The goal of the LENS experiment is to measure, in real time, the primary low energy (sub-MeV) solar neutrino spectrum, with special attention to the pp-, CNO- and 7Be-neutrinos. The detector is an indium based liquid scintillator.
The main reaction is:
νe + 115In → e- (Ee- = Eν - 115keV) + 2 delayed γ's (coincidence tag) + 115Sn
The interaction of a neutrino with the target nucleus is followed by a coincident γ-emission providing a powerful signature of νe interactions compared to background events.
LENS will determine the spectral shape of the low energy solar neutrino spectrum for the first time. Up until now we have only measured spectral shape of the higher-energy 8B portions of the spectrum (~5% of the total spectrum). The low-energy part of the neutrino spectrum is very important, since the Sun's energy is primarily produced in the pp-chain, which produces neutrinos only in the low energy portion of the spectrum. Measuring these neutrinos probes the dominant energy production mechanism in the sun. With new data on the low energy band of the spectrum we can answer questions such as: Is the Sun getting hotter? Are there sub-dominant non-nuclear sources of energy in the Sun?
The LENS design is a cubic lattice of low index of refraction material (Teflon FEP) in a higher index of refraction liquid (Indium liquid scintillator (InLS)). The cubic lattice structure of LENS allows for precision digitized localization of events in the detector allowing for extraordinary background reductions.
The idea to detect low energy solar neutrinos via the capture on Indium has been investigated since the 1970s (original publication by R. S. Raghavan: pdf).