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• Modified B and B/Ti austenitic stainless steels were fabricated and tested to be used as control rods of nuclear reactors. • Structural, mechanical, and slow neutrons attenuation properties of the analyzed stainless steels were studied. • The developed B/Ti austenitic stainless steel was nominated as control rods for nuclear reactors. Modified austenitic stainless steel alloys reinforced with B and B/Ti were fabricated and their suitability as nuclear reactor control rods was tested. A standard stainless steel AISI 316L was used as a base alloy and inlaid by 0.58 wt% of B (SSB). The structural examination of the modified SSB stainless steel, which was conducted through the Schaeffler diagram, optical micrographs (OM), and X-ray diffraction (XRD) patterns had referred to the domination of the austenite phase with the appearance of boride (M 2 B) and carboborides (M 23 X 6) phases along the grain boundaries. Mechanically, an augmentation in the hardness, yield strength (YS), and ultimate tensile strength (UTS) values was observed with the incorporation of B into the AISI 316L stainless steel. However, the addition of B led to a reduction in the values of elongation (El), reduction area (RD), and impact energy. Then, the SSB stainless steel was reinforced by 0.33 wt% of Ti (SSTiB1). The structural examination showed the formation of M 2 B, M 23 X 6 , TiC, TiN, and TiB 2 phases along the grain boundaries of the austenite matrix as well as little ferrite phases. Ti led to a significant increase in hardness, YS, UTS, El, RD, and impact energy of the SSB steel. Finally, a further addition of B and Ti (1.13 & 1.77 wt% of B & Ti, SSTiB2) was tested, as this increase led to the more enhancement of hardness, YS, UTS, and impact energy but reduced the El slightly. Due to the high slow neutrons absorption cross-section of B, the slow neutrons attenuation ability of the modified stainless steel increased effectively with increasing boron concentrations. The obtained distinctive mechanical properties and high attenuation efficiency of slow neutrons of the produced SSBTi2 stainless steel, make it a suitable choice for use as control rods in nuclear reactors. [ABSTRACT FROM AUTHOR]

A novel approach for efficiently imaging objects with slow neutrons in two dimensions is realized. Neutron sensitivity is achieved by use of a boron doped microchannel plate (MCP). The resulting electron avalanche is further amplified with a Z-stack MCP before being sensed by two orthogonally oriented wire planes. Coupling of the wire planes to delay lines efficiently encodes the position information as a time difference. To determine the position resolution, slow neutrons were used to illuminate a Cd-mask placed directly in front of the detector. Peaks in the resulting spectrum exhibited an average peak width of 329 μ m FWHM, corresponding to an average intrinsic resolution of 216 μ m. The center region of the detector exhibits a significantly better spatial resolution with an intrinsic resolution of < 100 μ m observed. [ABSTRACT FROM AUTHOR]

A neutron bandpass limiting chopper consisting of up to four discs and a slow neutrons wiper is described. It produces pulses rid of contamination by unwanted slow neutrons. The basic disc works as a single disc chopper and largely defines the TOF resolution. The widths and positions of the slots in an additional disc define the neutron bandpass. The wiper eliminates slow neutrons with wavelengths beyond the working range and can be designed not only as plates connecting the discs, but also as ribs attached to the basic disc, or else as a rotor with blades on one shaft with the basic disc. The TOF resolution can be varied by using constant width slots in the basic disc and moving the chopper as a whole to change the effective disc radius. Two supplementary discs can also be used, one phased with the additional disc to optimize TOF measurements with the detector at different positions and the other phased with the basic disc to vary the TOF resolution. Application of the bandpass limiting choppers in neutron reflectometers at steady flux reactors is considered. [ABSTRACT FROM AUTHOR]

The cold polycrystalline beryllium reflector-filter concept has been used to enhance the cold neutron emission of cryogenic hydrogen moderators, while suppressing the intermediate wavelength and fast neutron emission at the same time. While suppressing the fast neutron emission is often desired, the suppression of intermediate wavelength neutrons is often unwelcome. It has been hypothesized that replacing the polycrystalline reflector-filter concept with a single-crystal reflector-filter concept would overcome the suppression of intermediate wavelength neutrons and thereby extend the usability of the reflector-filter concept to shorter but still important wavelengths. In this paper we present the first experimental data on a single-crystal reflector-filter at a reflected neutron source and compare experimental results with hypothesized performance. We find that a single-crystal reflector-filter retains the long-wavelength benefit of the polycrystalline reflector-filter, without suffering the same loss of important intermediate wavelength neutrons. This finding extends the applicability of the reflector-filter concept to intermediate wavelengths, and furthermore indicates that the reflector-filter benefits arise from its interaction with fast (background) neutrons, not with intermediate wavelength neutrons of potential interest in many types of neutron scattering. [ABSTRACT FROM AUTHOR]

We have combined the low-energy neutron detector WINDS (Wide-angle Inverse-kinematics Neutron Detectors for SHARAQ) and the SAMURAI spectrometer at RIKEN Nishina Center RI Beam Factory (RIBF) in order to perform ( p , n ) reactions in inverse kinematics for unstable nuclei in the mass region around A ∼ 100 . In this setup, WINDS is used for detecting recoil neutrons and the SAMURAI spectrometer is used for tagging decay channel of heavy residue. The first experiment by using the setup was performed to study Gamow–Teller transitions from 132 Sn in April 2014. The atomic number Z and mass-to-charge ratio A / Q of the beam residues were determined from the measurements of time of flight, magnetic rigidity and energy loss. The obtained A / Q and Z resolutions were σ A / Q = 0.14 % and σ Z = 0.22 , respectively. Furthermore, owing to the large momentum acceptance ( 50 % ) of SAMURAI, the beam residues associated with the γ , 1 n and 2 n decay channel were measured in the same magnetic field setting. The kinematic loci of the measured recoil neutron energy and laboratory angle are clearly seen. It shows that the excitation energy up to about 20 MeV can be reconstructed. [ABSTRACT FROM AUTHOR]

The results of an experiment on transmitting UCN through a rotating disc made of silicon single crystal are reported. They demonstrate that the transmission of the sample remains constant if it moves parallel to its surface. The range of neutron velocities in the system of reference associated with the sample is 6-38 m/s. It is found that the real and imaginary parts of the effective potential are constant to within 3x10-3. [ABSTRACT FROM AUTHOR]

Abstract: In the next years the slow neutron scattering community is waiting for a continuous improvement of the neutron detectors because of the development of the new and more intense neutron sources and to obtain a better performance of the neutron instrumentation to face the higher demands and new capabilities necessary for the novel experiments. In particular detectors having a faster response and a better shape of the time response must be produced, while new and more flexible acquisition systems must be introduced in order to collect in the proper way the information carried by the scattered neutrons. At present inside the neutron detector community the lack for detectors having a spatial resolution below 1mm is evident. In the past it has been already demonstrated that a silicon microstrip detector coupled to a Gadolinium foil, used as neutron converter, provides a good performance neutron detector. In the present paper we present a 128 channel detector which has been designed for operation in the thermal neutron region with 0.55mm spatial resolution, 100ns time resolution and 25ns time stamp accuracy. We present a new approach for the acquisition of the neutron arrival time, based on a single event storage by manipulating the detector digital output using a programmable acquisition system which takes advantage from high performance industrial standard hardware employing a FPGA and a real-time on board processor. We suggest the use of the single neutron event storing to make the time to energy transformation more efficient in the case of time of flight inelastic scattering, where the conversion from angle and time to momentum and energy is necessary. [Copyright &y& Elsevier]

Abstract: I show the earliest neutron sources, exhibit the historical development of slow neutron sources, trace the early echnical and community developments and the origins of ICANS and of UCANS, and find parallels between them. [Copyright &y& Elsevier]

Abstract: We report Os isotope compositions of acid residues separated from six carbonaceous chondrites that were subjected to varying degrees of aqueous alteration on their parent bodies. The residues from three enstatite chondrites were also investigated in order to evaluate the effects of nebular and parent body processing on the survival of presolar grains in meteorites formed under redox conditions that were markedly reduced, compared to those under which carbonaceous and ordinary chondrites formed. All acid residues from CM and CR chondrites show enrichments in s-process Os isotopes relative to the Solar System average recorded in bulk chondrites. The extent of the anomaly present positively correlates with the degree of aqueous alteration of the host chondrites. This correlation was probably caused by selective destruction/modification of presolar grains carrying r-process-enriched Os during progressive aqueous alteration on the parent bodies. The r-process-enriched component was likely either presolar silicates formed in Type II supernova ejecta, or other unidentified reduced presolar phases such as metal alloys, carbides and silicides. Acid residues from enstatite chondrites have Os isotope anomalies that are much more enriched in the s-process components, relative to the residues from carbonaceous and ordinary chondrites that experienced the same grade of thermal metamorphism. This most likely reflects the selective destruction of s-process-enriched presolar phases that occurred under the more oxidized conditions experienced by carbonaceous and ordinary chondrites, either while components formed in the nebula, or on their parent bodies. To account for the uniform, terrestrial Os isotopic composition in all types of bulk chondrites, it is required that r-process or s-process-enriched Os, released from presolar phases during nebular or parent body processing, was re-incorporated into a new phase(s) which was not lost from the location where the bulk meteorites were derived. However, because parent body processing might have acted differently on other elements (e.g., open system behavior of fluid mobile elements during aqueous alteration), recent findings of isotopic heterogeneities in bulk meteorites should be evaluated not just by invoking nebular heterogeneities, but by also considering the effects of parent body processing. [Copyright &y& Elsevier]

Abstract: Fast neutron and gamma-ray flux spectra and time-of-arrival spectra of slow neutrons have been measured in a neutronics mock-up of the European Helium-Cooled Lithium–Lead Test Blanket Module with the aim to validate nuclear cross-section data. The mock-up was irradiated with fusion peak neutrons from the DT neutron generator of the Technical University of Dresden. A well characterized cylindrical NE-213 scintillator was inserted into two positions in the LiPb/EUROFER assembly. Pulse height spectra from neutrons and gamma-rays were recorded from the NE-213 output. The spectra were then unfolded with experimentally obtained response matrices of the NE-213 detector. Time-of-arrival spectra of slow neutrons were measured with a 3He counter placed in the mock-up, and the neutron generator was operated in pulsed mode. Monte Carlo calculations using the MCNP code and nuclear cross-section data from the JEFF-3.1.1 and FENDL-2.1 libraries were performed and the results are compared with the experimental results. A good agreement of measurement and calculation was found with some deviations in certain energy intervals. [ABSTRACT FROM AUTHOR]

Abstract: We have predicted and observed for the first time a new phenomenon of quasi-specular reflection of cold neutrons at small incidence angles from nano-dispersed media. this is due to multiple small-angle scattering of neutrons from nano-sized inhomogeneities in the scattering potential. The reflection angle as well as the half-width of angular distribution of diffusively reflected neutrons is approximately equal to the incidence angle. For the powder of diamond nanoparticles used, the reflection probability was equal to ∼30% within the detector angular size, which corresponds to 40–50% of total probability (albedo) of quasi-specular reflection. The tangential velocity component of incident neutrons was up to an order of magnitude larger than the critical velocity for pure diamond. We provide an example of potential application of the discovered phenomenon for increasing cold neutron fluxes available for experiments. [Copyright &y& Elsevier]

Abstract: Usually Ultra Cold Neutrons (UCN) and Very Cold Neutrons (VCN) are not efficiently scattered by individual atoms in matter due to their large wavelength. On the contrary, such neutrons are coherently scattered by nanoparticles, providing a powerful tool, in particular for VCN reflectors, for VCN storage in closed traps, probably for ‘quasi-specular’ reflectors for cold neutrons, and for cooling VCN to the UCN energy range. On the other hand, quasi-elastic scattering of UCN at nanoparticles and large molecules (as those of Fomblin oil) in all presently used UCN trap wall materials causes false effects in the neutron lifetime measurements because of poorly controlled spectrum evolution. [Copyright &y& Elsevier]

Abstract: Thermal neutrons’ flux near the Earth’s crust is very sensitive regarding different processes and phenomena both in the near-Earth space and in the Earth’s crust by reason of the dual nature of the thermal neutron flux. Its first source is associated with high-energy particles of cosmic rays penetrating into the Earth’s atmosphere and interacting with its elements. The second source originates from the radioactive gases contained in the Earth’s crust. So the contributions of these two sources are specified by the Earth’s crust conditions and its movements, on one hand and variations of high-energy particles flux near the Earth. The paper presents the observations of the thermal neutrons flux during the Ground level enhancements (GLEs) recorded on January 20, 2005 and December 13, 2006. January 20, 2005 event became the first clear response to GLE in thermal neutrons’ data during the whole period of observations (from 1994). The biggest response observed at Antarctic experimental unit, was in good time correspondence with the response at Neutron Monitors (NMs). The difference of the amplitudes of the response at these units must be explained by different energy ranges of the registered particles. GLE on December 13, 2006 registered by one of Moscow thermal neutrons’ units, corresponded to NM data both in amplitude and time of the observed effect. The absence of the response at another Moscow unit must be linked to energy spectra of this event different from the previous and higher sensitivity of the first unit to the relative low energy neutrons coming from above due to “thin roof”. [Copyright &y& Elsevier]

Abstract: We developed a simple model to describe the interaction of slow neutrons with solid methane in phase II, including the main dynamical features of the system and the effect of spin correlations. This effect occurs in molecules containing identical nuclei whenever spin and rotational states are coupled, thus imposing symmetry requirements on the molecular wave function. The model is not intended to produce a detailed description of the neutron interaction with the isolated quantum excitations of the system, as it is based on simple frequency spectra to represent the molecular translational and rotational motions and Einstein oscillators for the vibrational motion. A central motivation for the development of this new scattering kernel has been the generation of cross section libraries appropriate for the calculation of neutron thermalization properties in CH4 II. Its predictions are in good agreement with a quantum mechanical calculation over the limited range where the latter was formulated and with available experimental information over the complete thermal energy range. Bearing in mind the general nature of the approximations involved in the present prescription and besides its predictive capacity demonstrated for solid methane in phase II, the model can be useful for the analysis of neutron scattering experiments designed to study spin species conversion of different rotational tunneling molecules at low temperatures, or in a wider context, to perform reliable multiple-scattering corrections in experiments oriented to precise determinations of density of states. [Copyright &y& Elsevier]

Abstract: A new polarimeter for low-energy electrons has been built and tested. The device was developed for the measurement of the transverse polarization of beta particles emitted in the decay of polarized cold neutrons. The decay electrons are identified by multi-wire proportional chambers made of low-Z materials and are detected with plastic scintillator hodoscopes. The transverse polarization is analyzed by means of large angle Mott scattering on a thin Pb foil. We describe here the elements of the apparatus and present the results of test measurements which illustrate its performance. [Copyright &y& Elsevier]

Abstract: Nowadays, promising digital active pixel detector systems are available and make real time imaging with high sensitivity and broad dynamic range possible. The hybrid silicon pixel detector device Medipix-2 was originally designed for single X-ray photon detection. The device consists of a sensor chip with 256×256 square pixels of 55μm size. The detector can be adapted for neutron detection by deposition of a converter layer to its surface. Thermal neutrons are converted in the layer into the secondary radiation which can be subsequently detected by the pixel detector. Different types of converter materials were examined with the aim to reach maximal spatial resolution at reasonable detection efficiency. The results demonstrate superior properties of the Medipix-2-based thermal neutron imager with a 6LiF converter in terms of spatial resolution, signal-to-noise ratio, linearity and dynamic range. Several images of real objects demonstrating the capabilities of the device are presented. The performance of the imager was compared with several types of contemporary neutron imaging systems (Medipix-1, CCD camera, imaging plates). [Copyright &y& Elsevier]

Neutron transmission radiography (neutronography) is based on the attenuation of radiation passing through matter. Thanks to different values of neutron and X-ray attenuation coefficients in matter, neutronography can image material properties which cannot be obtained by roentgenography (e.g. materials containing light elements such as Hydrogen in plastic or biological samples). The reliable performance of the neutron detecting device is essential for the acquisition of high-quality neutronograms. A single neutron pixel detector based on a single X-ray photon pixel Medipix-1 detector device is presented. Slow neutrons are converted in a converter layer into heavy charged particles which are subsequently detected by the Medipix-1 device. Detection efficiency, spatial resolution and other detector properties are determined for different converter materials (6LiF, 10B) and compared with results of Monte-Carlo simulations. Several neutronograms of real objects demonstrating the capabilities and possible applications of the technique are presented. [Copyright &y& Elsevier]

Abstract: I provide a personal overview of the 2008, International Workshop on Particle Physics with Slow Neutrons. [Copyright &y& Elsevier]

Abstract: The ATLAS detector is now installed at the CERN LHC and a precise evaluation of the radiation environment within and around the detector is required to understand the performance of the various detector systems, and to predict their useful lifetime. Furthermore, validation of earlier Monte Carlo predictions about the radiation field in ATLAS is necessary. In particular, it is important to perform these measurements in the early phases of the LHC operation. Many other radiation measuring devices lack sensitivity to low doses, and usually do not provide information on the composition of the radiation during this low intensity period. A network of 15 ATLAS-MPX devices has been installed at various positions in the ATLAS detector. These devices are capable of providing quantitative real-time information on the fluxes and flux distributions of the main radiation types in the experiment, including slow and fast neutrons. The technical description of the ATLAS-MPX detector network as well as the principles of the data analysis is presented. [Copyright &y& Elsevier]

Abstract: Fifteen ATLAS-MPX devices are installed in the ATLAS detector and cavern by the ATLAS-MPX collaboration. This network of sensors provides a real-time measurement of the composition of the radiation field inside the ATLAS detector and its cavern. This article reports calibration measurements of the thermal and fast neutron detection efficiency of the ATLAS-MPX devices. In order to detect neutrons, the 300-μm-thick silicon sensor of each device was covered with mask of 6LiF and polyethylene (PE) converters. Efficiency measurements were performed with calibrated natural thermal neutron source, calibrated 252Cf and 241AmBe sources. Fast neutrons with monochromatic energy of 14MeV were delivered by a Van de Graaff (VDG) accelerator beam. The devices showed a mean efficiency of 1.02×10−2 for thermal neutrons (6LiF–Si region), 3.17×10−4 for 252Cf, 7.51×10−4 for 241AmBe and 1.81×10−3 for 14MeV neutrons (PE-Si region) while all background signals generated by X-rays, gamma-rays and electrons were fully suppressed by appropriate discrimination level. These data allow the estimation of the neutron fluxes in ATLAS and provide initial data for precise simulation of the detector environment at the ATLAS-MPX devices locations. [Copyright &y& Elsevier]