Neutron Response Research Articles

Comparison Between Silicon Carbide and Diamond for Thermal Neutron Detection at Room Temperature

Neutron radiation detector for nuclear reactor applications plays an important role in getting information about the actual neutron flux. Such a detector must be able to operate at high neutron flux levels (>109 cm−2 s−1) and discriminate the neutron and gamma responses in the nuclear reactor’s mixed neutron–gamma environment. Silicon carbide and diamond are the most attractive semiconductor materials for neutron detection, thanks to their outstanding properties, such as high displacement threshold energy and wide bandgap energy, which allow them to operate in high radiation levels and high temperature. The aim of this article is to compare the ability to detect thermal neutrons of these two semiconductors at the same irradiation conditions. For this purpose, the neutron irradiation tests of detectors were implemented at MINERVE research reactor at CEA Cadarache. The 4H-silicon carbide (SiC) p+n diode has demonstrated better neutron–gamma discrimination at 0-V bias voltage than at −200 V which is explained by its increased sensitivity to gamma photons at −200 V caused by a wider charge collection region than at 0 V. Therefore, it is preferable to use the 4H-SiC p+n diode without an external electric field for applications in the mixed neutron–gamma environment such as nuclear reactor environment. The results show that the single-crystal chemical vapor-deposited (sCVD) diamond-based detector has better neutron to gamma discrimination, thanks to the use of 6Li as a neutron converter instead of 10B. However, the study of the radiation stability of detectors showed that the sCVD diamond-based detector suffers from the “polarization effect” when it operates at a high neutron flux (~109 cm $^{-2}\,\,\cdot \,\,\text{s}^{-1}$ ).

Geant4 performance optimization in the ATLAS experiment

Software improvements in the ATLAS Geant4-based simulation are critical to keep up with evolving hardware and increasing luminosity. Geant4 simulation currently accounts for about 50% of CPU consumption in ATLAS and it is expected to remain the leading CPU load during Run 4 (HL-LHC upgrade) with an approximately 25% share in the most optimistic computing model. The ATLAS experiment recently developed two algorithms for optimizing Geant4 performance: Neutron Russian Roulette (NRR) and range cuts for electromagnetic processes. The NRR randomly terminates a fraction of low energy neutrons in the simulation and weights energy deposits of the remaining neutrons to maintain physics performance. Low energy neutrons typically undergo many interactions with the detector material and their path becomes uncorrelated with the point of origin. Therefore, the response of neutrons can be efficiently estimated only with a subset of neutrons. Range cuts for electromagnetic processes exploit a built-in feature of Geant4 and terminate low energy electrons that originate from physics processes including conversions, the photoelectric effect, and Compton scattering. Both algorithms were tuned to maintain physics performance in ATLAS and together they bring about a 20% speed-up of the ATLAS Geant4 simulation. Additional ideas for improvements, currently under investigation, will also be discussed in this paper. Lastly, this paper presents how the ATLAS experiment utilizes software packages such as Intel’s VTune to identify and resolve hot-spots in simulation.

Proton Light Yield of Fast Plastic Scintillators for Neutron Imaging

Plastic organic scintillators have been tailored in composition to achieve ultra-fast temporal response, thereby enabling the design and development of fast neutron detection systems with high timing resolution. Eljen Technology's plastic organic scintillators -- EJ-230, EJ-232, and EJ-232Q -- are prospective candidates for use in emerging neutron imaging systems, where fast timing is paramount. To support the neutron response characterization of these materials, the relative proton light yields of EJ-230, EJ-232, and EJ-232Q were measured at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a broad-spectrum neutron source and a double time-of-flight technique, the proton light yield relations were obtained over a proton recoil energy range of approximately 300 keV to 4 MeV. The EJ-230, EJ-232, and EJ-232Q scintillators exhibited similar proton light yield relations to each other as well as to other plastic scintillators with the same polymer base material. A comparison of the relative proton light yield of different sized cylindrical EJ-232 and EJ-232Q scintillators also revealed consistent results. This work provides key input data for the realistic computational modeling of neutron detection technologies employing these materials, thereby supporting new capabilities in near-field radionuclide detection for national security applications.

Sensing Area‐Average Snow Water Equivalent with Cosmic‐Ray Neutrons: The Influence of Fractional Snow Cover

AbstractCosmic‐ray neutron sensing (CRNS) is a promising non‐invasive technique to estimate snow water equivalent (SWE) over large areas. In contrast to preliminary studies focusing on shallow snow conditions (SWE 130 mm), more recently the method was shown experimentally to be sensitive also to deeper snowpacks providing the basis for its use at mountain experimental sites. However, hysteretic neutron response has been observed for complex snow cover including patchy snow‐free areas. In the present study we aimed to understand and support the experimental findings using a comprehensive neutron modeling approach. Several simulations have been set up in order to disentangle the effect on the signal of different land surface characteristics and to reproduce multiple observations during periods of snow melt and accumulation. To represent the actual land surface heterogeneity and the complex snow cover, the model used data from terrestrial laser scanning. The results show that the model was able to accurately reproduce the CRNS signal and particularly the hysteresis effect during accumulation and melting periods. Moreover, the sensor footprint was found to be anisotropic and affected by the spatial distribution of liquid water and snow as well as by the topography of the nearby mountains. Under fully snow‐covered conditions the CRNS is able to accurately estimate SWE without prior knowledge about snow density profiles or other spatial anomalies. These results provide new insights into the characteristics of the detected neutron signal in complex terrain and support the use of CRNS for long‐term snow monitoring in high elevated mountain environments.

Evaluation of lithium glass scintillation detector responses for tritium production rate measurement in blanket neutronics experiments using the PHITS code

Lithium (Li) glass scintillation detectors were utilized by the neutron response of a 7Li glass subtracted from the neutron response of a 6Li glass to evaluate the tritium production rate (TPR) in the fusion blanket neutronics experiments, which is a so called Li glass method. TPRs in the Li2O blanket and the Li/V-alloy blanket were measured by a 6Li2O and a 6Li2CO3 pellet method, and by the Li glass method in the benchmark neutronics experiment with D-T neutrons at the Fusion Neutronics facility (FNS) of JAERI. TPRs measured by the Li glass method are lower than TPRs measured by the pellet method. The neutron responses of Li glass detectors have been calculated to study the discrepancies of two different methods by using the PHITS code. In the blanket, the neutron spectra change to harder from the backside to the front side of blanket. The reaction rate of several reactions, such as 6Li(n, n’α)D, 7Li(n, n’α)T, 7Li(n, 2n)6Li, and the elastic scattering of 6Li and 7Li increase with the neutron energy. The low-energy neutron peak was considered only for the calculation of TPR from Li glass, which loses the information of the 6Li(n, α)T reaction from high-energy neutron range. In addition, the reaction rate of this peak evaluated by the Li glass method is lower than real TPR of this peak for 6Li glass caused by weakened effect from other reactions. Therefore, the ratios of this peak reaction rate from the Li glass method against the total TPR of 6Li glass were evaluated to be a correction factor to correct Li glass method. After the correction, TPRs measured by Li glass method agree well with TPRs measured by pellet method.

Comparative study between the developed simulators based on the direct and indirect methods for calculation of the energy spectrum of the neutron source

The purpose of the present paper is to compare the various computer codes used in fast-neutron spectroscopy for spectrum unfolding and calculation of the response of the organic scintillation detectors. For neutron spectrum unfolding, the Fredholm integral equation is solved using iterative and soft computing algorithms. In the present paper, the Modified Least SQuaRe (MLSQR) method (iterative algorithm) and some soft computing algorithms are presented. The latter comprise Artificial Neural Network (ANN), Support Vector Machine (SVM) and Adaptive Group of Ink Drop Spread (AGIDS) methods. Furthermore, a MCNPX based algorithm for calculating the neutron response of organic scintillation detectors is presented which is used for Time-Of-Flight based fast-neutron spectroscopy (nTOF) . To this end, the ability for simulating the emission and tracking of two simultaneously emitted particles as well as the light production and light transport in the scintillator were added to the MCNPX computer code. Also, a post-processing software was developed to analyze the massive amounts of data in the output of the PTRAC card. The presented techniques are benchmarked with a published spectrum from an 241Am-9Be neutron source. The results obtained from the calculation using the proposed methods have an acceptable agreement with the standard ISO-8592 spectrum of the 241Am-9Be neutron source. However, the accuracy of the calculation using the SVM and AGIDS is better than the accuracy of the other presented methods.

Neutron irradiation response of a Co-free high entropy alloy

Low dose neutron irradiation has been conducted on a NiFeMnCr (Co-free) high entropy alloy (HEA) near room temperature. Post-irradiation examination (PIE) at room temperature revealed that this HEA exhibited qualitatively similar change in mechanical properties (hardness, strength and ductility) as conventional austenitic stainless steels. Isochronal annealing was performed to determine the hardness, electrical resistivity and defect property evolution with respect to annealing temperature. Different annealing behavior was observed. Irradiation hardening nearly completely anneals by 650 °C, although the annealing trend is different following exposure to 0.1 and 1 displacements per atom (dpa). Positron Annihilation Spectroscopy (PAS) measurements indicate that the temperature to initialize vacancy cluster (stage V) recovery is ∼400 °C, and that the density of vacancy-type defects is reduced to that of the unirradiated control specimen at 500 °C. No significant change in the chemical ordering near defects was measured by PAS after neutron irradiation or after isochronal annealing up to 700 °C. Electrical resistivity measurements revealed a large increase in resistivity following irradiation, and this resistivity increase does not significantly recover even after the 700 °C anneal. Overall, these annealing results indicate the HEA vacancy cluster annealing behavior is similar to conventional face centered cubic (FCC) alloys whereas solute diffusion is limited up to 700 °C (significantly more sluggish than conventional FCC alloys). X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicated that this HEA exhibit good phase stability upon neutron irradiation up to 1 dpa and post-irradiation annealing up to 700 °C.

Effect of Ga substitution for In in LiInSe2 crystals on carrier transport behaviors and alpha particles detection

Due to high density of 6Li isotope and the ability to respond to ionizing radiation through direct charge carrier transport, Li-containing chalcogenides are expected to be the replacement of 3He-tube or neutron reactive material coated semiconductor films for thermal neutron detection. However, the neutron detection efficiency of 6LiInSe2 is limited to 82% ascribed to that 115In isotope captures neutrons and generates gamma rays, which deteriorated the neutron response. Neutron detection efficiency could be improved by gallium substitution since its low neutron capture cross-section. In this work, the electron and hole mobility (μ) of LiIn1−xGaxSe2(x = 0, 0.25, 0.5, 0.75, 1) were studied by first-principles density functional theory (DFT) calculation, which demonstrated the electron mobility (μ e) of LiIn0.5Ga0.5Se2 is close to that of LiInSe2 while the hole mobility (μ h) is much improved. To further certify, both LiIn0.5Ga0.5Se2 and LiInSe2 crystals were grown under similar condition by vertical Bridgman method, exhibited comparable bandgap and bulk resistivity at room temperature. The charge transport behaviors were evaluated under 241[email protected] alpha particles. The full energy peak is clearly resolved in the pulse height spectra. The electron and hole mobility-lifetime products of LiIn0.5Ga0.5Se2 are 1.5×10−5 cm2/V and 6.9×10−5 cm2/V, respectively. The resulting μ e of LiIn0.5Ga0.5Se2 and LiInSe2 crystals are 270 cm2V−1s−1 and 180 cm2V−1s−1, respectively, fitted by time of flight (TOF) technique. In addition, the μ h of LiIn0.5Ga0.5Se2 is obtained with the value of 110 cm2V−1s−1, but the hole response is too weak to be resolved for LiInSe2.

Investigation of the thermal and neutron irradiation response of BAM-11 bulk metallic glass

Zr52.5Cu17.9Ni14.6Al10Ti5 (BAM-11) bulk metallic glass was irradiated by neutrons to a fluence of 1.4 × 1020 n/cm2 (E > 0.1 MeV) (0.1 displacements per atom, dpa) at a temperature of ∼70 °C and then analyzed using multiple mechanical property and structural characterization techniques. Nanoindentation hardness measurements revealed that irradiation led to softening and a reduced Young's modulus in the alloy while annealing at 300–325 °C caused an increase in the hardness and modulus. Neutron diffraction results indicated that primary knock-on events caused rejuvenation (structural disordering) while annealing resulted in structural relaxation. Furthermore, it was found that annealing after irradiation reversed the disordering effects caused by the irradiation. The increased disordering in the alloy during irradiation is thought to be attributed to the enhanced free volume content caused by the neutron collision cascades in the matrix. Indeed, immersion density measurements revealed that irradiation led to a decrease in the density of the alloy. This decrease in the macroscopic density was linked to an increase in the structural disorder of the alloy while an increase in the density corresponded to an increasing degree of order. Additionally, synchrotron X-ray diffraction related the structural relaxation of the alloy to a loss of ductility, which is in agreement with the literature. Overall, an increase in the structural disorder in the sample is linked to a softening of the alloy and to a higher concentration of soft-zone defects in the glass.

Spin-orbit excitons in CoO

CoO has an odd number of electrons in its unit cell, and therefore is expected to be metallic. Yet, CoO is strongly insulating owing to significant electronic correlations, thus classifying it as a Mott insulator. We investigate the magnetic fluctuations in CoO using neutron spectroscopy. The strong and spatially far-reaching exchange constants reported in [Sarte et al. Phys. Rev. B 98 024415 (2018)], combined with the single-ion spin-orbit coupling of similar magnitude [Cowley et al. Phys. Rev. B 88, 205117 (2013)] results in significant mixing between $j_{eff}$ spin-orbit levels in the low temperature magnetically ordered phase. The high degree of entanglement, combined with the structural domains originating from the Jahn-Teller structural distortion at $\sim$ 300 K, make the magnetic excitation spectrum highly structured in both energy and momentum. We extend previous theoretical work on PrTl$_{3}$ [Buyers et al. Phys. Rev. B 11, 266 (1975)] to construct a mean-field and multi-level spin exciton model employing the aforementioned spin exchange and spin-orbit coupling parameters for coupled Co$^{2+}$ ions on a rocksalt lattice. This parameterization, based on a tetragonally distorted type-II antiferromagnetic unit cell, captures both the sharp low energy excitations at the magnetic zone center, and the energy broadened peaks at the zone boundary. However, the model fails to describe the momentum dependence of the excitations at high energy transfers, where the neutron response decays faster with momentum than the Co$^{2+}$ form factor. We discuss such a failure in terms of a possible breakdown of localized spin-orbit excitons at high energy transfers.

A design study of application of the CsI self-activation method to the neutron rem-counter technique

A design study of application of the CsI self-activation method to the “neutron rem-counter technique” was investigated. A CsI crystal served as both the main target material and 4π counter of neutron activation method in our proposed CsI self-activation method. A commercially available CsI gamma-ray dosimeter was selected as the neutron detector and surrounded with several neutron filters made of polyethylene and silicon rubber containing B4C. The geometric structure of these neutron filters was optimized by a Monte Carlo calculation to make the neutron response similar to the ICRP-74 rem-response. Optimization of this method, the residual sum of squares (RSS) of the calculated neutron response and the ICRP-74 rem-response were minimized by changing the thickness of each filter sequentially. In addition, experimental verification using a Pu–Be source and photoneutrons from a 10 MV-X medical linac has been conducted. From these results, it is concluded that it may be practical for evaluating neutron ambient dose-equivalent simply around medical linacs.

Resolving Continua of Fractional Excitations by Spinon Echo in THz 2D Coherent Spectroscopy.

We show that the new technique of terahertz 2D coherent spectroscopy is capable of giving qualitatively new information about fractionalized spin systems. For the prototypical example of the transverse field Ising chain, we demonstrate theoretically that, despite the broad continuum of excitations in linear response, the 2D spectrum contains sharp features that are a coherent signature of a "spinon echo," which gives previously inaccessible information such as the lifetime of the two-spinon excited state. The effects of disorder and finite lifetime, which are practically indistinguishable in the linear optical or neutron response, manifest in dramatically different fashion in the 2D spectra. Our results may be directly applicable to model quasi-1D transverse field Ising chain systems such as CoNb_{2}O_{6}, but the concept can be applied to fractionalized spin systems in general.

Measured neutron light-output response for trans-stilbene and small-molecule organic glass scintillators

Abstract The neutron light-output response from quasi-monoenergetic neutrons was measured for a O5.08 × 5.08 cm trans-stilbene and a O5.08 × 5.08 cm small-molecule organic glass scintillator . Quasi-monoenergetic neutrons were isolated from a time-of-flight measurement of a Cf-252 spontaneous fission source with a flight distance of 200 cm. Two different methods of waveform analysis were implemented, where the neutron light output response proportional to the detected pulse height distribution (PHD) and pulse integral distribution (PID) were extracted for both types of scintillators. The light output response proportional to the pulse integral was determined by integrating the digitized waveform with an integration window length of 150 ns, which contained > 90% and > 95% of the scintillation light for an averaged neutron and photon waveform above 0.5 MeVee. The extracted light-output data were fitted with a semi-empirical function based on the Birks’ formula. The results show that the small-molecule organic glass scintillator produced more light than the trans-stilbene scintillator for a range of neutron energies of 0.79 ± 0.04 MeV to 3.65 ± 0.38 MeV. The fitted semi-empirical function was used in MCNPX-PoliMi with MPPost to simulate the detector response from an independent measurement of a Cf-252 spontaneous fission source to test the fidelity of the extracted light output response functions. The simulated and measured total neutron count rate agreed to within ± 3 % and ± 1% for the trans-stilbene and small-molecule organic glass scintillators. Due to the different light-output response of the two scintillators, the intrinsic neutron detection efficiency was calculated for equal observable ranges in light output and neutron-equivalent energy units. The intrinsic neutron detection efficiency in the observable light-output range of 0.06 MeVee to 2.4 MeVee was calculated to be 28.66 ± 1.43 % and 34.66 ± 1.73 % for pulse height and pulse integral analysis, respectively. For the same observable light-output range, the intrinsic efficiency of small-molecule organic glass was calculated to be 32.54 ± 1.63 % and 37.39 ± 1.87 % for pulse height and pulse integral analysis, respectively. When observing equal light-output ranges, the small-molecule organic glass was 11.92 ± 6.23% and 7.88 ± 7.35% more efficient than the trans-stilbene using pulse height and pulse integral analysis, respectively. When observing equal neutron-equivalent energy ranges, the trans”–stilbene scintillator was 8.4 ± 6.46% and 11.95 ± 6.23% more efficient than the small-molecule organic glass for pulse height and pulse integral analysis, respectively.

Neutronic developments on TOSCA and VESPA: Progress to date

We report recent developments regarding the TOSCA (ISIS, UK) and VESPA (ESS, Sweden) neutron broadband chemical spectrometers, both joint ventures between CNR (IT) and ISIS (UK). TOSCA has seen the first major upgrade since it first became operational over fifteen years ago. The new design of the primary spectrometer, which exploits a state-of-the-art, high-m neutron guide and associated chopper system, is boosting the useful neutron flux by over an order of magnitude. Feasibility studies for an upgrade of the secondary spectrometer have been performed, outlining an additional order-of-magnitude gain in performance. In the case of VESPA, the novel characteristics and challenges arising from a long-pulse spallation source such as ESS are part of the drivers of the instrument design. For both the primary and secondary spectrometers, a detailed analysis of expected performance, supported by both simulations and analytical models, is being carried out, also capitalizing from experience on TOSCA. Indeed, for instrument design and optimization, extensive neutron-transport simulations and baseline studies of neutronic response have become a must, along with extensive benchmarking against much-needed experimental data. All these combined efforts represent the first opportunity to benchmark a broadband, high-resolution chemical spectrometer in terms of measured vs. simulated response.

Acoustic instrumentation for a bubble chamber towards dark matter searches

Dark matter is one of the top unsolved mysteries in physics. Its existence is well-established although its nature remains unknown. Despite the progress made in the direct search effort, reflecting over 10 orders of magnitude in sensitivity since 1984, no true candidates to explain this phenomenon have appeared in searches covering a range from ~10 GeV to 1 TeV. This article reports on the development of a 1 kg freon bubble chamber prototype, including the chamber recompression system design and testing, initial acoustic detection of bubble formation, and initial neutron and alpha detector response studies. The prototype constructed was a transparent acrylic containment vessel, capable of withstanding recompression cycles to a pressure of 16 bar. The acoustic signal accompanying bubble formation was investigated using three different sensors: a low frequency microphone (Panasonic) with a flat response over 0.020-16 kHz, an ultrasound externallypolarized condenser microphone (AviSoft) with a flat response over 10-150 kHz, and an hydrophone (Reson) with a flat response over 5-170 kHz. Acoustic signatures of several induced events were successfully registered. The data acquisition digitizer used, to meet the range of the three microphones, was the NI PCI-6251 16-Bit, with at least 1.25 MSps for 1-Channel.

Can Drip Irrigation be Scheduled with Cosmic‐Ray Neutron Sensing?

Core Ideas Cosmic‐ray neutron sensing (CRNS) was used in a drip‐irrigated field. Soil water content was estimated from CRNS. Neutron transport was simulated for the drip‐irrigated field. CRNS has limitations for irrigation scheduling of drip‐irrigated fields. Irrigation is essential for maintaining food production in water‐scarce regions. The irrigation need depends on the water content of the soil, which we measured with the novel technique of cosmic‐ray neutron sensing (CRNS). The potential of the CRNS technique for drip irrigation scheduling was explored in this study for the Picassent site near Valencia, Spain. To support the experimental evidence, the neutron transport simulation URANOS was used to simulate the effect of drip irrigation on the neutron counts. The overall soil water content (SWC) in the CRNS footprint was characterized with a root mean square error <0.03 cm3/cm3, but the experimental dataset indicated methodological limitations to detect drip water input. Both experimental data and simulation results suggest that the large‐area neutron response to drip irrigation is insignificant in our specific case using a standard CRNS probe. Because of the small area of irrigated patches and short irrigation time, the limited SWC changes due to drip irrigation were not visible from the measured neutron intensity changes. Our study shows that CRNS modeling can be used to assess the suitability of the CRNS technique for certain applications. While the standard CRNS probe was not able to detect small‐scale drip irrigation patterns, the method might be applicable for larger irrigated areas, in drier regions, and for longer and more intense irrigation periods. Since statistical noise is the main limitation of the CRNS measurement, the capability of the instrument could be improved in future studies by larger and more efficient neutron detectors.

A neutron beam monitor based on silicon carbide semiconductor coated with 6LiF converter

A neutron beam monitor was developed for the time-of-flight neutron reflectometer (NR) instrument at the China Mianyang Research Reactor (CMRR). The SiC neutron monitor employs a wide-bandgap silicon carbide (SiC) semiconductor detector coated with a 6LiF neutron converter film evaporated on a thin ceramic sheet. Given the relatively large active area [(10 × 10) mm2] and sufficiently thick epitaxial layer (30μm), the monitor can discriminate the gamma background from the signals. Prior to assembling the monitor, the I–V characteristics and alpha responses of the SiC detector were measured. Next, the SiC detector and 6LiF neutron converter were installed in a small aluminum shielding box, and the neutron and gamma responses were measured with an Am–Li neutron source and a 137Cs plus 60Co gamma source, respectively. The fabricated SiC neutron monitor was mounted inside the slit of the NR instrument (after the focusing neutron guide), and the intensity of the transmitted neutron beam was measured. To measure the incident neutron flux, the distinct triton peaks from the 6Li (n, α) T reaction were counted as normalized data for the NR instrument. This paper describes the fabrication details of the SiC neutron monitor, and discusses the preliminary measurements.

Neutronic assessments towards a comprehensive design of DEMO with DCLL breeding blanket

On the way towards a comprehensive design of DEMO, step by step all the systems and components must be introduced as their definition or refinement progresses, in order to demonstrate the viability of a design on larger scale, i.e. leaving fewer margins to undetermined questions.Among the EUROfusion Programme, new aspects have been recently fixed or further developed as the Divertor, the First Wall (FW) and the Flow Channel Inserts (FCI) designs. Furthermore, the integration of Heating and Current Drive (H&CD) systems, as the Neutral Beam Injector (NBI), has started.The introduction or modification of these systems and components could seriously jeopardize the nuclear behaviour of an initially validated Breeding Blanket (BB) DEMO concept, since many neutronics criteria - among others - could be no more fulfilled. Since the design of DEMO is a continuous upgrade under iterative process, as the advances push on, most of the studies have to be repeated to demonstrate that criteria are still respected in a fully integrated design. The consequences of these upgrades over the neutronic responses are addressed in this paper. Among others, the influence on Tritium Breeding Ratio (TBR) of a new design of detached FW protecting BB from high heat fluxes is investigated. The impact of different typologies of FCIs is assessed also according to the degree of detail in the neutronic description. The divertor composition also reveals to have strong impact on responses apparently not related with its design, as the tritium production in the BB. Besides, the integration of NBI minimizing its invasiveness in the BB is verified by neutronic analyses concerning the main BB functions: fuel breeding and heat generation. Accordingly, TBR and Nuclear Heating (NH) are assessed.The study is performed for a Dual Coolant Lead Lithium (DCLL) BB DEMO although can be extrapolated to other BB concepts.

A plastic scintillator array for reactor based anti-neutrino studies

Indian Scintillator Matrix for Reactor Anti-Neutrinos (ISMRAN), a plastic scintillator array (10 × 10), is being constructed for the purpose of electron anti-neutrino (ν¯e) detection for reactor monitoring applications. A prototype detector called mini-ISMRAN, which consists of 16% of ISMRAN, has been setup for studying the detector response, background rates and event characterization in the reactor and non-reactor environment. The data acquisition system based on waveform digitizers is being used for pulse processing and event triggering. Monte-Carlo based simulations using GEANT4 are performed to optimize lead (Pb) and borated polyethylene (BP) shielding for background reduction and to study the positron, neutron and γ-ray response in the ISMRAN detector. Characterization of plastic scintillator detectors with known radioactive sources is performed for energy, timing and position measurements. Using the energy summation and bar multiplicity selection, coincident events from 60Co decay are reconstructed in non-reactor environment. Results from background measurements using various detectors are quantified in reactor ON and OFF condition. The shielding of 10 cm Pb and 10 cm BP along with the requirement of hits in multiple bars, reduces the uncorrelated background in reactor ON condition.

Modeling the one-dimensional imager of neutrons (ODIN) for neutron response functions at the Sandia Z facility.

The one-dimensional imager of neutrons (ODIN) at the Sandia Z facility consists of a 10-cm block of tungsten with rolled edges, creating a slit imager with slit widths of either 250, 500, or 750 μm. Designed with a 1-m neutron imaging line of sight, we achieve about 4:1 magnification and 500-μm axial spatial resolution. The baseline inertial confinement fusion concept at Sandia is magnetized liner inertial fusion, which nominally creates a 1-cm line source of neutrons. ODIN was designed to determine the size, shape, and location of the neutron producing region, furthering the understanding of compression quality along the cylindrical axis of magnetized liner implosions. Challenges include discriminating neutrons from hard x-rays and gammas with adequate signal-to-noise in the 2 × 1012 deuterium-deuterium (DD) neutron yield range, as well as understanding the point spread function of the imager to various imaging detectors (namely, CR-39). Modeling efforts were conducted with MCNP6.1 to determine neutron response functions for varying configurations in a clean DD neutron environment (without x-rays or gammas). Configuration alterations that will be shown include rolled-edge slit orientation and slit width, affecting the resolution and response function. Finally, the experiment to determine CR-39 neutron sensitivity, with and without a high density polyethylene (n, p) converter, an edge spread function, and resolution will be discussed.