DSPEC 50
®
and DSPEC 502
®
Digital Gamma-Ray Spectrometer User’s Manual
932502G / 0618
Gate
— This allows you to select a positive TTL logic gating function. With gating
Off
, no
gating is performed (that is, all detector signals are processed); with gating in
Coincidence
mode, a gating input signal
must be
present at the proper time for the conversion of the event;
in
Anticoincidence
, the gating input signal
must not be
present for the conversion of the detec-
tor signal. The gating signal must occur prior to and extend 500 ns beyond peak detect (peak
maximum).
Coincidence and Gate Options (Advanced models only)
— When enabled the
Coincidence
option compares the Gate signal time to the Fast Channel time to determine if they are in
coincidence. The delay can be positive or negative to align the pulses depending on their
arrival times. A positive value delays the gate, and a negative value delays the fast channel.
The
Window
determines how closely the gate and fast channel signals must match to be in
coincidence (or anti-coincidence depending on the Gate option selected) after the delay is
applied. If the Coincidence option is disabled, or it is enabled and the coincidence condition
satisfied, then the Gate is applied based on the Delay and Window settings. In order for the
peak to be considered in Coincidence or Anti-Coincidence the Gate must be enabled when the
peak detect occurs the same as if an external gate signal were applied. The peak detect time
can be determined from the Rise Time and Flat Top settings for peak detection. Note that the
Gate cannot start until after the coincidence has been determined so the coincidence delay and
window should be accounted for when setting the Gate Delay. For example, if the coincidence
delay is negative 4 uS and the combination of Rise Time and Flat Top is 12 uS, then the Gate
Delay would have to be somewhat less than 8 uS for the Gate to be enabled after coincidence.
Since the Gate is only enabled when the more restrictive Coincidence Window has been
satisfied the Gate can be nominally set a few microseconds before and after the peak detect is
expected to occur with excellent results.
Gate Route Mode (Advanced models only)
— When the Gate is in Coincidence or Anti-
Coincidence this option is enabled to store gated and non-gated events simultaneously. This
option will reduce the maximum ADC Conversion Gain to 32K channels. When saving the
spectrum to the ANSI N42 (2012) format (available in GammaVision 8.10 and later) the Gated,
Ungated, and Total Spectrum are all stored within the same file. This option must be checked
before spectrum acquisition begins to ensure that all events are accounted for as gated or
ungated.
ZDT Mode
— See Section 1.6 for a detailed discussion of this feature. Use this droplist to
choose the
Off
(LTC spectrum only) or
CORR_ERR
(ERR and ZDT spectra) mode.
13
If a
ZDT mode is selected, both spectra are stored in the same spectrum (
.SPC
) file. If you do not
need the ZDT spectrum, you should select
Off
.
13
The NORM_CORR (LTC and ZDT) mode is typically not used; see Section 1.6.2.
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