1. 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

2. 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
Pmeas, atoms 71Ge/d
14.0±1.5±0.8
±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)

3. 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.

4. 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

5. 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

6. 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

7. 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.

8. 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 = g/cm3
1 = g/cm3
2 = g/cm3

9. 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

10. 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

11. 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

12. 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
Am, Cm, 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 …

13. 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

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

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

16. 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

17. 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

18. 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