Structure functions of /sup 12/C, /sup 63/Cu, and /sup 208/Pb nuclei in photoproduction of cumulative protons

Results are reported of an investigation of the structure functions f(..cap alpha.., p/sub perpendicular/) of the nuclei /sup 12/C, /sup 63/Cu, and /sup 208/Pb in the course of photoproduction of cumulative protons at E/sup max//sub ..gamma../ = 4.5 GeV. It is shown that for /sup 12/C nuclei (K. Sh. Egiyan et al., Sov. J. Nucl. Phys. 37, 730 (1983); Report 525(12), Erevan Phys. Inst., 1982) as well as for /sup 63/Cu and /sup 208/Pb the function f(..cap alpha../sub 1/ p/sub perpendicular/) can be represented as the product f/sub 1/(..cap alpha..)f/sub 2/(p/sub perpendicular/), with f(..cap alpha..)approx.exp(-..cap alpha../..cap alpha../sub 0/). The parameter ..cap alpha../sub 0/ determined in the region ..cap alpha..>1.5 is equal to 0.134 +- 0.01 and is independent of p/sub perpendicular/ at p/sub perpendicular/> or =0.5 GeV/c, but tends to increase with A. The ratio R/sub A//C = f/sub A/(..cap alpha.., p/sub perpendicular/)/f/sub C/(..cap alpha.., p/sub perpendicular/) is discussed. It is shown that R/sub A//C increases noticeably in the region ..cap alpha.. = 0.6 to 2.0. This may offer evidence that the fraction of hard quarks increases with increasing A.