Automatic procedure for the calibration in energy of the silicon detectors of the 4π INDRA array II. Heavy fragments

In order to minimize the dead zones resulting from the mechanical supports, 3 or 4 pads from two adjacent rings (2-3, 4-5, 6-7, 8-9) were designed on the same silicon wafer (48 wafers in all). The pulse height defect (PHD) ΔE of the heavy ions in the Si detectors was measured during the second experimental campaign by means of elastically scattered beams of Ni, Ta and Au at intermediate energies. According to the kinematics, the final energy E of a scattered projectile is a function of θ, the same for one ring. In the framework of the Moulton method the PHD is related to the energy of the fragment by the relation ΔE 10b9Z)*Ea(Z) with a(Z) = 0.0223(Z2/103) + 0.5682 and b(Z) p2*(100/Z)+p1 where the p1 and p2 coefficients depend on the detector. The individual values of b(Z=73) determined in the case of Ta indicate that the wafers were cut from ingots produced in four loads. As expected, the individual detectors built on the same wafer belong to the same load. By 'projecting' these loads on the adjacent rings, we have finally found 9 groups of detectors and for each group we have calculated the mean value of b(Z) for Ni (in two circumstances), Ta and Au. A similar partition has resulted in the first experimental campaign (1993) by means of a slightly different criterion of classification. The fact allowed us to put together the present data with those obtained earlier for Ar, Ni and Xe. Nice agreement of data described by the above equation was observed. The resulting coefficients p2, p1 are used for the energy calibration of the physics runs