GALLEX

GALLEX or Gallium Experiment was a radiochemical neutrino detection experiment that ran between 1991 and 1997 at the Laboratori Nazionali del Gran Sasso (LNGS). This project was performed by an international collaboration of French, German, Italian, Israeli, Polish and American scientists led by the Max-Planck-Institut für Kernphysik Heidelberg. After brief interruption, the experiment was continued under a new name GNO (Gallium Neutrino Observatory) from May 1998 to April 2003.

It was designed to detect solar neutrinos and prove theories related to the Sun's energy creation mechanism. Before this experiment (and the SAGE experiment that ran concurrently), there had been no observation of low energy solar neutrinos.

Location

The experiment's main components, the tank and the counters, were located in the underground astrophysical laboratory Laboratori Nazionali del Gran Sasso in the Italian Abruzzo province, near L'Aquila, and situated inside the 2912-metre-high Gran Sasso mountain. Its place under a depth of rock equivalent of 3200 metres of water was important to shield from cosmic rays. This laboratory is accessible by a highway A-24, which runs through the mountain.
Detector

The 54-m3 detector tank was filled with 101 tons of gallium trichloride-hydrochloric acid solution, which contained 30.3 tons of gallium. The gallium in this solution acted as the target for a neutrino-induced nuclear reaction, which transmuted it into germanium through the following reaction:

νe + 71Ga → 71Ge + e−.

The threshold for neutrino detection by this reaction is very low (233.2 keV), and this is also the reason why gallium was chosen: other reactions (as with chlorine-37) have higher thresholds and are thus unable to detect low-energy neutrinos. In fact, the low energy threshold makes the reaction with gallium suitable to the detection of neutrinos emitted in the initial proton fusion reaction of the proton-proton chain reaction, which have a maximum energy of 420 keV.

The produced germanium-71 was chemically extracted from the detector, converted to germane (71GeH4). Its decay, with a half life of 11.43 days, was detected by counters. Each detected decay corresponded to one detected neutrino.
Results

During the period 1991-1997, the detector measured capture rate of 73.1 SNU (Solar neutrino units). The follow-up GNO experiment found the capture rate 62.9. [1]

The rate of neutrinos detected by this experiment disagreed with standard solar model predictions. Thanks to the use of gallium, it was the first experiment to observe solar initial pp neutrinos. Another important result was the detection of a smaller number of neutrinos than the standard model predicted (the solar neutrino problem). After detector calibration the amount did not change. This discrepancy has since been explained: such radiochemical neutrino detectors are sensitive only to electron neutrinos, and not to muon neutrinos or tau neutrinos, hence the neutrino oscillation of electron neutrinos emitted from the sun and travelling to the earth accounts for the discrepancy.
Other experiments

The first solar neutrino detection, the Homestake Experiment, used chlorine-37 to detect neutrinos with energies down to 814 keV.

After the end of GALLEX its successor project, the Gallium Neutrino Observatory or G.N.O., was started at LNGS in April 1998.[2] The project continued until 2003.

A similar experiment detecting solar neutrinos using liquid gallium-71 was the Russian-American Gallium Experiment SAGE.
References

Gavrin, Vladimir N. (2011). "The Russian-American gallium experiment SAGE". Physics-Uspekhi. 54 (9): 941–949. Bibcode:2011PhyU...54..941G. doi:10.3367/UFNe.0181.201109g.0975.

GNO (Gallium Neutrino Observatory), October 2000. Retrieved 1 Oct. 2018.

External links

The GALLEX experiment

vte

Neutrino detectors, experiments, and facilities
Discoveries

Cowan–Reines ( ν e) Lederman–Schwartz–Steinberger ( ν μ) DONUT ( ν τ) Neutrino oscillation SN 1987 neutrino burst

Operating
(divided by
primary
neutrino
source)
Astronomical

ANITA ANTARES ASD BDUNT Borexino BUST HALO IceCube LVD NEVOD SAGE Super-Kamiokande SNEWS

Reactor

Daya Bay Double Chooz KamLAND RENO STEREO

Accelerator

ANNIE ICARUS (Fermilab) MicroBooNE MINERνA MiniBooNE NA61/SHINE NOνA NuMI T2K

0νββ

AMoRE COBRA CUORE EXO GERDA KamLAND-Zen MAJORANA NEXT PandaX SNO+ XMASS

Other

KATRIN WITCH

Construction

ARA ARIANNA Baikal-GVD BEST DUNE Hyper-Kamiokande JUNO KM3NeT SuperNEMO FASERν

Retired

AMANDA CDHS Chooz CNGS Cuoricino DONUT ERPM GALLEX Gargamelle GNO Heidelberg-Moscow Homestake ICARUS IGEX IMB K2K Kamiokande KARMEN KGF LSND MACRO MINOS MINOS+ NARC NEMO OPERA RICE SciBooNE SNO Soudan 2 Utah

Proposed

CUPID GRAND INO LAGUNA LEGEND LENA Neutrino Factory nEXO Nucifer SBND UNO JEM-EUSO WATCHMAN

Cancelled

DUMAND Project Long Baseline Neutrino Experiment NEMO Project NESTOR Project SOX BOREX