Search

For the production of exotic nuclei at the IGISOL facility, an ion guide for neutron-induced fission has been developed and tested in experiments. Fission fragments are produced inside the ion guide and collected using a helium buffer gas. Meanwhile, a GEANT4 model has been developed to simulate the transportation and stopping of the charged fission products. In a recent measurement of neutron-induced fission yields, implantation foils were located at different positions in the ion guide. The gamma spectra from these foils and the fission targets are compared to the results from the GEANT4 simulation. In order to allow fission yield measurements in the low yield regions, towards the tails and in the symmetric part of the mass distribution, the stopping and extraction efficiency of the ion guide has to be significantly improved. This objective can be achieved by increasing the size while introducing electric field guidance using a combination of static electrodes and an RF-carpet. To this end, the GEANT4 model is used to optimise the design of such an ion guide.

Isomeric states in 128In and 130In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. By employing state-of-the-art ion manipulation techniques, three different beta-decaying states in 128In and 130In have been separated and their masses measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spectroscopy station. A new beta-decaying high-spin isomer feeding the 15 − isomer in 128Sn has been discovered in 128In at 1797.6 (20) keV. Shell-model calculations employing a CD-Bonn potential re-normalized with the perturbative G-matrix approach suggest this new isomer to be a 16 + spin-trap isomer. In 130In, the lowest-lying (10 −) isomeric state at 58.6 (82) keV was resolved for the first time using the phase-imaging ion cyclotron resonance technique. The energy difference between the 10 − and 1 − states in 130In, stemming from parallel/antiparallel coupling of (π 0 g 9 / 2 − 1) ⊗ (ν 0 h 11 / 2 − 1) , has been found to be around 200 keV lower than predicted by the shell model. Precise information on the energies of the excited states determined in this work is crucial for producing new improved effective interactions for the nuclear shell model description of nuclei near 132Sn. [ABSTRACT FROM AUTHOR]

Precision mass measurements of 104Y, 106Zr, 104 , 104 m , 109 Nb, and 111,112Mo have been performed with the JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line facility. The order of the long-lived states in 104Nb was unambiguously established. The trend in two-neutron separation energies around the N = 66 neutron midshell appeared to be steeper with respect to the Atomic Mass Evaluation 2020 extrapolations for the 39 Y and 40 Zr isotopic chains and less steep for the 41 Nb chain, indicating a possible gap opening around Z = 40. The experimental results were compared to the BSkG2 model calculations performed with and without vibrational and rotational corrections. All of them predict two low-lying minima for 106Zr. While the unaltered BSkG2 model fails to predict the trend in two-neutron separation energies, selecting the more deformed minima in calculations and removing the vibrational correction, the calculations are more in line with experimental data. The same is also true for the 2 1 + excitation energies and differences in charge radii in the Zr isotopes. The results stress the importance of improved treatment of collective corrections in large-scale models and further development of beyond-mean-field techniques. [ABSTRACT FROM AUTHOR]

We report the first high-precision mass measurements of the neutron-rich nuclei 74,75Ni and the clearly identified ground state of 76Cu, along with a more precise mass-excess value of 78Cu, performed with the double Penning trap JYFLTRAP at the Ion Guide Isotope Separator On-Line (IGISOL) facility. These new results lead to a quantitative estimation of the quenching for the N = 50 neutron shell gap. The impact of this shell quenching on core-collapse supernova dynamics is specifically tested using a dedicated statistical equilibrium approach that allows a variation of the mass model independent of the other microphysical inputs. We conclude that the impact of nuclear masses is strong when implemented using a fixed trajectory as in the previous studies, but the effect is substantially reduced when implemented self-consistently in the simulation. [ABSTRACT FROM AUTHOR]

A precise determination of the ground state 111In (9 / 2 +) electron capture to ground state of 111Cd (1 / 2 +) Q value has been performed utilizing the double Penning trap mass spectrometer, JYFLTRAP. A value of 857.63(17) keV was obtained, which is nearly a factor of 20 more precise than the value extracted from the Atomic Mass Evaluation 2020 (AME2020). The high-precision electron-capture Q value measurement along with the nuclear energy level data of 866.60(6) keV, 864.8(3) keV, 855.6(10) keV, and 853.94(7) keV for 111Cd was used to determine whether the four states are energetically allowed for a potential ultra-low Q -value β decay or electron-capture decay. Our results confirm that the excited states of 866.60(6) keV with spin-parity (J π) of 3/2+ and 864.8(3) keV with J π = 3 / 2 + are ruled out due to their deduced electron-capture Q value being smaller than 0 keV at the level of around 20 σ and 50 σ , respectively. Electron-capture decays to the excited states at 853.94(7) keV (J π = 7 / 2 +) and 855.6(10) keV (J π = 3 / 2 +), are energetically allowed with Q values of 3.69(19) keV and 2.0(10) keV, respectively. The allowed decay transition 111In (9/2+) → 111Cd (7/2+), with a Q value of 3.69(19) keV, is a potential new candidate for neutrino-mass measurements by future EC experiments featuring new powerful detection technologies. The results show that the indium level 2 p 1 / 2 for this decay branch leads to a significant increase in the number of EC events in the energy region sensitive to the electron neutrino mass. [ABSTRACT FROM AUTHOR]

The ground-state-to-ground-state β − -decay 131I (7/2+) → 131Xe (3/2+) Q value was determined with high precision utilizing the double Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. The Q value of this β − -decay was found to be Q = 972.25(19) keV through a cyclotron frequency ratio measurement with a relative precision of 1.6 × 10−9. This was realized using the phase-imaging ion-cyclotron-resonance technique. The new Q value is more than 3 times more precise and 2.3 σ higher (1.45 keV) than the value extracted from the Atomic Mass Evaluation 2020. Our measurement confirms that the β − -decay to the 9 / 2 + excited state at 971.22(13) keV in 131Xe is energetically allowed with a Q value of 1.03(23) keV while the decay to the 7 / 2 + state at 973.11(14) keV was found to be energetically forbidden. Nuclear shell-model calculations with established two-body interactions, alongside an accurate phase-space factor and a statistical analysis of the log ft values of known allowed β decays, were used to estimate the partial half-life for the low- Q -value transition to the 9 / 2 + state. The half-life was found to be (1.97 − 0.89 + 2.24) × 10 7 years, which makes this candidate feasible for neutrino mass searches. [ABSTRACT FROM AUTHOR]