Preliminary results from a feasibility test of mixed alpha source detection by prototype bare silicon devices

A project on development of a satellite-borne silicon-based cosmic ray ion detector was started. Semiconductor detectors based on P-I-N junctions are widely used in space experiments due to their light weight, compact design and high stopping power. The position-sensitive parts of the detector are designed to be silicon-based detectors. A prototype silicon detector without the outermost layer of insulators was prepared. The detector is expected to have the potential to identify the elements of high energy ions using the ∆E-E technique. Thus, for the beginning step of this project, a detector response proportional to the deposited energy has to be confirmed. We set up a detection system of a mixed standard alpha source including Am-241, Pu239 and Cm-244 with our devices and a photodiode (Hamamatsu S1223 with glass removed). The detector response is indicated by the digitized signal pulse height distribution from a 2048-channel ADC. The feasibility of our devices to distinguish the difference of energy in terms of several hundred keV was confirmed. A linear relation between the pulse height peaks and the emitted energy of each radiation source was also indicated.