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

Calibration and Monitoring
2.3 Detector Design
The calibration program for BOREXINO covers the energy and time response of the detector
using built-in systems, active tags of trace impurities in the scintillator, and the insertion of
localized radioactive sources [Man00]:
- The pulse timing and gain of each phototube is calibrated by a laser system. Photons
from a laser are carried by thin optical fibers connected to each light concentrator, with
a light yield corresponding to single photoelectron signals.
- C present in the scintillator can be used to monitor the stability of the energy response
of the detector in the low energy range. Also the 2.2 MeV ­ ray emitted after neutron
capture on a proton can be used for an energy calibration. Neutrons are created in the
scintillator by cosmic ray muons at a rate of about 0.3 per day and ton (experimentally
determined in the CTF), and are captured by protons in the scintillator after a lifetime
of s.
- Optical sources will be used to monitor the scintillator and buffer transparency. Laser
light with several different wavelengths will be carried into different regions of the detector
by optical fibers.
- As the energy response of the detector will be position dependent, a calibration with
a point-like source at several known positions in the detector is needed. The plan is
to insert a small encapsulated source that can be moved to known positions inside the
scintillator.
- An unambiguous, straightforward test of the overall detector response will be provided
by a calibration with a Cr source with an activity in the MegaCurie range. It emits
neutrinos of 740 keV energy, which is close to the Be neutrino energy. The source
would be placed in an existing tunnel under the detector.
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