Measurements and Monte-Carlo simulations of the particle self-shielding effect of B4C grains in neutron shielding concrete

A combined measurement and Monte-Carlo simulation study was carried out in order to characterize the particle self-shielding effect of B4C grains in neutron shielding concrete. Several batches of a specialized neutron shielding concrete, with varying B4C grain sizes, were exposed to a 2 {\AA} neutron beam at the R2D2 test beamline at the Institute for Energy Technology located in Kjeller, Norway. The direct and scattered neutrons were detected with a neutron detector placed behind the concrete blocks and the results were compared to Geant4 simulations. The particle self-shielding effect was included in the Geant4 simulations by calculating effective neutron cross-sections during the Monte-Carlo simulation process. It is shown that this method well reproduces the measured results. Our results show that shielding calculations for low-energy neutrons using such materials would lead to an underestimate of the shielding required for a certain design scenario if the particle self-shielding effect is not included in the calculations.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0

Formation of PAHs and Carbonaceous Solids in Gas-Phase Condensation Experiments

Carbonaceous grains represent a major component of cosmic dust. In order to understand their formation pathways, they have been prepared in the laboratory by gas-phase condensation reactions such as laser pyrolysis and laser ablation. Our studies demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles. At temperatures lower than 1700 K, the condensation by-products are mainly polycyclic aromatic hydrocarbons (PAHs), that are also the precursors or building blocks for the condensing soot grains. The low-temperature condensates contain PAH mixtures that are mainly composed of volatile 3-5 ring systems. At condensation temperatures higher than 3500 K, fullerene-like carbon grains and fullerene compounds are formed. Fullerene fragments or complete fullerenes equip the nucleating particles. Fullerenes can be identified as soluble components. Consequently, condensation products in cool and hot astrophysical environments such as cool and hot AGB stars or Wolf Rayet stars should be different and should have distinct spectral properties.Comment: 7 pages, 5 figure

Response of a Li-glass/multi-anode photomultiplier detector to collimated thermal-neutron beams

The response of a position-sensitive Li-glass scintillator detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using collimated beams of thermal neutrons. The detector was moved perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and vertical steps. Scintillation was detected in an 8 X 8 pixel multi-anode photomultiplier tube on an event-by-event basis. In general, several pixels registered large signals at each neutron-beam location. The number of pixels registering signal above a set threshold was investigated, with the maximization of the single-hit efficiency over the largest possible area of the detector as the primary goal. At a threshold of ~50% of the mean of the full-deposition peak, ~80% of the events were registered in a single pixel, resulting in an effective position resolution of ~5 mm in X and Y. Lower thresholds generally resulted in events demonstrating higher pixel multiplicities, but these events could also be localized with ~5 mm position resolution.Comment: 23 pages, 8 figure

The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o

Chloride substitution induced by mechano-chemical reactions between NaBH 4 and transition metal chlorides

Cl - to BH4- ion substitution was induced in NaBH 4 through mechano-chemical reactions with all the first period transition metal chlorides and CdCl 2. The products were identified by Rietveld refinement of powder X-ray and neutron diffraction data to be mainly Na(BH 4) 1-xCl x. These possess cubic NaCl-type structures, with unit cell parameters between 5.7801(3) and 5.6576(2), and compositions ranging from x = 0.69 (with Cu) to 0.92 (with Zn). Infrared spectroscopy of selected samples confirms the substitution through a shift of the vibrational modes of the BH4- group towards higher wavenumbers. An observed shape change of the vibrational features from Lorentzian to Gaussian is related to the presence of the transition metal. There is no correlation between x and the thermal behavior of the samples. The lowest decomposition temperature is found for the Zn containing sample (103 °C), while Cd leads to the highest value (521 °C). Their behavior is related to the presence of NaZn(BH 4) 3 and metallic Cd in the samples, respectively. © 2011 Elsevier B.V. All rights reserved

First measurements with new high-resolution gadolinium-GEM neutron detectors

European Spallation Source instruments like the macromolecular diffractometer (NMX) require an excellent neutron detection efficiency, high-rate capabilities, time resolution, and an unprecedented spatial resolution in the order of a few hundred micrometers over a wide angular range of the incoming neutrons. For these instruments solid converters in combination with Micro Pattern Gaseous Detectors (MPGDs) are a promising option. A GEM detector with gadolinium converter was tested on a cold neutron beam at the IFE research reactor in Norway. The mu TPC analysis, proven to improve the spatial resolution in the case of B-10 converters, is extended to gadolinium based detectors. For the first time, a Gd-GEM was successfully operated to detect neutrons with a measured efficiency of 11.8% at a wavelength of 2 angstrom and a position resolution better than 250 mu m

A Round Robin Test exercise on hydrogen absorption/desorption properties of a magnesium hydride based material

A Round Robin Test exercise on magnesium hydride (MgH2) was performed by 14 laboratories with the aim to compare experimental isothermal data such PCI curves, kinetics curves and formation enthalpies together with a basic statistical evaluation of the results. The full hydrogen capacity was found to vary in the range 5.1-6.4 wt.% at 280 °C (553 K) and in the range 5.3-6.6 wt.% at 320 °C (593 K) (value for 1 MPa hydrogen pressure). The relative standard deviations of 6.9% and 7.2%, respectively, were measured for absorption. The absorption plateau pressure of magnesium hydride varies between 0.08 and 0.14 MPa with an average of 0.10 MPa and a relative standard deviation of 17.3% at 280 °C (553 K). At 320 °C (593 K) the absorption plateau pressure results fall in the range 0.26-0.45 MPa, with a relative standard deviation of 17.6%. Kinetics curves were affected by much higher data dispersion than the PCI data. The enthalpy of absorption was −75.7 KJ/moleH2, with a relative standard deviation of 4.4%. The results highlight the importance of well defined measuring and reporting protocols as a base for future standard procedures

A Round Robin Test exercise on hydrogen absorption/desorption properties of a magnesium hydride based material

A Round Robin Test exercise on magnesium hydride (MgH2) was performed by 14 laboratories with the aim to compare experimental isothermal data such PCI curves, kinetics curves and formation enthalpies together with a basic statistical evaluation of the results. The full hydrogen capacity was found to vary in the range 5.1-6.4 wt.% at 280 °C (553 K) and in the range 5.3-6.6 wt.% at 320 °C (593 K) (value for 1 MPa hydrogen pressure). The relative standard deviations of 6.9% and 7.2%, respectively, were measured for absorption. The absorption plateau pressure of magnesium hydride varies between 0.08 and 0.14 MPa with an average of 0.10 MPa and a relative standard deviation of 17.3% at 280 °C (553 K). At 320 °C (593 K) the absorption plateau pressure results fall in the range 0.26-0.45 MPa, with a relative standard deviation of 17.6%. Kinetics curves were affected by much higher data dispersion than the PCI data. The enthalpy of absorption was −75.7 KJ/moleH2, with a relative standard deviation of 4.4%. The results highlight the importance of well defined measuring and reporting protocols as a base for future standard procedures

Response of a Li-glass/multi-anode photomultiplier detector to collimated thermal-neutron beams

The response of a position-sensitive Li-glass scintillator detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using collimated beams of thermal neutrons. The detector was moved perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and vertical steps. Scintillation was detected in an 8 × 8 pixel multi-anode photomultiplier tube on an event-by-event basis. In general, several pixels registered large signals at each neutron-beam location. The number of pixels registering signal above a set threshold was investigated, with the maximization of the single-hit efficiency over the largest possible area of the detector as the primary goal. At a threshold of ∼50% of the mean of the full-deposition peak, ∼80% of the events were registered in a single pixel, resulting in an effective position resolution of ~5 mm in X and Y. Lower thresholds generally resulted in events demonstrating higher pixel multiplicities, but these events could also be localized with ∼5 mm position resolution