Radionuclide productions in thick iron targets bombarded with 1- and 3-Gev protons

The effective production cross sections of a number of radionuclides have been measured in thick iron targets (30 cm by 30 cm by 95 cm) bombarded with collimated beams of 1- and 3-Gev protons. Low-energy products, Mn54, Cr51, and V48, show varying buildup factors near the front of the target; high-energy products, Be7, Na24, and P32, show little if any buildup. The buildup factors are larger in the 3-Gev target and extend to greater depths. All the production cross sections eventually decrease exponentially with depth, corresponding to mean absorption lengths along the primary beam of ∼65 and 125 g cm−2 at 1 and 3 Gev, respectively. The radial distribution of the products was measured, and contours of constant concentration were determined. The radial spreading becomes very significant for low-energy products near the back of the targets, whereas high-energy products are fairly well collimated along the beam axis. The results of the 3-Gev experiment are in good agreement with those reported by Honda in 1962. These experiments are helpful for an understanding of the distribution of cosmogenic products in meteorites.