderbreen, Spitsbergen, Svalbard (by detection of the 1962–63 radioactive peak from the 1961–62 atmospheric nuclear tests), we collected 14 ice cores, at elevations of 445–730 m, in the springs of 1994 and 1995. The corresponding samples were melted and filtered for laboratory gamma spectrometry. In the accumulation area, the 1962–63 radioactive layer is found well below the surface. The mean annual accumulation is not invariably related to altitude. The EL, averaged to 545 in a.s.l., leads to an accumulation area ratio of 0.3 and indicates a strong negative balance. The 584 Bq m−2 mean137 Cs deposition rate (1954–74 nuclear tests) for eight ice cores in the accumulation area is nearly twice the 340 Bq m−2 mean Svalbard value obtained from six other glaciers (at time of deposition).An in situ gamma-ray detector was lowered down each borehole, and137 Cs levels were recorded. The counting rate is proportional to the apparent deposition rate and the specific activity. The laboratory measurements perfectly match the in situ determinations. In the ablation area, a dust layer and the associated nuclear test deposits are concentrated close to the bare ice surface of the glacier, under the winter snow layer and present maximum 137 Cs and 210 Pb contents. The dust layer acts like a filter for radioactive materials removed from the glacier and its basin by melting and water flow. The original specific activities and deposition rates at a given location are enhanced by adsorption of additional radioactivity on the dust particles. A linear relationship exists between 137 Cs and 210 Pb deposition rates. This process is almost constant for all studied ice cores. The apparent 137 Cs deposition rate for seven ice cores in the ablation area is 465 Bq m−2 (at date of measurement: 1 July 1995).

Inversion of multiple thermal indicators: Quantitative methods of determining paleoheat flux and geological parameters. I. Theoretical development for paleoheat flux

The quantitative inversion of present-day downhole thermal indicator information enables (a) assessment of the effective paleoheat flux recorded by thermal indicators, and (b) determination of geological parameters related to the dynamical burial history of sedimentary strata. The logic of the general inversion scheme underlying seven thermal indicators, viz. vitrinite reflectance, sterane, and/or hopane isomers, sterane aromatization, optical rotation,39Ar/40Ar, pollen translucency, and fission scar tracks in apatite is presented, and their capability for resolving paleoheat flux is noted. In a second paper, determination of chemical and physical parameters, as well as several other quantities of geological interest (such as the sizes and erosion times of multiple unconformities, stratigraphic ages, paleo-overpressure, igneous intrusion timing, overthrust timing and frictional heat generation, fault and slump timing, thermal effects due to radioactive layer emplacement, and salt emplacement and dissolution timing) are discussed. Such events impact on both burial and thermal histories of sedimentary layers.

Postapocalypse stratigraphy: Some considerations and proposals

An imminent nuclear apocalypse will be a geologically significant event characterized by widespread extinction and marked by a highly radioactive lower boundary layer. The concept of a fallout-enriched Cenozoic/postapocalypse boundary layer is significant in that such a horizon would constitute an ideal, global isochron that is both readily detectable and correlatable; the only other systemic boundary that appears to be analogous is the Cretaceous/Tertiary boundary. New terminology consistent with the established stratigraphic nomenclature is herein proposed for the major anticipated postapocalypse geochronologic units.

Heat flow in the Indian Peninsula—its geological and geophysical implications

The distribution of surface heat flow in the various geological units of the Indian Peninsula is presented and discussed in the light of other related geodata. The heat flow data show a large variation (26 to 107 mW m −2), but indicate, in general, a thermal regime characteristic of stable continental areas. The Dharwar schist belts—greenstone belts, and greenstone-like geosynclinal piles—arc characterised by low heat flow. It appears very probable; (a) that favourable conditions for the generation of the Earth's crust and the melting near the surface developed at the very early stages of the Earth's evolution; and (b) that true greenstone belts, which represent the relics of the primitive basic ultrabasic crust, may have been more or less continuous once. It is our contention that their association with low surface heat flow is primarily due to their initial evolution and growth. The low heat flow values in green stone belts show a general increase in Archaean-Proterozoic granitic and gneisic terrains. The average heat flow in Archaean areas is significantly lower than in Proterozoic parts of the Indian Shield. In general, the average heat flow shows an inverse relation with the age of Precambrian orogeny. Further, the Proterozoic geosynclinal belts, in which sedimentation and mobility continued up to Upper Proterozoic, have been found to mark the highest heat flow areas of Precambrian India. Surprisingly, the Deccan Traps, the Cretaceous-Paleocene basic effusives, are associated with low heat flow values (40 mW m −2). The observed high heat flow in the northern part of a basin, in which a full sequence of Tertiary to Recent sediments overlie the Deccan Traps, has been ascribed to a shallow basic crustal Miocene-Pliocene intrusive body. The Gondwanas, which occur in intracratonic small, isolated, elongate trough-like, and semi-elliptical depressions, show a contrasting geothermal character with many zones of high surface heat flow, for which there is no clear explanation at present. Most of the Indian Peninsula is comprised of three cratons-the Dharwar, the Aravallis, and the Singhbhum. The Dharwar craton appears to be associated with the lowest surface heat flow, and the heat flow from the mantle and the lower crust is q r≈ 23 mW m −2 . This is followed by q r≈ 30 mW m −2 for the Aravalli craton and about 38 mW m −2 for the Singhbhum craton. Thus for the same surface radioactivity and heat flow, crustal temperatures are lowest in the Dharwar craton. For this craton, the temperatures at the base of the crust are similar to those in the western Australian shield, and in the Superior Province of the Canadian shield. We further suggest that U, Th and K in the top radioactive layer, probably do not follow the same concentration-depth pattern i.e., the characteristic depth, D, for these heat producing radioactive elements is most likely different and is the main cause of a wide scatter in the values of q r for various heat flow-heat production pairs within a heat flow province. We demonstrate that it is not worthwhile to study the correlation of surface heat flow to the gravity anomaly in the Indian Peninsula without removing the effects of the pronounced Indian Ocean gravity low from the gravity anomalies. Surface heat flow, q s , and crustal thickness. Zm, as obtained from DSS and earthquake data, show a positive (slightly exponential) correlation, which is compatible with crustal properties and dynamics. It is demonstrated that the correlation between q s and Zm in Precambrian shields can be positive or negative or even negligible, depending upon their past geological history.

A reinterpretation of the linear heat flow and heat production relationship for the exponential model of the heat production in the crust

Summary. The conventional assumption of the equality of the slope of the empirical linear heat flow/heat generation relation and the logarithmic decrement in the exponential model of the heat production is not valid. The rigorous analysis of the heat flow equation shows that, with the increase of the magnitude of the slope, the invalidity becomes significant. In the Indian shield region, the available estimate of the slope is 14.8 km, while the corresponding logarithmic decrement value is 17.2 km. However, it may be emphasized that in the step model the slope is rightly interpreted as the thckness of the radioactive layer.

Electret device having charge maintained by radioactivity

An electret device has a dielectric layer containing electret charges and a radioactive layer on one of the surfaces of the dielectric layer.

Étude expérimentale de la diffusion cationique dans un verre basaltique : alcalins et alcalino-terreux

Experimental study of the diffusion of alkali and alkali-earth ions has been realized in a basaltic glass by the thin radioactive layer technique, in the range 750-1 000° C, and under usual conditions of pressure and oxygen fugacity. The diffusion coefficients (D) vary between 10-7 and 10-12 cm2 s_1, and they fit Arrhenius laws [D = Do exp (— E/RT)], with activation energies of 13 to 60 kcal/mole. These new results are consistent with our previous experiments on obsidians and feldspar glasses, and confirm the observed magnitudes and trends. The matrix composition has no significant effect, whereas the diffusi-vities strongly depend on the nature of the element under consideration. For most elements, an increase of temperature of 100° C results in a 5-10 fold decrease of D values, except for Na and K which vary more slowly.