High-spin states in 38K

Abstract High-spin states in 38 K are investigated with the 24 Mg( 16 O, pnγ) 38 K reaction at E( 16 O ) = 36–44 MeV . A recently developed Compton-suppression spectrometer with 120 msr solid angle and a pulsed beam are employed to study their γ-decay. For the E4 transition from the isomeric level at E x = 3458 keV to the ground state a branching ratio of (0.15 ± 0.02)% is found. On the basis of angular distribution and polarization measurements, in which the delayed feeding component is eliminated, spin-parity assignments are obtained of J π (2646 keV) = (2, 4) − , J π (3420 keV) = (4, 6) − and J π (3458 keV) = (5, 7) + . Prompt-delayed and prompt γγ coincidence experiments are performed to locate high-spin levels above the isomer. Hitherto unobserved levels of high spin are found at E x = 5254, 7397, 8693, 8747 and 10980 keV and assignments of J π = (9 + ), (10 − ), (12 − ), (11 − ) and (13 − ) respectively, are suggested by weak-coupling considerations. The experimental results are compared with a large-scale shell-model calculation performed in a configuration space with a 28 Si core and ten active particles distributed over the ( 2 s 1 2 , 1 d 3 2 , 1 f 7 2 , 2 p 3 2 ) shells. The high-spin states appear to have a rather simple shell-model structure.