Resolution and Size

The main benefit of SSBs is that the resolution of the SSB detectors is typically an order of magnitude greater than the resolution of gas ionization chamber detectors. The reason for this is that the energy required to produe an electron-hole pair in a semi-conductor (approximately 1 eV) is ten times less than the energy required to create a electron-ion pair (approximately 10 eV). Obviously, the same amount of ionizing radiation will create ten electron- hole pairs in a SSB for every one electron-ion pair produced in a gas. With a larger current produced, the resolution of a SSB detector will correspondingly be improved.

In addition to their resolution, another benefit of the SSBs is their size. The detectors are very small and compact. In our expe riment, we were able to fit five detectors in the scattering chamber at very small separation distances.

Radiation Damage

The major weakness of SSB detectors is their vulnerability to radiation damage over time. When incident particles of radiation collide with SSB detectors, the ionizing radiation often causes structural defects in the lattice structure of the silicon. These incident particles can knock lattice atoms out of their normal positions, causing point defects, or they can cause dislocations in the crystal structure. All of these structural defects lead to the creation of intermediate "trapping" levels in the forbidden energy band gap which trap electrons or holes and reduce the amount of charge carriers in the detector.

These defects negatively affect the detector's performance by causing a degradation of the energy resolution of the detector as well as increasing the amount of leakage current. In heavily damaged detectors, double energy spectra peaks have even been seen. To compensate for this damage, one can try to increase the bias voltage or to operate the system at a lower temperature. By increasing the bias voltage, the collection time will be decreased and the resolution should be improved somewhat. This increase in bias voltage will also lower the amount of noise that is detected which will make the obtained signal clearer. By decreasing the operating temperature of the detectors, the leakage current can be decreased, and the overall quality of the detector will be improved. As the temperature is decreased, the thermal energy of the electrons in the detector will decrease and fewer charge carriers will be able to move about the depletion region in thermal equilibrium. From the principles of solid state physics, this will result in a better detector. For each ten degree decrease in temperature, the leakage current should experience a threefold decrease.