The odd–even effect of fragmentation cross sections for 36Ar and 40Ar

Projectile fragmentation cross sections are calculated for reactions of 36Ar and 40Ar on C, Al, Cu, and Pb targets at 400 A MeV by using the improved quantum molecular dynamics model, together with the statistical model code GEMINI. The total cross sections increase with increasing target mass, which is in good agreement with the experimental results and other theoretical predictions. The isotopic distributions and isospin distributions suggest that the odd–even effect is dependent on the projectile nuclei. For a 36Ar projectile with TZ=0, the partial cross sections appear an obvious odd–even effect, and the isotopic distributions show that the maximal cross sections for the even-Z isotope are larger than that for the neighboring odd-Z isotope. However, the fragmentation cross sections and the isotopic distributions for the 40Ar projectile have not shown these characteristics. The isospin distributions show that the odd–even effect of fragments from the TZ=0 projectile is stronger than that from the TZ=−2 projectile. (paper)