Pulse Height Defects Due to Nuclear Collisions Measured with Thin Window Silicon Surface Barrier Detectors

Nuclear collisions undergone by an ion in a detector introduce a lack of ionization called pulse height defect, the importance of which varies with energy and type of particles. This defect has been measured for He, N and Ne ions with energies below 150 keV impinging on a gold silicon surface barrier detector. The results are compared with Lindhard´s and Haines´s theories and are in good agreement. The energy loss of a charged particle in a medium occurs mainly by electronic and nuclear collisions, the relative importance of which depends on the velocity v and the average charge Z1 of the particle. In the case of protons or heavier ions with velocities such as v > v0 Z2/31 (v0 = e2/h), the energy is essentially lost by electronic collisions and the slowing down is well described by the relation of Bethe. For particles with v < v0 Z2/31, Bethe´s theory of stopping by electronic collisions is no more valid, and, on the other hand, nuclear collisions become important and must be taken into account. Usually, the energy lost in the sensitive region of a detector is indirectly determined by measuring the number of free carriers created by the ionizing particle. This number is proportional to the part ¿(E0) of the particle energy E0 which is lost in electronic collisions. The other part ¿(E0) lost through nuclear collisions, does not contribute to ionization. For electrons (or ¿ rays) the energy ¿(E0) can generally be neglected.