Heavy Ion Induced Intermixing at Ta/Si and Ta/SiO 2 Interfaces

Systematic ion beam mixing experiments have been performed on Ta/SiO 2 and Ta/Si interfaces. Tantalum was evaporated on silicon and SiO2/silicon substrates by means of molecular beam epithaxy. Samples were subsequently irradiated with 500 keV Si, 100 ke

Orientation Dependent Ion Beam Mixing of Ta/Si Interfaces

Ta/Si interfaces were systematically studied concerning ion beam mixing effects. Tantalum was evaporated on silicon of (1 0 0) and (1 1 1) orientation using the molecular beam epitaxy (MBE) method. The samples were then irradiated with 1.85 MeV and 6 Me

Detection and identification of radioactive sources covert under water

Conventional measuring equipment for radioactive material is predominantly constructed for stationary application in a laboratory. There are only a few systems for use in the field. In the context of a terrorist threat it might be of great importance to localize and identify radioactive or nuclear material underwater. Up to now only very few measurement systems are available which can be used in such environments. The complexity of the situation follows from the shielding effect of the water. Depending on the source strength a depth of the water of few meters is sufficient to make the detection of the radioactive material above the water surface impossible. Another consequence of the underwater situation is a change in the shape of the measured gamma spectra. Possibilities for measurements with radioactive sources placed in a pond or lake are limited. Therefore only a few experiments in real water environment have been carried out. A 60Co source with an activity of 50 MBq was placed in a pond. From a bridge above that pond the detector was lowered in the water and placed at different positions relative to the source. For this investigation we used a detector system based on a Sodium-Iodide (NaI) scintillator. Both operating modes PHA (Pulse Height Analysis) and MCS (Multi Channel Scaling) were used for obtaining gamma spectra or measuring the total count rate in search mode, respectively. The aim was a feasibility test for locating and identifying radioactive material hidden in the pond. It was shown that localization as well as identification was basically successful. Several improvements are planned because of this exceptional environment. This includes an appliance for pulling the detector fast and safe through the water, for example while crossing a lake with a boat. The paper presents first experiences with measurements carried out under water. This technical improvement may ease the task of inspecting special environments where objects containing radioactive or nuclear material are presumed and thus may help to combat nuclear terrorism

Tracking of fissile material by means of coincident neutron detection - Fission Meter vs. Slab Counter

In the context of fissile material detection, discrimination between changes of the natural neutron background, industrial material, and a real neutron source, indicating the presence of nuclear material, is tremendously important. The negligence of such material may lead to drastic if not fatal consequences to the general public in case the material in question is used in explosive devices such as Improvised Nuclear Devices (IND). To achieve the discrimination required, measurements of coincident neutrons are feasible because only fissile material emits coincident neutrons. Two neutron detection systems, the Fission Meter by Ametek/Ortec and the Slab Counter by Canberra, were tested concerning their quality of detecting nuclear material as mentioned above, using primarily a variety of Plutonium sources with different isotopic compositions provided by the Institute of Transuranium Elements (ITU) of the Joint Research Centre at Ispra, Italy, where the measurements were performed. We also examined the influence of shielding effects of the materials which would possibly be part of an IND. The results of these measurements and an assessment of the reliability of the two detecting systems concerning fissile material verification will be presented.JRC.E.8-Nuclear securit

Identification of nuclear material with hand-held and portable gamma and neutron measuring devices

Performing fast measurements in the field at places where suspicious objects were found is essential in the context of nuclear terrorism. Especially if nuclear material is involved, it is necessary to identify small amounts of plutonium or uranium and to gain information concerning isotopic composition. Therefore, measurements at different uranium and plutonium samples were carried out. Samples with different isotopic compositions have been used for the present work. For gamma measurements hand-held and portable devices using different detector materials were investigated. The nuclide identification results of implemented automatic identification routines were compared for the different devices and to the given source information. As hand-held device with germanium detector (Ge) the ORTEC Micro Detective with electrical cooling was used. The identiFINDER from ICx was used as an example for an hand-held device and gamma-ray spectrometer with the most common detector material sodium iodide (NaI). Another investigated detection system was the InSpector 1000 from Canberra which contains a lanthanum bromide (LaBr3) crystal. A fourth type of detector material is used by the INTERCEPTOR from Thermo which is equipped with two cadmium-zinc-telluride (CZT) crystals. Some of the measurement devices also have neutron detectors but with very small volume and therefore low efficiency. A portable neutron detector with an implemented analysis routine for the discrimination between industrial and nuclear neutron sources is the Fission Meter from ORTEC. The paper presents results obtained with the different measurement systems. The quality of the outcome of the automatic identification routines of the different detection systems varied significantly. These results depended not only on the different detector materials but also on the type of nuclear material. In general identification of uranium was considerably better than the identification of plutonium

Mercury Exposure and Poor Nutritional Status Reduce Response to Six Expanded Program on Immunization Vaccines in Children: An Observational Cohort Study of Communities Affected by Gold Mining in the Peruvian Amazon

Background: Poor nutritional status combined with mercury exposure can generate adverse child health outcomes. Diet is a mediator of mercury exposure and evidence suggests that nutritional status modifies aspects of mercury toxicity. However, health impacts beyond the nervous system are poorly understood. This study evaluates antibody responses to six vaccines from the expanded program on immunization (EPI), including hepatitis B, Haemophilus influenzae type B, measles, pertussis, tetanus, and diphtheria in children with variable hair mercury and malnutrition indicators. Methods: An observational cohort study (n = 98) was conducted in native and non-native communities in Madre de Dios, Peru, a region with elevated mercury exposure from artisanal and small-scale gold mining. Adaptive immune responses in young (3–48 months) and older children (4–8 year olds) were evaluated by vaccine type (live attenuated, protein subunits, toxoids) to account for differences in response by antigen, and measured by total IgG concentration and antibody (IgG) concentrations of each EPI vaccine. Mercury was measured from hair samples and malnutrition determined using anthropometry and hemoglobin levels in blood. Generalized linear mixed models were used to evaluate associations with each antibody type. Results: Changes in child antibodies and protection levels were associated with malnutrition indicators, mercury exposure, and their interaction. Malnutrition was associated with decreased measles and diphtheria-specific IgG. A one-unit decrease in hemoglobin was associated with a 0.17 IU/mL (95% CI: 0.04–0.30) decline in measles-specific IgG in younger children and 2.56 (95% CI: 1.01–6.25) higher odds of being unprotected against diphtheria in older children. Associations between mercury exposure and immune responses were also dependent on child age. In younger children, one-unit increase in log10 child hair mercury content was associated with 0.68 IU/mL (95% CI: 0.18–1.17) higher pertussis and 0.79 IU/mL (95% CI: 0.18–1.70) higher diphtheria-specific IgG levels. In older children, child hair mercury content exceeding 1.2 µg/g was associated with 73.7 higher odds (95% CI: 2.7–1984.3) of being a non-responder against measles and hair mercury content exceeding 2.0 µg/g with 0.32 IU/mL (95% CI: 0.10–0.69) lower measles-specific antibodies. Log10 hair mercury significantly interacted with weight-for-height z-score, indicating a multiplicative effect of higher mercury and lower nutrition on measles response. Specifically, among older children with poor nutrition (WHZ = −1), log10 measles antibody is reduced from 1.40 to 0.43 for low (<1.2 µg/g) vs. high mercury exposure, whereas for children with good nutritional status (WHZ = 1), log10 measles antibody is minimally changed for low vs. high mercury exposure (0.72 vs. 0.81, respectively). Conclusions: Child immune response to EPI vaccines may be attenuated in regions with elevated mercury exposure risk and exacerbated by concurrent malnutrition