International Journal of Modern Physics: Conference Series

PROSPECT is a reactor antineutrino experiment whose primary goals are to search for short-baseline neutrino oscillations and perform a precise measurement of the ${}^{235}$U reactor antineutrino energy spectrum. Since March 2018, PROSPECT has operated a 4 ton antineutrino detector less than 10 m from the 85 MW High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory. Operating in this environment with tight space constraints and limited overburden to attenuate cosmic ray backgrounds is a significant technical challenge. The PROSPECT detector design uses efficient optical segmentation and a ⁶Li-doped liquid scintillator with good light yield and pulse-shape discrimination properties to achieve excellent energy reconstruction and background rejection in a compact, space efficient system. Initial results from PROSPECT have demonstrated the ability to detect 100 s of antineutrino events per day with good signal-to-background in this aboveground location and perform precise measurements of the HFIR antineutrino energy spectrum.

LUX (Large Underground Xenon) was a dark matter experiment, which was housed at the Sanford Underground Research Facility (SURF) in South Dakota until late 2016, and previously set world-leading limits on Weakly Interacting Massive Particles (WIMPs), axions and axion-like particles (ALPs). This proceeding presents an overview of the LUX experiment and discusses the most recent analysis efforts, which are probing various dark matter models and detection techniques. In particular, studies of signals from inelastic scattering processes and of single scintillation photon events have improved the sensitivity of the experiment to low mass WIMPs. Additionally, a model-independent search for modulations in the LUX electron recoil rate is presented, demonstrating the most sensitive annual modulation search to date.

Detection of special nuclear materials (SNM) requires instruments that can detect and characterize uranium and plutonium isotopes, having at the same time the ability to discriminate among different types of radiation. For many decades, neutron detection has been based on ³He proportional counters sensitive primarily to thermal neutrons. The most common methods for detection of fast neutrons have been based on liquid scintillators with pulse shape discrimination (PSD). The shortage of ³He and handling issues with liquid scintillators stimulated a search for efficient solid-state PSD materials. Recent studies conducted at LLNL led to development of new materials, among which are organic crystals with excellent PSD and first PSD plastics for fast neutron detection. More advantages are introduced by plastics doped with neutron capture agents, such as ¹⁰B and ⁶Li, that can be used without moderation for combined detection of both thermal and fast neutrons, offering, in addition, a unique “triple” PSD for signal separation between fast neutrons, thermal neutrons, and gamma-rays. More recent studies have been focused on development of deuterated scintillators that can be used for neutron spectroscopy without time-of-flight (ToF). Among commercially produced materials are large-scale (>10 cm) stilbene crystals grown by the inexpensive solution technique, and different types of PSD plastics that, due to the deployment advantages and ease of fabrication, create a basis for the widespread use of solid-state scintillators as large-volume and low-cost neutron detectors.

Spaceflight instruments that measure the energy and intensity of gamma rays and neutrons emitted by the surfaces of planetary bodies have been included in planetary science missions since 1966. These instruments use nuclear techniques to determine the elemental composition and related information about planetary surface and near-surface materials from the analysis of these gamma ray and neutron data. This paper provides a short review of these nuclear techniques as they have been used in current and past orbital and landed missions. A description of the nuclear instrumentation on many such missions is provided. Finally, descriptions of future missions that will employ gamma ray and neutron instruments will be presented.

Experiments of nuclear physics have been carried out at the Bern medical cyclotron, in which a beam line dedicated to research activities is available. Our main goal is to upgrade this facility as a well-characterized neutron source for studies of radiation hardness and for tests of new neutron detectors. To achieve this result, preliminary measurements have been carried out among which the measurement of the incident proton energy by means of a method based on Rutherford backscattering spectroscopy. The analysis of the energy spectrum corresponding to protons elastically and inelastically backscattered by the carbon target allowed the precise identification of the excited states of ¹²C, including the Hoyle state. These results confirmed the Bern medical cyclotron as a reliable facility to perform research activities in the field of fundamental nuclear physics as well as of applied physics.

The European Spallation Source (ESS), which is established as a European Research Infrastructure Consortium (ERIC), is a multi-disciplinary research facility that is currently under construction. ESS has as vision to develop to a world class facility, enabling scientific breakthroughs in research related to materials, energy, health and the environment. The ESS facility is built by a collaboration of some 100 research institutes and universities.

With its 5 MW average beam power, its linac will be the most powerful linac of all neutron spallation sources. Neutrons are obtained by delivering 2 GeV protons at a repetition rate of 14 Hz to the He-cooled solid tungsten rotating target. The Accelerator is built with a high percentage of In-Kind Contributions (IKC) with major accelerator systems being designed, prototyped and built outside ESS. The first major accelerator elements are now being assembled and tested with their first parts being installed. Future similar large-scale projects could likely be IKC-based, which is a powerful model. Within ESS, the Mechanical Engineering & Technology (MET) section is responsible for developing and maintaining mechanical engineering and design throughout the facility. The mechanical design is consolidated in the master model and available under the ESS Plant Layout, including all In-Kind Contributions as well as other related mechanical engineering content. Consequently, the MET section is also responsible for the design, development and supervision of the proton accelerator and tungsten target in terms of civil and infrastructure design for the physical plant. In parallel, ESS has set stringent goals for high availability and reliability on the machines during operations. In order to deliver these goals and monitor the aging status of critical parts of the machines, prototypes and one-of-a-kinds, the MET section has developed and currently implements Structural Health Monitoring (SHM) program on the accelerator primarily and other machines for Operations. The innovative strategy and application of Non-Destructive Testing for Machines (NDTM) is under development by the MET section with the leading benefit of utilizing the technology of Resonant Ultrasound Spectroscopy (RUS). Both reference and irradiated samples undergo RUS measurements to obtain spectral responses of the dedicated materials, for machine reliability and operations availability purposes.

The latest generation of light sources, the Free Electron Lasers that are capable of delivering high-intensity photon beams of unprecedented brilliance and quality, provide a substantially novel way to probe matter with a very high, largely unexplored potential for science and innovation. The CompactLight Collaboration intends to design a hard X-ray FEL facility beyond today’s state of the art using the latest concepts for bright electron photoinjectors, very high-gradient X-band structures at 12 GHz, and innovative compact short-period undulators. When compared to existing facilities, the proposed facility will benefit from a lower electron beam energy, due to the enhanced undulator performance, will be significantly more compact with a smaller footprint, as a consequence of both the lower energy and the high-gradient X-band structures, and will have a much lower electrical power demand. This paper gives an overview of different candidate photocathode materials for use in conjunction with a laser and presents the proposed design of the photocathode and the related laser. Also presented are the e-gun with solenoid selection and design, together with relevant simulation results.

Scintillation detectors with SiPM readout are developed for trigger systems and neutron time-of-flight measurements in the framework of the NICA project at JINR. Some detectors are operated in a strong magnetic field of the BM@N and MPD setups. New projects of detectors with picosecond time resolution for trigger of nucleus–nucleus collisions in collider experiment and neutron time-of-flight measurements are discussed.

Low energy threshold detectors are necessary in many frontier fields of experimental physics. In particular, these are extremely important for probing possible dark matter (DM) candidates. We present a novel detection approach that exploits the energy levels of atoms maintained at cryogenic temperature. We exploit laser-assisted transitions that are triggered by the absorption of the incident particle in the material and lead to the emission of a fluorescent photon or an electron. In this approach, the incident particle will in fact excite the first low-lying energy level that is then up-converted using an opportune narrow-band laser system. Two different detection schemes are thus possible in our active material: one is based on a photon signal while the other takes advantage of high efficiency in-vacuum charge detection.

Directional detection plays an important role in the search for rogue or illicit radioactive sources but is often complicated by Poisson statistics, large distances, and various sources of noise. A currently used directional detection method involves extracting the angular information of a source’s location from a cluster of detectors in a set geometry. Traditional algorithms designed to process detected data typically involve performing a least squares assessment against a database prepopulated with detector responses of known source locations. These algorithms perform best when the standoff distance is like that available in the prepopulated database; they lose accuracy when distances and environments of measurements are not well represented in the database. Analysis of highly variable and noisy data can often benefit from the robustness of machine learning, which has been implemented in applications such as isotope identification and radium mapping. This work aims to investigate the utility of machine learning algorithms capable of analyzing data with large amounts of statistical variability to improve directional location capabilities for large area source searches. Preliminary results with a fully connected residual neural network include the successful source location for simulated search scenarios to within 1 degree in 24% of trials. The same simulated data analyzed using traditional methods resulted in 1 degree location for 11% of trials. The traditional and neural network algorithms were compared in terms of error and accuracy as well performance as a function of distance for a simulated dataset of source searches. Results indicate that more robust algorithms, such as the implemented neural network, can improve system-inherent accuracy and over all directional capabilities.

The ${}^{235}$U(n,f) cross section plays a key role for nuclear physics due to its widespread use as a standard reference for neutron cross section measurements and for neutron flux measurements. Recent experimental data of the fission cross section have suggested the presence of discrepancies around 6–8% with respect to the most used libraries, precisely in the range between 10 keV and 30 keV. In order to shed light on this disagreement, an accurate measurement of the ${}^{235}$U(n,f) fission cross section has been performed at n_TOF facility @CERN, using the standard reactions ⁶Li(n,t) and ${}^{10}$B(n,$\alpha )$ as reference. A custom experimental setup based on a stack of silicon detectors sandwiched between pairs of ${}^{235}$U, ⁶Li and ${}^{10}$B targets, has been installed along the neutron beam line to intercept the same neutron flux, allowing the detection of the fission fragments and the products of the reference reactions at the same time. Such a technique allows calculation of the cross section via the “ratio method”, by normalizing the ${}^{235}$U(n,f) reaction yields with respect to the reference reactions and to the recommended data in the IAEA libraries; in particular, the integral between 7.8 and 11 eV has been chosen. Accurate Monte Carlo simulations have allowed evaluation of the neutron absorption in the different layers, as well as the detection efficiency of each detector. The data are in excellent agreement with the standard values and highlight the overestimation of the ${}^{235}$U(n,f) cross section between 9 and 18 keV in the most recent libraries.

Recent results in the field of film dosimetry demonstrated that the Green–Saunders equation, a solution of the logistic equation describing phenomena of kinetics of chemical reactions, is the absolute calibration function for all radiochromic film types. Taking advantage of the new opto-electronics-based radiochromic film reading method, which allows real-time measurements of the spectral response of radiochromic films, we confirm that the film darkening is ruled by the Green–Saunders equation independently both from the reading instrument or the choice of the observable used for the calibration. In order to demonstrate it, we exposed an XR-QA2 Gafchromic film to ⁹⁰Sr/⁹⁰Y beta rays up to 1400 mGy. Film spectra are recorded in real-time. The calibration is performed by means of two analytic methods: evaluation of the integral under the curves from 500 nm to 645 nm and evaluation of the intensity at 570, 600 and 643 nm. Experimental data fit to the Green–Saunders equation for both methods.

In this paper, we report recent results obtained in the development of digital pulse processing mathematics for prompt fission neutron (PFN) investigations using a twin ionization chamber (TIC) along with a fast neutron time-of-flight detector (ND). Due to some ambiguities in the literature concerning a pulse induction on TIC electrodes by fission fragment (FF) ionization, we first presented a detailed mathematical analysis of FF signal formation on the TIC anode. The analysis was done using the Shockley–Ramo theorem, which gives the relation between charged particle motion between TIC electrodes and the so-called weighting potential. The weighting potential was calculated by direct numerical solution of the Laplace equation (neglecting space charge) for the TIC geometry and ionization caused by FFs. Formulae for GI correction and digital pulse processing algorithms for PFN time-of-flight measurements and pulse shape analysis are presented and used in experiments for PFN investigations of two reactions, ${}^{235}$U(n${}_{th}$,f) and ${}^{252}$Cf(sf). Results of the measurements were compared to literature data to demonstrate the feasibility of the new developed techniques. These results were necessary for the development of a new PFN investigation facility consisting of a position sensitive fission fragment detector combined with 32 liquid scintillation neutron detectors.

The measurement procedure based on the continuous thermal neutron beam modulation with a mechanical chopper was developed for delayed neutron yield measurement of the thermal neutron induced fission of ${}^{237}$Np. The idea of the procedure is similar to that widely used in modern computer communications to prevent unauthorized data access. The data is modulated with a predefined pattern before transmission to the public network, and only the recipient that has the modulation pattern is able to demodulate it upon receipt. For thermal neutron induced reaction applications, the thermal neutron beam modulation pattern was used to demodulate the measured delayed neutron intensity signals on the detector output, resulting in nonzero output only for the detector signals correlated with the beam modulation. The comparison of the method with the conventional measurement procedure was provided, and it was demonstrated that the cross-correlation procedure has special features making it superior to the conventional one, especially when the measured value is extremely small in comparison with the background. Due to the strong sensitivity of the measurement procedure on the modulation pattern of the neutron beam, one can implement the modulation pattern of a specific shape to separate the effect of the thermal part of the beam from the higher energy part in the most confident way in the particular experiment. The remarkable property of our method is related to the unique possibility of separation of the effects caused exclusively by thermal neutrons using the neutron time-of-flight measurement available on the IBR-2 pulsed reactor.

Progress in the establishment of a fast neutron beam reference facility for the non-destructive testing of concrete and other materials used in the nuclear industry is described. An additional area of interest is the development of methods for the independent verification of the alignment to regulatory codes of the constituent materials used in concrete mixes for nuclear facilities, both existing and planned. The project is based on the principle of analyzing the distributions in energy of the neutrons transmitted through the sample. Modern methods of spectrum unfolding allow such analyses to be undertaken without the need for the neutron beam to be ns-pulsed in order to measure neutron energies by time-of-flight. First measurements and analyses of mortar (concrete without large aggregate) using continuous beams of fast neutrons are presented.

The evaluation of nuclear fragmentation contribution on the delivered dose during particle therapy treatment is still an open point. The FOOT (FragmentatiOn Of Target) experiment aims to improve the actual knowledge of nuclear physics by measuring the differential cross section as a function of the energy and angle of the fragments produced when an external particle beam interacts with patent tissues during hadrontherapy treatment. Depending on the beam energy, the purpose of the measurements is dual: in the range of 150–400 MeV/u, they will be used to evaluate the side effects of the nuclear fragmentation in the hadrontherapy treatment, while in the range of 700–1000 MeV/u (typical of cosmic galactic rays) they will be used to optimize the shielding of the spaceship for long term space missions. The FOOT detector includes a pre-target region with a first plastic scintillator for time of flight (TOF) and trigger purpose, and a beam monitor drift chamber to evaluate the beam direction (necessary for the inverse kinematic approach); a magnetic spectrometer to measure the momentum of fragments; and finally a second plastic scintillator for deposited energy (ΔE) and TOF measurements, and a scintillating crystal calorimeter to measure the kinetic energy of fragments. These measurements will be combined to accurately identify the charge and mass of fragments. The experiment, funded by the INFN since September 2017, is in the construction phase. It has performed several test beams, while the full detector data taking is scheduled in the next few years. A full description of the different setups together with the performances obtained with the latest geometry studies are reported here.

High detection efficiency and good room temperature performance of Schottky barrier CdTe semiconductor detectors make them well suited especially for X-ray and gamma-ray detectors. In this contribution, we studied the effect of electron irradiation on the spectrometric performance of the Schottky barrier CdTe detectors manufactured from the chips of size $4\times 4\times 1$ mm³ with In/Ti anode and Pt cathode electrodes (Acrorad Co., Ltd.). Electron irradiation of the detectors was performed by 5 MeV electrons at RT using a linear accelerator UELR 5-1S. Different accumulated doses from 0.5 kGy up to 1.25 kGy were applied and the consequent degradation of the spectrometric properties was evaluated by measuring the pulse-height gamma-spectra of ${}^{241}\mathrm{Am}$ radioisotope source. The spectra were collected at different reverse voltages from 300 V up to 500 V. The changes of selected significant parameters, like energy resolution, peak position, detection efficiency and leakage current were monitored and evaluated to quantify the radiation hardness of the studied detectors. The results showed remarkable worsening of their spectrometric parameters even at relatively low applied doses of 1.25 kGy.

A recent advancement in a new high transparency monitor device based on Micro Channel Plate (MCP) has been proposed for monitoring flux and beam spatial profiles of neutrons. It consisted of the assembly of a very thin aluminum (Al) foil with a ⁶Li deposit placed along the beam and a MCP equipped with a phosphor screen readout viewed by a CCD camera outside the beam line. The peculiar feature of this device is that it uses an electrostatic mirror to minimize the perturbation of the neutron beam, i.e. absorption and scattering. It can be used at existing time-of-flight facilities, in particular at the neutron Time-of-Flight (n_TOF) facility at CERN, for monitoring the flux and the spatial profile of neutron beams in the thermal and epithermal region. In this contribution, the device experimental test carried out on the n_TOF neutron beam at CERN will be presented and discussed.