Service manual

8
6. APPLICATIONS
6.1. TIMING WITH FAST SCINTILATORS
Figure 6.1. shows a typical system for timing with
fast scintillation detectors such as Naton-136, Pilot
B, KL-236, NE-102, NE-111, NE-213, etc. A 584
Constant-Fraction Discriminator is used in each of
the two channels of the Time-to-Amplitude
Converter (TAC). Selection of the constant-fraction
shaping delay for best timing performance with a
given scintillator and PMT is usually accomplished
experimentally (Section 3.5). A useful empirical
formula for the initial trial selection of the external
shaping delay is
t 1.1 t 0.8 ns
d(Ext) r
where t is the 10% to 90% rise time of the anode
r
pulses.
The timing resolution obtainable in a given
application with fast scintillators depends on many
variables, including the energy range selected by
the SCAs; the threshold setting, external CF Delay,
and walk adjustment of the 584; the rise time and
type of the PMT; the size and shape of the
scintillator; and the presence of noise in the system.
Typical timing resolution for a narrow dynamic
range (.1:1.1), for Co is 200 ps FWHM and
60
360 ps FWTM (Fig. 6.1.).
For additional data see Section 6.5, "References."
Also, contact your local ORTEC representative to
obtain the latest information on the state-of-the-art
in timing with fast scintillators.
Figure 6.1. A System for Gamma-Gamma Lifetime Measurement.