Development of an instrument for non-destructive identification of Unexploded Ordnance using tagged neutrons - a proof of concept study

Range clearance operations at munitions testing grounds must discriminate Unexploded Ordnance (UXO) from clutter items and distinguish UXO filled with High Explosives (HE) from those with inert fillers. Non-destructive technologies are thus necessary for the cost-effective disposal of UXO during remediation of such sites. The only technique showing promise so far for the non-destructive elemental characterization of UXO fillers utilizes neutron interactions with the material to detect carbon (C), nitrogen (N) and oxygen (O) which have unique ratios in HE. However, several unresolved issues hinder the wide application of this potentially very suitable technique. The most important one is that neutrons interact with all surrounding matter in addition to the interrogated material, leading to a very high gamma-ray background in the detector. Systems requiring bulky shielding and having poor signal-to-noise ratios (SNRs) for measuring elements are unsuitable for field deployment. The inadequacies of conventional neutron interrogation methods are overcome by using the tagged-neutron approach, and the availability of compact sealed neutron generators exploiting this technique offers field deployment of non-intrusive measurement systems for detecting threat materials, like explosives and drugs. By accelerating deuterium ions into a tritium target, the subsequent fusion reaction generates nearly back-to-back emissions of neutrons and alpha particles of energy 14.1 and 3.5 MeV respectively. A position-sensitive detector recognizes the associated alpha particle, thus furnishing the direction of the neutron. The tagged neutrons interact with the nuclei of the interrogated object, producing element-specific prompt gamma-rays that the gamma detectors recognize. Measuring the delay between the detections of the alpha particle and the gamma-ray determines where the reaction occurred along the axis of the neutron beam (14.1 MeV neutrons travel at 5 cm/nanosecond, while gamma rays cover 30 cm/nanosecond). The main advantage of the technique is its ability to simultaneously provide 2D and 3D imaging of objects and their elemental composition. This work reports on the efficacy of using 14 MeV neutrons tagged by the associated particle neutron time-of-flight technique (APnTOF) to extract neutron induced characteristic gamma-rays from an object-of-interest with high SNR and without interference from nearby clutter

Effects of Pairing in the Pseudo-SU(3) Model

An extended version of the pseudo-SU(3) model which includes both spin and proton-neutron degrees of freedom is used to study the influence of the pairing interaction on K-band mixing, B(E2) values and quadrupole moments. Using the asymmetric rotor model as a backdrop, specific consequences of a many-particle shell-model based description of these collective properties are demonstrated and fundamental limits of the collective model's approach are investigated. Finally, the pseudo-SU(3) model, including representation mixing induced by pairing, is used to calculate the energies of 140Ce and the results are compared to experimental data and other theories.Comment: 21 pages, Latex, 11 figures available on request via mail or fax, accepted by Nucl. Phys.

Neutron Spectroscopy by Double Scatter and Associated Particle Techniques.

Multiple detectors can provide [1,2] both directional and spectroscopic information. Neutron spectra may be obtained by neutron double scatter (DSNS), or the spontaneous fission associated particle (AP) technique. Spontaneous fission results in the creation of fission fragments and the release of gamma rays and neutrons. As these occur at the same instant, they are correlated in time. Thus gamma ray detection can start a timing sequence relative to a neutron detector where the time difference is dominated by neutron time-of-flight. In this paper we describe these techniques and compare experimental results with Monte Carlo calculations

14-MeV Neutron Generator Used as a Thermal Neutron Source

One of the most important applications of the general purpose Monte Carlo N-Particle (MCNPS and MCNPX) codes is neutron shielding design. We employed this method to simulate the shield of a 14-MeV neutron generator used as a thermal neutron source providing an external thermal neutron beam for testing large area neutron detectors developed for diffraction studies in biology and also useful for national security applications. Nuclear reactors have been the main sources of neutrons used for scientific applications. In the past decade, however, a large number of reactors have been shut down, and the importance of other, smaller devices capable of providing neutrons for research has increased. At Brookhaven National Laboratory a moderated Am-Be neutron source with shielding is used for neutron detector testing. This source is relatively weak, but provides a constant flux of neutrons, even when not in use. The use of a 14 MeV energized neutron generator, with an order of magnitude higher neutron flux has been considered to replace the Am-Be source, but the higher fast neutron yield requires a more careful design of moderator and shielding. In the present paper we describe a proposed shielding configuration based on Monte Carlo calculations, and provide calculated neutron flux and dose distributions. We simulated the neutron flux distribution of our existing Am-Be source surrounded by a paraffin thermalizer cylinder (radius of 17.8 cm), 0.8 mm cadmium, and borated polyethylene as biological shield. The thermal neutrons are available through a large opening through the polyethylene and cadmium. The geometrical model for the MCNPS and MCNPX2 simulations is shown in Fig. 1. We simulated the Am-Be source neutron energy distribution as a point source having an energy distribution of four discrete lines at 3.0 (37%), 5.0 (35%), 8.0 (20%) and 11.0 (8%) MeV energies. The estimated source strength based on the original specifications is 6.6 {center_dot} 10{sup 6} neutrons/sec. The simulation accurately predicts the measured thermal neutron flux at the collimator (Figure 2), thus providing validation for this method. Using MCNPX we simulated the neutron and photon dose distribution and also obtained a good agreement with the measured values. Having established a validated framework for the shield calculation we then scaled up the Am-Be arrangement to simulate the shielding required for the higher neutron energy and flux of the neutron generator (-10{sup 8} neutrodsec at 14 MeV). Given the physical dimensions of the generator we have chosen a cylindrical geometry, where the generator tube is placed vertically into a cylindrical thermalizer (25 cm paraffin) from above. The thermalizer is surrounded by 0.8 mm cadmium, and a cylindrical borated polyethylene shield. A cylindrical opening (radius of 7.6 cm) serves to direct the neutrons out towards the experimental area (on the right side). The initial model is shown in figure 3. The first goal of the calculations was to establish the minimal required radius of the biological shield. For this purpose we performed MCNPX neutron and photon dose distribution calculations by tallying the absorbed dose on a 200 x 200 cm mesh in the vertical center plane superimposed over the geometry. Figure 4. displays the neutron dose distribution along the central horizontal (X) axis. As observed from the figure, a shielding radius of -80 cm is sufficient to obtain a dose level of < -4 mrem/hour outside the shield (except from the open neutron channel on the right). In the next step we studied the optimization of the thickness of the paraffin thermalizer by increasing the depth of the neutron exit channel into the paraffin cylinder. It was found, that the thermal flux greatly increases if we have thinner paraffin layer, an optimal value being about 5 cm thickness. But as a drawback the flux of fast neutrons also increased. A thicker thermalizer layer, in fact, acts as shielding. A slightly off centered, tangential placement of the neutron channel provides a solution which maximizes the thermal flux to fast neutron yield. Figure 5. and 6. display the final results, where we included an outside biological shield (20 cm thickness) providing a shielded experimental area. There is a 10-100 n/cm{sup 2}sec flux near the neutron beam exit, and outside the shield the neutron dose is below the radiation area limit (-5 mrem/hour)

Implementácia moderných prístupov v elektronickom zdravotnom zázname

V predloženej práci sa študujú možnosti implementácie elektronického zdravotného záznamu pomocou moderných technológií. Hlavným cieľom je väčšia dekompozícia serverovej časti implementácie EHR v porovnaní s minulými verziami. Je použitá myšlienka webových služieb, pri ktorej každá časť aplikácie poskytuje ostatným vzdialené služby. Jednotlivé komponenty medzi sebou komunikujú pomocou protokolu SOAP. Takisto sa študuje možnosť separovať administratívne údaje o pacientoch do samostatného skladišťa, ktoré sa na tento účel hodí viac ako dátové stromy, ktoré sú použité na uloženie klinických údajov. Toto oddelenie údajov je vhodné aj z pohľadu anonymizácie dát pri štatistickom spracovaní. V práci ostáva zachovaný spôsob uloženia pacientových klinických dát v dátových stromoch a možnosť flexibilného modelovania dátovej vrstvy pomocou znalostných stromov združených v znalostnej báze.In the present work we study the possible implementations of electronic health record using modern technologies. The main goal is decomposition of server functionality among multiple parts. We use the idea of web-services, which means that each part of the system offers services available for remote hosts. The components communicate with each other using the SOAP protocol. We also study the possibility of storing patient's administrative information into separate storage, which suits the purpose better than original data trees, which are used to store clicnical information. Besides, this separation is suitable for anonymization of data used by statistical computing. In my work the manner of storing patient's clinical data in data trees and possibility of flexible modeling of data layer using knowledge trees, which together create a knowledge base, is preserved.Katedra softwarového inženýrstvíDepartment of Software EngineeringFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Directional stand-off detection of fast neutrons and gammas using angular scattering distributions

We have investigated the response of a DoubleScatter Neutron Spectrometer (DSNS) for sources at long distances (gr than 200 meters). We find that an alternative method for analyzing double scatter data avoids some uncertainties introduced by amplitude measurements in plastic scintillators.Time of flight is used to discriminate between gamma and neutron events, and the kinematic distributions of scattering angles are assumed to apply. Non-relativistic neutrons are most likely to scatter at 45°, while gammas with energies greater than 2 MeV are most likely to be forward scattered. The distribution of scattering angles of fission neutrons arriving from a distant point source generates a 45° cone, which can be back-projected to give the source direction. At the same time, the distribution of Compton-scattered gammas has a maximum in the forward direction, and can be made narrower by selecting events that deposit minimal energy in the first scattering event. We have further determined that the shape of spontaneous fission neutron spectra at ranges gr than 110 m is still significantly different from thecosmic ray background

The recency effect in cognitive network activation

The recency effect has been documented extensively in cognitive psychology yet has mostly been overlooked in the field of social networks. We use an online sample (n=214) to test how the recency effect manifests in cognitive network activation. Based on a social recall task in which participants are asked to list specific acquaintances, we find that people they had seen or thought about more recently came to mind earlier and more quickly, whilst dormant ties were rarely recalled. We discuss implications of our findings for future research, calling for greater incorporation of the recency effect in network scholarship

Bridging the gap: boundary spanners’ selective network mobilization across the industry-academia divide

Network boundary spanners have been shown to be in a privileged position to generate innovation outcomes, yet it is unclear how they decide which contacts to rely on when. This paper posits that many boundary spanners will forgo the opportunities their structural position affords, as stronger identification with one of the two domains they span may lead them to predominantly mobilize network contacts in that domain, irrespective of the type of input specific situations may require. We argue that those with a high self-monitoring orientation, however, will overcome tendencies to have identity inform network choices, and will thus selectively mobilize contacts from both sides of the boundary. We test these predictions in the context of scientists with dedicated boundary-spanning roles between industry and academia who are expected to routinely draw on network resources on both sides of the “divide” to perform their jobs. Using a multi-study setup which includes two framed field experiments, we find support for our predictions. Our findings imply that it may not be sufficient for organizations seeking to promote the cross-fertilization of ideas to allocate individuals to boundary-spanning roles; they need to train and encourage their staff to identify with the domains at both sides of the boundary to enable selective network mobilization to help them leverage the potential from boundary spanning

Influence of Additives on Thermal Expansion of Silica in Sand Casting Applications

Silica sand is extensively used as a moulding sand for both mould and core making in the cast iron and steel casting industries. The pouring temperatures of cast iron and steel create a nonlinear distribution of temperatures across mould/core. The temperature fluctuations in mould/core establish different heat transport zones and result in a temperature-dependent undesirable expansion of silica. The expansion of silica is one of the primary sources for the formation of surface defects on castings. Additives are incorporated to mitigate the volumetric expansion of mould/core resulting from the granular expansion of silica sand. The paper aims to investigate the thermal dilation of unbonded silica sand integrated with different amounts of additive in the sand (0.8%, 1.0%, and 1.3%) using a horizontal dilatometer. The dilatometric investigations identified a decreasing trend in the thermal expansion behaviour of silica mixture with increasing content of additive inclusions in the mixtures. In theory, the additives in the sand mixtures decompose prior to the α↔β endothermic phase transition of quartz and provide intergranular spacing for the free expansion of silica. DSC and TGA were conducted to identify the phase change in silica and the degradation temperature of the additives, respectively

Understanding expertise search strategies at networking events: an exploratory study using sociometric badges

In this study we ask how individuals search for experts at networking events. Building on the intuition that individuals’ propensities to engage in certain search actions, as well as their effectiveness in locating experts, will depend on the quality and salience of the metaknowledge they have about others, we conducted an expert search game as a field experiment in which we randomly assigned participants – researchers in a multinational corporation – to one of three treatment conditions, reflecting varying degrees of search planning. Based on data from sociometric badges, we derive a taxonomy of the micro-decisions individuals make at events. We find that letting others approach yields more referrals than taking the initiative in starting conversations, and that planning increases the tendency to maintain such initiative even when doing so is ineffective – a possible manifestation of the Einstellung effect