HiRA detector dead layer determination at the NSCL

One of the primary ways to discover new information about nuclei is to detect the remnants of collisions between two different nuclei moving at high (relativistic) speeds. The HiRA (high resolution array) is capable of resolving the energies of these collision remnants to an accuracy of about 35 keV. To accurately determine the energies of these particles an accurate calibration is required. Obtaining this accurate calibration necessitates the knowledge of the areas of the detector where no signal will be detected (this is known as the dead layer of the detector). This dead layer consists of regions of the detector that do not record the energy deposited in them by particles, and thus this information is lost to the experimenters. This data can be recovered by an accurate knowledge of the thickness of this dead layer, which can then be used to calculate the energy lost by the particles. This is done by using geometric determinations and observing the shifts in peaks caused by changes in the incident angle (and thus the effective dead layer thickness) of incoming alpha particles on the silicon detectors. By observing the results of these changes in angle it was determined that the dead layer of a standard detector, HiRA telescope # 1 is (.93 ± .08) microns of Silicon.