ilicon detectors are commonly used in high-energy physics applications, such as vertex detectors in colliding particle beams experiments, where ionizing particle tracks are looked for, or electromagnetic calorimeters, where one measures the ionizing particle energy loss per unit length of silicon.

n most applications the silicon chip surface, that is the detector itself , is placed at right angles to the incoming radiation direction and therefore radiation can be absorbed only within a few hundred microns of silicon, which is the typical chip thickness. In medical applications, however, the amount of radiation needed to obtain a significant image must be minimized and it is essential to extract all the information contained in the beam used to produce the image. One way to do this is to maximize detector efficiency.

The SYRMEP detector achieves a high efficiency, in the energy interval 15 to 35 keV, thanks to its choice of geometry: the chip faces the incomimg beam with its side, rather than with its surface, and impinging photons can be absorbed within the entire chip width, which can reach a few centimeters. This ensures, in the above energy interval, total absorption of all incoming photons.

he picture shows a view of a constructive element of the currently used SYRMEP detector along with its read-out electronics. The detector proper is the trapezoidal structure at left in the picture. X-rays impinge on the left side of this structure where pixels are defined by a comb shaped series of microstrips. Each one of the 256 microstrips is 1 cm long and two microstrips are separated by 200 mm: since chip thickness is 300 mm, the resulting pixel size is 200x300 mm

and the entire detector covers a length of 5.12 cm. Every microstrip is connected to a channel of the read-out electronics by means of conductive paths deposited on kapton foils. Read-out circuits consist of VLSI analog/digital chips (at right in the picture) and are capable of single photon counting.