MEASUREMENT OF THE L-FORBIDDEN GAMOW-TELLER BRANCH OF K-37

The beta decay of K-37 is studied in detail. Several new beta decay br anches and gamma-ray transitions are assigned to this nucleus. The l-f orbidden 0d(3/2)-->1s(1/2), Gamow-Teller branch to the first excited S tate in Ar-37 is observed for the first time and its branching ratio m easured to be (42.2+/-7.5) x 10(-6). Such l-forbidden branches are ver y sensitive to extranucleonic effects such as meson-exchange currents and Delta-isobar excitations. A calculation of these as well as core-p olarization and relativistic effects, predict branching ratios of 8 x 10(-6) with universal s-d wave functions and 52 x 10(-6) with Chung-Wi ldenthal wave functions.