Physics

We present a measurement of the rate of correlated neutron captures in the WATCHBOY detector, deployed at a depth of approximately 390 meters water equivalent (m.w.e.) in the Kimballton Underground Research Facility (KURF). WATCHBOY consists of a cylindrical 2 ton water target doped with 0.1% gadolinium, surrounded by a 40 ton undoped water hermetic shield. We present a comparison of our results with the expected rate of correlated neutron captures arising from high-energy neutrons incident on the outside of the WATCHBOY shield, predicted by a hybrid FLUKA/GEANT4-based simulation. The incident neutron energy distribution used in the simulation was measured by a fast neutron spectrometer, the 1.8-ton Multiplicity and Recoil Spectrometer (MARS) detector, at the same depth. We find that the measured detection rate of two correlated neutrons is consistent with that predicted by simulation. The result lends additional confidence in the detection technique used by MARS, and therefore in the MARS spectra as measured at three different depths. Confirmation of the fast neutron flux and spectrum is important as it helps validate the scaling models used to predict the fast neutron fluxes at different overburdens.

Large liquid argon time projection chambers (LArTPCs), especially those operating near the surface, are susceptible to space charge effects. In the context of LArTPCs, the space charge effect is the build-up of slow-moving positive ions in the detector primarily due to ionization from cosmic rays, leading to a distortion of the electric field within the detector. This effect leads to a displacement in the reconstructed position of signal ionization electrons in LArTPC detectors ("spatial distortions"), as well as to variations in the amount of electron-ion recombination experienced by ionization throughout the volume of the TPC. We present techniques that can be used to measure and correct for space charge effects in large LArTPCs by making use of cosmic muons, including the use of track pairs to unambiguously pin down spatial distortions in three dimensions. The performance of these calibration techniques are studied using both Monte Carlo simulation and MicroBooNE data, utilizing a UV laser system as a means to estimate the systematic bias associated with the calibration methodology.

Plastic scintillators are widely used in high-energy and medical physics, often for measuring the energy of ionizing radiation. Their main disadvantage is their non-linear response to highly ionizing radiation, called ionization quenching. This nonlinearity must be modeled and corrected for in applications where an accurate energy measurement is required. We present a new experimental technique to granularly measure the dependence of quenching on energy-deposition density. Based on this method, we determine the parameters for four commonly used quenching models for two commonly used plastic scintillators using protons with energies of 30 MeV to 100 MeV; and compare the models using a Bayesian approach. We also report the first model-independent measurement of the dependence of ionization quenching on energy-deposition density, providing a purely empirical view into quenching.

The Advanced Molybdenum-based Rare process Experiment in its second phase (AMoRE-II) will search for neutrinoless double-beta (0{\nu}\b{eta}\b{eta}) decay of 100Mo in 200 kg of molybdate crystals. To achieve the zero-background level in the energy range of the double-beta decay Q-value of 100Mo, the radioactive contamination levels in AMoRE crystals should be low. 100EnrMoO3 powder, which is enriched in the 100Mo isotope, is used to grow the AMoRE crystals. A shielded array of fourteen high-purity germanium detectors with 70% relative efficiency each was used for the measurement of background activities in a sample of 9.6-kg powder. The detector system named CAGe located at the Yangyang underground laboratory was designed for measuring low levels of radioactivity from natural radioisotopes or cosmogenic nuclides such as 228Ac, 228Th, 226Ra, 88Y, and 40K. The activities of 228Ac and 228Th in the powder sample were 0.88 \pm 0.12 mBq/kg and 0.669 \pm 0.087 mBq/kg, respectively. The activity of 226Ra was measured to be 1.50 \pm 0.23 mBq/kg. The activity of 88Y was 0.101 \pm 0.016 mBq/kg. The activity of 40K was found as 36.0 \pm 4.1 mBq/kg.

We show that measured optical transmittance of an ultra thin gas depends on the detector size. To this end we conducted an experiment that compares transmittances measured in parallel with a pair of detectors with different diameters ranging from 2 μ m to 200 μ m. A Tunable Diode Laser Absorption Spectroscopy type system was used. Transmittance of ∼ 1e-2 mbar water vapor on NIR absorption line λ =1368.60 nm was measured using a 60 m long multi-pass cell placed inside the 300 l vacuum chamber. The result of the experiment shows higher transmittances when the measurement is performed using smaller detectors. The difference reaches as much as 1.23 ± 0.1 %, which is greater than 0 with >5 σ statistical significance. Qualitatively it is in agreement with the recently developed model of thin gas optical transmittance taking into account the quantum mechanical effects of spreading of the wave functions of individual gas particles.

The ion backflow is the main limiting factor for operating time projection chambers at high event rates. A significant effort is invested by many experimental groups to solve this problem. This paper explores a solution based on operating a passive bi-polar wire grid. In the presence of the magnetic field, the grid more effectively attenuates the ion current than the electron current going through it. Transparencies of the grid to electrons and ions are measured for different gas mixtures and magnitudes of the magnetic field. The results suggest that in a sufficiently strong magnetic field, the bi-polar wire grid can be used as an effective and independent device to suppress the ion backflow in time projection chambers.

The measurement of the angle between the interferometer front mirror and the diffracting planes is a critical aspect of the Si lattice-parameter measurement by combined x-ray and optical interferometry. In addition to being measured off-line by x-ray diffraction, it was checked on-line by transversely moving the analyser crystal and observing the phase shift of the interference fringe. We describe the measurement procedure and give the miscut angle of the 28 Si crystal whose lattice parameter was an essential input-datum for, yesterday, the determination of the Avogadro constant and, today, the kilogram realisation by counting atoms. These data are a kindness to others that might wish to repeat the measurement of the lattice-parameter of this unique crystal.

We report the first precision measurement of the superheat temperature required for bubble nucleation in liquid xenon of Δ T wall,ONB = (16.9 ± 0.5) K and Δ T wall,ONB = (19.2 +0.4 −1.1 ) K at pressures of P = (0.98±0.02) bar and P = ( 1.32 +0.05 −0.01 ) bar, respectively. Both are measured at a subcooled bulk fluid temperature of ∼ 162 K. A dedicated liquid xenon setup is used to measure the temperature at which bubble nucleation first appears on the flat surface of a resistor. The associated average heat flux at the surface of the resistor is determined using fluid dynamics simulations. Future experiments can use these experimental results to determine the likelihood of boiling in liquid xenon and to design effective thermal sinks that prevent bubble nucleation.

Hadron therapy is a novel treatment against cancer. The main advantage of this therapy causes less side effect in comparison to X-ray irradiation methods. Hadron therapy is just ahead of a significant breakthrough since this technique can be more precise, applying proton computer tomograph (pCT) to map the stopping power in the tissues. The research and development of a pCT require a fast detector to measure the energy of hadrons behind the patient. The best detector option is called hadron-tracking calorimeter, which consists of sandwich layers of silicon tracking detectors and absorber layers. The combination of measuring the trajectory (tracking process), and, in parallel, the energy of relativistic particles, can provide high-resolution hadron imaging. This semiconductor-based technology requires stable temperature and homogeneous cooling. I have worked in the development of this detector in the Bergen pCT Collaboration for two years. Last year my work was to investigate the temperature distribution in the calorimeter and examine two cooling concepts in detail. I performed both analytical and numerical calculations to analyze the temperature distribution of the calorimeter. The final decision about the design takes into account many engineering aspects, such as reliability, flexibility, and performance.

The development of detectors that provide high resolution in four dimensions has attracted wide-spread interest in the scientific community for several applications in high-energy physics, nuclear physics, medical imaging, mass spectroscopy as well as quantum information. In addition to high time resolution and thanks to the AC-coupling of the electrodes, LGAD silicon sensors can provide high resolution in the measurement of spatial coordinates of an incident minimum ionizing particle. Such AC-coupled LGADs, also known as AC-LGADs, are therefore considered as candidates for future detectors to provide 4-dimensional measurements in a single sensing device with 100 % fill factor. This article presents the first characterization of an AC-LGAD sensor with a proton beam of 120 GeV momentum at Fermilab. The sensor consists of strips with 80 μ m width, fabricated at Brookhaven National Laboratory. The signal properties, efficiency, spatial, and time resolution are presented. The experimental results show that the time resolution of such an AC-LGAD is compatible to standard LGADs with similar gain, and that AC-LGADs can be segmented with fine pitches as standard strip or pixel detectors.