8
amplitude of the resulting output pulse, E
out
, is
measured in volts with an oscilloscope. The noise
spread can then be calculated from the formula
where E
rms
is output noise in volts on the 3400A
meter, E
in
is the input signal in keV particle energy,
and E
out
is the output signal in volts corresponding to
the above input. If the gain of the shaping amplifier
is adjusted so that the output pulse height is 2.35 V
for an input of 1 MeV equivalent input charge, then
the rms meter will be calibrated to read directly in
energy (1 mV = 1 keV).
7. The noise performance of the preamplifier, as
measured by these methods, should not differ
significantly from that given in the Specifications in
Section 2.
8. If, during testing of the preamplifier and detector,
the noise performance of the preamplifier has been
verified as outlined in the previous steps or is
otherwise not suspected, a detector may be tested
to some extent by duplicating the noise performance
tests with the detector connected in place and with
normal operating bias applied. The resulting
combined noise measurement, made by either the
analyzer or voltmeter method, indicates the sum in
quadrature of the separate noise sources of the
amplifier and the detector. In other words, the total
noise is given by
9. Each quantity is expressed in keV FWHM. The
quantity N
det
is known as the “noise width” of the
detector and is included as one of its specified
parameters. By use of the above equation and with
a knowledge of the noise of the preamplifier, the
noise width of the detector can be determined. The
significance of this noise width in evaluating the
detector is subject to interpretation, but generally
the actual resolution of the detector is related
directly to the noise width in its normal applications.
The most useful purpose for determining this quality
for the detector is to occasionally monitor the
detector noise width to verify that its characteristics
have not undergone any significant changes during
use.
10. Use an ORTEC 419 Precision Pulse Generator
with a matched charge termination to measure the
risetime of the 142IH through the T or E output
connector. Connect the 419 output through the
charge terminator to the Input of the 142IH and use
an oscilloscope with a fast risetime (1 ns if
possible). The risetime of the preamplifier can then
be computed by
(Total risetime)
2
= (Preamplifier risetime)
2
+
(Pulser risetime)
2
+ (Oscilloscope risetime)
The risetime of the 419 is typically 3 ns.
5.2. FACTORY REPAIR
This instrument can be returned to ORTEC for
service and repair at a nominal cost. The standard
procedure for repair ensures the same quality
control and checkout that are used for a new
instrument. Always contact Customer Services at
ORTEC (865) 482-4411, before sending in an
instrument for repair to obtain the necessary
shipping instructions and so that the required
Return Authorization Number can be assigned to
the unit. Write this number on the address label and
on the package to ensure prompt attention when it
reaches the factory.
Summary of Contents for 142IH
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