# Solar neutrino unit

The solar neutrino unit (SNU) is a unit of Solar neutrino flux widely used in neutrino astronomy and radiochemical neutrino experiments. 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. Typical rate is expected to be from tens SNU to hundred SNU.[2]

In principle there are two ways of detecting solar neutrinos: radiochemical and real time experiments. The principle of radiochemical experiments is the reaction of the form

$^{A}_{N}Z + \nu_{e}\longrightarrow^{A}_{N-1}(Z+1)+e^{-}$.

The daughter nucleus's decay is used in the detection. Production rate of the daughter nucleus is given by $R = N\int\Phi(E)\sigma(E)dE$, where

• $\Phi$ is the solar neutrino flux
• $\sigma$ is the cross section for the radiochemical reaction
• $N$ is the number of target atoms.

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.