Collimator
Any heavy metal collimator can be provided on request.
BGO crystal and surface preparation
BGO crystals are cut out of first grade boules with an attenuation length greater than 400 cm.
All crystals are prepared for optimum internal light collection and transmission towards photocathodes.
Phototubes and voltage divers
The back polished surface of each BGO element is coupled to a low noise phototube and its voltage divider.
Signal pulses and high voltage supply are connected on standard Lemo sockets. Phototubes are wired for a positive HV supply as this wiring gives a better noise figure (negative wiring on request).
An high voltage filter is provided also on each voltage divider. Gains of phototubes inside an anti-Compton are factory selected and equalized.
Energy resolution
<18% (FWHM) on side crystals inside the Compton suppression detector. Specification measured with a source placed inside the well in the center of the detector.
These measurements are made under the following conditions :
 radiation line pulse shaping counting rate |
: 137CS-662 keV : l µs peaking time. : 20 000 counts per second. |
Peak to valley ratio
> 10 on crystals of the side elements, lower level energy limit smaller than 10 keV.
These measurements are made under the same conditions as for the energy resolution, but using an Americium source (59 KeV) screened by a 4 mm thick Aluminium filter (absorption of the low energy X-rays emitted by the source).
Suppression factor (SF)
SF > 0.55**, measured with a source placed at the focal point, the BGO anti-Compton surrounding a Ge detector.
These measurements are made with the 60CO 1.17 and 1.33 MeV radiation lines.
SF = area of the peak/area of the total spectrum*
| * ** |
: spectrum bounded at 100 keV : figure subject to further refinement. |
Preamplifiers
On every phototube or phototube pair can be attached on customer request a very fast low noise preamplifier/buffer - 50 ohms coaxial cable drivers.
| gain bandwidth product slew rate output drive capability voltage supply current consumption |
: 180 MHz : 2 000 V/µs. : 100 mA short circuit protected. : ± 12 V compatible with the Nim standard. : ± 20 mA. |
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40 anti-compton detectors
....Gasp experiment INFN Legnaro Italy
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