| In order to provide new insights into the character of the giant dipole resonance in nuclei the photoproton and photoalpha cross sections for ('28)Si in the energy region 15.62 through 22.50 MeV were measured with gamma ray resolution of approximately 200 KeV using the University of Illinois bremsstrahlung monochromator. A silicon particle detector was used both as a target and as a 4(pi) solid angle detector for the reaction products. Three detectors were used; a 1 mm surface barrier detector, a 3 mm Si(Li) detector, and a 5 mm Si(Li) detector. All three detectors had an area of 300 mm('2).;The measured partial cross sections were analyzed using the statistical compound nucleus model. The results of this analysis indicate that, for the most part, the proton decays are neither direct nor statistical in nature. The alpha particle decays are most probably statistical in nature.;The total photoabsorption cross section for ('28)Si shows four major peaks. This general trend is observed in most of the partial cross sections, suggesting that theoretical descriptions of the ('28)Si giant dipole resonance, which have invoked differing particle-hole configurations for each of the four major peaks, are incorrect.;The partial cross sections for ('28)Si((gamma),p) reactions leaving ('27)Al in its ground state and first ten excited states were measured. The experimental energy resolution was not adequate to permit the separation of the fifth and sixth excited states or the eighth and ninth excited states. The partial cross sections for ('28)Si((gamma),(alpha)) reactions leaving ('24)Mg in its ground state and first two excited states were also measured. The data confirm the fine structure seen in earlier experiments, but do not have the resolution of the earlier inverse reaction experiments which provide information on the ground state decays through detailed balance. |
