IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
For SLFIT System, stuck-at 1 is
an unsafe fault, which needs to
be detected on-line in a
minimum possible time. To
prevent Safety Logic System
failing in unsafe mode, an online
test facility i.e. Fine Impulse
Test (FIT) logic is provided. FIT
Logic monitors the health of
Safety Logic System on-line and
detects safe and unsafe
failures. FIT logic injects short
duration (1 ms) trip pulses
periodically at the input of
Safety Logic in required
combinations and verifies the
propagation of these pulses at
the output of Safety Logic
System. Each parameter is
tested with a periodicity of 3
minutes. Whenever a fault is
detected, the information is
sent to the Control Room (CR)
for further action.
SLFIT system shall remain
functional even under stringent
environmental conditions.
Hence, the system will be
subjected to Electro Magnetic
Interference (EMI) / Electro
Magnetic Compatibility (EMC),
Environmental and Seismic
qualifications. Industrial
Prototype of SLFIT System has
been fabricated and testing is
under progress.
V.C.5. Development and Commissioning of Pulse Shape
Discrimination Electronics for Phoswich Detector System
Phoswich detectors [Thin
NaI(Tl) + Thick CsI] are
generally used for measuring X-
ray or low energy gamma
emitting radionuclide
contamination in lungs. In
phoswich detectors the
interference due to high energy
(HE) scatter component in low
energy (LE) region is reduced
using different schemes of pulse
shape discrimination (PSD)
electronics. The PSD electronics
utilizes the difference in the
decay time characteristics of
two phosphors to discriminate
the interactions of HE and LE
photons. Previously a custom
built electronics with discrete
components was being used,
which has suffered frequent
failure of components, thereby
resulting in poor performance
and timing resolution. The new
PSD electronics is configured
using readily available nuclear
electronic modules, which
makes it convenient to replace
any of the modules for easy
maintenance.
The phoswich is of SCIONIX
make having 203 mm dia, 3
Fig.1 Phoswich system electronics with typical signal details
132 ENABLING TECHNOLOGIES