The CRAB facility at the TU Wien TRIGA reactor: status and related physics program

A series of experiments has been conducted at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) in order to study the possibility of determining the moisture content of coke using a standard neutron source. The proposed method is based on a measurement of the spectrum of prompt γ rays emitted when samples are irradiated by fast and/or thermal neutrons. The moisture content is determined from the area of the peaks of characteristic γ rays produced in the radiative capture of thermal neutrons by the proton (Eγ = 2.223 MeV) and inelastic scattering of fast neutrons by 16O (Eγ = 6.109 MeV). The 239Pu–Be neutron source (〈E n 〉 ~ 4.5 MeV) with an intensity of ~5 × 106 n/s was used to irradiate the samples under study. A scintillation detector based on a BGO crystal was used to register the characteristic γ radiation from the inelastic fast neutron scattering and slow (thermal) neutron capture. This paper presents the results of humidity measurement in the range of 2–50% [1, 2].

Cryogenic detectors can detect the smallest energy depositions via the scattering of the incoming particle with the detector material. The deposited energy leads to minimal temperature rises of a few μ K , read out via transition edge sensors and SQUIDs. Using scintillating crystals as detector material offers the possibility of discriminating between nuclear recoils from dark matter scattering and electromagnetic background events. The CRESST experiment pioneered this technology and is still among the most sensitive experiments searching for sub-GeV dark matter particles. The technology is now also used by other experiments for dark matter searches (COSINUS) and for measuring coherent elastic neutrino-nucleus scattering (NUCLEUS). We discuss cryogenic detectors’ detection principle and their application. We present the latest dark matter results from CRESST, a new type of background, and the status of the COSINUS and NUCLEUS experiments. This article is part of the theme issue ‘The particle-gravity frontier’.

A diffusion cloud chamber was built which had to be of a material with a relatively low macroscopic cross section for radiative capture of thermal neutrons. 61-S aluminum alloy was used. A polystyrene cylinder of a diameter a little smaller than that of the cylindrical body is used to insulate the sensitive region from the outside walls and to provide by means of a tape heater, the right temperature distribution along the boundaries of the sensitive region. (M.H.R.)

We have measured the cross section for radiative capture of thermal neutrons on $^{3}\mathrm{He}$. The measured cross section of 54\ifmmode\pm\else\textpm\fi{}6 \ensuremath{\mu}b is used to estimate the astrophysical S factor for the reaction $^{3}\mathrm{He}$(p,${e}^{+}$\ensuremath{\nu}${)}^{4}$He which gives rise to high-energy neutrinos from the Sun.

. The problem of introducing pulse neutron probing in the process of geological and geophysical studies has been updated. The main factors that increase the sensitivity and information content of pulse methods in comparison with stationary neutron methods have been considered. It has been shown that the efficiency of pulse neutron probing depends on the length of the probe, time and energy characteristics of the equipment used. The principal features of various modifications of pulse neutron probing for solving geological and geophysical problems have been noted. The aspects of the efficient use of pulse modification in neutron gamma-ray spectrometry and inelastic scattering of fast neutrons have been discussed. Improved modifications of neutron probing based on the complex application of instrumental signals arising from inelastic scattering of fast and radiative capture of thermal neutrons have been proposed

PROMPT GAMMA RAYS FROM RADIATIVE CAPTURE OF THERMAL NEUTRONS BY ELEMENTS FROM HYDROGEN THROUGH ZINC

The threshold electrodisintegration cross section and electromagnetic form factors of the deuteron are calculated by using the Argonne ${\mathit{v}}_{14}$ model for the nucleon-nucleon interaction to generate the bound- and scattering-state wave functions. The exchange-current operator is constructed to be consistent with the interaction model. The calculated electrodisintegration cross section is in good qualitative agreement with the experimental data over the whole measured momentum-transfer range, and is sensitive to the electromagnetic form factors of the nucleon. The calculated form factors appear to be in good agreement with the empirical values, although uncertainties in the isoscalar model-dependent exchange-current contributions and nucleon electromagnetic form factors prevent definite predictions to be made at high values of momentum transfer. Finally, the cross section for radiative capture of thermal neutrons on protons is found to be within less than 1% of the measured value.

Isotope effects in radiative thermal neutron capture

SuperCDMS SNOLAB will be a next-generation experiment aimed at directly detecting low-mass (< 10 GeV/c$^2$) particles that may constitute dark matter by using cryogenic detectors of two types (HV and iZIP) and two target materials (germanium and silicon). The experiment is being designed with an initial sensitivity to nuclear recoil cross sections ~ 1 x 10$^{-43}$ cm$^2$ for a dark matter particle mass of 1 GeV/c$^2$, and with capacity to continue exploration to both smaller masses and better sensitivities. The phonon sensitivity of the HV detectors will be sufficient to detect nuclear recoils from sub-GeV dark matter. A detailed calibration of the detector response to low energy recoils will be needed to optimize running conditions of the HV detectors and to interpret their data for dark matter searches. Low-activity shielding, and the depth of SNOLAB, will reduce most backgrounds, but cosmogenically produced $^{3}$H and naturally occurring $^{32}$Si will be present in the detectors at some level. Even if these backgrounds are x10 higher than expected, the science reach of the HV detectors would be over three orders of magnitude beyond current results for a dark matter mass of 1 GeV/c$^2$. The iZIP detectors are relatively insensitive to variations in detector response and backgrounds, and will provide better sensitivity for dark matter particle masses (> 5 GeV/c$^2$). The mix of detector types (HV and iZIP), and targets (germanium and silicon), planned for the experiment, as well as flexibility in how the detectors are operated, will allow us to maximize the low-mass reach, and understand the backgrounds that the experiment will encounter. Upgrades to the experiment, perhaps with a variety of ultra-low-background cryogenic detectors, will extend dark matter sensitivity down to the "neutrino floor", where coherent scatters of solar neutrinos become a limiting background.

A novel active veto prototype detector with an inner target for improved rare event searches

Parity non-conservation in radiative thermal neutron capture by protons

RECENT investigations have shown that crystal defects determine the fate of the fragments generated in solids by radiative thermal neutron capture as well as the kinetics of subsequent annealing reactions1,2. So far, there has been no experimental evidence for the influence of defects on the annealing of chemical damage produced in solids by irradiation. We have now obtained such evidence in the case of annealing in lead nitrate.

The Cryogenic Underground Test (CUTE) facility will be located 2 km underground in the SNOLAB laboratory, near Sudbury (Ontario, Canada). It is primarily designed to test the performances of cryogenic detectors of the Super-Cryogenic Dark Matter Search (SuperCDMS) experiment which will be installed next to CUTE. As a facility, it will also be accessible to scientists developing innovative cryogenic detectors for rare events search like dark matter or double-beta decay. The low temperature required to operate the cryogenic detectors is reached via an advanced dry dilution refrigerator from CryoConcept (France). The ‘Ultra Quiet Technique’ (UQT®) reduces the vibration transmission by using a proprietary gas-coupled thermal link between the two-stage pulse tube and the cryostat. In order to install the cryostat into a shielding water tank, we have developed a suspension system which decouples the cryostat from the environment with a low stiffness support, making a mechanical low-pass filter with a roll-off below 2 Hz for the vertical attenuation. We report the design choices made for the mechanical architecture to limit the vibration transmission and the material selection to achieve a low radioactive background rate in the detector. The expected background rate is less than 5 counts/day per kg of Ge detector in the 0–1 keV energy range.

The NUCLEUS experiment aims for the detection of coherent elastic neutrino-nucleus scattering at a nuclear power reactor with gram-scale, ultra-low-threshold cryogenic detectors. This technology leads to a miniaturization of neutrino detectors and allows to probe physics beyond the Standard Model of particle physics. A 0.5 g NUCLEUS prototype detector, operated above ground in 2017, reached an energy threshold for nuclear recoils of below 20 eV. This sensitivity is achieved with tungsten transition edge sensors which are operating at temperatures of 15 mK and are mainly sensitive to non-thermal phonons. These small recoil energies become accessible for the first time with this technology, which allows collecting large-statistics neutrino event samples with a moderate detector mass. A first-phase cryogenic detector array with a total mass of 10 g enables a 5-sigma observation of coherent scattering within several weeks. We identified a suitable experimental site at the Chooz Nuclear Power Plant and performed muon and neutron background measurements there. The operation of a NUCLEUS cryogenic detector array at such a site requires highly efficient background suppression. NUCLEUS plans to use an innovative technique consisting of separate cryogenic anticoincidence detectors against surface backgrounds and penetrating (gamma, neutron) radiation. We present first results from prototypes of these veto detectors and their operation in coincidence with a NUCLEUS target detector.

A high precision study of the gamma ray spectrum following neutron capture by a target of natural sulfur is reported. The energy precision obtained has permitted construction of decay schemes for33S and35S. In the case of the former isotope a total of 22 levels have been identified while for the latter and much weaker reaction 7 states have been observed. While some transitions attributable to capture by33S are observed, their weakness prohibited detailed analysis. The neutron separation energies, based upon the14N(n, γ)15N standard are found to be 8,641.60 (3) keV and 6,985.84 (5) keV for33S and35S respectively.