Within the EC-funded CHANCE project several non-destructive techniques are being considered for the assay of waste bearing drums. Such techniques include calorimetry, gamma-ray spectrometry and ...neutron coincidence counting. The aim is to quantify uncertainties on the inventory of radionuclides, and how these are potentially reduced by combining the signatures from different techniques in the data analysis.
In this framework, neutron coincidence measurements were carried out with two slab counters based on
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He detectors coupled to shift register electronics. Such a system consists of two identical slabs with 6 detectors each, and is transportable, rather compact and flexible in terms of sizes and geometries that can be measured. With this system three 200 L drums containing certified reference nuclear material and different filling materials were measured. The certified nuclear material was in the form of 21 pellets of mixed oxide of U and Pu with a total mass of about 10.5 g; in addition, a single pellet of about 10.05 g was also available. The pellets could be placed in predefined positions within the drum in a reproducible way. The geometry and composition of the three drums was well characterized and consisted of Ethafoam, a mixture of Ethafoam, stainless steel and PVC, and mortar with an inner core of extruded polystyrene. The measurement setup was arranged such that the drum was placed between the two slab counters. The positions of the slab counters relative to the drum were accurately measured before each measurement, and a dedicated system was used to minimize the uncertainty on the detector positioning.
The measurement data were first analysed by applying the point model of Hage and the mass of nuclear material in the drum was determined from the rate of totals and reals and the radionuclide composition. Due to the fact that not all the point model conditions were met, we found that the point model overestimates the mass up to about 50%. In addition, a Monte Carlo model of the measurement geometry was developed using the MCNP code. The model was used to determine a calibration factor between the reals rate and the mass of the sample. Measurements with a calibrated
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Cf source were used to verify the model. With a Monte Carlo based approach the mass of the mixed oxide pellets is within a few percent from the nominal values, except for strongly asymmetrical configurations where the deviation is up to about 20%. The results reveal the importance of an accurate background correction and of accounting for surrounding materials of the building such as walls, floor and ceiling in the Monte Carlo model.
Resonance parameters for neutron induced reactions in 106,108,110,111,112,113,114,116Cd have been evaluated. The parameters are the result of an analysis of experimental data available in the ...literature together with a parameter adjustment to transmission and capture data obtained at the time-of-flight facility GELINA. The parameters derived from the GELINA data are in reasonable agreement with those quoted in the literature. From the analysis of the GELINA transmission data a thermal neutron total cross section equal to 2450±40b has been deduced for natCd at 300K. This value is in agreement with results of previous measurements which have been performed at thermal reactor beams using different techniques. It differs by about 1.5% from the value 2413b which was recently deduced from an adjustment to results of an integral experiment. The GELINA transmission and capture data in the low energy region are not fully consistent with resonance parameters recommended in evaluated data files. The impact of the resonance parameters obtained in this work on cadmium transmission factors and on the interpretation of an integral experiment is discussed.
The resonance structure in neutron induced reaction cross sections can be used to determine the elemental compositions of materials or objects. The occurrence of resonances is the basis of neutron ...resonance capture analysis (NRCA) and neutron resonance transmission analysis (NRTA). NRCA and NRTA are fully non-destructive methods to determine the bulk elemental composition without the need of any sample preparation and resulting in a negligible residual activity. They have been applied to determine the elemental composition of archaeological objects and to characterize reference materials used for cross section measurements. For imaging applications a position sensitive neutron detector has been developed within the ANCIENT CHARM project. The detector is based on a 10 x 10 array of super(6)Li-glass scintillators mounted on a pitch of 2.5 mm, resulting in a 25 x 25 mm super(2) active area. The detector has been tested at the time-of-flight facility GELINA and used at the ISIS spallation source to study cultural heritage objects.
Nowadays, there is interest in developing gamma-ray measuring devices based on the room temperature operated medium resolution detectors such as semiconductor detectors of the CdZnTe type and ...scintillators of the LaBr3 type. This is true also for safeguards applications and the International Atomic Energy Agency (IAEA) has launched a project devoted to the assessment of medium resolution gamma-ray spectroscopy for the verification of the isotopic composition of U and Pu bearing samples. This project is carried out within the Non-Destructive Assay Working Group of the European Safeguards Research and Development Association (ESARDA). In this study we analyze medium resolution spectra of U and Pu standards with the aim to develop an isotopic composition determination algorithm, particularly suited for these types of detectors. We show how the peak shape of a CdZnTe detector is influenced by the instrumentation parameters. The experimental setup consisted of a 500 mm3 CdZnTe detector, a 2×2 inch LaBr3 detector, two types of measurement instrumentation – an analogue one and a digital one, and a set of certified samples – a 207Bi point source and U and Pu CBNM standards. The results of our measurements indicate that the lowest contribution to the peak asymmetry and thus the smallest impact on the resolution of the 500 mm3 CdZnTe detector was achieved with the digital MCA. Analysis of acquired spectra allowed to reject poor quality measurement runs and produce summed spectra files with the least impact of instrumentation instabilities. This work is preliminary to further studies concerning the development of an isotopic composition determination algorithm particularly suited for CZT and LaBr3 detectors for safeguards applications.
A data format for time-of-flight spectra (transmission, reaction andself-indication yields) and their covariance matrices based on the AGS(Analysis of Geel Spectra) format is discussed in ...collaboration betweenEC-JRC IRMM and IAEA-NDS for the EXFOR library. Experimentalists areencouraged to consider the uncertainty propagation following the AGSprinciple and submission of their data to the International Networks NuclearReaction Data Centres (NRDC) for EXFOR compilation using a proposedtemplate. KCI Citation Count: 10
Relative humidity with respect to ice (RHi) is a key variable in the formation of cirrus clouds and contrails. We document its probability density function (PDF) using long-term Measurements of ...Ozone, Water Vapour, Carbon Monoxide and Nitrogen Oxides by In-Service Airbus Aircraft (MOZAIC) and the In-service Aircraft for a Global Observing System (IAGOS) observations over the period 1995–2022 in the upper troposphere (UT) and the lower stratosphere (LS) between 325 and 175 hPa. The characteristics of the RHi PDF differ in the UT and in the LS of the high-latitude regions (HLs) and mid-latitude regions (MLs) of the Northern Hemisphere. In the LS, this PDF decreases exponentially with increasing RHi. In the UT, it first increases exponentially in subsaturated conditions and then decreases exponentially in supersaturated conditions. Because of these different behaviors, the PDF for the combined UT and LS is bimodal. In contrast to the HLs and the MLs, the RHi PDF in the tropical troposphere decreases exponentially with increasing RHi. The different forms of PDF, in the tropics and in the higher-latitude regions, lead to a global PDF of RHi in subsaturated tropospheric conditions that is almost uniform. These findings invite caution when using MOZAIC and IAGOS measurements to calibrate large-scale simulations of RHi. The variability in RHi properties associated with that of temperature also has implications for the formation of contrails. We examined the impact of switching fuel (from kerosene to bioethanol or liquid hydrogen) on the frequency of contrail formation using the Schmidt–Appleman criterion. We show that bioethanol and, to a larger extent, liquid hydrogen would produce more contrails. The impact of a potential change from kerosene to these alternative fuels decreases with decreasing pressure but increases when moving from the higher latitudes of the Northern Hemisphere to the tropics. Finally, we emphasize that investigations of the impact on contrail occurrence frequency as a result of switching from fossil kerosene to more sustainable fuels must be carried out in various meteorological conditions.
•Systematic overestimation discovered in previously reported fission chamber neutron sensitivity data.•Tallying neutron flux from Maxwellian distribution source in MCNP was identified as the source ...of error.•New procedure to properly simulate neutron moderation was implemented.•Corrected results are reported.
During the course of the work carried out for the estimation of the sensitivity of 6Li loaded fiber detectors (Borella, 2022), it was realized that the MCNP simulations carried out with the approach described in (Borella et al., 2013) were affected by a systematic bias. In this paper, we explain the source of the systematic bias and report the new results for (Borella et al., 2013).
Isolation-rearing of rats causes a variety of behavioral changes, including anxiety, learning deficits and sensory changes related to schizophrenia. Similar changes are seen following loss of ...serotonin during development. Thus, the effects of isolation-rearing on behavior may be due to changes in serotonin.
Sprague-Dawley rats were raised in groups of four (social animals) or in isolation, from postnatal day 22 until postnatal day 64. The hippocampi were examined immunochemically for changes in serotonin. Our findings show that serotonin terminals are lost throughout the CA regions of hippocampus, where there is also an associated loss of dendrites, but not in the molecular layer of the dentate gyrus. Thus, some of the brain and behavioral changes seen in isolation-reared animals could be due to loss of serotonin.
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