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

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7 The Source Runs in CTF2 7.4 Analysis of the Source Runs 7.4.1 Event Selection To select the Po alpha decay events, which originated from the Rn source, the following cuts were applied: - they are detected by the second electronic group; - they have a coincidence time delay of 10 s-1ms; - they have a pulse height in the range Ô Õ Ô ( Ô Õ Ô for source no. 2); - the preceding group 1 event ( Bi) has a pulse height between 100 and 1200 pe (the lower energy threshold is set to reject accidental coincidences involving C events); - there is no muon flag on this event or the preceding group 1 event. With these cuts, the Po alphas and the preceding Bi betas can be tagged very efficiently with negligible background. Their energy spectra are shown in fig. 7.6. Fitting an exponential to the coincidence time distribution reproduces very well the decay time of Po, Ø × ÐÒ Ø ¡ × while the fit gives ¡ × (see fig. 7.6, lower plot). Background The two sources of potential background events are Bi- Po events in the bulk scintillator volume and accidental coincidences: - The background due to Rn present in the scintillator containment vessel can be estimated to be at about the same level as in the previous runs before the source insertion, counts per hour. Due to the fact that the scintillator inside the source vial was quenched and the energy of the Po alpha peak shifted towards lower energies, the actual background contribution is even smaller. - The accidental background can be estimated by applying the energy cuts mentioned above for the group 1 and group 2 events, but taking a coincidence time window shifted to much greater delay times (7010 - 8000 s). For run 797 this gives an accidental background rate of counts per hour. Compared to the source activity of 200 - 800 counts per hour (for source 1 and 2 respectively) both background contributions are negligible. 104
7.4 Analysis of the Source Runs Figure 7.6: Bi and Po events from source run 797. The energy of the Bi ¬ and the Po « events are shown, their coincidence time which corresponds to the Po lifetime, and the reconstructed position (x,y,z) of the Po events. 105
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Fakultät für Physik der Technisch
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Abstract The first chapter contains
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Übersicht an Radionukliden in BORE
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Contents 3 The Counting Test Facili
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Contents viii
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1 Solar Neutrinos Figure 1.1: The p
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1 Solar Neutrinos 1.2 Detection of
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1 Solar Neutrinos With this detecti
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1 Solar Neutrinos 1.2.3 Future Expe
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1 Solar Neutrinos 1.3.2 Astrophysic
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1 Solar Neutrinos Using the unitari
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1 Solar Neutrinos km in the earth.
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1 Solar Neutrinos 16 Solution ¡Ñ
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2 The Borexino Experiment The relat
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2 The Borexino Experiment Figure 2.
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2 The Borexino Experiment 2.2 The D
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2 The Borexino Experiment 2.3 Detec
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2 The Borexino Experiment 2.3.2 Anc
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2 The Borexino Experiment which per
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2 The Borexino Experiment 2.4 Backg
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2 The Borexino Experiment ns; Rn-
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2 The Borexino Experiment volume wo
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3 The Counting Test Facility (CTF)
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4 Position Reconstruction of Scinti
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Page 64 and 65: 4 Position Reconstruction of Scinti
Page 72 and 73: 5 Particle Identification with a Ne
Page 86 and 87: 6 Test of a PXE based scintillator
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Page 110 and 111: 7 The Source Runs in CTF2 7.3 The S
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Page 124 and 125: Summary and Outlook possible to dis
Page 126 and 127: Bibliography [Ade98] E. G. Adelberg
Page 128 and 129: Bibliography [Bra00] L. De Braeckel
Page 130 and 131: Bibliography [Lom97] P. Lombardi, D
Page 132 and 133: Bibliography [Vog96] R. B. Vogelaar
Page 134 and 135: Danksagung An dieser Stelle möchte
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Development of a Liquid Scintillator and of Data ... - Borexino - Infn

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