  The production of the artificial 51Cr neutrino source with activity > 3 MCi
for the experiment BEST is presented. This procedure consisted of making a 50Cr
target and irradiating it with thermal neutrons in a nuclear reactor SM-3. The
production of a target in the form of disks with a thickness of 4 mm and a
diameter of 84 and 88 mm included enrichment (to 96.5% in 50Cr) of natural
chromium in the form of oxyfluoride by gas centrifugation, electrolytic
reduction and refining of metallic chromium, as well as the formation of
chromium disks by spark plasma sintering. Simulations of various source
geometries, neutron flux and nuclear transmutation were carried out to validate
the design of the source, the irradiation device and the transport container,
the required chemical purity of the target and the irradiation schedule in the
reactor. The calculated activity of the source after 75 effective days of
irradiation was 3.55 MCi. The activity of the source was measured by the
calorimetric method and amounted to 3.41 MCi at the time of its delivery to the
Baksan Neutrino Observatory. This is the most intense chemically pure neutrino
source ever produced.
