8 Neutrino Detectors
373
Germanium nuclei to the counters is measured to be 95–98% using nonradioactive Germanium carriers.
• X-rays occurring through the reactions e − + (A, Z + 1) → (A, Z) + ν e are
detected over a period of about 6 months although the mean life of the reaction
is only 16.5 days, allowing a good estimate of the background.
• The 71 Ge decays produce pulses of 10.4 keV or 1.1 keV for K and L captures
respectively. The localized nature of this ionization allows the reduction of
background using amplitude and shape analysis of the recorded pulses to a level
of less than 0.1 event/day.
• The counters are calibrated 5 times during a 6-month exposure using a Gd/Ce
X-ray source.
Gallex measured [114] their extraction efficiency using a 60 PBq 51 Cr source
of 750 keV neutrinos (90%) and 430 keV (10%) neutrinos. They found a ratio
of measured/expected signal of 0.93 ± 0.08. Their extraction efficiency was also
confirmed [115] to be as expected to within 1% by introducing several thousand
atoms of 71 As that decay to 71 Ge.
The SAGE detector was built using up to 60 tons of metallic Gallium. It
was housed in the Baksan Neutrino Observatory in the Caucasus at a depth of
4700 m.w.e. While the liquid gallium was stirred at a rate of 80 rpm the Germanium
was extracted from it by oxidizing it using a weakly acidic aqueous solution. The
subsequent steps are similar to the procedure described above. Their extraction
efficiency was also measured with a Chromium source.
The reaction threshold in chlorine only allows the observation of the beryllium
and boron neutrinos whereas the threshold in gallium allows, in addition, the
observation of some of the pp neutrinos.
8.3.7 Bubble Chambers
Bubble chambers were heavily used in earlier studies of neutrino interactions
and were instrumental in making significant advances in the understanding of the
properties of neutrinos [116]. Their filling varied from liquid hydrogen to heavy
liquids, the latter used to increase the overall target mass, to contain the secondary
hadrons produced and to convert photons. They were placed within a magnetic
field in order to measure the momenta of the charged particles produced in the
neutrino interactions. Their time resolution was poor as they were sensitive to all
events occurring within a beam spill of typically millisecond duration. This could
be improved by associating them to external electronic detectors.
Gargamelle was a cylindrical chamber 4.8 m long and 1.8 m in diameter. It was
situated in a 2 T magnetic field produced by two coils. Neutral currents were first
identified using this chamber [117] with a heavy freon (CF 3 Br) filling resulting in
a density of 1.5 g · cm −3 and an interaction length of 58 cm. The identification of
373
Germanium nuclei to the counters is measured to be 95–98% using nonradioactive Germanium carriers.
• X-rays occurring through the reactions e − + (A, Z + 1) → (A, Z) + ν e are
detected over a period of about 6 months although the mean life of the reaction
is only 16.5 days, allowing a good estimate of the background.
• The 71 Ge decays produce pulses of 10.4 keV or 1.1 keV for K and L captures
respectively. The localized nature of this ionization allows the reduction of
background using amplitude and shape analysis of the recorded pulses to a level
of less than 0.1 event/day.
• The counters are calibrated 5 times during a 6-month exposure using a Gd/Ce
X-ray source.
Gallex measured [114] their extraction efficiency using a 60 PBq 51 Cr source
of 750 keV neutrinos (90%) and 430 keV (10%) neutrinos. They found a ratio
of measured/expected signal of 0.93 ± 0.08. Their extraction efficiency was also
confirmed [115] to be as expected to within 1% by introducing several thousand
atoms of 71 As that decay to 71 Ge.
The SAGE detector was built using up to 60 tons of metallic Gallium. It
was housed in the Baksan Neutrino Observatory in the Caucasus at a depth of
4700 m.w.e. While the liquid gallium was stirred at a rate of 80 rpm the Germanium
was extracted from it by oxidizing it using a weakly acidic aqueous solution. The
subsequent steps are similar to the procedure described above. Their extraction
efficiency was also measured with a Chromium source.
The reaction threshold in chlorine only allows the observation of the beryllium
and boron neutrinos whereas the threshold in gallium allows, in addition, the
observation of some of the pp neutrinos.
8.3.7 Bubble Chambers
Bubble chambers were heavily used in earlier studies of neutrino interactions
and were instrumental in making significant advances in the understanding of the
properties of neutrinos [116]. Their filling varied from liquid hydrogen to heavy
liquids, the latter used to increase the overall target mass, to contain the secondary
hadrons produced and to convert photons. They were placed within a magnetic
field in order to measure the momenta of the charged particles produced in the
neutrino interactions. Their time resolution was poor as they were sensitive to all
events occurring within a beam spill of typically millisecond duration. This could
be improved by associating them to external electronic detectors.
Gargamelle was a cylindrical chamber 4.8 m long and 1.8 m in diameter. It was
situated in a 2 T magnetic field produced by two coils. Neutral currents were first
identified using this chamber [117] with a heavy freon (CF 3 Br) filling resulting in
a density of 1.5 g · cm −3 and an interaction length of 58 cm. The identification of