A strong correlation between the LiDAR aerosol backscattering signal and air ion concentration in an enclosed underground room is detected for the first time. Nowadays, air ions monitoring is considered to be the main tool in the search for earthquake precursors, and the revealed correlation opens interesting opportunities of using LiDARs in the search for precursors. LiDARs allow sensing the dynamics of aerosols generated by air ions as condensation nuclei on long tracks along the laser beam, compared to pointwise detection of air ions utilizing appropriate sensors.

^235 U, ^238 U, ^239 Pu, and ^241 Pu antineutrino spectra were obtained from the measurement done by the near detector in Double Chooz experiment. Method of converting the experimental positron spectrum into the antineutrino one has been developed. The spectrum conversion function obtained from Monte Carlo calculations is used. The experimental antineutrino spectrum taken by this method corresponds to a certain fuel composition of a nuclear reactor core in parts of fission. It is possible to split the experimental antineutrino spectrum on nuclear fuel components spectra. Nuclear fuel individual isotope antineutrino spectra from uranium and plutonium were fitted by the calculated ones obtained by summation of individual fragment spectra. In the calculation, a strength function was used to describe the probability distribution of beta transitions for unknown fragments. The most accurate experimental cross sections of inverse beta decay reaction measured in a number of experiments are consistent with sections calculated on base of our experimental and calculated ^235 U, ^238 U, ^239 Pu, and ^241 Pu antineutrino spectra.

In addition to solar-neutrino fluxes, the Borexino detector is able to record antineutrino fluxes by employing reactions of elastic neutrino- and antineutrino-electron scattering. Antineutrino fluxes are produced within the Earth by natural-radioactivity isotopes and at the Earth’s surface by nuclear reactors of nuclear power plants. The most recent data accumulated by the Borexino detector are analyzed upon adding known antineutrino fluxes to the backgrounds and fluxes of solar neutrinos. This analysis made it possible to determine the flux of ^40 K antineutrinos, which turned out to be quite significant in magnitude. At the same time, all fluxes of solar neutrinos are compatible with the low-metallicity model of the Sun.

Measurements and correlation analysis of radon and aeroion concentrations in the underground laboratory were carried out. For pairs of variables “pressure — radon” and “pressure — ions”, a delayed pumping effect was found, similar to that previously observed for neutrons and gamma quanta. A simple phenomenological model explaining the results is presented. In this model, the reason for the delay is the gradual accumulation of radon in the room with a decrease in atmospheric pressure. The balance of the radon accumulation rate, the time of its radioactive decay and the characteristic time of pressure variations leads to an effective delay of 2 days between atmospheric pressure variations and radon concentration. Correlation analysis for the variables “pressure — ions” indicates that ions formed in the pores of the soil are already present in the air carrying radon to the laboratory. These ions make up approximately 21% of the total number of ions in the laboratory.

Получены новые спектры антинейтрино делящихся изотопов, составляющих топливо ядерного реактора. Использовалась комбинированная методика: расчет спектров антинейтрино и подгонка их к полученным в эксперименте на Ровенской АЭС в 80-х гг. прошлого века. Вычисленные с этими спектрами сечения делящихся изотопов хорошо описывают экспериментально полученное сечение в эксперименте Double Chooz \({}^{\mathrm{DC}}\sigma_{f}=(5.71\pm 0.06)\times 10^{-43}\) см \({}^{2}/\) деление. Полученное по расчетным спектрам сечение при том же составе активной зоны ядерного реактора \({}^{\mathrm{INR}}\sigma_{f}=(5.82\pm 0.12)\times 10^{-43}\) см \({}^{2}/\) деление. Для полученных спектров нет проблемы выпуклости спектра в области 5 МэВ в наблюдаемой энергии спектра позитронов.

The problem of detection of recoil electrons from neutrino scattering at low energies is considered. The use of the spectrum of an antineutrino tritium source ( ^3 H) with a small boundary energy of 18.6 keV is of interest for searches for the neutrino magnetic moment. At small neutrino energies, the electron binding energy in an atom becomes important. The cross sections for electrons of Cs, I, and Si atoms as possible targets in an experiment with a tritium source are calculated.

We provide the indication of high flux of $^{40}$K geo-antineutrino and geo-neutrino ($^{40}$K-geo-($\bar{\nu} + \nu$)) with Borexino Phase III data. This result was obtained by introducing a new source of single events, namely $^{40}$K-geo-($\bar{\nu} + \nu$) scattering on electrons, in multivariate fit analysis of Borexino Phase III data. Simultaneously we obtained the count rates of events from $^7$Be, $pep$ and CNO solar neutrinos. These count rates are consistent with the prediction of the Low metallicity Sun model SSM B16-AGSS09. MC pseudo-experiments showed that the case of High metallicity Sun and absence of $^{40}$K-geo-($\bar{\nu} + \nu$) can not imitate the result of multivariate fit analysis of Borexino Phase III data with introducing $^{40}$K-geo-($\bar{\nu} + \nu$) events. We also provide arguments for the high abundance of potassium in the Earth.

We provide the indication of high flux of $^{40}$K geo-antineutrino and geo-neutrino ($^{40}$K-geo-($\bar{\nu} + \nu$)) with Borexino Phase III data. This result was obtained by introducing a new source of single events, namely $^{40}$K-geo-($\bar{\nu} + \nu$) scattering on electrons, in multivariate fit analysis of Borexino Phase III data. Simultaneously we obtained the count rates of events from $^7$Be, $pep$ and CNO solar neutrinos. These count rates are consistent with the prediction of the Low metallicity Sun model SSM B16-AGSS09. MC pseudo-experiments showed that the case of High metallicity Sun and absence of $^{40}$K-geo-($\bar{\nu} + \nu$) can not imitate the result of multivariate fit analysis of Borexino Phase III data with introducing $^{40}$K-geo-($\bar{\nu} + \nu$) events. We also provide arguments for the high abundance of potassium in the Earth.

The results of analysis for the single events energy spectrum obtained in phase III of Borexino detector operation are considered. The experimental spectrum was fitted by a set of standard single events sources with the addition of events from potassium geo-antineutrinos (40K-geo-v) scattering on electrons. The addition of 40K-geo-v events makes it possible to improve the agreement of the experimental and fitted spectra. Experimental results indicate the presence of a significant amount of potassium in the Earth.

The authors consider results from analyzing the energy spectrum of single events obtained in Phase III of the Borexino experiment. The experimental spectrum is fitted by a set of standard sources of single events with the addition of events from potassium geo-antineutrino (40K-geo-ν) scattering on electrons. The adding of 40K-geo-ν events improves the agreement between the experimental and fitted spectra. Experimental results indicate considerable amounts of potassium in the Earth.

The possibility of large geo-antineutrino fluxes from ^40 K decays and the presence of an excess of positive electric charge in the Earth’s crust are predicted by the Hydridic Earth model. The data of the Borexino experiment do not contradict the proportion of potassium equal to several percent of the Earth’s mass and predicted by this model. The detection of an excess of positively charged air ions in underground laboratories can be explained by the presence of an excess of positive electric charge in the Earth’s crust. Further studies are needed to confirm the existence of both of these effects.

Рассматривается проблема регистрации электронов отдачи от рассеяния нейтрино при малых энергиях. Для поиска магнитного момента нейтрино представляет интерес использование спектра антинейтрино источника трития ( \({}^{3}\) Н) с малой граничной энергией (18.6 кэВ). При малых энергиях нейтрино начинает сказываться энергия связи электрона в атоме. Приводится расчет сечений для электронов атомов Cs, I и Si как возможных мишеней для эксперимента с тритиевым источником.

Low concentrations aerosols quantification is rather challenging for LIDAR instruments due to eye-safety restrictions so high energy pulses cannot be utilized to improve the sensitivity. Highly sensitive but eye-save LIDAR has been developed for the quantification of the water droplet aerosol which was induced by air ions. Few days sensing of aerosols in closed tunnel revealed a strong correlation between air optical transparency (LIDAR measurements) and concentrations of positive/negative ions (ion counter Sapphir 3-M). The correlation coefficient was observed to be almost unity for the air transparency signal and air ions unipolarity coefficient. High sensitivity of the water droplet aerosol quantification makes the developed eye-safe LIDAR a perspective instrument for space resolved measurements of the air ions distribution. Space and time resolved measurements of air ions exhalation can be a new instrument for tectonic activity study including new earthquake forecasting indicators search.

Low background segmented liquid scintillator detector, doped with an indium as a target for solar neutrino registration, can be used for measuring total solar neutrino spectrum including pp neutrinos. A detector consisting of small modules filled with liquid scintillator in the volume of 1–2 L is considered. Silicon matrices are used for light collection. The background of indium beta-activity is suppressed by triple coincidences. The detector of such a type can measure ^7 Be neutrino flux with high accuracy and independently check the measurement performed by the Borexino Collaboration.

U-235,U-238,Pu-239, and(241)Pu antineutrino spectra were obtained from the measurement doneby the near detector in Double Chooz experiment. Method of converting the experimental positron spectruminto the antineutrino one has been developed. The spectrum conversion function obtained from MonteCarlo calculations is used. The experimental antineutrino spectrum taken by this method corresponds to acertain fuel composition of a nuclear reactor core in parts offission. It is possible to split the experimentalantineutrino spectrum on nuclear fuel components spectra. Nuclear fuel individual isotope antineutrinospectra from uranium and plutonium were fitted by the calculated ones obtained by summation of individual fragment spectra. In the calculation, a strength function was used to describe the probability distribution of beta transitions for unknown fragments. The most accurate experimental cross sections of inverse beta decay reaction measured in a number of experiments are consistent with sections calculated on base of our experimental and calculated(235)U,U-238,Pu-239, and(241)Pu antineutrino spectra.

A modification of the LENS (Low Energy Neutrino Spectroscopy) project for spectroscopy of solar neutrinos with energies above about 715 keV on the basis of new technologies and solutions is examined. The respective detector employs $${}^{115}$$ In nuclei as a target for neutrinos. The creation of a detector containing about 200 t of a scintillator loaded with 10 t of indium will make it possible to measure, within five years, the energy spectra of solar neutrinos from $${}^{7}$$ Be, neutrinos from the CNO cycle, and $$pep$$ neutrinos with small systematic errors. The detector was simulated in the form of a set of cells of a liquid scintillator doped with indium (about 10 $${\%}$$ in weight). Necessary technical conditions for detector cells are formulated, and the possible counting rate for events induced by internal and external backgrounds and characterized by an energy release of 600 to 1600 keV is estimated. It is shown that such a detector is implementable, in principle.

New antineutrino spectra of fissile isotopes (^235U, ^238U, ^239Pu and ^241Pu) which are containing in a nuclear reactor fuel have been obtained. A combined technique was used: calculation of antineutrino spectra and their fitting to those obtained in the experiment at the Rovno NPP in the 80s of the last century. The cross sections of fissile isotopes calculated with these spectra describe well the cross section obtained experimentally in the Double Chooz experiment. The calculated cross section for the same reactor core composition is σ_f = (5.82 ± 0.12)×10^-43 cm^2/fission. It is the closest result between all predicted. The obtained spectra have the same "bump" as experimental ones in 5 MeV observed energy region.

We present the results of measurements of the air ion densities of both signs in the unventilated underground laboratory of the Moscow State University. We used the stationary station based on a Sapfir-3M modified air ion counter. We solved the problems of accuracy of relative measurements of air ion densities and stability of measurements in conditions of high humidity of underground cavities. We investigated the spatial distribution of air ion densities and their variability over time. An excess of positively charged air ions was found everywhere in the laboratory. The obtained data indicate the presence of a weak electric field directed downward in the underground laboratory. We observed the dependence of the air ion densities of both signs on the atmospheric pressure. We found the correlation of air ion densities with radon activity in the laboratory air and show that the ionization of air by alpha particles from the decay of radon and its daughter elements is the main source of air ions in closed underground cavities. A variant for explaining the presence of an excess of positive charge in underground cavities is proposed.

New antineutrino spectra of fissile isotopes entering into the composition of nuclear-reactor fuel are obtained. A method that combines a calculation of antineutrino spectra and a fit of the results to the spectra obtained experimentally at the Rovno nuclear power plant in the 1980s is used. The cross sections calculated for fissile isotopes by employing these spectra describe well the cross section of ^DCσ_f=(5.71± 0.06)× 10^-43 cm ^2/ fission obtained in the Double Chooz experiment. The cross section obtained on the basis of the calculated spectra at the same composition of the reactor core is ^INRσ_f=(5.82± 0.12)× 10^-43 cm ^2/ fission. For the resulting spectra, there is no problem of a bump in the region around 5 MeV in the observed energy spectrum of positrons.

This article describes the setup and performance of the near and far detectors in the Double Chooz experiment. The electron antineutrinos of the Chooz nuclear power plant were measured in two identically designed detectors with different average baselines of about 400 m and 1050 m from the two reactor cores. Over many years of data taking the neutrino signals were extracted from interactions in the detectors with the goal of measuring a fundamental parameter in the context of neutrino oscillation, the mixing angle θ13. The central part of the Double Chooz detectors was a main detector comprising four cylindrical volumes filled with organic liquids. From the inside towards the outside there were volumes containing gadolinium-loaded scintillator, gadolinium-free scintillator, a buffer oil and, optically separated, another liquid scintillator acting as veto system. Above this main detector an additional outer veto system using plastic scintillator strips was installed. The technologies developed in Double Chooz were inspiration for several other antineutrino detectors in the field. The detector design allowed implementation of efficient background rejection techniques including use of pulse shape information provided by the data acquisition system. The Double Chooz detectors featured remarkable stability, in particular for the detected photons, as well as high radiopurity of the detector components.