The paper examines the possibility of using 3D printing technology to manufacture structural elements of ionizing radiation detectors under low-background conditions. The results of measurements conducted with a scintillation detector housed in a housing made of PETG plastic are presented.

To create a prototype of a detector based on a neodymium-containing liquid organic scintillator for the search for neutrinoless double-beta decay of ^150 Nd, measurements of the spectra of radioactive impurities from various materials used in the manufacture of the detector were carried out using low-background semiconductor gamma spectrometers at the Baksan Neutrino Observatory, Institute of Nuclear Research of the Russian Academy of Sciences. The potential use of 3D printing in low-background conditions was considered. This could potentially allow creating the detector structural elements with a record-low content of radioactive impurities for experiments in neutrino astrophysics, dark matter searches, neutrinoless double-beta decay experiments. The activity of radioactive impurities in plastic parts produced on a 3D printer, which were intended for use in creating a prototype of a detector and its low-background shielding, were measured.

The internal detector background arising in searches for neutrinoless double-beta decay of the isotope ^150 Nd from the two-neutrino beta decay of the same isotope is calculated. The calculation is performed for a detector several liter in volume based on a neodymium-doped liquid organic scintillator and implemented in various configurations and at various neodymium concentrations of up to 5.5 g/l. Limits on the detector sensitivity in searches for neutrinoless double-beta decay of the isotope ^150 Nd are obtained.

The energy resolution is calculated for a neodymium-containing liquid organic scintillation detector (Nd-OS) with a volume of several liters to search for neutrinoless double beta decay of 150 Nd as a function of the neodymium concentration up to 5 g/L. The results are presented in detailed tables and graphs.

Metal-loaded liquid organic scintillators (MeLS) are discussed from the point of view of light yield at high metal loading (Gd, Nd, Zr, In). It is shown that, when metal β -diketonates are introduced into the scintillator, its light yield is always lower than when carboxylates are used, which is explained by the structural difference between these complexes. The nature of the metal in some cases (Nd) also affects the light attenuation length and, consequently, the MeLS light yield. The composition of the solvent (the fraction of aromatics in the main solvent) and the degree of purification of the introduced metal complex also have a significant effect on the light yield.

Рассматриваются новые базовые растворители синтин и ракетное топливо Т-6 для создания жидких органических сцинтилляторов. Измерена длина ослабления света этих растворителей (как полученных от производителя, так и после хроматографической очистки на Al \({}_{2}\) O \({}_{3}\) ), а также относительный световыход сцинтилляторов, созданных на их основе. Методом хроматомасс-спектрометрии и УФ-спектрофотометрии определен химический состав синтина. На основе смеси синтина и псевдокумола создан Nd-содержащий сцинтиллятор ( \(C_{\mathrm{Nd}}\) 9 г/л) и измерен его световыход (LY 60 \({\%}\) ) по отношению к сцинтиллятору на основе линейного алкилбензола (ЛАБ).

Synthine and T-6 propellant are studied as new basic solvents for creating liquid organic scintillators. The light attenuation length in these solvents (both those obtained from the manufacturer and those subjected to chromatographic purification on Al _2 O _3 ) was measured along with the relative light yield of scintillators based on them. The chemical composition of synthine was determined by the method of chromato-mass spectrometry and UV spectrophotometry. A Nd-loaded scintillator ( C_Nd 9 g/L) based on a synthine–pseudocumene mixture was created, and its light yield (LY 60 % ) was measured with respect to a scintillator based on linear alkyl benzene (LAB).

Because of a high energy of the neutrinoless double-beta decay (0ν2β) of the isotope 150Nd and a high value of the daughter-nucleus charge Zf, 150Nd is one of the most promising isotopes for 0ν2β-decay searches. A 150Nd-containing detector on the basis of a liquid organic scintillator permits employing large isotope masses. Requirements on the radiation purity of the neodymium sample used are determined. The possible design of a large-scale detector of this type and expected results are considered.

Constructing a large-volume detector filled with 10 kt of liquid scintillator is envisaged at the Baksan Neutrino Observatory in the Caucasus. This is aimed at detecting fluxes of natural neutrinos with energies up to 100 MeV. The predicted fluxes of such neutrinos and the response of the proposed detector are discussed. This facility is conceived as an integral part of the worldwide net of neutrino detectors aimed at measuring the natural neutrino fluxes.

I. R. Barabanov 1 , L. B. Bezrukov 1 , A. V. Veresnikova 1 , Yu. M. Gavrilyuk 1 , A. M. Gangapshev 1 , V. Yu. Grishina 1 , V. I. Gurentsov 1 , V. V. Kazalov 1 , S. D. Krokhaleva 1,2 , V. V. Kuz’minov 1 , A. S. Kurlovich 1 , B. K. Lubsandorzhiev 1 , S. B. Lubsandorzhiev 1 , A. K. Mezhokh 1 , V. P. Morgalyuk 2 , P. Yu. Naumov 4 , G. Ya. Novikova 1 , V. B. Petkov 1 , A. M. Pshukov 1 , A. Yu. Sidorenkov 1 , V. V. Sinev 1,* , Sh. I. Umerov 1 , E. A. Yanovich 1 , T. Enqvist 5 , P. Kuusiniemi 5 , J. Joutsenvaara 5 , A. Virkajarvi 5 and V. P. Zavarzina 1

A series of measurements has been started where the C-14 concentration is determined from several liquid scintillator samples. A dedicated setup has been designed and constructed with the aim of measuring concentrations smaller than 10(-18). Measurements take place in two underground laboratories: in the Baksan Neutrino Observatory, Russia, and in the new Callio Lab in the Pyhasalmi mine, Finland. Low-energy neutrino detection with a liquid scintillator requires that the intrinsic C-14 concentration in the liquid is extremely low. In the Borexino CTF detector the concentration of 2 x 10(-18) has been achieved being the lowest value ever measured. In principle, the older the oil or gas source that the liquid scintillator is derived from and the deeper it situates, the smaller the C-14 concentration is supposed to be. This, however, is not generally the case and the concentration is probably due to the U and Th content of the local environment.

A setup for measuring natural-radioactivity backgrounds and ultralow concentrations of the isotope 14 C in samples of a liquid organic scintillator was created at the low-background laboratory of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) at a depth of 4900 mwe. The concentration of the radiocarbon 14C in a sample of a scintillator based on domestically produced linear alkylbenzene was measured, and it was found that 14 C/ 12 C (3.3 ± 0.5) × 10 −17 .

We are going to perform a series of measurements where the 14C/12 C ratio will be measured from several liquid scintillator samples with a dedicated setup. The setup is designed with the aim of measuring ratios smaller than 10-18. Measurements take place in two underground laboratories: in the Baksan Neutrino Observatory, Russia and in the Pyhäsalmi mine, Finland. In Baksan the measurements started in 2015 and in Pyhäsalmi they start in the beginning of 2015. In order to fully understand the operation of the setup and its background contributions a development of simulation packages has also been started. Low-energy neutrino detection with a liquid scintillator requires that the intrinsic 14C content in the liquid is extremely low. In the Borexino CTF detector at Gran Sasso, Italy the 14C/12C ratio of 2 × 10-18 has been achieved being the lowest 14C concentration ever measured. In principle, the older the oil or gas source that the liquid scintillator is derived of and the deeper it situates, the smaller the 14C/12C ratio is supposed to be. This, however, is not generally the case, and the ratio is probably determined by the U and Th content of the local environment.

A procedure was developed for removing uranium, thorium, and potassium from a liquid organic scintillator based on linear alkylbenzene (LAB) by stripping with water. The volume ratio of the scintillator and water in the process should be no less than 1: 5. The attenuation length ( L 420 ) of LAB after treatment with water does not change and is as high as 13.0 ± 1.8 m. The solubility of water in LAB and of LAB in water was determined to be 46 and 5.1 ppm, respectively.

The AMoRE (Advanced Mo-based Rare process Experiment) project is a series of experiments that use advanced cryogenic techniques to search for the neutrinoless double-beta decay of \mohundred. The work is being carried out by an international collaboration of researchers from eight countries. These searches involve high precision measurements of radiation-induced temperature changes and scintillation light produced in ultra-pure \Mo[100]-enriched and \Ca[48]-depleted calcium molybdate ($\mathrm{^{48depl}Ca^{100}MoO_4}$) crystals that are located in a deep underground laboratory in Korea. The \mohundred nuclide was chosen for this \zeronubb decay search because of its high $Q$-value and favorable nuclear matrix element. Tests have demonstrated that \camo crystals produce the brightest scintillation light among all of the molybdate crystals, both at room and at cryogenic temperatures. $\mathrm{^{48depl}Ca^{100}MoO_4}$ crystals are being operated at milli-Kelvin temperatures and read out via specially developed metallic-magnetic-calorimeter (MMC) temperature sensors that have excellent energy resolution and relatively fast response times. The excellent energy resolution provides good discrimination of signal from backgrounds, and the fast response time is important for minimizing the irreducible background caused by random coincidence of two-neutrino double-beta decay events of \mohundred nuclei. Comparisons of the scintillating-light and phonon yields and pulse shape discrimination of the phonon signals will be used to provide redundant rejection of alpha-ray-induced backgrounds. An effective Majorana neutrino mass sensitivity that reaches the expected range of the inverted neutrino mass hierarchy, i.e., 20-50 meV, could be achieved with a 200~kg array of $\mathrm{^{48depl}Ca^{100}MoO_4}$ crystals operating for three years.

The light yield in CaMoO 4 scintillating crystals irradiated with α particles and γ rays from 241 Am and 137 Cs radioactive isotopes, respectively, have been measured. It is shown that the light yield in this crystal for γ rays, measured in the wavelength range of 400–700 nm at room temperature (22°C), is ∼3000 photons/MeV, and the ratio α/β is ∼0.25.

Search for neutrino-less double beta decay of Mo-100 is proposed using active method with Ca (MoO4)-Mo-100 scintillation crystals which show the brightest scintillation light among variety of inorganic scintillation materials containing Mo. Study of X-ray luminescence and scintillation properties such as energy response, number of photoelectrons/keV, absolute light yield, decay time, pulse shape discrimination and radioactive contamination of CaMoO4 crystals grown by the Czochralski method with different conditions are presented. Further R&D of resolution optimization, crystal quality improvement and background reduction are underway. Significant improvement of sensitivity to neutrino-less double beta decay can be achieved by using Mo-100 enriched Ca (MoO4)-Mo-100 crystals with good energy resolution and low background. Further reduction of background induced by Ca-48 two neutrino double beta decay can be achieved by using Ca-48 depletion. We are planning to install several kilograms of Ca (MoO4)-Mo-100 crystals depleted in Ca-48 at underground laboratory for the neutrino-less double beta decay experiment in the near future.