[en] Significant progress have been made over the last decade in experimental investigation of the ⁷⁸Ni and its neighbors. Nuclear Decay studies acieved life-time measurement of the doublt-ymagic ⁷⁸Ni and provided excitation enrgies of low lying levels up to ⁷⁶Ni, establishing the 'baseline' systematics of the nuclear structure knowledge for this region of nuclear chart. Perspective studies which will build on this research are presented. One major goal is determine, if ⁷⁸Ni is a good double closed-shell nucleus. The answer to this question may have profound consequences for astrophysics and also our understanding of the nuclear models describing properties of very neutron rich nuclei.

[en] Recent progress in experimental decay studies in the region of the doubly magic nucleus ⁷⁸Ni is discussed. In particular new data on low-energy excitations in nickel isotopes has been obtained in experiments employing fragmentation reactions. The experimental data are confronted with different shell-model calculations. The position of the 2⁺ energy levels and behavior of 8⁺ isomers in even-even ^70-76Ni isotopes has been interpreted

[en] Significant advantages can be obtained through the application of digital electronics to nuclear physics experiments by replacing the traditional timing and shaping circuits by numerical algorithms implemented in real time. One example demonstrating the power of digital techniques is the achievement of a low-energy threshold, <50 keV, for the detection of beta-decay electrons in a thick Si detector. Such a low beta detection threshold would dramatically improve the detection efficiency in standard beta decay correlation experiments.

[en] An island of isomers have recently been observed on both sides of the N=40 shell below the Ni isotopes. Isomeric states in the 65Fe and 67Fe allow the knowledge of the single particle structure around the g9/2 shell. Moreover, the excitation energy of the first 2+ and 4+ states in the 68Fe have been established by β-γ correlation. The evolution of the structure of the Fe isotopes going far away from the valley of stability is, for the first time, given for N>40

[en] The discovery of the new isotopes 109Xe and 105Te was enabled by the application of a new experimental method using selective pulse shape storage from silicon detectors with digital signal processing electronics. Essential data processing algorithms were developed, which are able to find unique nuclear decay signatures, such as overlapping alpha decay induced signals. An experiment using this method led to the simultaneous detection of isotopes with dramatically different half lives T1/2(109Xe)=13(2) ms and T1/2(105Te)=620(70) ns. The ground state decay energies have been measured to be E (109Xe)=4062(7) keV and E (105Te)=4703(5) keV via observation of correlated events in the decay chain 109Xe 105Te 101Sn

[en] β-delayed one-neutron and two-neutron branching ratios (P_1n and P_2n) have been measured in the decay of A=84 to 87 Ga isotopes at the Radioactive-Isotope Beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of 3He neutron counters (BRIKEN). Two-neutron emission was observed in the decay of ^84,85,87Ga for the first time and the branching ratios were measured to be P_2n=1.6(2)%,1.3(2)%, and 10.2(28)_stat(5)_sys%, respectively. One-neutron branching ratio of ⁸⁷Ga(P_1n=81(9)_stat(8)_sys%) and half-life of 29(4) ms were measured for the first time. The branching ratios of ⁸⁶Ga were also measured to be P_1n=74(2)_stat(8)_sys% and 16.2(9)_stat(6)_sys% with better precision than a previous study. The observation that P_1n>P_2n for both ^86,87Ga was unexpected and is interpreted as a signature of dominating one-neutron emission from the two-neutron unbound excited states in ^86,87Ga. In order to interpret the experimental results, shell-model and Hauser-Feshbach statistical model calculations of delayed particle and γ-ray emission probabilities were performed. This model framework reproduces the experimental results. The shell model alone predicts P_2n significantly larger than P_1n for the ⁸⁷Ga decay, and it is necessary to invoke a statistical description to successfully explain the observation that P_1n > P_2n. Our new results demonstrate the relevance and importance of a statistical description of neutron emission for the prediction of the decay properties of multineutron emitters and that it must be included in the r-process modeling.

[en] The single-particle structure and shell gap of ¹⁰⁰Sn is inferred from prompt in-beam and delayed γ-ray spectroscopy of seniority and spin-gap isomers. Recent results in ^94,95Ag and ⁹⁸Cd stress the importance of large-scale shell model calculations employing realistic interactions for the isomerism, np-nh excitations and E2 polarization of the ¹⁰⁰Sn core. The strong monopole interaction of the Δl = 0 spin-flip partners πg_9/2- νg_7/2 in N. = 51 isotones below ¹⁰⁰Sn is echoed in the Δl = 1 pf5/2- ?g9/2 pair of nucleons, which is decisive for the persistence of the N. = 50 shell gap in ⁷⁸Ni. This is corroborated by recent experimental data on ^70,76Ni, ⁷⁸Zn. The importance of monopole driven shell evolution for the appearance of new shell closures in neutron-rich nuclei and implications for r-process abundances near the N. = 82 shell is discussed

[en] Proton emitter studies enable precise probing of the composition of the wave function of nuclei beyond the proton dripline. In a decay of proton radioactive odd-odd nuclei excited levels in the (even-Z,odd-N) daughters can be populated allowing us to deduce the properties of single particle neutron states. So far, fine structure in proton emission was observed for only one odd-odd emitter, ¹⁴⁶Tm. The neighboring odd-odd isotope ¹⁴⁴Tm is an obvious candidate to exhibit similar decay pattern. Its decay should be dominated by a large πh_11/2 component present in the ground and isomeric state wavefunction, as it was observed for ¹⁴⁶Tm and ¹⁴⁵Tm. The admixture of the 2⁺ (o)times πf_7/2 component or of the mirror (νh_11/2 πs_1/2) proton-neutron configuration can cause the fine structure in proton emission. Evidence for the proton decay of ¹⁴⁴Tm was found in an experiment at the Recoil Mass Spectrometer at Oak Ridge National Laboratory. The ¹⁴⁴Tm events were found in a weaK. (σ ∼ 10 nb) p5n channel of the fusion reaction of ⁵⁸Ni beam at 340 MeV on a ⁹²Mo target. The observed decay energy of about 1.8 MeV and the half-life of the order of ∼ 1 (micro)s suggest proton emission from the dominant πh_11/2 part of the wave function. The detection of this very short proton emitter was made possible by use of a double-sided silicon strip detector connected to a fast Digital-Signal-Processing-based acquisition system

[en] Recently the observation of a new type of spontaneous radioactive decay has been claimed in which two protons are simultaneously ejected by an atomic nucleus from the ground state1,2,3. Experimental data obtained for the extremely neutron-deficient nuclei 45Fe and 54Zn, were interpreted as the first evidence of such a decay mode which has been sought since 1960.4 However, the technique applied in those studies allowed only measurements of the decay time and the total energy released. Particles emitted in the decay were not identified and the conclusions had to be supported by theoretical arguments. Here we show for the first time, directly and unambiguously, that 45Fe indeed disintegrates by two-proton decay. Furthermore, we demonstrate that the decay branch of this isotope leads to various particle emission channels including two-proton and three-proton emission. To achieve this result we have developed a new type of detector V the Optical Time Projection Chamber (OTPC) in which digital photography is applied to nuclear physics for the first time. The detector records images of tracks from charged particles, allowing for their unambiguous identification and the reconstruction of decay events in three dimensions. This new and simple technique provides a powerful method to identify exotic decay channels involving emission of charged particles. It is expected that further studies with the OTPC device will yield important information on nuclei located at and beyond the proton drip-line, thus providing new material for testing and improving models of very unstable atomic nuclei

[en] The β⁺ decay of very neutron-deficient ⁴³Cr was studied by means of an imaging time projection chamber that allowed recording tracks of charged particles. Events of β-delayed emission of one, two, and three protons were clearly identified. The absolute branching ratios for these channels were determined to be (81±4)%, (7.1±0.4)%, and (0.08±0.03)%, respectively. ⁴³Cr is thus established as the second case in which the β-3p decay occurs. Although the feeding to the proton-bound states in ⁴³V is expected to be negligible, the large branching ratio of (12±4)% for decays without proton emission is found.