The active part of NINA is a telescope composed of 16 silicon planes.
Each plane consists of two n-type silicon detectors, 60x60 mm2, attached to a supporting ceramic frame.
The 16 strips of the two silicon detectors are orthogonal in order to measure the x and y coordinates of the detected particle.
The thickness of the first two detectors is 150 micron; all the others, instead, are 380 micron thick, so to have
11.7 silicon mm in total. The indetermination in the total silicon thickness comes from the process of manufacturing,
and is greater (in percentage) for the first two thinner layers.
A summary of the silicon detectors characteristics is reported in the Table 1, while a photo of one single silicon
detector is shown in Figure 1.
In order to reduce to the minimum the thickness of dead area interposed between the silicon detectors, a special ceramic (Al2O3) frame, passing only under the lateral strips 1 and 16 and 625 micron thick, has been built. The role of the ceramic is to sustain the single silicon structures and connect them mechanically and electronically, by means of 64 pins, to the corresponding mother-boards.
A sketch of the whole detector is shown in Figure 2. The 16 planes are vertically stacked; interplanar distance is 1.4 cm, except for the first and second planes separated by 8.5 cm, for a better measurement of the particle incident angle. The 16 planes are modular, so that mechanically and electronically they are interchangeable. This allows fast modifications, even between the Flight and Engineering Model, if necessary. Below the 16 modules, other 4 modules are placed, dedicated to the trigger electronics, silicon power supply, analog-digital conversion, FIFO. The 20 plane structure is fixed at the four corners of the lower part of the vessel by four vertical connecting rods. Every silicon plane is surrounded by an aluminum cage 1.5 mm thick.
The vessel is a cylinder of 284 mm diameter and 480 mm height. The top part is rounded, while in the bottom part the connectors for the interfaces with the other parts of the detector are placed. All the structure is aluminum made, 2 cm thick, apart from a little window in correspondence to the first silicon plane where it is reduced to 300 micron; this choice has been made so to reduce the amount of passive material the particles cross before reaching the real sensitive detector. Nitrogen at 1 atm is fluxed inside the box D1.
A photograph of the whole detector without the vessel is shown in Figure 3.
|Characteristics of the silicon detectors|
|Strip width||3.6 mm|
|Strip thickness - plane 1||(150 ± 15) micron|
|Strip thickness - planes 2-16||(380 ± 15) micron|
|Number of strips/plane||16 (X) + 16 (Y)|
|Strip capacity||65 ± 5 pF|
|Polarization tension||20 - 40 V|
|Leakage current||1 nA|
|Maximum leakage||5 nA|