I've attached single PMT ADC spectra for the blast TOF obtained with a
Sr90 beta source as a function of CFD threshold. The source was located
close the PMT. The data are internally normalized accounting only for
measurament time and coda dead-times. It was not possible to take source
data at lower threshold becuase of the high rate.
This source had an endpoint of 2.2 MeV. After energy loss correction
(0.010" Pb + plastic) I estimate the maximum deposited energy in the
detector to be 1.8 MeV. The endpoint is clearly visible around channel 500
above pedestal, which provides the energy calibration.
In the second plot I show peak position (in MeV) vs read-out threshold.
We typically run with a 31.3 mV threshold, however 20.9 mV is also an option.
For this PMT gain, these thresholds correspond to
CFD-thresh dE (MeVee) dE-hadronic (MeV) dE-coinc,hadrons (MeV)
20.9 mV 1.13 3.53 5.78
31.3 mV 0.82 4.05 6.64
The threshold for hadrons is estimated using the formula (dE+1.3)/0.6
In the last column the estimated minimum energy deposited by a hadron
to be detected in coincidence. This is what matters for detection of
low energy protons and deuterons.
This threshold is calculated considering the 0.61 attenuation of the signal
across the 1.9 mt length of scintillator (BC408 has an attenuation lenght of
380 cm). This factor should hopefully resonate well with previous light
attenuation measuraments of the TOF's (if any).
-- ________________________________________________________________________________ Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124 research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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