Measuring the ß-decay Properties of Neutron-rich Exotic Pm, Sm, Eu, and Gd Isotopes to Constrain the Nucleosynthesis Yields in the Rare-earth Region

The ß-delayed neutron-emission probabilities of 28 exotic neutron-rich isotopes of Pm, Sm, Eu, and Gd were measured for the first time at RIKEN Nishina Center using the Advanced Implantation Detector Array (AIDA) and the BRIKEN neutron detector array. The existing ß-decay half-life (T1/2) database was significantly increased toward more neutron-rich isotopes, and uncertainties for previously measured values were decreased. The new data not only constrain the theoretical predictions of half-lives and ß-delayed neutron-emission probabilities, but also allow for probing the mechanisms of formation of the high-mass wing of the rare-earth peak located at A ˜ 160 in the r-process abundance distribution through astrophysical reaction network calculations. An uncertainty quantification of the calculated abundance patterns with the new data shows a reduction of the uncertainty in the rare-earth peak region. The newly introduced variance-based sensitivity analysis method offers valuable insight into the influence of important nuclear physics inputs on the calculated abundance patterns. The analysis has identified the half-lives of 168Sm and of several gadolinium isotopes as some of the key variables among the current experimental data to understand the remaining abundance uncertainty at A = 167–172.Peer ReviewedPostprint (published version

Configuration mixing investigation in germanium isotopes through measurement of E0 transition strengths

Experimental and theoretical studies of the germanium isotopes on the neutron-rich side of the stability valley point increasingly toward the emergence of triaxiality, configuration mixing, and shape coexistence phenomena. Studies of the E0 strengths, which can provide a direct measure of the amount of configuration mixing, are lacking. Thus, determining E0 transition strengths is essential for an understanding of the evolution of structures in the Ge isotopes. Beta-decay experiments populating excited states in the 72,74,76,78Ge isotopes were performed at the TRIUMF-ISAC radioactive beam facility. Gamma-ray and electron spectroscopic investigations have been performed, to measure E0 strengths between states of J > 0, exploiting the GRIFFIN spectrometer combined with the PACES silicon detector array. Preliminary results from this study are presented

Studying the Exotic Decay 70^{70}Kr →70\rightarrow {}^{70}Br

Beta-decay of the very neutron-deficient Kr isotope, 70Kr, was studied at RIKEN-RIBF using the EURICA cluster array. The experiment significantly increased our knowledge of the beta-decay of this isotope. Namely, 16 new γ-ray transitions were identified and the half-life was derived from time correlations of the beta particles (t iβ 1/2 = (44.99 ± 0.16) ms) and from the decay curves of the observed γ-ray transitions (t iβγ 1/2 = (45.16±0.71) ms), respectively

The β-decay of 70^{70}Kr into 70^{70}Br: Restoration of the pseudo-SU(4) symmetry

International audienceThe β-decay of the even-even nucleus 70Kr with Z=N+2, has been investigated at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center using the BigRIPS fragment separator, the ZeroDegree Spectrometer, the WAS3ABI implantation station and the EURICA HPGe cluster array. Fifteen γ-rays associated with the β-decay of 70Kr into 70Br have been identified for the first time, defining ten populated states below Eexc=3300 keV. The half-life of 70Kr was derived with increased precision and found to be t1/2=45.19±0.14 ms. The β-delayed proton emission probability has also been determined as εp=0.545(23)%. An increase in the β-strength to the yrast 1+ state in comparison with the heaviest Z=N+2 system studied so far (62Ge decay) is observed that may indicate increased np correlations in the T=0 channel. The β-decay strength deduced from the results is interpreted in terms of the proton-neutron quasiparticle random-phase approximation (pnQRPA) and also with a schematic model that includes isoscalar and isovector pairing in addition to quadrupole deformation. The application of this last model indicates an approximate realization of pseudo-SU(4) symmetry in this system

Half-life Measurement Using Implant-(β−γ)(\beta -\gamma ) Time Correlations in the Region of Neutron-rich Lanthanides

Neutron-rich lanthanides were produced via in-flight fission of a 238U primary beam at the RIBF, RIKEN Nishina Center to measure half-lives (T1/2) and beta-delayed neutron emission probabilities (Pn) in order to constrain r-process abundance calculations. 159–166Pm, 161–168Sm, 165–170Eu, and 167–172Gd ions were implanted in the Advanced Implantation Detector Array (AIDA), and β-delayed neutrons and γ-rays were detected by the surrounding detector array (BRIKEN). For the validation of T1/2 values derived from implantation–β (i–β) time correlations, γ-spectroscopic methods were used as well. The experimental results of the β-delayed γ-spectroscopy of 162Pm are presented here as an example. A half-life value from γ-decay curves was derived with a comparable uncertainty to the result from the i–β method, and a mean value well within the 1σ range