Production of the artificial 51Cr neutrino source in the BEST project

TL;DR

This paper details the production process of the most intense chemically pure 51Cr neutrino source with activity over 3 MCi for the BEST experiment, including target preparation, irradiation, and validation through simulations and measurements.

Contribution

It presents a comprehensive method for producing a high-activity 51Cr neutrino source, including target fabrication, irradiation, and validation, advancing neutrino source technology.

Findings

Achieved a 3.41 MCi activity measured at delivery.

Validated source design through simulations and calorimetric measurements.

Produced the most intense chemically pure 51Cr neutrino source to date.

Abstract

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.