Differential production cross sections of multiply charged fragments in 800 MeV proton-induced spallation of carbon, aluminum, and nickel

Abstract

Differential production cross sections for multiply charged fragments from 800-MeV proton-induced spallation of /sup 12/C, /sup 27/Al, and natural Ni were measured at 30 and 90 degrees. The ion fragments were identified by use of time-of-flight, ..delta..E--E detector telescope capable of complete particle identification for energies as low as .25 MeV/nucleon. The very short ranges of the particles of interest required the construction of very thin detectors with minimal deadlayer material. The time-pick-off detectors and gas ionization chamber developed are unique, and represent the state-of-the-art in fast timing for time-of-flight measurements and in construction of thin detectors. The resolutions achieved allowed the cross sections of /sup 3/He, /sup 4/He, /sup 6/Li, /sup 7/Li, /sup 7/Be, /sup 9/Be, /sup 10/Be, /sup 10/B, /sup 11/B, /sup 11/C, /sup 12/C, and /sup 13/C to be determined, along with those of nitrogen and oxygen without isotope separation. The cross sections were found to have weak angular dependence. Consequently, pseudo cross sections were calculated from the 90/sup 0/ data by integrating the differential cross sections from 0 to 25 MeV for each product and multiplying by 4..pi... Pseudo theoretical cross sections were similarly calculated from theoretical differential cross sections. These differential cross sections were calculatedmore » by use of a Monte Carlo computer code which incorporated the cascade-evaporation model of high-energy nuclear reactions. Implications are drawn for modifications of the model. The results suggest reducing the transparency of the struck nucleus to pions produced in the cascade stage of the reaction model in order that a higher excitation energy be left for the evaporation stage. Also, there is some evidence that evaporations of nuclear aggregates more massive than /sup 4/He occur. Inclusion of such evaporations should improve the model. 82 figures, 1 table.« less