Development of a Liquid Scintillator and of Data ... - Borexino - Infn

1 Solar Neutrinos
With this detection technique it is possible to measure the time of the event and the energy
and direction of the recoil electron. Kamiokande began observing solar neutrinos in 1986
(almost two decades after the Chlorine experiment) with 680 tons of water, 1000 PMTs and
a detection threshold of 7.5 MeV (limited due to background from natural radioactivity). The
upgraded version, Super-Kamiokande, started data taking in 1996. With 50 000 tons of water
(22 500 tons fiducial volume) and 12 000 PMTs, and thanks to the higher purity components
and better shielding, Super-Kamiokande is able to measure down to a threshold of 5.5 MeV.
The measured rate after 1117 days is
ÊÜÔ ¦ ×ØØ
×Ý× ¢ Ñ
The comparison with the theoretical prediction [Bah98] leads to a ratio of
ÊÜÔÊËËÅ ¦ ×ØØ
×
×Ý×
Suz01℄
The shape of the measured B neutrino spectrum is consistent with no distortion. As a realtime
detector, Super-Kamiokande is able to measure the day flux and night flux separately.
The ratio obtained is
Æ
Æ
¦ ×ØØ
The Gallium Experiments: GALLEX, GNO and SAGE
×Ý×
To observe the low energy pp neutrinos, which have a maximum energy of 422 keV, V. Kuzmin
proposed in 1966 [Kuz66] a radiochemical experiment based on the inverse beta decay
with a threshold of 233 keV. There are two experiments using this reaction: GALLEX (renamed
GNO in 1998) in the INFN Gran Sasso underground laboratory (Italy) at a depth of
3600 mwe, and SAGE in the INR Baksan valley neutrino laboratory in the Caucasus mountains
(Russia) at a depth of 4700 mwe. The target consists of 30 tons gallium in an aqueous
gallium chloride solution for GNO, and of 60 tons of metallic gallium for SAGE. The germanium
nuclides produced by solar neutrinos are extracted from the target every 4 - 5 weeks, and
their back decay (Ø d) is measured in low background proportional counters. The
prediction for the gallium experiments is
GALLEX measured after 7 years a signal of
ÊËËÅ
ËÆÍ Bah98℄
ÊÜÔ ¦ ×ØØ
the successor GNO measured after 2 years
6
ÊÜÔ
×ØØ
×Ý× ËÆÍ Ham99℄
×Ý× ËÆÍ Alt00℄