I. V. Orekhov

A method for registration of the coherent scattering reactor antineutrino on nuclei using a three-section low-background proportional counter was proposed. It is planned to use argon and xenon as the working substance. As has been shown on a test bench, pulse shape discrimination can effectively suppress the background from electromagnetic interference and microphonic effects in the energy range from 20 to 100 eV where the effect of coherent scattering of neutrinos on nuclei is expected with a factor of about 10³. Problems of the neutron background generated by cosmic-ray muons are analyzed. The scheme of the experimental setup is presented.

Data obtained by the radiotracer method on a specially designed test bench show that a lithium oxide film serves as a trap for beryllium extracted from lithium. No tangible chemisorption of beryllium on the titanium surface is observed. These finding are used to design and fabricate a lithium detector for solar neutrinos. They will also find application in designing power nuclear facilities with liquid-metal heat carriers.

An experimental prototype of thick-walled gas-electron multiplier (THGEM) has been designed and manufactured using metal-coated fluoroplast as a low-background material. Working characteristics of the proposed device have been measured in detecting alpha-, beta-, and X-rays of ultralow intensity. Based on these data, the design of a low-background THGEM is developed for operating in the regime of counting single-electron pulses.

A method for the detection of solar neutrino has been developed using the laboratory bench installations. The efficiency of the extraction of beryllium from lithium as high as 96.4{%} has been achieved, and it was shown that lithium losses during the extraction were less than 1{%}. The prospects of a full-scale experiment with a 10-t lithium detector consisting of twenty 500-kg lithium modules are discussed. The technical solutions formulated on the basis of this study enable to make design of a pilot lithium installation containing 500 kg of metallic lithium

A method for solar neutrino recording on a laboratory bench with a lithium detector is developed. The efficiency of extraction of beryllium from lithium as high as 96.4% is achieved, and it is shown that lithium extraction losses are less than 1%. The results of a full-scale experiment with a 10-t lithium detector consisting of 20 500-kg modules are presented. Technical solutions based on the experimental results open the way to designing a pilot facility intended for 500 kg of lithium.

Experiments sensitive to pp neutrinos from the Sun are very promising for precise measurement of the mixing angle ϑ ₁₂. A νe ⁻ scattering experiment (XMASS) and/or a charged-current experiment (indium detector) can measure the flux of electron pp neutrinos. One can find the total flux of pp neutrinos from a luminosity constraint after the contributions of ⁷Be and CNO neutrinos to the total luminosity of the Sun are measured. A radiochemical experiment utilizing a lithium target has high sensitivity to the CNO neutrinos; thus, it has a good promise for precise measurement of the mixing angle and for a test of the current theory of evolution of the stars.