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

6 Test of a PXE based scintillator for Borexino
volumetric exchange with water from the Inner Vessel. To avoid overpressure of the Inner
Vessel, a few 100 l water were pumped out of the Inner Vessel prior to the filling. During the
filling the pump was working in a mode, that it pumped water out of the Inner Vessel into
the buffer tank, and the scintillator was pushed in a passive mode out of the buffer tank into
the Inner Vessel. Once the filling was completed, the Inner Vessel was isolated, and the water
was drained from the buffer tank. Then the tank was dried with nitrogen and was then ready
to be filled again with the next batch of scintillator. The filling of the total volume of PXE (4
tons) was realized in three batches (1 ton, 2 tons, 1 ton). The data taking with the CTF2 can
be divided into 5 different phases:
1. Water Run: The data acquisition was first running from March 19 to March 31 (run
706 - 716). At that time, the Inner Vessel was filled with water. These runs were used
to calibrate the electronics; and, by measuring the Cerenkov light from muons crossing
the detector, to develop criteria to reject these Cerenkov events.
2. 1 Ton Runs: The first ton of PXE was filled in the CTF on June 3rd 2000. The Inner
Vessel used in the CTF2 had several small leaks bearing the risk of enlarging under
stress. Therefore we filled only 1 ton of PXE in the beginning in order to keep the
buoyancy small. Data was taken from June 4th to June 9th (run 717 - 723). After it
turned out that there were no substantial leaks, we continued the filling.
3. 3 Ton Runs: Another Ñ were inserted in the IV on June 11th 2000. Data was
taken from June 13th until July 15th (run 724 - 757).
4. 4 Ton Runs: The remaining amount of PXE was inserted on July 15th 2000. The data
taking period with 4 tons of PXE, without any scintillator operations, lasted from 16th
July 2000 until 6th September 2000, i.e. about 6 weeks in total (run 758 - 789).
5. Source Test: From September 12 until September 20 we carried out a number of calibration
measurements with a localized source introduced into the Inner Vessel (run 790
-810). The source was placed at various locations inside the Inner Vessel to test the
homogeneity of the detector response and the systematic effects of the position reconstruction.
The results of these tests will be reported in chapter 7.
At the end of September 2000, the scintillator was unloaded from the Inner Vessel into one EP
tank by volumetric exchange with water. Later, the PXE was removed from the Module-0 and
placed into storage for later use in another experiment. The water was drained from the CTF
tank so that the leaky Inner Vessel could be replaced.
86