to insurmountable technical problems in the fabrication of the antineutrino source. The entire Borexino experiment was ended in October 2021. History and notable results The initial BOREX proposal was made in 1986. In 1990, the design was fundamentally altered, and the name of the experiment was changed to "Borexino". Research and development began on the detector at that time. By 2004, the structure of the detector had been completed, and by May 2007 the detector chamber had been filled and data taking began. The first results by the collaboration were published in August 2007 in: “First real time detection of 7Be solar neutrinos by Borexino”. The subject was further extended in 2008. In 2010, "geoneutrinos" from Earth's interior were observed for the first time using Borexino. These are anti-neutrinos produced in radioactive decays of uranium, thorium, potassium, and rubidium, although only the anti-neutrinos emitted in the 238U/232Th chains are visible because of the inverse beta decay reaction channel Borexino is sensitive to. That year, the lowest-threshold (3 MeV) measurement of the 8B solar neutrino flux was also published. Additionally, a multi-source detector calibration campaign took place, where several radioactive sources were inserted in the detector to study its response to known signals which are close to the expected ones to be studied. In 2011, the experiment published a precision measurement of the beryllium-7 neutrino flux, as well as the first evidence for the pep solar neutrinos. The results of measurements of the speed of CERN Neutrinos to Gran Sasso were published in 2012. These results were consistent with the speed of light, thus providing confirmation that the Faster-than-light neutrino anomaly reported earlier in the year was an erroneous measurement. An extensive scintillator purification campaign was also performed, achieving the successful goal of further reducing the residual background radioactivity levels to unprecedented low amounts (up to 15 orders of magnitude under natural background radioactivity levels). In 2013, Borexino experiments added new limits on sterile neutrino parameters. They also extracted a signal of geoneutrinos, which gives insight into radioactive element activity in the earth's crust, a hitherto unclear field. An analysis of the proton–proton fusion activity in the solar core, published in 2014, found that solar activity has been consistently stable on a 105-year scale. Once the phenomenon of neutrino oscillations, as described by MSW theory, is considered, the measurement of Borexino is consistent with the expectations from the standard solar model.