Relative Phases ofE2andM1Matrix Elements in1p-Shell Nuclei

The predictions of the independent-particle model for seven mixed $E2\mathrm{}-M1\mathrm{}$ gamma-ray transition in the $1p$-shell nuclei are compared with experiment. Agreement is excellent both for the $M1\mathrm{}$ widths and for the $\frac{E2\mathrm{}}{M1\mathrm{}}$ mixing ratios if, in the latter case, collective enhancement of $E2\mathrm{}$ transitions is included. This collective enhancement is discussed first in terms of effective charges, then in terms of perturbation theory in a Nilsson model. The seven transitions considered are ones for which the experimental results are especially reliable, and the theoretical results are relatively insensitive to details of the model. The main motive of this work was to compare the measured phases of the $\frac{E2\mathrm{}}{M1\mathrm{}}$ mixing ratios with theory. The agreement both for the absolute phases and the magnitudes was good enough to establish these seven transitions as standards for later consideration of the phases of $\frac{E2\mathrm{}}{M1\mathrm{}}$ mixing ratios for less well-understood transitions. Some general relationships between $\frac{E(L+1\mathrm{})\mathrm{}}{\mathrm{ML}}$ and $\frac{M(L+1\mathrm{})\mathrm{}}{\mathrm{EL}}$ mixing ratios of corresponding transitions in conjugate nuclei are discussed.