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Some remarks on the treatment of secondary reactions in the evaluation of isotopic reaction cross sections Karl-Heinz Schmidt, 13. 2. 2000 Reaction cross sections often are evaluated in a thin-target approximation. If the reaction probability is not very small, this treatment is not sufficient for obtaining high-precision results. The following remarks refer to the experimental program performed at GSI, Darmstadt, to determine the formation cross sections of residual nuclei in fragmentation reactions. The target is not transparent, neither to the projectile nor to the reaction products one wants to measure. Therefore, the effective primary-beam intensity reduces along the target according to the reaction rate. In addition, the reaction products themselves may undergo consecutive nuclear reaction. Both effects have to be corrected for in order to extract reliable formation cross sections. Considering the attenuation of the primary beam is rather simple. It will not be discussed further. The exact consideration of multiple reactions requires the knowledge of all reaction cross sections involved. We will discuss an approximate treatment which allows to correct the data on the basis of available experimental information.
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