Physics

Reactivity measurement is an essential part of a zero-power physics test, which is critical to reactor design and development. The rod drop experimental technique is used to measure the control rod worth in a zero-power physics test. The conventional rod drop experimental technique is limited by the spatial effect and the difference between the calculated static reactivity and measured dynamic reactivity; thus, the method must be improved. In this study, a modified rod drop experimental technique that constrains the detector neutron flux shape function based on three-dimensional space-time dynamics to reduce the reactivity perturbation and a new method for calculating the detector neutron flux shape function are proposed. Correction factors were determined using Monte Carlo N-Particle transport code and transient analysis code for a pressurized water reactor at the Ulsan National Institute of Science and Technology and Xi'an Jiaotong University, and a large reactivity of over 2000 pcm was measured using the modified technique. This research evaluated the modified technique accuracy, studied the influence of the correction factors on the modification, and investigated the effect of constraining the shape function on the reactivity perturbation reduction caused by the difference between the calculated neutron flux and true value, using the new method to calculate the shape function of the detector neutron flux and avoiding the neutron detector response function (weighting factor) calculation.

This paper describes a new method for optical readout of Time Projection Chambers (TPCs), based on the Linearly Graded Silicon Photomultiplier (LG-SiPM). This is a single photon-sensitive detector with excellent timing and 2D position resolution developed at Fondazione Bruno Kessler, Trento (FBK). The LG-SiPM produces time-varying voltage signals that are used to reconstruct the 3D position and energy of ionisation tracks generated inside the TPC. The TPC used in this work contained room-temperature CF 4 gas at a pressure of 100 mbar, with two THGEMs to produce secondary scintillation light. A collimated 241 Am source (Q α = 5.486 MeV) was used to produce the ionisation tracks. The successful reconstruction of these tracks is demonstrated, and the consistency of the methodology characterised through varying the geometry of the tracks within the TPC. Energy reconstruction and deposition studies are also described, demonstrating the feasibility of the LG-SiPM as a potential option for optical TPC readout.

The ProtoDUNE-SP detector is a single-phase liquid argon time projection chamber with an active volume of 7.2×6.0×6.9 m 3 . It is installed at the CERN Neutrino Platform in a specially-constructed beam that delivers charged pions, kaons, protons, muons and electrons with momenta in the range 0.3 GeV /c to 7 GeV/ c . Beam line instrumentation provides accurate momentum measurements and particle identification. The ProtoDUNE-SP detector is a prototype for the first far detector module of the Deep Underground Neutrino Experiment, and it incorporates full-size components as designed for that module. This paper describes the beam line, the time projection chamber, the photon detectors, the cosmic-ray tagger, the signal processing and particle reconstruction. It presents the first results on ProtoDUNE-SP's performance, including noise and gain measurements, dE/dx calibration for muons, protons, pions and electrons, drift electron lifetime measurements, and photon detector noise, signal sensitivity and time resolution measurements. The measured values meet or exceed the specifications for the DUNE far detector, in several cases by large margins. ProtoDUNE-SP's successful operation starting in 2018 and its production of large samples of high-quality data demonstrate the effectiveness of the single-phase far detector design.

Superconducting electronics often require high-density microwave interconnects capable of transporting signals between temperature stages with minimal loss, cross talk, and heat conduction. We report the design and fabrication of superconducting 53 wt% Nb-47 wt% Ti (Nb47Ti) FLexible coAXial ribbon cables (FLAX). The ten traces each consist of a 0.076 mm O.D. NbTi inner conductor insulated with PFA (0.28 mm O.D.) and sheathed in a shared 0.025 mm thick Nb47Ti outer conductor. The cable is terminated with G3PO coaxial push-on connectors via stainless steel capillary tubing (1.6 mm O.D., 0.13 mm thick) soldered to a coplanar wave guide transition board. The 30 cm long cable has 1 dB of loss at 8 GHz with -60 dB nearest-neighbor forward cross talk. The loss is 0.5 dB more than commercially available superconducting coax likely due to impedance mismatches caused by manufacturing imperfections in the cable. The reported cross talk is 30 dB lower than previously developed laminated NbTi-onKapton microstrip cables. We estimate the heat load from 1 K to 90 mK to be 20 nW per trace, approximately half the computed load from the smallest commercially available superconducting coax from CryoCoax

We present a MHz frequency-division dc-SQUID multiplexer that is based on flux ramp modulation and a series array of N identical current-sensing dc-SQUIDs with tightly coupled input coil. By running a periodic, sawtooth-shaped current signal through an additional modulation coil being tightly, but non-uniformly coupled to the individual SQUIDs, the voltage drop across the array changes according to the superposition of the flux-to-voltage characteristics of the individual SQUIDs within each cycle of the modulation signal. In this mode of operation, an input signal injected in the input coil of one of the SQUIDs and being quasi-static within a time frame adds a constant flux offset and leads to a phase shift of the associated SQUID characteristics. The latter is inherently proportional to the input signal and can be inferred by channelizing and down-converting the sampled array output voltage. Using a prototype multiplexer as well as a self-developed high-speed readout electronics for real-time phase determination, we demonstrate the simultaneous readout of four signal sources with MHz bandwidth per channel.

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to measure the neutrino mass with a sensitivity of 0.2eV ( 90% CL). This will be achieved by a precision measurement of the endpoint region of the β -electron spectrum of tritium decay. The electrons from tritium β -decay are produced in the Windowless Gaseous Tritium Source (WGTS) and guided magnetically through the beamline. In order to accurately extract the neutrino mass the source properties, in particular the activity, are required to be stable and known to a high precision. The WGTS therefore undergoes constant extensive monitoring from several measurement systems. The Forward Beam Monitor (FBM) is one such monitoring system. The FBM system comprises a complex mechanical setup capable of inserting a detector board into the KATRIN beamline inside the Cryogenic Pumping Section with a positioning precision of better than 0.3mm . The electron flux density at that position is on the order of 10 6 s ?? m m ?? . The detector board contains a hall sensor, a temperature gauge, and two silicon detector chips of p - i - n diode type which can measure the β -electron flux from the source with a precision of 0.1% in less than a minute with an energy resolution of FWHM = 2keV .

A milestone revision of the International System of Units (SI) was made at the 26th General Conference on Weights and Measures that four of the seven SI base units, i.e. kilogram, ampere, kelvin, and mole, are redefined by fundamental physical constants of nature. The SI base unit founding the electrical measurement activities, i.e. ampere, is defined by fixing the numerical value of the elementary charge to e=1.602176634× 10 −19 C. For electrical measurement, several major adjustments, mostly positive, are involved in this SI revision. In this paper, the main impacts of the new SI for electrical measurement activities are surveyed under the new framework.

Nuclear physics experiments are always in need of more and more advanced detection systems. During the last years relevant technological developments have come out with many improvements in terms of performance and compactness of detector materials, transducers, electronics, computing and data transmission. In light of these achievements some applications previously prohibitive, mainly because of size and cost, have become feasible. A few applications of nuclear detection techniques are discussed, starting from the neighboring field of particle beam diagnostics, moving to the medical diagnostics and ending up into the radioactive waste handling. New radiation sensors are shown and explained, as exploited in the DMNR project for the radioactive waste online monitoring which merged into the MICADO Euratom project.

The v-Angra experiment aims to estimate the flux of antineutrino particles coming out from the Angra II nuclear reactor. Such flux is proportional to the thermal power released in the fission process and therefore can be used to infer the quantity of fuel that has been burned during a certain period. To do so, the v-Angra Collaboration has developed an antineutrino detector and a complete acquisition system to readout and store the signals generated by its sensors. The entire detection system has been installed inside a container laboratory placed beside the dome of the nuclear reactor, in a restricted zone of the Angra II site. The system is supposed to work standalone for a few years in order to collect enough data so that the experiment can be validated. The detector's readout electronics and its environmental conditions are crucial parts of the experiment and they should work autonomously and be controlled and monitored remotely. Additionally, threshold configuration is a central issue of the experiment since antineutrino particles produce low energy signals in the detector, being necessary to carefully adjust it for all the detector channels in order to make the system capable of detecting signals as low as those generated by single photons. To this end, an embedded system was developed and integrated to the detection apparatus installed in the container at the Angra II site and is now operational and accessible to the v-Angra Collaboration. This article aims at describing the proposed embedded system and presenting the results obtained during its commissioning phase.

Safeguarding the disposal of spent nuclear fuel in a geological repository needs an effective, efficient, reliable and robust non-destructive assay (NDA) system to ensure the integrity of the fuel prior to disposal. In the context of the Finnish geological repository, Passive Gamma Emission Tomography (PGET) will be a part of such an NDA system. We report here on the results of PGET measurements at the Finnish nuclear power plants during the years 2017-2020. Gamma activity profiles are recorded from all angles by rotating the detector arrays around the fuel assembly that has been inserted into the center of the torus. Image reconstruction from the resulting tomographic data is defined as a constrained minimization problem with a data fidelity term and regularization terms. The activity and attenuation maps, as well as detector sensitivity corrections, are the variables in the minimization process. The regularization terms ensure that prior information on the (possible) locations of fuel rods and their diameter are taken into account. Fuel rod classification, the main purpose of the PGET method, is based on the difference of the activity of a fuel rod from its immediate neighbors, taking into account its distance from the assembly center. The classification is carried out by a support vector machine. We report on the results for ten different fuel types with burnups between 5.72 and 55.0 GWd/tU, cooling times between 1.87 and 34.6 years and initial enrichments between 1.9 and 4.4%. For all fuel assemblies measured, missing fuel rods, partial fuel rods and water channels were correctly classified. Burnable absorber fuel rods were classified as fuel rods. On rare occasions, a fuel rod that is present was falsely classified as missing. We conclude that the combination of the PGET device and our image reconstruction method provides a reliable base for fuel rod classification.