Recoil studies of some light-mass products from the proton-induced fission of ²³⁸U at intermediate energies

Abstract

The recoil properties of 66Ni, 6 7 C~, and "Zn produced in the fission of 238U by protons of 40-85 MeV energy have been studied radiochemically by the thick target -thick catcher technique. The average kinetic energy of each product has been calculated from the ranges by use of known range-energy relationships. The calculated impact velocity v shows that these fission products are formed predominantly via a compound nucleus ~llechanism in this energy region. The average total kinetic release in fission is found to be insensitive to the bombarding energy.Canadian Journal of Chemistry, 47, 655 (1969) Hnatrodactionscission. Information about the momentum The study of recoil ranges of fission products has proved to be of considerable interest in providing useful information about the fission process. A number of investigations involving measurements of recoil ranges (1-8) have been made by the use of a thick target -thick catcher technique. All these experiments involve the measurement of the average ranges of fission products and the subsequent conversion of the ranges into kinetic energies of these products by the use of a suitable range-energy relationship. Attempts have been made to correlate these results with the fission mechanism. In some of these studies (1,5,7,8), additional information about the cascade deposition energy and the angular distribution of fission fragments has also been gathered. All these experiments have, however, been performed for either thermal fission or highenergy proton fission (> 150 MeV) of heavy elements. We have investigated the recoil properties of fission products in the energy range of MeV. This study is of particular interest since a transition from compound nucleus formation to a direct interaction is generally believed to take place in this energy range.We have measured the recoil ranges of the lowmass fission products, 66Ni, 67Cu, and 72Zn, in 40-85 MeV proton fission of 238U by the thick target -thick catcher technique. The kinetic energies of the fission products have been calculated and attempts have been made to explain these energies in terms of coulombic repulsion between two charged centers at the moment of IThis research received financial support from the National Research Council of Canada. transfer in the initial impact between the incident Droton and 238U nucleus has been obtained. In addition a correlation between our results and higher energy data has been attempted. Experimental ProcedureThe targets used in the present work consisted of uranium foils of normal isotopic composition having a superficial density of about 140 mg/cm2. High purity aluminium foils (0.0008 in. thick) were used as catchers. The target foil was cleaned with nitric acid prior to bombardment, and then sandwiched between two aluminium catcher foils. The dimensions of the catcher foils were larger than that of the target so that any recoils originating in the edge of the target nere all caught. An additional aluminium foil was introduced in the stack in order to determine the activati...