E.G. Wikner

Correlation of Radiation Types with Radiation Effects

The effects produced by different types of nuclear radiation can be compared by making use of the available information on radiation-effects mechanisms. One can separate radiation-effects manifestations into three categories: transient radiation effects, which are due to excited and ionized electrons; displacement radiation effects, which are manifestations of atoms displaced from their normal lattice sites in crystalline solids; and chemical radiation effects, which are due to molecular rearrangements occurring as a second stage to ionizing interactions. The effects produced by different primary radiations can be compared by first identifying the manifestation as belonging to one of these three types. For displacement effects one should then compute the relative cross sections for producing displaced atoms and the average size of the displacement cascade produced by the primary recoil atom. Similarly, for transient and chemical effects one should compute the ionization density produced by the incident radiation. Examples of the pertinent cross sections have been calculated for electrons, gamma rays, protons, and neutrons of various energies.

Study of n- and p-Type Silicon Exposed to Highly Energetic Radiation

For an understanding of displacement effects in semiconductors, it is important to establish a correlation of the magnitude of these effects with various types of radiation. A study has been made of the effect of highly energetic radiation on n-type silicon using two techniques. First, with electron-spin resonance studies, the energy dependence of formation of the Si-Bl center at 80° and 300°K by 1.5, 2.5, 5, and 30 MeV electrons and by reactor neutrons has been determined. In addition, the energy dependence of the production of the divacancy by electrons with energies between 2.5 and 30 MeV in n-type silicon have been obtained. Second, using galvanomagnetic techniques, information has been obtained on the irradiation response and subsequent recovery during annealing of the conductivity, Hall coefficient, and Hall mobility of n-and p-type silicon. The samples were bombarded at 80°K with 5 to 30 MeV electrons and isochronally annealed to 400°K. A considerable amount of annealing was observed in all cases, but the recovery was never complete.