EG&G ORTEC 463 Bedienings- en onderhoudshandleiding - Pagina 7
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Pagina afdrukkenORTEC 463 CONSTANT FRACTION DISCRIMINATOR
1. GENERAL
The ORTEC 463 Constant Fraction Discriminator provides
logic outputs that are used for precise timing signals. Fast
logic outputs are derived from input pulses from almost any
style of nuclear detector. The Constant Fraction technique
of obtaining timing signals ensures accuracy and precision
through a wide dynamic range of input signals. The details
of shaping are all selected properly by a front panel switch
that is marked for the four most common types of
detectors in current use.
The types of detectors with which the 463 can be used are
Ge(Li), Nal(TI), fast plastic scintillators, and surface
barrier, identified on the 463 by a front panel selector
switch, with the last two detectors
marked "Scint"
and "SB". Because of the signal shapes from a Ge(Li)
detector, an ORTEC 454 Timing Filter Amplifier should
be included between the preamplifier and the 463 when
this type of detector is used as a pulse source. The use
of a 454 is also advantageous when detector signals
require amplification.
This easily used single-width module virtually eliminates
timing walk caused by amplitude (energy) and also pulse
shape variations. When used with the ORTEC 454 Timing
Amplifier, it generates a walk-free timing signal that can be
obtained from any detector over a 100:1 dynamic range
of pulse heights.
The adjustments and selections are simple. Just set the
input discriminator to the lowest energy level of interest,
select the appropriate detector switch setting, and connect
the input and output cables, and it is ready to operate. The
463 then provides the most stable timing signal, suitable
for even the most sophisticated time spectroscopy measure
ment.
For convenience, monitor test points are included for
inspection of input and output signals and of the specially
shaped internal signal that is used to derive the walk-free
timing signal. The selections of the compatible delay and
attenuation are made automatically by the switch selection
of the detector type. The benefits of this modern Constant
Fraction technique are obtained without any necessity
for calculations and experimentations.
2. SPECIFICATIONS
PERFORMANCE
INPUT PULSE CHARACTERISTICS
Accepts negative
pulses to 10 V without saturation: protected to 100 V for
duty cycle of 10%; f^^l nsec.
REFLECTIONS Typically <10% for 0-to 10-V amplitude
range and rise time >1 nsec.
LOWER LEVEL DISCRIMINATOR
Temperature Drift <0.5 mV/°C, 0 to 50°C.
Integral Nonllnearity <±0.3%.
WALK AND DYNAMIC RANGE
Ge(LI) Mode <±2 nsec for range of 100 mV to 10 V with
40-nsec tf.
Scint/SB Mode <+150 psec for range of 100 mV to 10 V
(using signal from Naton-136 and RCA-8575 PM tube).
Nal Mode <+0.5 nsec for range of 100 mV to 10 V with
5-nsec t/-.
DELAY TEMPERATURE STABILITY <10 psec/°C, 0 to
50°C, for TV input signal with <2-nsec tr-
CONTROLS
SHAPING MODE 3-position selector switch selects delay
and fraction for optimum Constant Fraction timing signal
derivation according to the type of detector:
Ge(Li) Selects 12-nsec delay and compatible fraction for
optimum shaping of signals from Ge(Li) detectors.
Sclnt/SB
Selects 'v2-nsec delay and compatible fraction
for optimum shaping of signals from fast plastic scin
tillators or from surface barrier detectors.
Nal
Selects 'V4-nsec delay and compatible fraction for
optimum shaping of signals from Nal(TI) and similar
scintillators; also selects an internal dead time of
lisec from the leading edge of the input signal to prevent
multiple triggering on slow decay waveforms.
DISC. LEVEL
10-turn precision locking potentiometer
adjusts trigger level of the lower level discriminator;
range -50 mV to -5 V.