Beta-delayed proton emission from 20 Mg has been measured at ISOLDE, CERN, with the ISOLDE Decay Station (IDS) setup including both charged-particle and gamma-ray detection capabilities. A total of 26 delayed proton branches were measured including seven so far unobserved. An updated decay scheme, including three new resonances above the proton separation energy in 20 Na and more precise resonance energies, is presented. Beta-decay feeding to two resonances above the Isobaric Analogue State (IAS) in 20 Na is observed. This may allow studies of the 4032.9(2.4) keV resonance in 19 Ne through the beta decay of 20 Mg, which is important for the astrophysically relevant reaction 15 O(α, γ) 19 Ne. Beta-delayed protons were used to obtain a more precise value for the half-life of 20 Mg, 90.9(1.2) ms. PACS. 23.20.Lv γ transitions and level energies-26.30.Ca Explosive burning in accreting binary systems (novae, x-ray bursts)-27.30.+t 20 ≤ A ≤ 38-29.30.Ep Charged-particle spectroscopy

The β − decay of 34 Mg was used to study the 34 Al nucleus through γ spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two β-decaying states in 34 Al having spin-parity assignments J π = 4 − dominated by the normal configuration π (d 5/2) −1 ⊗ ν(f 7/2) and J π = 1 + by the intruder configuration π (d 5/2) −1 ⊗ ν(d 3/2) −1 (f 7/2) 2. Their unknown ordering and relative energy have been the subject of debate for the placement of 34 Al inside or outside the N = 20 "island of inversion." We report here that the 1 + intruder lies only 46.6 keV above the 4 − ground state. In addition, a new half-life of T 1/2 = 44.9(4) ms, that is twice as long as the previously measured 20(10) ms, has been determined for 34 Mg. Large-scale shell-model calculations with the recently developed SDPF-U-MIX interaction are compared with the new data and used to interpret the mechanisms at play at the very border of the N = 20 island of inversion.

Excited states in 133 Sn were investigated through the β decay of 133 In at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for 133 In, allowing us to study separately, and in detail, the β-decay branch of 133 In J π = (9/2 +) ground state and its J π = (1/2 −) isomer.

In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of γ-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 108 n s−1cm−2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr3:(Ce) detectors from the FATIMA collaboration. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The triggerless acquisition system allowed a signal collection rate of up to 6 × 105 Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr3:(Ce) detectors to analyze half-lives of excited levels in the pico- to microsecond range. Precise energy and efficiency calibrations of EXILL were performed using standard calibration sources of 133Ba, 60Co and 152Eu as well as data from the reactions 27Al(n,γ)28Al and 35Cl(n,γ)36Cl in the energy range from 30 keV up to 10 MeV.

The 12 C(α, γ) 16 O reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced α width, γ11, of the bound 1 − level in 16 O is particularly important to determine the cross section. The magnitude of γ11 is determined via sub-Coulomb α-transfer reactions or the β-delayed α decay of 16 N, but the latter approach is presently hampered by the lack of sufficiently precise data on the β-decay branching ratios. Here we report improved branching ratios for the bound 1 − level [b β,11 = (5.02 ± 0.10) × 10 −2 ] and for β-delayed α emission [b βα = (1.59 ± 0.06) × 10 −5 ]. Our value for b βα is 33% larger than previously held, leading to a substantial increase in γ11. Our revised value for γ11 is in good agreement with the value obtained in α-transfer studies and the weighted average of the two gives a robust and precise determination of γ11, which provides significantly improved constraints on the 12 C(α, γ) cross section in the energy range relevant to hydrostatic He burning.