Coulomb Excitation of Ta, W, and Au

By using protons as bombarding particles, a study has been made of the yields and angular distributions of Coulomb-excited gamma rays in tantalum (137, 166, 303 kev), tungsten (114 kev), and gold (277, 195, 545 kev). Coincidence experiments show that the 277-kev and the previously unreported 545-kev transition go to the ground state and that the Ta 166-kev line represents a cascade from 303 kev. Thin-target yield data for the 277-kev gamma gives an absolute cross section which is in approximate agreement with the theory while the absolute cross section for the 545-kev transition is seven times too large. [Note added in proof.—On correcting an arithmetical error the absolute cross section for the 545-kev transition is also found to be in approximate agreement with the theory.] In both cases the experimental cross sections increase more rapidly than the theory. Thick-target yields from the five strongest gamma rays are greater than the theory by factors ranging from 6 to 100 percent between proton energies of 2 and 4 Mev. Agreement with the theory becomes worse with increasing level energy and decreasing proton energy. On the basis of the theory the angular distribution data permit an unambiguous spin assignment of $\frac{7}{2}$ to the 545-kev level and give agreement with the previously established spins for the 277 (Au), 137, 303 (Ta), and 114-kev (W) levels. The ratio of $E2\mathrm{}$ to $M1\mathrm{}$ radiation is $\frac{{7_{-5\mathrm{}}}^{+13\mathrm{}}}{100}$ for the 277-kev radiation (Au) and less than $\frac{5}{100}$ for the 137-kev radiation (Ta).