Solar neutrino unit

The solar neutrino unit (SNU) is a unit of Solar neurino 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. It is convenient given he very low event rates in radiochemical experiments.

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

$^{A}_{N}Z %2B \nu_{e}\longrightarrow^{A}_{N-1}(Z%2B1)%2Be^{-}$ .

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 $10^{10}\left[\frac{1}{cm^{2}s}\right]$ and cross section of about $10^{-45}[{cm^{2}}]$ it is needed about $10^{30}$ (1 mole is equal to 6.022×10²³) target atoms to produce one event per day. This number corresponds to ktons of the target substances, whereas present neutrino detectors operate at much lower quantities of those.

Solar neutrino unit

See also