Baksan large volume scintillation telescope: a current status. V.B. Petkov 1,2 , A.M. Gangapshev 1,3 , Yu.M.Gavrilyuk 1 , V.N. Gavrin 1 , T.V.Ibragimova 1 , M.M. Kochkarov 1 , V.V. Kazalov 1 , D.Yu. Kudrin 1 , V.V.Kuzminov 1,3 , B.K. Lubsandorzhiev 1 , Yu.M. Malyshkin 1,4 , G.Ya. Novikova 1 , A.Yu. Sidorenkov 1 , N.A. Ushakov 1 , E.P. Veretenkin 1 , D.M.Voronin 1 , E.A.Yanovich 1 1 Institute for Nuclear Research of RAS, Moscow, Russia 2 Institute of Astronomy of RAS, Moscow, Russia 3 Kabardino-Balkarian State University, Nalchik, Russia 4 National Institute of Nuclear Physics, Rome, Italy
Scientific problems (neutrino geo- and astrophysics): • investigating the solar-neutrino spectrum and seeking neutrinos from CNO reactions; • studying the antineutrino flux emitted by daughter products of the decay of of uranium and thorium, contained in the Earth’s interior (geoneutrinos) and thereby determining the radiogenic component of the heat flux from the Earth; • estimating the potassium content in the Earth’s interior on the basis of the spectrum of electrons recoiling from neutrino scattering on electrons (similarly to detecting solar neutrinos); • testing, via searches for the flux of antineutrinos from the “georeactor,” the hypothesis that a chain fission reaction proceeds at the center of the Earth; • exploring the dynamics of supernova explosions by detecting the neutrino- burst intensity and spectrum; • seeking an isotropic flux of antineutrinos accumulated in the Universe over billion years in gravitational collapses of massive-star cores and in the formation of neutron stars and black holes; • detecting the total antineutrino flux from all power nuclear reactors that are present on the Earth and studying electron-antineutrino oscillations.
Baksan Large Volume Scintillation Telescope A large volume detector filled with liquid scintillator at the Baksan neutrino observatory is discussed during many years. The main research directions of the BLVST are neutrino geophysics and neutrino astrophysics. Estimation of target mass of future detector is changed over time: 1 kton target mass of LS: G.V. Domogatsky et al., Phys.Atom.Nucl., 68, 69, 2005. 5 kton target mass of LS: G.V. Domogatsky et al., Phys.Atom.Nucl., 70, 1081, 2007; 10 kton target mass of LS: I.R. Barabanov et al., Physics of Atomic Nuclei, 2017, Vol. 80, No. 3, pp. 446 – 454. At present a complex of research and development aimed at the creation of a new-generation scintillation detector using an extra-pure scintillator of 10 kiloton mass is performed .
BNO location: vicinity of mountain Elbrus, in the Baksan valley of Kabardino-Balkaria (Russia). mountain Andyrchy Baksan valley Baksan Neutrino Observatory and Neutrino village
Baksan Neutrino Observatory of INR RAS: unique complex of surface and underground experimental facilities Andyrchy EAS array Carpet-3 EAS array BUST Tunnel entrance Neutrino village
of muons Schematic view of a section of the Andyrchy slope along the adit (right scale) and dependence of underground muon flux on the laboratory location depth (left scale). General view of underground objects of the Baksan neutrino observatory
Entrance BUST’s hall Low Bkg Lab2 + Laser Interferom. 620 m – 1000 m w.e. Low Bkg Lab1 «НИКА» Low Bkg Lab3 « DULB-4900 » GeoPhys OGRAN’s hall Lab1 GeoPhys Lab2 4000 m GGNT’s hall BLVST Underground Laboratories of the BNO INR RAS
Counting rate for antineutrinos from nuclear reactors and geoneutrinos at the resumed detector locations I. R. Barabanov et al. Large-Volume Detector at the Baksan Neutrino Observatory for Studies of Natural Neutrino Fluxes for Purposes of Geo- and Astrophysics. Physics of Atomic Nuclei, 2017, Vol. 80, No. 3, pp. 446 – 454. Jinping 27.8 6.8 59.4 0.1 L. Wan et al. Geoneutrinos at Jinping: Flux prediction and oscillation analysis. Phys. Rev. D 95, 053001 (2017)
Experiment preparation Liquid scintillator for the target: Liquid scintillator on base of linear alkyl benzene (LAB) • A scintillator on the basis of LAB has indisputable advantages, since LAB is a low-cost compound produced by the industry in large amounts. Flash point is 143 ° C. Density is between 0.855 and 0.858 g/cm 3 . LAB has a high transparency and compatibility with polymeric constructional materials. • The sample from KINEF refinery (Kirishi, Russia) is examined now, using chromato-mass-spectrometric analysis. • This LAB consists of 20 alkylbenzene with general formula C 6 H 5 C n H 2n+1 (n = 10 – 13). It can be divided into 4 fractions: C 16 H 26 (12.5%), C 17 H 28 (29.3%), C 18 H 30 (31.5%), C 19 H 32 (26.7%).
Linear alkyl benzene (LAB): spectrophotometric studies Light attenuation length for wavelength: 440 nm, 430 nm, 420 nm L 440 , m L 430 , m L 420 , m crude LAB 25.6 18.1 14.0 refined LAB 72.5 48.3 39.5 refined LAB after 1 year 25.6 18.1 14.5 Decrease of light attenuation length is the result of interaction of hydrocarbons with oxygen and the formation of primary oxidation products → Blowdown the tank with an inert gas to store LAB after its purification or introduce antioxidants can solve this problem N.I. Bakulina et al. Linear alkyl benzene (LAB): chemical composition, stability and oxidation by air oxygen in the presence of cobalt stearate. Chemical industry today, 2018, #3, p.38 (in Russian).
Liquid scintillator for the target: radioactive impurity • An important task for such a detector is to suppress the natural background from natural radioactivity and the radioactive carbon isotope 14 C contained in the liquid scintillator • We performed measurements with an LAB-based liquid organic scintillator containing 2 g/l of a BPO scintillation addition. • Light yield is about 8000 photons per MeV • Attenuation length is 15 m at the light wavelength of 420 nm. • Measurement results for the sample of LAB from KINEF refinery (Kirishi, Russia) 232 Th : 6.2x10 -12 g/g • 238 U : 1.8x10 -11 g/g •
Determination of 14 C abundance in liquid scintillator • The background from 14 C does not allow lowering the threshold for detecting solar neutrinos below 200 keV and makes it difficult to detect neutrinos from the pp cycle. With a large mass of the target, coincidence of pulses from 14 C decays in different parts of the detector begins to affect, which leads to an extension of the 14 C spectrum to high energies (up to 300 keV). • Measured 14 C/ 12 C ratio the sample of LAB from KINEF refinery: • (3.3 0.5) 10 -17 • The measurement was performed in the low background Laboratory Baksan Neutrino Observatory at a depth of 4900 m.w.e. I. R. Barabanov et al. Measurement of the 14C Content in Liquid Scintillators by Means of a Small-Volume Detector in the Low-Background Chamber of the Baksan Neutrino Observatory. Physics of Atomic Nuclei, v.80, p. 1146, 2017.
First prototype: 0.5 t of LAB-based liquid organic scintillator in a acrylic sphere. Structurally, the prototype of the scintillation detector consists of an external cylindrical tank and the inner part, including the acrylic sphere and stainless steel construction, which are attached photodetectors, and which provides additional fixation of acrylic sphere. An array of 20 10-inch Hamamatsu R7081-100 PMTs surrounds the acrylic sphere. The acrylic sphere: inner diameter of 960 mm.
First prototype. The external tank is a polypropylene cylinder with an inner diameter of 2400 mm (wall thickness of 20 mm) and 2800 mm high. To fill the tank with ultrapure water, a piping system was installed connecting the housing with water purification system. The prototype is installed in the hall of the GGNT (4800 m.w.e.) External tank from polypropylene Water purification system
To calculate the response of the detector, a new universal modeling tool LSC (Liquid Scintillator Monte Carlo) is used. Yu.M. Malyshkin et al. Modeling of a MeV-scale Particle Detector Based on Organic Liquid Scintillator . Submitted to NIM-A PMT arrangement and size of the light concentrators was optimized using this tool. Concentrators used for the prototype should Detector response to 1 MeV electrons uniformly distributed have a height of about 9 – 11 cm and radius of over the LS volume. about 20 – 23 cm.
Conclusion and outlook • Baksan neutrino observatory is attractable place for installing geoneutrino detector (existing infrastructure, high counting rate, low nuclear reactors rate). • Large detector installed at BNO will be a part of international detector net for geoneutrinos. • Now there is the work on the development of the detector and the creation of its prototypes. • The first prototype is now under construction (supported by the Russian Science Foundation, project no. 17-12-01331) and will be in operation before the end of this year. • We plan to construct second prototype with 5 t of liquid scintillator next year.
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