| 1. |
- Aartsen, M. G., et al.
(författare)
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Computational techniques for the analysis of small signals in high-statistics neutrino oscillation experiments
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 977
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Tidskriftsartikel (refereegranskat)abstract
- The current and upcoming generation of Very Large Volume Neutrino Telescopes - collecting unprecedented quantities of neutrino events - can be used to explore subtle effects in oscillation physics, such as (but not restricted to) the neutrino mass ordering. The sensitivity of an experiment to these effects can be estimated from Monte Carlo simulations. With the high number of events that will be collected, there is a trade-off between the computational expense of running such simulations and the inherent statistical uncertainty in the determined values. In such a scenario, it becomes impractical to produce and use adequately-sized sets of simulated events with traditional methods, such as Monte Carlo weighting. In this work we present a staged approach to the generation of expected distributions of observables in order to overcome these challenges. By combining multiple integration and smoothing techniques which address limited statistics from simulation it arrives at reliable analysis results using modest computational resources.
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| 2. |
- Bradbury, J., et al.
(författare)
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Lifetime measurements using a plunger device and the EUCLIDES Si array at the GALILEO gamma-ray spectrometer
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 979
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Tidskriftsartikel (refereegranskat)abstract
- The GALILEO gamma-ray spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), benefits from intense stable beams provided by the Tandem-ALPI-PIAVE accelerator complex and from radioactive beams to be delivered in the near future by the SPES facility. The spectrometer is complemented with a variety of ancillary devices to allow for nuclear structure and reaction studies. The 4 pi Si-ball array EUCLIDES coupled to the GALILEO gamma-ray spectrometer represents one of the commonly used setup for experiments aiming at spectroscopic studies. High-efficiency detection of light-charged particles in a fusion-evaporation reaction guarantees good discrimination of different reaction channels and provides essential information for the kinematic reconstruction. In this paper we discuss a configuration of the EUCLIDES array developed for the lifetime measurements of nuclear excited states populated in a fusion-evaporation reaction. In such a configuration a part of the EUCLIDES detectors is disassembled allowing for the installation of a plunger device in the reaction chamber. The reduced configuration of EUCLIDES provides high detection efficiency necessary for reliable light charged-particle discrimination. We report on the commissioning experiment focused on the Ni-58(Ni-58,3p)I-113 reaction. The lifetimes of 11/2(-) and 15/2(-) states were measured by applying the Recoil Distance Doppler Shift method to be equal to 206(20) ps and 7.9(12) ps correspondingly and were in good agreement with the values cited in the literature. Thus, the combination of the GALILEO and EUCLIDES arrays, and the plunger device has resulted in a powerful experimental setup to determine lifetimes of excited states in neutron-deficient nuclei in the picosecond range.
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| 3. |
- Grape, Sophie, 1982-, et al.
(författare)
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Determination of spent nuclear fuel parameters using modelled signatures from non-destructive assay and Random Forest regression
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 969
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Tidskriftsartikel (refereegranskat)abstract
- Verification of fuel parameters is a central undertaking for nuclear inspectors aiming at verifying the completeness and correctness of operator declarations. Traditionally, such verification is done analysing data from one instrument at a time. Here we present a study based on simulated data from various non-destructive assay measurement techniques applied on modelled PWR nuclear fuel assemblies. The data comprised multiple signatures and were analysed using machine learning algorithms. These signatures included activities from gamma-ray emitting fission product radionuclides, the parametrised early die-away time.. from the prototype Differential Die-away Self-Interrogation (DDSI) instrument, as well as the total Cherenkov light intensity which is directly measurable. The objective of the work is to systematically explore the capability to predict values of the fuel parameters initial enrichment (IE), burnup (BU) and cooling time (CT) independently of operator declarations, using Random Forest regression and modelled pressurised water reactor (PWR) fuel. The results show that passive gamma-ray activities alone can be used to predict IE, BU and CT for CT<20 years, and that by adding a feature proportional to the total gamma-ray activity, the errors in the predictions are significantly reduced. In this work, two measures proportional to total gamma activity have been studied: the sum of all considered gamma-ray intensities, and the total Cherenkov light intensity. From this work it was concluded that for fuels with CTs between 20 and 70 years, CT can be well determined by a multivariate analysis of the activities of Cs-134, Cs-137, Eu-154. For a BU determination, an additional feature corresponding to total gamma activity is required. This is, however, not sufficient to determine IE, which requires inclusion of the neutron signature.. as well.
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| 4. |
- Holz, Michael, et al.
(författare)
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Envelope dynamics and stability with non-linear space-charge forces
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 951
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Tidskriftsartikel (refereegranskat)abstract
- We developed a model to calculate the stability of Gaussian beam distributionswith non-linear space-charge forces in the presence of random and skewquadrupoleerrors. The eect of the space-charge force on the beam matrix iscalculated analytically including full cross-plane coupling in 4D phase space,which allows us to perform fast parameter studies. For stability analysis, wend the xed points of the beam including the space-charge forces and constructa Jacobi-matrix by slightly perturbing the periodic solution. The stability ofenvelope oscillations is inferred by eigenvalue analysis. Furthermore, we employenvelope tracking as a complementary method and compare the results ofthe eigenvalue analysis with FFT data from the tracked envelope. The nonlinearityof the space-charge force in combination with lattice errors and beamcoupling opens up for envelope-lattice resonances and envelope coupling resonances.Hitting these resonances leads to envelope blow-up, causing an eectivebeam mismatch. Therefore, we nally examine the eect of beam mismatch onthe envelope tune-shift and its stability.
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| 5. |
- Rennie, A. R., 1957-, et al.
(författare)
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Understanding neutron absorption and scattering in a polymer composite material
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER. - 0168-9002 .- 1872-9576. ; 984
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Tidskriftsartikel (refereegranskat)abstract
- The neutron transmission and scattering from a composite of 25% weight boron carbide and nylon (Addbor N25) has been measured as a function of wavelength. Samples with different thicknesses on a support were prepared by an additive manufacturing (or 3D-printing) process, fused filament fabrication. Data are provided that demonstrate that the material is effective to absorb thermal and cold neutrons, and this information will permit calculation of performance as a shielding material. The results show that the attenuation by absorption can be predicted adequately using a simple dependence of the absorption cross-section on the reciprocal of velocity. The scattering at small values of the momentum transfer, Q, is dominated by a Porod law variation, 1/Q(4) that is consistent with particles dispersed in a hydrogenous polymer matrix of low scattering length density. M large momentum transfer, Q > 0.06 angstrom(-1), incoherent inelastic scattering is predominant, and this is seen to increase significantly with the wavelength of the incident neutrons. The new results are described in the context of various possibilities to fabricate shielding or absorbers in complex shapes, to replace the toxic alternative of cadmium and to exploit an engineering plastic as the basis of a neutron absorbing composite.
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| 6. |
- Trahan, Alexis C., et al.
(författare)
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Results of the Swedish spent fuel measurement field trials with the Differential Die-Away Self-Interrogation Instrument
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER. - 0168-9002 .- 1872-9576. ; 955
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Tidskriftsartikel (refereegranskat)abstract
- Differential Die-Away Self-Interrogation (DDSI) is a method by which the characteristic die-away of neutrons from spontaneous and induced fissions is used to characterize a spent nuclear fuel assembly. A nondestructive assay (NDA) instrument was built at Los Alamos National Laboratory to implement and test the DDSI method. The DDSI instrument contains He-3 detectors which measure thermal neutrons, and the time and location of detection of each neutron is recorded via list-mode data acquisition. The instrument was sent to the Clab interim storage facility in Sweden for measurement and characterization of 50 spent pressurized water reactor (PWR) and boiling water reactor (BWR) fuel assemblies. The result was over 40 h of neutron list-mode data from a wide variety of fuel assemblies with high enough efficiency to perform neutron coincidence counting, i.e. detection of time-correlated neutrons from fission. Analysis algorithms for characterization of the fuel assemblies were tested on the Swedish spent fuel dataset. Using the measured data, multiplication, fissile mass, initial enrichment, burnup, and total plutonium mass were determined in the 50 assemblies with root mean square errors ranging from 1.5% for PWR multiplication to 11.4% for BWR fissile mass. The results in this work demonstrate that the DDSI concept is capable of characterizing spent power reactor fuel with levels of accuracy that are compatible with the requirements and objectives of various applications such as safeguards verification or facility material control and accounting.
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| 7. |
- Zheng, Yifan, et al.
(författare)
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Robustness of optimal energy thresholds in photon-counting spectral CT
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER. - 0168-9002 .- 1872-9576. ; 953
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Tidskriftsartikel (refereegranskat)abstract
- An important question when developing photon-counting detectors for computed tomography is how to select energy thresholds. In this work thresholds are optimized by maximizing signal-difference-to-noise ratio squared (SDNR2) in an optimally weighted image and signal-to-noise ratio squared (SNR2) in a gadolinium basis image in a silicon-strip detector and a cadmium zinc telluride (CZT) detector, factoring in pileup and imperfect energy response based on real-world detector systems. To investigate to what extent one single set of thresholds could be applied in various imaging tasks, the robustness of optimal thresholds with 2 to 8 bins is examined with the variation of phantom thicknesses, target materials and detector configurations. In contrast to previous studies, the optimal threshold locations do not always increase with increasing attenuation if pileup is included. With respect to the tradeoff between higher SDNR2 or SNR2 and less data, setting optimal thresholds for a 30 cm phantom yields robust SDNR2 and setting optimal thresholds for a 50 cm phantom yields robust SNR2 with 6 to 8 bins in the silicon-strip detector. Furthermore, setting optimal thresholds for a 30 cm phantom yields robust SDNR2 or SNR2 with 6 to 8 bins and a pixel size less than or equal to 0.5 x 0.5 mm(2) in the CZT detector.
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| 8. |
- Ahmadiannamin, S., et al.
(författare)
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Design of 100 MHz RF cavity for the storage ring of the Iranian Light Source Facility (ILSF)
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 981
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Tidskriftsartikel (refereegranskat)abstract
- The Iranian Light Source Facility is a fourth-generation low emittance synchrotron light source under development in Iran. The design and in-house fabrication of RF cavities are key elements of this project. The choice of 100 MHz capacity loaded RF cavities offers many advantages compared to other cavity types due to a simpler geometry, ease of fabrication, and lower costs for manufacturing and RF power system development. Here we present comprehensive simulation studies of these accelerating RF cavities. This includes electromagnetic, mechanical, and thermal calculations. In addition, in the electromagnetic design section, discussions of higher-order modes, their impact on beam instabilities during machine operation and beam loading effects are addressed. Finally, thermomechanical simulation results are presented. The fabrication of a 100 MHz capacity-loaded cavity has started based on the design presented in this article.
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| 9. |
- Andersen, K. H., et al.
(författare)
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The instrument suite of the European Spallation Source
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 957
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Tidskriftsartikel (refereegranskat)abstract
- 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 of the early years of the ESS, and provide a solid base for completion and further expansion of the facility.
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| 10. |
- Cabanelas, P., et al.
(författare)
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Performance recovery of long CsI(Tl) scintillator crystals with APD-based readout
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 965
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Tidskriftsartikel (refereegranskat)abstract
- CALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, intended for detecting high energy light charged particles and gamma rays in scattering experiments, and is being commissioned during the Phase-0 experiments at FAIR, between 2018 and 2020. It surrounds the reaction target in a segmented configuration with 2432 detection units made of long CsI(Tl) finger-shaped scintillator crystals. CALIFA has a 10 year intended operational lifetime as the R3B calorimeter, necessitating measures to be taken to ensure enduring performance. In this paper we present a systematic study of two groups of 6 different detection units of the CALIFA detector after more than four years of operation. The energy resolution and light output yield are evaluated under different conditions. Tests cover the aging of the first detector units assembled and investigates recovery procedures for degraded detection units. A possible reason for the observed degradation is given, pointing to the crystal-APD coupling.
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