Decay of neutron deficient Eu, Sm and Pm isotopes near the proton drip line

Abstract

The β-delayed proton and γ-ray decays of the two new isotopes 134,135Eu and of 136Eu, 134,135,136Sm, 134,135,136Pm and 135Nd were studied This is the flrst observation of β-delayed proton decay in europium isotopes. On-line mass separation and X-ray coincidences were used for isotope identification. Half-lives of 0.5 ±0.2 s and 1.5 ±0.2 s were measured for 134Eu and 135Eu respectively. For 136Eu evidence for two isomers with half-lives of 3.7 ±0.3 s and ~3.0 s was obtained. Betadelayed proton emission was assigned to the decays of 134Eu, 135Sm and 136Eu based on proton K X-ray coincidences and mass separation. Proton branching ratios of (9±3) × 10 −4 for 136Eu and (2±1) × 10 −4 for 135Sm were measured. Beta-delayed proton emission to the 0 + ground and to the 2 + excited states in 134Nd was observed following the 135Sm decay. The 135Eu activity was identified by Sm K α X-rays from its electron-capture decay, and one γ-ray was assigned to this decay. Fast allowed Gamow-Teller 0 + → 1 + β-transitions to the 118.9keV level in 134Pm and 114.4keV level in 136Pm were identified. The low-spin β-decays of 136Pm and 135Nd were studied without significant interference from the high-spin decays, and decay schemes were constructed for 134,135,136Sm, 134,135,136pm and 136Eu