Carrier Board (SCN 7078120)
Gem-5 User’s Manual 337
Detectors
Gamma Scintillation Detectors
The Mirion Technologies (Canberra CA) Ltd. large area gamma detectors used on
the Argos-3/-5AB Zeus and the GEM-5 monitors (they are identical) are based on 2
in. thick plastic scintillators. Each detector is approximately 58.4 cm (23 in.) by 38.1
cm (15 in.) with a 22.9 cm (9 in.) by 5.1 cm (2.0 in.) cutout for the PMT and
preamp assembly, giving each detector a surface area of 2103 cm² (26 in.²). The
small gamma scintillation detectors (for the head position etc.) on the Argos-5AB
Zeus measures 33 cm (13 in.) by 11.4 cm (4.5 in.). Each scintillator is equipped
with one photomultiplier tube (PMT) and associated electronics. The PMT housing
is made from black anodized aluminum and is attached directly to the scintillator
slab. To ensure the most efficient light collection 2 mm thick silicone optical
interface pads (not silicone grease) are used between the PMT face and the
scintillator. The light tightness of the assembly is ensured by the special self-
adhesive light masking tape that is applied over all areas that may be prone to light
leaks. The scintillator and PMT are secured in a detector frame assembly for
mounting in the chassis.
The PMT is mounted directly on the HV Divider Board Assembly (SCN 816041)
inside its light tight housing. The HV Divider Board provides the required voltage to
the PMT's dynodes and extracts the output signal from its anode. The board also
gives mechanical support to the PMT and, by means of the spring-loaded mounts,
applies the required pressure to the PMT and its optical interface with the scintillator.
Computer Box (SCN 7079642)
Details on page 367.
Carrier Board (SCN 7078120)
The Carrier Board (model number can be identified by the number stamped on the
board), which is located in the computer box, is the electronic backbone of the
Mirion Technologies (Canberra CA) Ltd. monitor. It provides the interface between
the computer board (which is installed on the Carrier Board) and the Detector
Boards, the Sensor Board, the LCD screen, and the peripheral connectors (badge
reader, keyboard/mouse, Ethernet, speakers, I/O ports, etc.). It also contains an over
temperature alarm that can take the unit out of service The ETX form factor
computer board includes built-in sound board functionality that eliminates the need
for a separate sound card.
The Carrier Board communicates with up to 255 peripheral boards that are connected
to the proprietary Detector Serial Interface Bus. Each peripheral board has a unique
address as defined in the following table.
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