Latest results of the LUX dark matter experiment

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.

PROSPECT – A precision reactor oscillation and spectrum experiment

PROSPECT is a reactor antineutrino experiment whose primary goals are to search for short-baseline neutrino oscillations and perform a precise measurement of the [Formula: see text]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.

Effects of electron irradiation on spectrometric properties of Schottky barrier CdTe radiation detectors

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 [Formula: see text] 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 [Formula: see text] 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.

Neutron transmission studies for concrete used in the nuclear industry

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.

Absolute calibration for film dosimetry

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.

New solid-state organic scintillators for fast and thermal neutron detection

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.

Measurement of the 235 U(n,f) cross section at n_TOF from thermal to 170 keV

The [Formula: see text]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 [Formula: see text]U(n,f) fission cross section has been performed at n_TOF facility @CERN, using the standard reactions 6Li(n,t) and [Formula: see text]B(n,[Formula: see text] as reference. A custom experimental setup based on a stack of silicon detectors sandwiched between pairs of [Formula: see text]U, 6Li and [Formula: see text]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 [Formula: see text]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 [Formula: see text]U(n,f) cross section between 9 and 18 keV in the most recent libraries.

Development of scintillation detectors with SiPM readout for the NICA project

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.

Nuclear fission investigation with twin ionization chamber

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, [Formula: see text]U(n[Formula: see text],f) and [Formula: see text]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.