Transition from direct to sequential two-proton decay in ss-dd shell nuclei

Transitions among different mechanisms of two-proton decay are studied in general. The introduced improved direct-decay model generalizes the semi-analytical models used before and provides flawless phenomenological description of three-body correlations in $2p$ decays. This is demonstrated by examples of the low-lying $^{16}$Ne state decays. Different forms of transition dynamic are shown to be highly probable beyond the proton dripline for the $s$-$d$ shell nuclei. It is demonstrated that transition dynamic of $2p$ emitters can provide means for extraction of a width of the ground-state resonance of a core+$p$ subsystem of the core+$2p$ system. Practical applicability of the method is demonstrated by properties of the $^{14}$F ground state derived from the ^{15}\mbox{Ne}\rightarrow ^{\,13\!\!}\mbox{O}+2p decay data and of the $^{29}$Cl ground state derived from the ^{30}\mbox{Ar}\rightarrow ^{\,28\!\!}\mbox{S}+2p decay data.Comment: 8 pages, 10 figure

Lifetime and fragment correlations for the two-neutron decay of 26^{26}O ground state

The structure and decay of $^{26}$O are investigated in a three-body $^{24}$O+$n+n$ model suitable for studies of the long-lived (including radioactivity timescale) states. We have found extremely strong effect of the subbarrier configuration mixing on the decay width of true $2n$ emitters due to core recoil and neutron-neutron final state interaction. This effect is far exceeding analogous effect in the true $2p$ emitters. Our calculations provide reasonably narrow boundaries for the lifetime vs.\ decay energy dependence for the true $2n$ emission. An upper limit of $\sim 1$ keV for the decay energy of the unbound $^{26}$O is inferred based on the recent experimental lifetime value.Comment: 6 pages, 4 figure

Deep excursion beyond the proton dripline. II. Towards the limits of nuclear structure existence

Prospects of experimental studies of argon and chlorine isotopes located far beyond the proton dripline are studied by using systematics and cluster models. The deviations from the widespread systematics observed in 28 , 29 Cl and 29 , 30 Ar have been theoretically substantiated, and analogous deviations have been predicted for the lighter chlorine and argon isotopes. The limits of nuclear structure existence are predicted for Ar and Cl isotopic chains, with 26 Ar and 25 Cl found to be the lightest sufficiently long-living nuclear systems. By simultaneous measurements of protons and γ rays following decays of such systems as well as their β -delayed emission, an interesting synergy effect may be achieved, which is demonstrated by the example of 30 Cl and 31 Ar ground-state studies. Such a synergy effect may be provided by the new EXPERT setup (EXotic Particle Emission and Radioactivity by Tracking) being operated inside the fragment separator and spectrometer facility at GSI, Darmstadt.This work was supported in part by the Hessian Ministry for Science and Art (HMWK) through the LOEWE funding scheme Helmholtz International Center for FAIR (HIC for FAIR); the Helmholtz Association (Grant No. IK-RU-002); the Russian Science Foundation (Grant No. 17-12-01367); the Polish National Science Center (Contract No. UMO-2015/17/B/ST2/00581); the Polish Ministry of Science and Higher Education (Grant No. 0079/DIA/2014/43, Grant Diamentowy); the Helmholtz-CAS Joint Research Group (Grant No. HCJRG-108); the Ministry of Education & Science, Spain (Contract No. FPA2016-77689-C2-1-R); the Ministry of Education, Youth and Sports, Czech Republic (Projects No. LTT17003 and No. LM2015049); and the Justus-Liebig-Universitat Giessen (JLU) and the GSI under the JLU-GSI strategic Helmholtz partnership agreement. This work was carried out in the framework of the Super-FRS Experiment collaboration. This article is a part of the Ph.D. thesis of D. Kostyleva

Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains

The proton-unbound argon and chlorine isotopes have been studied by measuring trajectories of their decay-in-flight products by using a tracking technique with micro-strip detectors. The proton (1p) and two-proton (2p) emission processes have been detected in the measured angular correlations “heavy-fragment”+p and “heavy-fragment”+p+p, respectively. The ground states of the previously unknown isotopes 30Cl and 28Cl have been observed for the first time, providing the 1p separation energies Sp of −0.48(2) and −1.60(8) MeV, respectively. The relevant systematics of 1p and 2p separation energies have been studied theoretically in the core+p and core+p+p cluster models. The first-time observed excited states of 31Ar allow to infer the 2p-separation energy S2p of 6(34) keV for its ground state. The first-time observed state in 29Ar with S2p = −5.50(18) MeV can be identified either as a ground or an excited state according to different systematics.This work was supported in part by the Helmholtz International Center for FAIR (HIC for FAIR); the Helmholtz Association (Grant No. IK-RU-002); the Russian Science Foundation (Grant No. 17-12-01367); the Polish National Science Center (Contract No. UMO-2015/17/B/ST2/00581); the Polish Ministry of Science and Higher Education (Grant No. 0079/DIA/2014/43, Grant Diamentowy); the Helmholtz-CAS Joint Research Group (Grant No. HCJRG-108); the Ministry of Education & Science, Spain (Contract No. FPA2016-77689-C2-1-R); the Hessian Ministry for Science and Art (HMWK) through the LOEWE funding scheme Helmholtz International Center for FAIR (HIC for FAIR); the Justus-Liebig-Universitat Giessen (JLU) and the GSI under the JLU-GSI strategic Helmholtz partnership agreement. This work was carried out in the framework of the Super-FRS Experiment collaboration. This article is a part of the Ph.D. thesis of D. Kostyleva

Linking the exotic structure of 17{}^{17}C to its unbound mirror 17{}^{17}Na

The structure of ${}^{17}$C is used to define a nuclear interaction that, when used in a multichannel algebraic scattering theory for the $n+{}^{16}$C system, gives a credible definition of the (compound) excitation spectra. When couplings to the low-lying collective excitations of the ${}^{16}$C-core are taken into account, both sub-threshold and resonant states about the $n+{}^{16}$C threshold are found. Adding Coulomb potentials to that nuclear interaction, the method is used for the mirror system of $p+{}^{16}$Ne to specify the low-excitation spectrum of the particle unstable $^{17}$Na. We compare the results with those of a microscopic cluster model. A spectrum of low excitation resonant states in ${}^{17}$Na is found with some differences to that given by the microscopic-cluster model. The calculated resonance half-widths (for proton emission) range from $\sim 2$ to $\sim 672$ keV.Comment: 13 pages, 5 figure

Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains

The proton-unbound argon and chlorine isotopes have been studied by measuring trajectories of their decay-in-flight products by using a tracking technique with micro-strip detectors. The proton (1p) and two-proton (2p) emission processes have been detected in the measured angular correlations “heavy-fragment”+p and “heavy-fragment”+p+p, respectively. The ground states of the previously unknown isotopes 30Cl and 28Cl have been observed for the first time, providing the 1p separation energies Sp of −0.48(2) and −1.60(8) MeV, respectively. The relevant systematics of 1p and 2p separation energies have been studied theoretically in the core+p and core+p+p cluster models. The first-time observed excited states of 31Ar allow to infer the 2p-separation energy S2p of 6(34) keV for its ground state. The first-time observed state in 29Ar with S2p = −5.50(18) MeV can be identified either as a ground or an excited state according to different systematics.Helmholtz Association grant IK-RU-002Helmholtz International Center for FAIR HIC for FAIRRussian Science Foundation grant No. 17-12-01367Polish National Science Center Contract No. UMO- 2015/17/B/ST2/00581Polish Ministry of Science and Higher Education Grant No. 0079/DIA/2014/43, Grant DiamentowyHelmholtz- CAS Joint Research Group grant HCJRG-10

Deep excursion beyond the proton dripline. II. Toward the limits of existence of nuclear structure

Prospects of experimental studies of argon and chlorine isotopes located far beyond the proton dripline are studied by using systematics and cluster models. The deviations from the widespread systematics observed in 28 , 29 Cl and 29 , 30 Ar have been theoretically substantiated, and analogous deviations have been predicted for the lighter chlorine and argon isotopes. The limits of nuclear structure existence are predicted for Ar and Cl isotopic chains, with 26 Ar and 25 Cl found to be the lightest sufficiently long-living nuclear systems. By simultaneous measurements of protons and γ rays following decays of such systems as well as their β -delayed emission, an interesting synergy effect may be achieved, which is demonstrated by the example of 30 Cl and 31 Ar ground-state studies. Such a synergy effect may be provided by the new EXPERT setup (EXotic Particle Emission and Radioactivity by Tracking) being operated inside the fragment separator and spectrometer facility at GSI, Darmstadt.Helmholtz Association de Alemania. IK-RU-002Russian Science Foundation. 17-12-01367Polish National Science Center. UMO2015/17/B/ST2/00581Polish Ministry of Science and Higher Education. 0079/DIA/2014/43Helmholtz- CAS Joint Research Group de Alemania. HCJRG-108Ministerio de Educación y Ciencia, España. FPA2016-77689-C2-1-RMinistry of Education, Youth and Sports de la República Checa. LTT17003 y LM201504

Breakdown of the Z=8 shell closure in unbound 12O and its mirror symmetry

An excited state in the proton-rich unbound nucleus 12O was identified at 1.8(4) MeV via missing-mass spectroscopy with the 14O(p,t) reaction at 51  AMeV. The spin-parity of the state was determined to be 0+ or 2+ by comparing the measured differential cross sections with distorted-wave calculations. The lowered location of the excited state in 12O indicates the breakdown of the major shell closure at Z=8 near the proton drip line. This demonstrates the persistence of mirror symmetry in the disappearance of the magic number 8 between 12O and its mirror partner 12Be

Spectroscopy of excited states of unbound nuclei 30 Ar and 29 Cl

Several states of proton-unbound isotopes 30 Ar and 29 Cl were investigated by measuring their in-flight decay products, 28 S + proton + proton and 28 S + proton, respectively. A refined analysis of 28 S -proton angular correlations indicates that the ground state of 30 Ar is located at 2 . 45 + 0.05 − 0.10 MeV above the two-proton emission threshold. The investigation of the decay mechanism of the 30 Ar ground state demonstrates that it has the transition dynamics. In the “transitional” region, the correlation patterns of the decay products present a surprisingly strong sensitivity to the two-proton decay energy of the 30 Ar ground state and the one-proton decay energy as well as the one-proton decay width of the 29 Cl ground state. The comparison of the experimental 28 S -proton angular correlations with those resulting from Monte Carlo simulations of the detector response illustrates that other observed 30 Ar excited states decay by sequential emission of protons via intermediate resonances in 29 Cl . Based on the findings, the decay schemes of the observed states in 30 Ar and 29 Cl were constructed. For calibration purposes and for checking the performance of the experimental setup, decays of the previously known states of a two-proton emitter 19 Mg were remeasured. Evidences for one new excited state in 19 Mg and two unknown states in 18 Na were found.Helmholtz International Center for FAIR de Alemania (HIC for FAIR) IK-RU-002Russian Ministry of Education and Science. NSh-932.2014.2Russian Science Foundation. 17-12-01367Polish National Science Center. UMO-2011/01/B/ST2/01943Polish Ministry of Science and Higher Education. 0079/DIA/2014/43HelmholtzCAS Joint Research Group de Alemania. HCJRG-108Ministerio de Ciencia, Innovación y Universidades de España (MICINN). FPA2009-0884

Observation and spectroscopy of new proton-unbound isotopes 30ar and 29cl: an interplay of prompt two-proton and sequential decay

Previously unknown isotopes 30Ar and 29Cl have been identified by measurement of the trajectories of their in-flight decay products 28S+p+p and 28S+p, respectively. The analysis of angular correlations of the fragments provided information on decay energies and the structure of the parent states. The ground states of 30Ar and 29Cl were found at 2.25+0.15−0.10 and 1.8±0.1  MeV above the two- and one-proton thresholds, respectively. The lowest states in 30Ar and 29Cl point to a violation of isobaric symmetry in the structure of these unbound nuclei. The two-proton decay has been identified in a transition region between simultaneous two-proton and sequential proton emissions from the 30Ar ground state, which is characterized by an interplay of three-body and two-body decay mechanisms. The first hint of a fine structure of the two-proton decay of 30Ar∗(2+) has been obtained by detecting two decay branches into the ground and first-excited states of the 28S fragment.Polish National Science Center UMO-2011/01/B/ST2/0194