Design Concepts for BOREX
R.S. Raghavan et al. – March 31, 1988
The proposal for “BOREX” (BORon solar neutrino EXperiment), a very large liquid scintillator detector (2kT of Trimethyl borate, TMB for short) aimed at performing observation of neutrinos from 8B decays in the Sun.
(Hence the name: Boron would have been involved in the experiment both as the source of the observed neutrinos and as a component of the scintillator used for neutrino detection).
The initial idea dates back to 1986.
Such proposal was never realized.
Due to the background from natural radioactivity, the sensitivity of the proposed detector would have been limited only to high-energy neutrinos. Which constitutes only a very small fraction (0.01%) of the solar neutrino flux resulting from the reaction with 8B. But two other experiments with the same goal and similar energy thresholds (albeit with lower statistics), Superkamiokande and SNO (both based on the Cherenkov effect), were already in an advanced stage of preparation at that time.
Discussing with Raju Raghavan, Frank Calaprice, Franz Von Feilitsch and other italian scientists, Gianpaolo Bellini stubbornly supported a different idea. That of carring out a different, much more advanced and ambitious experiment. By creating a detector with extremely low background, sensible to the entire solar neutrino spectrum. Which would have made it possible to explore also the low-energy regions that had never been studied before. Therefore capable of providing significant results far beyond those that any other existing or planned detector of the time (including BOREX) could have achieved.
Despite widespread and persistent skepticism about the possibility of achieving the unprecedented, extremely low background which was required in a sufficiently large detector, some of the scientists involved in the BOREX proposal, including Raghavan himself, and the aforementioned physicists who had taken part in the discussion, embraced the new venture. An international collaboration began to form around the group of INFN Milano led by Gianpaolo Bellini.
So was born the Borexino project.
The name “Borexino” is the Italian diminutive of BOREX. Although Borexino was not really “a small Borex” – but rather a very different experiment – the old name stuck. Thanks to its ultra-low background, to achieve its objectives Borexino required a smaller scintillator volume than BOREX – hence the diminutive. The name was still somehow fitting: while no longer being the only goal, the observation of neutrinos from 8B decays in the Sun was still among the first results which had to be (and have been) achieved by Borexino.