Relativistic Fission Research Articles

Determination of beta-delayed neutron emission probability limits of rhodium isotopes by gamma-ray spectroscopy

The decay of five neutron-heavy rhodium isotopes were studied at the Radioactive Isotope Beam Factory (RIBF) Facility at the RIKEN Nishina Center after relativistic fission of 238U beam on a thick beryllium target. Previously unknown associated gamma-ray decay energies are reported for each nuclide, and through evaluating the intensity of the 2+ → 0+ E2 transition in the even-even palladium daughter nuclei, 120,122,124Pd, from the beta-tagged gamma-ray spectra an upper or lower limit of beta-delayed neutron emission is deduced for each nuclei. A general, expected trend of increasing Pn is observed in the direction of the neutron drip line.

Isomeric states in neutron-rich 129In and the πg−19/2 ⊗ vh−111/2 multiplet

Within the RISING stopped beam campaign the neutron-rich indium isotopes with masses A=125-130 have been studied using the method of isomer spectroscopy. The decays of several isomeric states have been observed and here we compare our results for 129In to previous measurements for this nucleus. The isomeric states were populated in the fragmentation of a 136Xe beam at 750 MeV/u and in the relativistic fission of a 238U beam at 650 MeV/u at the accelerator facility GSI (Darmstadt, Germany).

Picosecond resolution on relativistic heavy ions' time-of-flight measurement

We developed a time-of-flight measurement system for relativistic heavy ions with a requested resolution of 40ps Full Width Half Maximum. Such a resolution is mandatory to assign the correct mass number to every fission fragment, identified using the Bρ-ToF-ΔE method with the recoil spectrometer designed for the SOFIA experiment—which hold very recently at GSI. To achieve such a performance, fast plastic scintillators read-out by dedicated photomultiplier tubes were chosen among other possible options. We have led several test-measurements from 2009 to 2011, in order to investigate: the effect of the addition of a quenching molecule in the scintillator's matrix, the influence of the detector's size and the impact of the photomultiplier tube. The contribution of the dedicated electronics is also characterized. Time-of-flight measurements were performed realized with electron pulses and relativistic heavy ions, respectively provided by the LASER driven electron–accelerator (ELSA) at CEA–DAM Ile-de-France and by the SIS18/FRS facility at GSI. The reported results exhibit a time resolution better than 20ps Full Width Half Maximum reached with the last prototype at GSI with an Uranium beam. These results confirm that the SOFIA experiment should enable the measurement of the relativistic fission fragments' time-of-flight with the requested resolution.

Core-coupled states and split proton-neutron quasiparticle multiplets in122−126Ag

Neutron-rich silver isotopes were populated in the fragmentation of a 136Xe beam and the relativistic fission of 238U. The fragments were mass analyzed with the GSI Fragment separator and subsequently implanted into a passive stopper. Isomeric transitions were detected by 105 HPGe detectors. Eight isomeric states were observed in 122-126Ag nuclei. The level schemes of 122,123,125Ag were revised and extended with isomeric transitions being observed for the first time. The excited states in the odd-mass silver isotopes are interpreted as core-coupled states. The isomeric states in the even-mass silver isotopes are discussed in the framework of the proton-neutron split multiplets. The results of shell-model calculations, performed for the most neutron-rich silver nuclei are compared to the experimental data.

Single-particle isomeric states in 121Pd and 117Ru

Neutron-rich nuclei were populated in a relativistic fission of 238U. Gamma-rays with energies of 135 keV and 184 keV were associated with two isomeric states in 121Pd and 117Ru. Half-lives of 0.63(5) μs and 2.0(3) μs were deduced and the isomeric states were interpreted in terms of prolate deformed single-particle states.

Shape coexistence and isomeric states in neutron-richTc112andTc113

Isomeric states in Tc112 and Tc113, with half-lives of 150(17) ns and 500(100) ns, respectively, have been observed following the relativistic fission of U238. The fission fragments have been separated in a fragment separator and identified by means of energy-loss and time-of-flight techniques. In both nuclei, the ground-state configuration is calculated to have an oblate shape and the isomerism is proposed to arise due to transitions from a triaxial excited state to a low-lying oblate state.Received 9 September 2010DOI:https://doi.org/10.1103/PhysRevC.82.044312©2010 American Physical Society

G Factor of the [formula omitted] isomer in 126Sn and first observation of spin-alignment in relativistic fission

We report on the g factor measurement of the isomeric 7− state (E*=2219 keV, T1/2=5.9(8) μs) in the neutron-rich 126Sn nucleus. The nucleus was produced by the fission of a relativistic 238U beam and reaction products were selected by the FRS fragment separator at GSI. For the first time, spin-alignment was observed after relativistic fission. It was used to deduce the g factor of the 7− isomeric state, g(7−)=−0.098(9), from the measured perturbed angular distribution of its γ decay using the RISING Cluster detectors. The observed value confirms the suggested ν(h11/2−1d3/2−1) dominant configuration, which has been proposed for the 7− isomers in neutron-rich Sn isotopes. The failure of the g factor additivity rule and the importance of core polarization evolution with increasing distance from the doubly-magic 132Sn is discussed. The first observation of 18(8)% of spin-alignment produced by the relativistic fission of a 238U beam paves the way to study moments of neutron-rich (sub-)microsecond isomers, which are difficult to align by other means.

New sub-μs isomers in125,127,129Snand isomer systematics of124−130Sn

New sub-μs isomers have been observed in the neutron-rich Sn isotopes. 125,127,129Sn nuclei have been produced in a relativistic fission reaction of U238 on a Be9 target at 750 A·MeV and by the fragmentation of Xe136 at 600 A·MeV populating high-spin yrast states. In addition to the already known μs isomers, three new ones with sub-μs half-lives have been observed. These yrast isomers are the high-spin members of the ν(d3/2−1h11/2−2) and νh11/2−n, seniority v=3 multiplets leading to isomeric (23/2+) and (27/2−) states, respectively. Added to the already known 19/2+μs isomers in this region the current work completes the systematic information of neutron-hole excitations toward the filling of the last h11/2 orbital at N=82. The results are discussed in the framework of state-of-the-art shell-model calculations using realistic interactions.4 MoreReceived 27 March 2008DOI:https://doi.org/10.1103/PhysRevC.77.064313©2008 American Physical Society