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

7.4 Analysis of the Source Runs
short period of time. The event registered by the detector consists of an overlap of these single
interactions. The effective position of such an event is the ‘center of light’ of the various
energy deposits. A gamma event is hence called an ‘extended event’. The higher the energy of
the gamma, the larger the extension of the event. The Monte Carlo for the CTF gives for the
energy dependence of the spatial resolution a rather flat curve, after an initial decrease at low
energies.
The Bi-decay consists of a beta decay to an excited state of Po, followed by the emission
of one or more ­-rays. The energy dependence of the position resolution for these events is
shown in fig. 7.7 and compared to the Monte Carlo resolutions for beta and gamma events. The
resolution as measured in the CTF2 is worse than predicted by the Monte Carlo, indicating
that some effects on the timing are not fully accounted for in the Monte Carlo.
7.4.4 Energy Resolution
Ideally, the relative energy resolution should be directly proportional to Ô ÒÔ, where ÒÔ is
the number of photoelectrons. The Po alpha events correspond to 950 keV beta equivalent
energy, if the scintillator is not quenched. The measured pulse height during the runs 758 -
789 is ( ¦ ) photoelectrons (see fig. 7.8). This gives a relative energy resolution of
¡
Ô ÒÔ
For source no. 1 the measured pulse height is ( ¦ ) photoelectrons, leading to
¡
Ô ÒÔ
For source no. 2 the measured pulse height is ( ¦ ) photoelectrons, giving
¡
Ô ÒÔ
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