Levels of depleted uranium in Kosovo soils

The United Nations Environment Programme (UNEP) has performed a field survey at 11 sites located in Kosovo, where depleted uranium (DU) ammunitions were used by the North Atlantic Treaty Organization (NATO) during the last Balkans conflict (1999). Soil sampling was performed to assess the spread of DU ground contamination around and within the NATO target sites and the migration of DU along the soil profile. The 234U/238U and 235U/238U activity concentration ratios have been used as an indicator of natural against anthropogenic sources of uranium. The results show that levels of 238U activity concentrations in soils above 100 Bq x kg(-1) can be considered a 'tracer' of the presence of DU in soils. The results also indicate that detectable ground surface contamination by DU is limited to areas within a few metres from localised points of concentrated contamination caused by penetrator impacts. Vertical distribution of DU along the soil profile is measurable up to a depth of 10-20 cm. This latter aspect is of particular relevance for the potential risk of future contamination of groundwater.     

Efficacy of 3,4,3-LI(1,2-HOPO) for decorporation of Pu, Am and U from rats injected intramuscularly with high-fired particles of MOX

This study aimed to assess the efficacy of 3,4,3-LI(1,2-HOPO) for reducing uranium, plutonium and americium in rats after intramuscular injection of (U-Pu)O2 particles (MOX). Sixteen rats were contaminated by intramuscular injection of a 1 mg MOX suspension and then treated daily for 7 d with LIHOPO (30 or 200 micromol kg(-1)) or DTPA (30 micromol kg(-1)). LIHOPO was inefficient for removing Pu, Am and U from the wound site. However, it reduced Pu retention in carcass and liver by factors of 2 and 6 respectively, and Am retention in carcass and liver by factors of 10 and 30. In contrast, the effect of LIHOPO on U was to decrease the retention in kidneys by a factor of 75. These results confirm that LIHOPO is a good candidate for use after contamination with MOX, in combination with localised wound lavage or surgical treatment aimed at removing most of the contaminant at the wound site.     

Comparative study of femtosecond and nanosecond laser-induced breakdown spectroscopy of depleted uranium

We present spectra of depleted uranium metal from laser plasmas generated by nanosecond Nd:YAG (1064 nm) and femtosecond Ti:sapphire (800 nm) laser pulses. The latter pulses produce short-lived and relatively cool plasmas in comparison to the longer pulses, and the spectra of neutral uranium atoms appear immediately after excitation. Evidence for nonequilibrium excitation with femtosecond pulses is found in the dependence of spectral line intensities on the pulse chirp.     

Variations of the isotopic ratios of uranium in environmental samples containing traces of depleted uranium: theoretical and experimental aspects

The possibility of using conventional analysis, such as gamma spectrometry and alpha spectrometry, for the detection of traces of depleted uranium (DU) in environmental samples has been investigated. The expected values have been compared with the experimental results obtained by using mollusc samples gathered in the Adriatic Sea. The analysis has shown that it is possible to detect DU. if the percentage composition is about 20% depleted uranium and 80% natural uranium, for a sample containing 10 Bq x kg(-1) of 238U. The possibility of extending this approach to samples with any given uranium concentration is investigated.     

Development of shear bands in dynamic plane strain compression of depleted uranium and tungsten blocks

We study the initiation and growth of shear bands in prismatic bodies of rectangular cross-section made of either depleted uranium or tungsten and deformed in plane strain compression at a nominal strain-rate of 5000 s⁻¹. It is assumed that defects are distributed symmetrically with respect to the two centroidal axes and each quadrant has up to 300 randomly distributed defects in the form of a weaker material; the flow stress for the weaker material in a quasistatic simple compression test is taken to be 5% lower than that for the original material. It is found that, in the deformed configuration, shear bands in depleted uranium blocks are inclined at approximately 42.5° counterclockwise from the horizontal axis, those in tungsten are inclined at nearly 135°. When shear bands initiate, the total compressive force required to deform the body drops sharply for the uranium blocks but gradually for the tungsten blocks. After a shear band has developed, dead zones form in both uranium and tungsten blocks; the size of the dead zone in the tungsten block is more than that in the uranium block. When the shear modulus for the tungsten is artificially changed so as to equal that for the uranium, the angle of inclination for the shear bands in tungsten blocks changes to that found for the uranium blocks. This suggests that the value of the shear modulus plays a noticeable role in the development of shear bands. We have also studied the effect, on the initiation of shear band, of modeling the defects as either very weak or very strong material.     

Enhancement of damage indicators in wavelet and curvature analysis

Damage in a structural element induces a small perturbation in its static or dynamic displacement profile which can be captured by wavelet analysis. The paper presents the wavelet analysis of damaged linear structural elements using DB4 or BIOR6.8 family of wavelets. An expression is developed for computing the natural frequencies of a damaged beam using first order perturbation theory. Starting with a localized reduction ofEI at the mid-span of a simply supported beam, damage modelling is done for a typical steel beam element. Wavelet analysis is performed for this damage model for displacement, rotation and curvature mode shapes as well as static displacement profiles. Damage indicators like displacement, slope and curvature are magnified under higher modes. Instantaneous step-wise linearity is assumed for all the nonlinear elements. A localization scheme with arbitrararily located curvature nodes within a pseudo span is developed for steady state dynamic loads, such that curvature response and damages are maximized and the scheme is numerically tested and proved. This paper is dedicated to Prof R N Iyengar of the Indian Institute of Science on the occasion of his formal retirement.     

铀表面激光合金化处理层成分及相结构分析

应用激光技术对铀上铌镀层进行表面合金化处理,并应用能谱和X射线衍射仪对处理层中的铌元素分布和相结构进行了分析.结果表明,铌元素沿处理层深度方向有一定的浓度梯度,距离处理层表面越近,铌含量越高;处理层中铌和铀相互作用生成了相铀铌合金.     

Living with cracks: damage and repair in human bone

Our bones are full of cracks, which form and grow as a result of daily loading activities. Bone is the major structural material in our bodies. Although weaker than many engineering materials, it has one trick that keeps it ahead - it can repair itself. Small cracks, which grow under cyclic stresses by the mechanism of fatigue, can be detected and removed before they become long enough to be dangerous. This article reviews the work that has been done to understand how cracks form and grow in bone, and how they can be detected and repaired in a timely manner. This is truly an interdisciplinary research field, requiring the close cooperation of materials scientists, biologists and engineers.     

Laser ablation inductively coupled plasma mass spectrometry measurement of isotope ratios in depleted uranium contaminated soils

Laser ablation of pressed soil pellets was examined as a means of direct sample introduction to enable inductively coupled plasma mass spectrometry (ICP-MS) screening of soils for residual depleted uranium (DU) contamination. Differentiation between depleted uranium, an anthropogenic contaminant, and naturally occurring uranium was accomplished on the basis of measured 235U/238U isotope ratios. The amount of sample preparation required for laser ablation is considerably less than that typically required for aqueous sample introduction. The amount of hazardous laboratory waste generated is diminished accordingly. During the present investigation, 235U/238U isotope ratios measured for field samples were in good agreement with those derived from gamma spectrometry measurements. However, substantial compensation was required to mitigate the effects of impaired pulse counting attributed to sample inhomogeneity and sporadic introduction of uranium analyte into the plasma.     

Characterisation and dissolution of depleted uranium aerosols produced during impacts of kinetic energy penetrators against a tank

Aerosols produced during impacts of depleted uranium (DU) penetrators against the glacis (sloping armour) and the turret of a tank were sampled. The concentration and size distribution were determined. Activity median aerodynamic diameters were 1 microm (geometric standard deviation, sigma(g) = 3.7) and 2 microm (sigma(g) = 2.5), respectively, for glacis and turret. The mean air concentration was 120 Bq m(-3), i.e. 8.5 mg m(-3) of DU. Filters analysed by scanning electron microscopy (SEM) and X ray diffraction showed two types of particles (fine particles and large molten particles) composed mainly of a mixture of uranium and aluminium. The uranium oxides were mostly U3O8, UO2.25 and probably UO3.01 and a mixed compound of U and Al. The kinetics of dissolution in three media (HCO3-, HCl and Gamble's solution) were determined using in-vitro tests. The slow dissolution rates were respectively slow, and intermediate between slow and moderate, and the rapid dissolution fractions were mostly intermediate between moderate and fast. According to the in-vitro results for Gamble's solution, and based on a hypothetical single acute inhalation of 90 Bq, effective doses integrated up to 1 y after incorporation were 0.54 and 0.56 mSv, respectively, for aerosols from glacis and turret. In comparison, the ICRP limits are 20 mSv y(-1) for workers and 1 mSv y(-1) for members of the public. A kidney concentration of approximately 0.1 microg U g(-1) was predicted and should not, in this case, lead to kidney damage.     

Penetration of boron carbide, aluminum, and beryllium alloys by depleted uranium rods: Modeling and experimentation

As part of the US stockpile stewardship program, it is necessary to perform experiments with various metallic components and explosives. These experiments will be conducted within specially designed blast vessels to ensure that the debris from the experiment is contained. The debris includes fragments that are launched at hypervelocities. The blast vessels are built primarily of steel, but have windows of either aluminum or beryllium alloys for diagnostic equipment requirements. To contain the hypervelocity depleted uranium fragments, ceramic armoring of the windows and steel vessel is used. To develop the necessary design tools, a program of experiments and modeling was begun. Preliminary pre-test predictions were made to design experiments. The experiments were conducted with targets representative of the armored windows in the vessel. To assist in the vessel design, two- and three-layered target analytical models were developed to predict the penetration of depleted uranium rods striking at velocities up to 2 km/s into layered targets of ceramic (boron carbide and silicon carbide) and aluminum, beryllium and steel alloys. The agreement between the pre-test predictions, the developed layered-target analytical model, and the experiments is good.     

Heterogeneous accumulation of uranium in the brain of rats

Recent reports suggest that uranium can accumulate not only in known target organs, that is, kidneys or bones, but also in others such as central nervous system. In the present work, the accumulation of uranium in the brain of rats was studied after repeated exposure by inhalation, chronic exposure by ingestion and acute exposure by injection. For each route of administration, the amount of uranium entering the brain was low. The results showed different accumulation in the brain areas according to the route of intake. Injection gave a rather homogeneous distribution in the different brain areas, whereas both inhalation and ingestion yielded heterogeneous but specific accumulation. These differences in distribution suggest the operation of different mechanisms of delivery of uranium to the brain tissues.     

The nature of fatigue damage in bone

Bone is unusual among structural materials as it is alive and capable of self-repair. Fatigue-induced microdamage is repaired by bone remodelling, but if damage accumulates too quickly, or remodelling is deficient, fatigue failure may result. Fatigue is thought to contribute to both stress and fragility fractures which are of major clinical importance. Despite this, we do not fully understand the nature of fatigue damage in bone. Human rib sections, containing microcracks stained with basic fuchsin, were serially sectioned and microcracks identified and reconstructed in three dimensions using computer software. Microcracks were elliptical in shape, 400 μm long and 100 μm wide, typical of a transversely isotropic material. Chelating agents which bind Ca²⁺ were found to label microcracks in rib, as well as mineralising bone surfaces and resorption sites, suggesting that microcracks are Ca²⁺ ion-lined discontinuities in the hydroxyapatite matrix. Ca²⁺ ions were exposed by scratching the surface of bovine bone specimens and labelled with chelating agents in sequence. The optimal four agent sequence was: alizarin, xylenol orange, calcein and calcein blue. Two dye sequences were used to differentiate between pre-existing and test-induced microdamage in bovine samples fatigue tested in compression and longer sequences labelled microcrack growth. Microcrack dimensions can be used to calculate stress intensity values and, together with fatigue test data, can aid theoretical models to predict fatigue failure in bone.     

Determination of depleted uranium in urine via isotope ratio measurements using large-bore direct injection high efficiency nebulizer-inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS), coupled with a large-bore direct injection high efficiency nebulizer (LB-DIHEN), was utilized to determine the concentration and isotopic ratio of uranium in 11 samples of synthetic urine spiked with varying concentrations and ratios of uranium isotopes. Total U concentrations and (235)U/(238)U isotopic ratios ranged from 0.1 to 10 microg/L and 0.0011 and 0.00725, respectively. The results are compared with data from other laboratories that used either alpha-spectrometry or quadrupole-based ICP-MS with a conventional nebulizer-spray chamber arrangement. Severe matrix effects due to the high total dissolved solid content of the samples resulted in a 60 to 80% loss of signal intensity, but were compensated for by using (233)U as an internal standard. Accurate results were obtained with LB-DIHEN-ICP-MS, allowing for the positive identification of depleted uranium based on the (235)U/(238)U ratio. Precision for the (235)U/(238)U ratio is typically better than 5% and 15% for ICP-MS and alpha-spectrometry, respectively, determined over the concentrations and ratios investigated in this study, with the LB-DIHEN-ICP-MS system providing the most accurate results. Short-term precision (6 min) for the individual (235)U and (238)U isotopes in synthetic urine is better than 2% (N = 7), compared to approximately 5% for conventional nebulizer-spray chamber arrangements and >10% for alpha-spectrometry. The significance of these measurements is discussed for uranium exposure assessment of Persian Gulf War veterans affected by depleted uranium ammunitions.     

Probabilistic characteristics of random damage events and their quantification in acrylic bone cement

The failure of brittle and quasi-brittle polymers can be attributed to a multitude of random microscopic damage modes, such as fibril breakage, crazing, and microfracture. As the load increases, new damage modes appear, and existing ones can transition into others. In the example polymer used in this study—a commercially available acrylic bone cement—these modes, as revealed by scanning electron microscopy of fracture surfaces, include nucleation of voids, cracking, and local detachment of the beads from the matrix. Here, we made acoustic measurements of the randomly generated microscopic events (RGME) that occurred in the material under pure tension and under three-point bending, and characterized the severity of the damage by the entropy (s) of the probability distribution of the observed acoustic signal amplitudes. We correlated s with the applied stress (σ) by establishing an empirical s–σ relationship, which quantifies the activities of RGME under Mode I stress. It reveals the state of random damage modes: when ds/dσ > 0, the number of damage modes present increases with increasing stress, whereas it decreases when ds/dσ < 0. When ds/dσ ≈ 0, no new random damage modes occur. In the s–σ curve, there exists a transition zone, with the stress at the “knee point” in this zone (center of the zone) corresponding to ~30 and ~35% of the cement’s tensile and bending strengths, respectively. This finding explains the effects of RGME on material fatigue performance and may be used to approximate fatigue limit.     

Tandem mass spectrometry of uranium and uranium oxides in airborne particulates

A method for detection of uranium in airborne microparticles in real time has been developed. Positive identification of uranium is achieved by isolating UO(2+) ions and following their reaction with residual oxygen molecules to yield UO(2)(+).     

Finite element simulation of anisotropic damage accumulation and creep in acrylic bone cement

Acrylic bone cement is used to fixate hip replacement implants into the bone. Creep and fatigue failure of the cement promote failure of the implant. For the purpose of implant testing, we derived a finite element algorithm that simulates creep and damage accumulation in acrylic bone cement. The simulation combines a Maxwell creep model, with a 3-D continuum damage mechanics approach modeling anisotropic damage accumulation. The technical details of the simulation are described. In a first application tensile fatigue tests on tubular cement specimens are simulated. The creep elongation and fatigue life of the specimens, as predicted by the simulations, are successfully correlated to the experimental results. In a second application, the simulation is used to predict creep and fatigue failure of the cement mantle around two hip implants with different clinical outcomes. It is shown how the simulation is able to predict the locations of cement damage around the implants, and the amounts of implant migration attributable to creep.