Showing papers by "Ekaterina Borisova published in 2023"

First observation of neutral bremsstrahlung electroluminescence in liquid argon

Abstract: Recent discovery of additional mechanism of electroluminescence (EL) in noble gases due to neutral bremsstrahlung (NBrS) effect led to a prediction that NBrS EL should be present in noble liquids as well. A rigorous theory of NBrS EL in noble liquids was developed accordingly in the framework of Cohen-Lekner and Atrazhev approach. In this work, we confirm this prediction: for the first time, visible-range EL has been observed in liquid Ar at electric fields reaching 90~kV/cm, using Gas Electron Multiplier (GEM) and Thick GEM (THGEM) structures. Absolute light yields of the EL were measured and found to be in excellent agreement with the theory, provided that momentum-transfer cross section of electron-atom scattering (instead of energy-transfer one) is used for calculation of NBrS cross section.

Using the Two-Phase Emission Detector RED-100 at NPP to Study Coherent Elastic Neutrinos Scattering off Nuclei

Abstract: The two-phase emission detector RED-100 with 130 kg of liquid xenon as a working medium has been exhibited at a distance of 19 m from the core of the VVER-1000/320 nuclear power reactor at the fourth power unit of the Kalinin Nuclear Plant Power in 2021–2022. Due to the high sensitivity of the detector for weak ionization signals (down to single electrons), the detector has been used to search for the elastic coherent scattering of reactor electron antineutrinos off xenon nuclei. However, the observation of ~30 kHz single-electron noise did not quite allow for an effective selection of the useful events. The next experiment with the RED-100 detector is considered to be arranged with 62 kg of liquid argon as a working medium. The advantages of this approach are discussed in this paper.

PDT and PD of Human Glioblastoma with 5-ALA/PpIX and n-GalLuPc

Abstract: Glioblastoma (GBM) is the most common and severe type of brain tumor. Surgery and subsequent radiotherapy and chemotherapy do not lead to sufficient results in the treatment of this type of malignancy, mostly due to its specific morphology. Only about 6% of the patients of advanced age survive 5 years after being diagnosed with GBM. Therefore, scientists are working on alternative therapies that would lead to more effective and long-term treatment of glioblastoma. Photodynamic therapy (PDT) and photodiagnostics (PD) are such unconventional methods for treating and diagnosing malignant tumors. During our work, more than 20 experiments were carried out with stem cells cultivated from human glioblastoma tumors. We used two types of photosensitizers – delta-aminolevulinic acid (5-ALA) as a precursor of protoporphyrin IX (PpIX) and non-peripherally galactosylated lutetium phthalocyanine (n-GalLuPc). After the irradiation supernatant samples of photosensitizer-treated cell lines were used for evaluation of photosensitizers’ accumulation in the cell lines investigated. The emitting spectra is correlated with the total induced cell death in the treated cells. After considering the overall effectiveness of the two photosensitizers, n-GalLuPc showed higher efficiency. These in vitro results prompted the future investigation of the phthalocyanine for in vivo application in GBM treatments.

Unraveling the puzzle of slow components in gaseous argon of two-phase detectors for dark matter searches using Thick Gas Electron Multiplier

Abstract: The effect of proportional electroluminescence (EL) is used to record the primary ionization signal (S2) in the gas phase of two-phase argon detectors for dark matter particle (WIMP) searches and low-energy neutrino experiments. Our previous studies of EL time properties revealed the presence of two unusual slow components in S2 signal of two-phase argon detector, with time constants of about 4-5 $\mu$s and 50 $\mu$s. The puzzle of slow components is that their time constants and contributions to the overall signal increase with electric field (starting from a certain threshold), which cannot be explained by any of the known mechanisms of photon and electron emission in two-phase media. There are indications that these slow components result from delayed electrons, temporarily trapped during their drift in the EL gap on metastable negative argon ions of yet unknown nature. In this work, this hypothesis is convincingly confirmed by studying the time properties of electroluminescence in a Thick Gas Electron Multiplier (THGEM) coupled to the EL gap of two-phase argon detector. In particular, an unusual slow component in EL signal, similar to that observed in the EL gap, was observed in THGEM itself. In addition, with the help of THGEM operated in electron multiplication mode, the slow component was observed directly in the charge signal, unambiguously confirming the effect of trapped electrons in S2 signal. These results will help to unravel the puzzle of slow components in two-phase argon detectors and thus to understand the background in low-mass WIMP searches.

Diagnosis of skin lesions through prototype clinical device with diffuse reflectance spectroscopy

Abstract: Cancerous and precancerous skin conditions occupy one of the leading places in oncology. Early detection of suspects and temporary referrals to a specialist are critical to successful treatment. Numerous optical techniques are used for obtaining a new data from cutaneous neoplasia. Diffuse–reflectance spectroscopy is one of these techniques due to its high sensitivity in detecting subtle tissue alterations. Light scattering events inside the skin tissues change significantly in the development stage of skin lesions. These changes in the tissue scattering properties affect the diffuse reflectance spectrum and provide classification of different skin lesions based on diffuse reflectance measurements. We have investigated diffuse–reflectance spectroscopy for diagnostic of skin lesions and as a result, an optical device for clinical application was developed. The current study shows the obtained results by the prototype device for the reflective ability of pigmented and non-pigmented skin benign, dysplastic, and malignant cutaneous lesions in vivo.

Evidence for the production of Ar$_2^{*-}$ metastable negative molecular ions in two-phase argon detectors for dark matter searches

Abstract: The recent studies of electroluminescence (EL) properties in two-phase argon detectors for dark matter searches have revealed the presence of unusual delayed pulses in the EL signal in the form of two slow components with time constants of about 5 and 50 $\mu$s. These components were shown to be present in the charge signal itself, which clearly indicates that drifting electrons are temporarily trapped on two states of metastable negative argon ions which have never been observed before. In this work, using the pressure dependence of the ratio of slow component contributions measured in experiment, it is shown that these states are those of two types of metastable negative molecular ions, $\mathrm{Ar}_2^{*-}(b \ ^4\Sigma_u^-)$ and $\mathrm{Ar}_2^{*-}(a \ ^4\Sigma_g^+)$ for the higher and lower energy level respectively.