Artificial Cr-51 neutrino source for the experiment BEST "International Session-Conference of SNP PSD RAS “Physics of Fundamental Interactions”. June 6-8, 2017, Nalchik, Russia Artificial Cr-51 neutrino source  for the experiment BEST E.P. Veretenkina), V.N. Gavrina), Yu.P. Kozlovaa), S.N.Danshina), A.V. Logachevb), A.I. Logachevab), I.S. Lednevc), A.A. Okunkovac) , E.G.Romanovd), V.A.Tarasovd), A.P.Malkovd), A.V.Kupriyanovd) a) INR RAN, Moscow, Russia b) JSC “Kompozit”, Moscow region, Korolev, Russia c) Moscow State University of Technology “STANKIN”, Moscow, Russia d) JSC “SSC NIIAR”, JSC “Science and Innovation”, State Atomic Energy Corporation ROSATOM

The weighted-average R = 0.87 ± 0.05 Results of four Ga experiments with artificial neutrino sources. SAGE 51Cr SAGE 37Ar GALLEX Cr1 GALLEX Cr2 Activity, kCi 516.6±6.0 409±2 1714+30 -43 1868+89-57 Pmeas, atoms 71Ge/d 14.0±1.5±0.8 11.0+1.0-0.9±0.6 11.9±1.1±0.7 10.7±1.2±0.7 Ga mass (t) 13.1 (metal) 30.4 (GaCl3:HCl) R = Pmeas/ Ptheor. 0.95±0.12 0.79±0.10 0.953±0.11 0.812±0.11 Pmeas– measured production rate of 71Ge from sources. R – ratio of the measured production rate Pmeas to the production rate expected in the absence of oscillations Ptheor. The weighted-average R = 0.87 ± 0.05 (Ga anomaly)

Experiment BEST the search of neutrino oscillations by charged current reaction: νe + 71Ga → 71Ge + e- the use of a compact, nearly monochromatic neutrino source with well-known activity; the use of the metal Ga dense target ensures high interaction rate; the special geometry of the target provides for neutrino interaction rate at two distances; the short baseline; the low background (generally from the Sun); the use of the well-established procedure of measurement of neutrino capture rate on gallium developed for the Gallium-Germanium Neutrino Telescope.

Baksan Experiment on Sterile Transitions (BEST) Pee = 1- sin2 2 sin2(1.27m2(eV2) ) Two-zone Ga detector Target: 50 t Ga metal Masses of the zones: 7.5 t and 42.5 t Path length in each zone: <L> = 55 cm Ratio of measured capture rate to predicted rate in the inner (R1) and outer (R2) zones and their ratio R2/R1 as a function of m2 for the case of sin22 = 0.3. The evidence of nonstandard neutrino properties: ● a significant difference between the capture rates in the two zones ● the average rate in both zones is considerably below the expected rate

Expected isotopic composition 50Cr enrichment Isotopic composition of natural Cr 50Cr 4,35 % 52Cr 83,79 % 53Cr 9,50 % 54Cr 2,36 % Expected isotopic composition of the enriched Cr 97 % 3 % negligible 50Cr enrichment by gas centrifugation. The gaseous compound CrO2F2 is convenient material to chromium enrichment CrO2F2 properties rather high saturation vapor pressure at room temperature (> 5-10 mm Hg); passive with respect to equipment materials; existence of the only one stable isotope of oxygen and fluorine; thermal and chemical stability (no transition in nonvolatile substances) Cascade for isotope separation

Stages of metallic chromium production CrO2F2 hydrolysis CrO3 electrolysis Metallic Cr pressing gas-static CrO2F2 + H2O  CrO3 + 2HF water solution of sulphuric acid stainless steel as a cathode lead as an anode Hot-isostatic pressing of chromium powder

Hot isostatic pressing (HIP) of metallic powders HIP uses the high isotropic pressure at high temperature (below melting temperature) to compact metal powder by means of the plastic deformation and diffusion bonding.

HIP process of metallic Cr powder Powder production; Capsule production; Filling by powder; Evacuation; Sealing capsule; Use high temperature (1220°C) and high pressure (1600 atm) during 3 hours; Mechanical treatment of bars. Cr = 7.190 g/cm3 1 = 7.195 g/cm3 2 = 7.194 g/cm3

Electrical discharge machining (EDM) The metal-removal process is performed by applying a pulsating high-frequency current through the electrode to the workpiece. The wire-cut EDM is a computer numerical control (CNC) process in which a thin metal wire (usually brass) in conjunction with de-ionized water allows the wire to cut through metal by the use of heat from electrical sparks. It does not require a special shaped electrode, instead it uses a continuous-traveling vertical wire under tension as the electrode. Brass wire Electric sparks DC power source Workpiece Wire-cutting machine SEIBU M500SG

Electrical discharge machining of Cr rods Workpiece inserted in the holder Chromium hexagonal rods and titanium separator Cut pattern The chromium yield after EDM amounted to 95 per cent

High Flux “Super Power” Reactor SM-3 The unique high-flux reactor SM-3 is operated by RIAR (this is one of two reactors with the highest thermfl neutron flux available in the world. The second one is located in the USA, ORNL) The Reactor Hall

Main Parameters of SM-3 Reactor Thermal power output – 100MW Max thermal neutron flux ~5·1015 cm-2 s-1 Max fast neutron flux ~ 2 · 1015 cm-2 s-1 Irradiation positions are 27 neutron trap cells (12 mm), 30 beryllium reflector channels (69 mm), 24 in core cells (12 mm) Typical working schedule: 10 days -1.5 days - 10 days - 5 days Number of the effective days per year ~220 Radionuclides Produced by RIAR Trans-plutonium elements 241-243Am, 244-248Cm, 249Bk, 249,252Cf, 254Es Industry/Medical radionuclides 60Co, 192Ir, 75Se, 125I, 103Pd, 131Cs, 169Yb, 99Mo, 121Sn, 131I, 32-33P, 51Cr, 89Sr, 188W, 212Bi, 106Rh, 90Y, 121Sn, 59Fe, 177Lu, 153Gd Other isotopes 54Mn, 55Fe, 63Ni, 109Cd, 113,117m,119mSn,204Tl …

Reactor SM-3 Cross-section beryllium reflector reflector irradiation channel fuel assembly fuel assembly with irradiation cells central neutron trap automatic control rod control rod with suspended fuel assembly

Reactor SM-3 Central Neutron Trap beryllium block central control ring 27 irradiation cells water safety rod

Simulation Results A(51Cr), MCi Modular – composite Without a Central Control Rod Current without cell’s tubes Current trap Irradiation time, day

Expected Radionuclide purity of the neutrino source for the experiment BEST Element Conc. ppm Nuclide Half-life Activity (mCi) Expected in BEST source Measured in SAGE source Fe < 12 Fe-59 44,5 d <10 24±3 Co < 0,1 Co-60 5,27 y <20 65±15 Cu 1 Cu-64 12,7 h 780   Zn Zn-65 244 d 19 Mo 0,8 Mo-99 2,7 d 60 Sc < 0,4 Sc-46 83,8 d < 1320 1400±15 Sb < 0,5 Sb-122 < 2180 Sb-124 60,2 d < 500 Ag < 0.06 Ag-110m 249,8 d < 10 As < 0.4 As-76 1,1 d < 1680 W < 0,3 W-187 23,7 h < 880 La < 0,2 La-140 1,7 d < 230

51Cr neutrino source 51Cr + e-  51V + e Target requirements a) Limited volume of the reactor neutron trap b) Finite dimension of the two-zone Ga detector 51Cr + e-  51V + e W 51Cr 81 rods Nuclear decay scheme of 51Cr 51Cr neutrino source Metallic chromium is a reasonable compact material

Conclusions Compact artificial neutrino source based on chromium-51 of high activity ( 3 Mci) for the experiment BEST can be created. With this purpose it is necessary: To obtain the enriched chromium-50 with a degree of enrichment of 97%. To produce reactor metal target of enriched chromium weight 3 kg. The only reactor in Russia which can be made the source of the required activity is the reactor SM-3