Optimization of a moderator-neutron guide system for diffractometers of beam line 7A of the IBR-2M reactor

Neutron guides are widely used to transport the neutrons from the moderator to the sample. Due to the constructive features of the ring corridor of the fast pulsed reactor IBR-2, the minimal distance between the moderator and the guide entrance is around 6 m. The main goal of the paper is to optimize the neutron optical system between the moderator and the entrance of the new neutron guides. Using Monte Carlo simulations we calculate the possible best gain of the neutron flux density at the guide exit. After the described optimization process, the optimal system is obtained. The recommendations for construction of the new beam line are provided too. Similar technique and the proposed system could be easily adapted for another similar beam line at the neutron sources.     

The ICON beamline - A facility for cold neutron imaging at SINQ

The beamline for Imaging with COld Neutrons (ICON) at Swiss spallation neutron source (SINQ) at Paul Scherrer Institut has a flexible design to meet the requests from a wide user community. The current status of the beamline and its characteristics are described. The instrumentation includes three experimental positions from which two are equipped with digital camera based imaging detectors. Tomographic imaging is among the standard methods available at the beamline. Advanced methods such as energy-selective imaging and grating interferometry are available as instrument add-ons which are easily installed.     

Development of a neutron tomography system using a low flux reactor

A neutron tomography instrument was designed and developed at the Royal Military College (RMC) of Canada with Queen's University to enhance these institutions' non-destructive evaluation capabilities. The neutron imaging system was built around a Safe Low-Power C(K)ritical Experiment (SLOWPOKE-2) nuclear research reactor. The low power and physical geometry of the reactor required that a novel design be developed to facilitate tomography. A unique rotisserie style rotary stage and clamping apparatus was developed. Furthermore, the low flux at the image plane (3×10⁴ n cm⁻² s⁻¹), necessitated that the image acquisition and reconstruction processes be optimized. Tomographs of numerous samples were obtained using the new tomography instrument at RMC.     

Investigation of fuel cells using scanning neutron imaging and a focusing neutron guide

We present two different methods to increase the size of available neutron beams in order to allow for the investigation of large objects. Application of these methods is demonstrated for radiographic imaging of fuel cells. The first approach is a scanning procedure based on the coordinated translation of detector and sample through the beam. Further advancement was achieved by installing a focusing neutron guide, which offers an expanded neutron beam size after diverging from a focused point source.     

Study on beam geometry and image reconstruction algorithm in fast neutron computerized tomography at NECTAR facility

Investigations on the fast neutron beam geometry for the NECTAR facility are presented. The results of MCNP simulations and experimental measurements of the beam distributions at NECTAR are compared. Boltzmann functions are used to describe the beam profile in the detection plane assuming the area source to be set up of large number of single neutron point sources. An iterative algebraic reconstruction algorithm is developed, realized and verified by both simulated and measured projection data. The feasibility for improved reconstruction in fast neutron computerized tomography at the NECTAR facility is demonstrated.     

GEANT4 used for neutron beam design of a neutron imaging facility at TRIGA reactor in Morocco

Neutron imaging has a broad scope of applications and has played a pivotal role in visualizing and quantifying hydrogenous masses in metallic matrices. The field continues to expand into new applications with the installation of new neutron imaging facilities.In this scope, a neutron imaging facility for computed tomography and real-time neutron radiography is currently being developed around 2.0MW TRIGA MARK-II reactor at Maamora Nuclear Research Center in Morocco (Reuscher et al., 1990 [1]; de Menezes et al., 2003 [2]; Deinert et al., 2005 [3]).The neutron imaging facility consists of neutron collimator, real-time neutron imaging system and imaging process systems. In order to reduce the gamma-ray content in the neutron beam, the tangential channel was selected. For power of 250 kW, the corresponding thermal neutron flux measured at the inlet of the tangential channel is around 3×10¹¹ ncm²/s.This facility will be based on a conical neutron collimator with two circular diaphragms with diameters of 4 and 2 cm corresponding to L/D-ratio of 165 and 325, respectively. These diaphragms' sizes allow reaching a compromise between good flux and efficient L/D-ratio. Convergent-divergent collimator geometry has been adopted.The beam line consists of a gamma filter, fast neutrons filter, neutron moderator, neutron and gamma shutters, biological shielding around the collimator and several stages of neutron collimator. Monte Carlo calculations by a fully 3D numerical code GEANT4 were used to design the neutron beam line (http://www.info.cern.ch/asd/geant4/geant4.html[4]).To enhance the neutron thermal beam in terms of quality, several materials, mainly bismuth (Bi) and sapphire (Al₂O₃) were examined as gamma and neutron filters respectively. The GEANT4 simulations showed that the gamma and epithermal and fast neutron could be filtered using the bismuth (Bi) and sapphire (Al₂O₃) filters, respectively.To get a good cadmium ratio, GEANT 4 simulations were used to define the design of the moderator in the inlet of the radiation channel. A graphite block of 22 cm thickness seems to be the optimal neutron moderator.The results showed that the combination of 5 cm of bismuth with 5 cm of sapphire permits the filtration of gamma-rays, epithermal neutrons as well as fast neutrons in a considerable way without affecting the neutron thermal flux.     

Transmission of very slow neutrons through material foils and its influence on the design of ultracold neutron sources

At the Paul Scherrer Institute (PSI), a very intense source of ultracold neutrons (UCN) is being built. The UCN converter of solid deuterium must be contained in a vessel. Produced UCN leave that vessel through its top lid. To decide on the design of the vessel and the top lid, we have measured the transmission of neutrons with velocities between 3 and 20 m/s through different material foils. Contrary to expectations, we found that transmission through aluminium and aluminium alloys is equal or even higher compared to zirconium and reactor-grade zirconium alloys, respectively.     

On the development of computational tools for the design of beam assemblies for boron neutron capture therapy

This article is the first in a series devoted to the development of efficient and accurate computational tools for the design of beam assemblies for boron neutron capture therapy within the framework of discrete ordinates spectral nodal methods of neutron transport theory. We begin our study with a multi-layer representation of an assembly, and we derive a discrete ordinates matrix operator that replaces without spatial truncation error the entire multi-layer domain in neutron transmission computations. With the matrix operator derived here, we compute without further ado the angular distribution of neutrons leaving the multi-layer assembly, avoiding thus the use of general-purpose discrete ordinates codes founded in the discretization and numerical solution of the neutron transport equation over a number of spatial cells and angular directions throughout the domain. We perform numerical experiments with a four-layer model assembly, and we conclude this article with a discussion and directions for further developments.     

Measurement of the Neutron Spectrum at the Center of the Core in the FS-1M Critical Test Assembly

The data reported here for the energy spectrum in the core of the FS-1M critical test assembly were obtained by neutron activation measurements. The neutron spectra at the center of the critical assembly core and in the analog BR-1 reactor are compared. __________ Translated from Izmeritel'naya Tekhnika, No. 8, pp. 59–62, August, 2005.     

A new monitor set for the determination of neutron flux parameters in short-time k0-NAA

Multipurpose research reactors such as LVR-15 in ?e? require monitoring of the neutron flux parameters (f, α) in each batch of samples analyzed when k₀ standardization in NAA is to be used. The above parameters may change quite unpredictably, because experiments in channels adjacent to those used for NAA require an adjustment of the reactor operation parameters and/or active core configuration. For frequent monitoring of the neutron flux parameters the bare multi-monitor method is very convenient. The well-known Au-Zr tri-isotopic monitor set that provides a good tool for determining f and α after long-time irradiation is not optimal in case of short-time irradiation because only a low activity of the ⁹⁵Zr radionuclide is formed. Therefore, several elements forming radionuclides with suitable half-lives and Q₀ and ē_r parameters in a wide range of values were tested, namely ¹⁹⁸Au, ⁵⁶Mn, ⁸⁸Rb, ¹²⁸I, ¹³⁹Ba, and ²³⁹U. As a result, an optimal mixture was selected consisting of Au, Mn, and Rb to form a well suited monitor set for irradiation at a thermal neutron fluence rate of 3×10¹⁷ m⁻² s⁻¹. The procedure of short-time INAA with the new monitor set for k₀ standardization was successfully validated using the synthetic reference material SMELS 1 and several matrix reference materials (RMs) representing matrices of sample types frequently analyzed in our laboratory. The results were obtained using the Kayzero for Windows program.     

Measurement of the neutron fields produced by a 62 MeV proton beam on a PMMA phantom using extended range Bonner sphere spectrometers

The experimental characterization of the neutron fields produced as parasitic effect in medical accelerators is assuming an increased importance for either the patient protection or the facility design aspects. Medical accelerators are diverse in terms of particle type (electrons or hadrons) and energy, but the radiation fields around them have in common (provided that a given threshold energy is reached) the presence of neutrons with energy span over several orders of magnitude. Due to the large variability of neutron energy, field or dosimetry measurements in these workplaces are very complex, and in general, cannot be performed with ready-to-use commercial instruments.In spite of its poor energy resolution, the Bonner Sphere Spectrometer (BSS) is the only instrument able to simultaneously determine all spectral components in such workplaces. The energy range of this instrument is limited to E<20 MeV if only polyethylene spheres are used, but can be extended to hundreds of MeV by including metal-loaded spheres (extended range BSS, indicated with ERBSS).With the aim of providing useful data to the scientific community involved in neutron measurements at hadron therapy facilities, an ERBSS experiment was carried out at the Centro di AdroTerapia e Applicazioni Nucleari Avanzate (CATANA) of INFN—LNS (Laboratori Nazionali del Sud), where a proton beam routinely used for ophthalmic cancer treatments is available. The 62 MeV beam was directed towards a PMMA phantom, simulating the patient, and two neutron measurement points were established at 0° and 90° with respect to the beam-line. Here the ERBSS of UAB (Universidad Autónoma de Barcelona—Grup de Física de les Radiacions) and INFN (Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Frascati) were exposed to characterize the “forward” and “sideward” proton-induced neutron fields. The use of two ERBSS characterized by different set of spheres, central detectors, and independently established and calibrated, is important for guaranteeing the robustness of the measured spectra and estimating their overall uncertainties.     

Improvement of beam lifetime and vacuum system of the PF-AR

Successive improvements have been performed on the vacuum system for the Photon Factory Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK). The main purpose is to prolong electron beam lifetime for stable operation as an intense pulsed X-ray source. In the past three years, a total of 61 sputter ion pumps (SIPs) were additionally installed, and the increased effective pumping speed amounts to 13% of total. Comparison between calculated and observed beam lifetimes indicates that the lifetime is restricted mainly by the residual gas scatterings and that improvement of the vacuum will realize still longer lifetime. Sudden beam lifetime drops caused by dust trappings have been investigated for many years. The frequency of the lifetime drops has decreased as operation time elapsed after a large-scale reconstruction. Effect of distributed ion pumps (DIPs) on the lifetime drops has also been investigated experimentally.     

Generation of neutron multigroup constants in the energy range –10 MeV for light and heavy water at four different temperatures

On the basis of the cross section models of neutron scattering in liquid H₂O and D₂O, which have been developed in the previous papers, we have generated eight sets of multigroup constants (energy-averaged cross sections) for each liquid at 5, 27, 52 and . The multigroup constants cover a wide energy range –10 MeV with 140 energy groups at equal logarithmic intervals and represent an angular scattering distribution by the Legendre polynomial expansion up to order 3. Major characteristics of neutron scattering inherent to liquid water are fully included in terms of coherent and incoherent properties and temperature-dependent quasi-elastic and inelastic scattering. These characteristics are assured by comparison with relevant experimental results of scattering cross section and also by neutron slowing-down and thermalization analysis in liquid H₂O and D₂O. It is shown that the present multigroup constants serve for analysis of neutron moderation from fission/spallation to ultra-cold energies, in combination with the already-generated ones for liquid ⁴He, H₂, D₂ and CH₄ and solid CH₄.     

The vacuum system of the Low Energy Ion Ring at CERN: Requirements, design, and challenges

For the heavy ion program at CERN's Large Hadron Collider, lead-lead collisions with a design luminosity of 10²⁷ cm⁻² s⁻¹ are foreseen. This will be achieved after an upgrade of the ion injector chain where the Low Energy Antiproton Ring (LEAR) is currently converted into a Low Energy Ion Ring (LEIR). Avalanche-like heavy-ion induced molecular desorption, first observed at LEAR and systematically studied at CERN's Heavy Ion Accelerator (LINAC 3), is the major challenge to achieve the required average dynamic pressure of about 4×10⁻¹² mbar in LEIR. The LEIR vacuum requirements, the technical design, the implementation of non-evaporable getter coatings and low-outgassing collimators, and the concept of ion-beam scrubbing are reviewed in this paper.