[en] The experimental study of super-allowed nuclear β decays serves as a sensitive probe of the conservation of the weak vector current (CVC) and allows tight limits to be set on the presence of scalar or right-handed currents. Once CVC is verified, it is possible to determine the V_ud element of the CKM quark-mixing matrix. Similarly, the study of nuclear mirror β decays allows to arrive at the same final quantity V_ud. Whereas dedicated studies of 0⁺→0⁺ decays are performed for several decades now, the potential of mirror transitions was only rediscovered recently. Therefore, it can be expected that important progress is possible with high-precision studies of different mirror β decays. In the present piece of work the half-life measurements performed by the CENBG group of the proton-rich nuclei ⁴²Ti, ^38-39Ca, ^30-31S and ²⁹P are summarised.

[en] Reactions of ⁷Li+⁷Li at E_lab=34 MeV, which lead to charged particle decaying excited states of ¹⁰Be, have been studied by use of a detection system sensitive to decay energies of a few hundred keV. The α-particle branching fractions in ¹⁰Be^*→⁴He+⁶He have been measured for excited states at E_x=7.542 and ∼9.6 MeV. For the 7.542 MeV state an unusually large separation radius is required to explain the observed branching fraction of Γ_α/Γ=(3.5±1.2)x10^-3. This result is interpreted in terms of the energy level structure of ¹⁰Be as related to analogous states in ¹²C and to the recent molecular orbital calculations. A new J^π=0^- state is observed in the decay ¹⁰Be^*→⁷Li^*(0.478 MeV)+t

[en] This paper reports the first application of a new technique to measure the β-decay half-lives of exotic nuclei in complex background conditions. Since standard tools were not adapted to extract the relevant information, a new analysis method was developed. The time distribution of background events is established by recording time correlations in backward time. The β half-lives of the nuclides and the detection efficiency of the set-up are determined simultaneously from a least-squares fit of the ratio of the time-correlation spectra recorded in forward and in backward time, using numerical functions. The necessary numerical functions are calculated in a Monte-Carlo code using the known operation parameters of the experiment and different values for the two free parameters, half-life and detection efficiency, as input parameters

[en] Very neutron-rich nuclei near the A = 195 r-process waiting point were produced as projectile fragments from a ²⁰⁸Pb primary beam at GSI, Darmstadt, by cold fragmentation. After in-flight separation, the fragments were implanted in an active catcher, and time correlations to the subsequent beta-decay were established. Due to the periodic operation cycles of the synchrotron, providing the primary beam, the background shows a complex time structure, which prevents applying well established analytical methods to extract the half-life information. A new mathematical analysis method has been developed, which is based on a Monte Carlo code, simulating the time sequence of implantation and beta detection according to the experimental conditions, leaving the beta lifetimes and the beta detection efficiency as free parameters. In addition, both the analysis of the experimental data and the simulation were performed in time-reversed sequence. The ratio of forward/backward time spectra contains the information of the 'true' fragment-beta correlations. Half-lives were obtained from two-dimensional fits of the measured and simulated ratios of time correlations in forward- and backward-time direction by the least-squares method, being the lifetime and the beta-detection efficiency the two fitting parameters. Half-lives of 8 heavy neutron-rich nuclei approaching the r-process waiting point A = 195 have been determined. (authors)

[en] Heavy neutron-rich nuclei close to the neutron closed shell N = 126 were produced by fragmentation of a 1 A GeV 208Pb beam in a beryllium target at the Fragment Separator at GSI. Around 30 heavy neutron-rich isotopes have been synthesized for the first time and the half-lives of some of them have been determined

[en] The γ-decay branching ratios of ⁴⁹V have been studied in the β/EC decay of ⁴⁹Cr. The γ-ray spectrum has been measured with a 70% relative efficiency co-axial germanium detector calibrated in efficiency with a precision of about 0.5%. The primary result is the measurement of the relative branching ratios of the three main γ rays in the decay of ⁴⁹Cr. Large discrepancies were found with a previous experimental work. The ⁴⁹Cr sample was produced by proton impact on a ZrO₂ target and collected at the ISOLDE facility of CERN and enabled us to re-evaluate the decay scheme of ⁴⁹Cr. The new data allow the use of this nucleus for future high-precision calibration work. (orig.)

[en] The half-life of the mirror β decay of ³¹S has been measured at the IGISOL facility at the University of Jyvaeskylae. The value obtained is T_1/2(³¹S)=(2553.4±1.8) ms, in agreement with previous measurements, but with a precision that is better by a factor of ten than the literature value previously adopted. When the new result is combined with the Q_EC value measured recently at JYFLTRAP, a precision of better than 10^-3 is obtained for the ft value. (orig.)

[en] In an experiment at the LISE3 facility of GANIL, we have studied with high precision the 0⁺ → 0⁺ β decay of ³⁸Ca. The LISE3 facility allowed to produce close to pure samples of the nuclide of interest. We measured the half-life of this nucleus to be 443.63(35)ms, whereas the super-allowed branching ratio was determined to be 77.14(35)%. Both data are in nice agreement with previous high-precision measurements and thus improve the overall precision of the experimental inputs to determine the corrected Ft value for this nucleus. We also compare the experimental Gamow-Teller strength distribution with theoretical shell-model predictions. Finally, future opportunities at LISE3 are discussed. (orig.)

[en] Studies of β-delayed emission of protons for ⁴³Cr and ⁵¹Ni were performed with a Time Projection Chamber. This detection setup allows to reconstruct in the three-dimensional space the tracks of the protons emitted. For the first time, β-delayed emission of two protons is directly observed for ⁴³Cr and ⁵¹Ni. The question about correlations between protons can be accessed. Finally, we show that ⁴³Cr can emit up to three delayed protons.

[en] In the present work we were able to synthesize and measure with high accuracy the production cross sections of more than 190 heavy neutron-rich nuclei by the in-flight fragmentation of relativistic "2"0"8Pb projectiles, 26 of which were produced for the first time. This work has shown that the N = 126 region far below the doubly magic "2"0"8Pb has become accessible experimentally and represents a step further towards the study of heavy neutron-rich nuclei approaching the r-process waiting point at A = 195. (authors)