System Options: Optional Detectors
7-6
User Manual
C O N F I D E N T I A L –
limited rights
Feb 2018
Revision A
Directional Gaseous Analytical Detector (GAD)
This is a lens mounted low voltage silicon diode with an active area of approximately 100 mm
2
, that can be used at
pressures above 10 Pa. It is positioned directly over the sample to obtain maximum detector efficiency.
FIGURE 7-4:
Directional GAD Diode
The GAD can be used down to a high voltage about 1 kV and works best with slow scan conditions.
It can be used for HiVac, but because it limits the minimum achievable WD, it is disadvantageous for high
resolution imaging. It has a 500
µm
PLA cone for LoVac operation, especially the X-ray analysis. The cone extends
down from the unit to 7.5 mm, which reduces the gas path length for electrons to an efficient 2.5 mm at the
standard WD = 10 mm.
Installing / Removing
When not used, the GAD is placed at its parked position (inside the chamber
at the bottom right side) in the protective plastic box to prevent it from being
polluted. The cables are permanently connected to the feed-through
connector board by Thermo Scientific service.
1.
With your gloved hand grasp the detector in the protective box.
2.
Push the mounting collar gently up to the objective lens cone. The part
with the connector cables faces towards the chamber door.
3.
Push the sides of the protective box and release the installed detector.
When removing the detector, proceed in reverse.
FIGURE 7-5:
Directional GAD detector installation
C a u t i o n !
The diode is sensitive to mechanical damage. The active area (shiny diode) should never be touched.
The GAD is mounted close to the (optional) X-ray detector collimator, which must not be touched when changing
detectors. It is advisable to retract the EDX collimator when mounting / removing the detector on / from the objective
lens.
1
2
3
