It is equal to the neutrino flux producing 10−36 captures per target atom per second.
[1] It is convenient given the very low event rates in radiochemical experiments.
[2] There are two ways of detecting solar neutrinos: radiochemical and real time experiments.
, where With typical neutrino flux of 1010 cm−2 s−1 and a typical interaction cross section of about 10−45 cm2, about 1030 target atoms are required to produce one event per day.
Taking into account that 1 mole is equal to 6.022×1023 atoms, this number corresponds to ktons of the target substances, whereas present neutrino detectors operate at much lower quantities of those.