Journal of Neutron Research - Volume 22, issue 2-3

Authors: Grammer, Kyle B. | Gallmeier, Franz X. | Iverson, Erik B.

Article Type: Research Article

Abstract: Rotating objects, such as choppers, are common components of a neutron beamline, and the motion of these components is not described in the static geometry of an MCNPX model. The special case of non-static surfaces for rotation about a stationary point in space has been developed for MCNPX. In addition, velocity dependent kinematics due to the motion of the medium have been implemented. This implementation allows for the simulation of rotating objects at speeds comparable to the velocity of cold neutrons. Applications of the chopper extension will be discussed, including the direct simulation of a bandwidth chopper system, the thermalization …of neutrons inside a spinning material, and the discussion of the implementation of a spinning single crystal. Show more

Keywords: Monte Carlo, MCNPX

DOI: 10.3233/JNR-200148

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 191-198, 2020

Authors: Miller, Thomas M. | DiJulio, Douglas D. | Santoro, Valentina

Article Type: Research Article

Abstract: Monte Carlo radiation transport codes have become the primary tool for shielding and activation analysis at high-powered spallation neutron sources. However, use of these codes to model facilities that have large amounts of shielding requires the use of variance reduction methods. This paper presents examples that apply ADVANTG generated variance reduction parameters to analyses performed at ESS using MCNP6. This requires some limitations in ADVANTG to be overcome and little-known features to be used. The focus of this paper is to describe how these limitations were overcome so other analyst at spallation sources can benefit from these methods as well.

Keywords: Variance reduction, ADVANTG, CADIS, FW-CADIS, spallation

DOI: 10.3233/JNR-200158

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 199-208, 2020

Authors: Santoro, V. | Andersen, K.H. | DiJulio, D.D. | Klinkby, E.B. | Miller, T.M. | Milstead, D. | Muhrer, G. | Strobl, M. | Takibayev, A. | Zanini, L. | Zimmer, O.

Article Type: Research Article

Abstract: The European Spallation Source being constructed in Lund, Sweden will provide the user community with a neutron source of unprecedented brightness. By 2025, a suite of 15 instruments will be served by a high-brightness moderator system placed above the spallation target. The ESS infrastructure, consisting of the proton linac, the target station, and the instrument halls, allows for implementation of a second source below the spallation target. We propose to develop a second neutron source with a high-intensity moderator able to (1) deliver a larger total cold neutron flux, (2) provide high intensities at longer wavelengths in the spectral regions of Cold …(4–10 Å), Very Cold (10–40 Å), and Ultra Cold (several 100 Å) neutrons, as opposed to Thermal and Cold neutrons delivered by the top moderator. Offering both unprecedented brilliance, flux, and spectral range in a single facility, this upgrade will make ESS the most versatile neutron source in the world and will further strengthen the leadership of Europe in neutron science. The new source will boost several areas of condensed matter research such as imaging and spin-echo, and will provide outstanding opportunities in fundamental physics investigations of the laws of nature at a precision unattainable anywhere else. At the heart of the proposed system is a volumetric liquid deuterium moderator. Based on proven technology, its performance will be optimized in a detailed engineering study. This moderator will be complemented by secondary sources to provide intense beams of Very- and Ultra-Cold Neutrons. Show more

Keywords: Moderator, neutrons, source, ESS, ultra cold neutron, very cold neutron

DOI: 10.3233/JNR-200159

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 209-219, 2020

Authors: Esposito, Raffaele | Calviani, Marco

Article Type: Research Article

Abstract: The neutron Time-Of-Flight (n_TOF) facility at the European Laboratory for Particle Physics (CERN) is a pulsed white-spectrum neutron spallation source producing neutrons for two experimental areas: EAR1, located 185 m downstream of the spallation target, and EAR2, located 20 m above the target. The facility is based on a lead target impacted by a high-intensity 20 GeV/c proton beam. It is designed to study neutron-nucleus interactions for neutron kinetic energies from a few meV to several GeV, with applications in nuclear astrophysics, nuclear technology, and medical research. The facility is undergoing a major upgrade in 2019–2020, which will include the installation of …the new third-generation target. The second-generation target consists in a water-cooled lead cylinder, while the new target will be cooled by nitrogen to avoid erosion-corrosion phenomena and contamination of the cooling water with radioactive lead spallation products. The new design will be optimized also for the vertical flight path. The operation of the new spallation target will start in 2021. This paper presents an overview on the evolution of the design and on the related R&D activities (including beam irradiation tests) carried out to ensure the best performance for both experimental areas and avoid the contamination issues of the previous targets. Show more

Keywords: Neutron, spallation, target, source, n_TOF

DOI: 10.3233/JNR-190137

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 221-231, 2020

Authors: Mastinu, Pierfrancesco | Bisello, Dario | Barrera, Rogelio Alfonso | Porras, Ignacio | Prete, Gianfranco | Silvestrin, Luca | Wyss, Jeffery

Article Type: Research Article

Abstract: In this contribution we describe NEPIR, the fast-neutron irradiation facility under construction at the 70 MeV cyclotron SPES facility of the INFN laboratory of Legnaro (LNL). NEPIR will be constructed in stages, according to the available funds. The initial configuration, based on a thick Be neutron production target, will be operational in 2022; it will be used for shielding studies against fast neutrons for space applications and to investigate neutron-induced Single Event Effects (SEE) in microelectronic devices and systems. In its final configuration NEPIR will have two target systems: one will deliver a Quasi Mono-energetic Neutron (QMN) beam, of general …interest, with an adjustable energy peak in the 20–70 MeV range; the second target will deliver a specialized continuous energy neutron beam for studying the effects of fast neutrons produced in cosmic ray air-showers in electronic devices and systems. We review the use of NEPIR to characterize the sensitivity of electronics, describe the neutron production targets and the facility layout. In closing we describe ways, presently under investigation, to use the 15 MV XTU Tandem of LNL to produce nearly monochromatic fast neutrons that would complement the QMN system by allowing one to probe for SEE below 20 MeV. Show more

Keywords: Fast neutrons, Single Event Effects

DOI: 10.3233/JNR-200156

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 233-247, 2020

Authors: Flammini, D. | Bedogni, R. | Moro, F. | Pietropaolo, A.

Article Type: Research Article

Abstract: An experimental procedure is assessed to obtain moderated neutron fields starting from almost monochromatic 14 MeV neutrons generated by means of an accelerator-driven D-T source. The use of a metallic pre-moderator and a standard hydrogen-containing moderator is effective in producing neutron spectra featuring a thermal peak and an epithermal slowing down tail extending up to 14 MeV. The performance of proposed moderation system was investigated by means of MCNP Monte Carlo calculations, benchmarked against experimental measurements using an explorative set up, assembled at the Frascati Neutron Generator. The benchmarked calculations allow at making predictions about the brilliance of a 14 …MeV neutron moderator in view of possible applications in neutron science. Show more

Keywords: Fusion neutrons, neutron moderators, Monte Carlo simulations, neutron sources

DOI: 10.3233/JNR-190129

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 249-256, 2020

Authors: Capogni, M. | Capone, M. | Pietropaolo, A. | Fazio, A. | Dellepiane, G. | Falconi, R. | Colangeli, A. | Palomba, S. | Valentini, G. | Fantuzi, M. | Faccini, R. | Pizzuto, A.

Article Type: Research Article

Abstract: 64 Cu is an emerging radionuclide of great interest in personalized nuclear medicine. It is produced by a cyclotron via the reaction 64 Ni(p,n)64 Cu. This production method increased during the last decades, because small biomedical cyclotrons can be easily installed close to the nuclear medicine department of a hospital. As a matter of fact, 64 Ni is a very expensive target material. For this reason, an alternative 64 Cu production method was investigated at ENEA by using the quasi-monochromatic 14 MeV fusion neutron beam made available at the Frascati Neutron Generator (FNG) located at the ENEA – Frascati Research …Center. In particular, two nuclear reactions were studied: 65 Cu(n,2n)64 Cu and 64 Zn(n,p)64 Cu. The radiochemical analysis of the activated samples was performed at the ENEA-NMLNWM laboratory located in ENEA-Casaccia Research Center. The activity measurements were carried out at the ENEA-INMRI, located in the ENEA-Casaccia Research Center, with high metrological level conditions and by assuring their traceability to the 64 Cu primary activity standard here developed and maintained. A prediction of the 64 Cu production by means of the high-brilliance 14 MeV neutron source named Sorgentina is also discussed. Show more

Keywords: 64Cu, fast neutrons, radiopharmaceuticals, direct activity measurements

DOI: 10.3233/JNR-190140

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 257-264, 2020

Authors: Remec, Igor | Gallmeier, Franz X.

Article Type: Research Article

Abstract: The Spallation Neutron Source, in operation at the Oak Ridge National Laboratory since 2006, was designed to allow the addition of a second target station and an upgrade of the accelerator proton power. Both upgrades are now underway. This paper describes the evolution of the design of the target of the second target station with the emphasis on the effects of the proton beam footprint on the energy deposition in the target, stresses induced by the pulsed operation, and the importance of the residual heat. The moderator configurations and their optimization are discussed. With the utilization of pure parahydrogen moderators, …small neutron beam cross-sections, and the specific optimization, neutron beams of the second target station will achieve exceptionally high peak brightness and time-averaged brightness. Show more

Keywords: Neutron source, spallation, neutronics, target, moderators, brightness

DOI: 10.3233/JNR-200165

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 265-273, 2020

Authors: DiJulio, Douglas D. | Lee, Yong Joong | Muhrer, Gunter

Article Type: Research Article

Abstract: Beryllium reflectors are used at spallation neutron sources in order to enhance the low-energy flux of neutrons emanating from the surface of a cold and thermal moderator. The design of such a moderator/reflector system is typically carried out using detailed Monte-Carlo simulations, where the beryllium reflector is assumed to behave as a poly-crystalline material. In reality, however, inhomogeneities in the beryllium could lead to discrepancies between the performance of the actual system when compared to the modeled system. The dependence of the total cross-section in particular on crystallite size, in the Bragg scattering region, could influence the reflector performance, and …if such an effect is significant, it should be taken into account in the design of the moderator/reflector system. In this paper, we report on the preliminary results of using cross-section libraries, which include corrections for the crystallite size effect, in spallation source neutronics calculations. Show more

Keywords: Neutron cross-section, beryllium, spallation source, NJOY, MCNP

DOI: 10.3233/JNR-190135

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 275-279, 2020

Authors: Kirichek, O. | Lawson, C.R. | Draper, G.L. | Jenkins, D.M. | Haynes, D.J. | Lilley, S.

Article Type: Research Article

Abstract: The unique properties of solid methane enable the conversion of hot, energetic neutrons into cold neutrons, with an efficiency approximately 3.5 times that of liquid hydrogen based moderators. However, practical applications of solid methane in neutron moderators turned out to be much more challenging than initially expected. Exposure of solid methane at low temperatures to neutron radiation leads to a build-up of radiolysis products in the solid methane matrix. Accumulation of defects beyond some critical number can result in a spontaneous self-accelerated recombination process, which in combination with the expansion of hydrogen built up in bulk solid methane during irradiation, …was believed to be responsible for the moderator’s breakdown. Here we present results of our thermodynamic model, based on the theory of thermal explosion. Our model agrees well with the test data obtained using methane moderators developed at the IPNS neutron source, based at Argonne National Laboratory and the data acquired during commissioning of the ISIS Target Station 2 solid methane moderator. We also discuss the products of radiolysis reactions generated by exposure of the condensed methane to neutron radiation. The succession of radiolysis reactions may lead to the production of long chain hydrocarbons, which can contaminate the moderator system and significantly reduce efficiency of the heat-exchanger. The possible solutions for cleaning moderators using targeted solvents are considered. In the conclusion we give some practical recommendations, based on our simulation results and operational experience. Show more

Keywords: Neutron moderator, solid methane, radiolysis

DOI: 10.3233/JNR-190132

Citation: Journal of Neutron Research, vol. 22, no. 2-3, pp. 281-286, 2020