The primary objective of LENS is direct
real-time measurement of the solar ne spectrum < 2 MeV,
consisting of 7Be, the CNO and in particular, the
basic pp ne's with energy
1)
It offers the lowest ne capture threshold
known yet, 114 keV , so that a nearly complete spectrum of the
"standard candle" pp ne 's, indeed the total
low energy solar ne spectrum containing the dominant
flux can be observed;
2)
a relatively high theoretical pp ne signal rate
of ~1000 events /yr for a 10 ton In target is predicted;
3)
a highly selective ne tag that offers a strong
defense against the formidable backgrounds that are endemic in
general to the very low-energy regime of the pp solar neutrino
signals, and in particular in the case of indium, is
created by the natural radioactivity of 115In
(natural abundance=95.7%, half-life=6x1014 y);
4) the
temporal and energy regimes of the tag are conducive to practical
implementation.
Two possible In-LENS designs are under
study: 1) a homogeneous design consisting only of In-containing
modules arranged at high granularity (high number of
parallelepiped cells) , and 2) a " hybrid" design in
which In-containing cells at high granularity are interspersed
with In-free detection volumes at low granularity.
The efforts of the collaboration in the
years 2000-2003 concentrate on the following items: i)
development of a liquid scintillator highly doped with In
(previously Yb), having adequate light yields and
transmittance to detect low energy events in a big detector, ii)
installation undergound @LNGS of a shielded test facility to test
module of detector, iii) Montecarlo computation of signal and
noise (coming mainly from 115In b decay to 115Sn)
to define granularity, tagging efficiency ecc.