I. Dillmann

Constraining the astrophysical origin of the p-nuclei through nuclear physics and meteoritic data

A small number of naturally occurring, proton-rich nuclides (the p-nuclei) cannot be made in the s- and r-processes. Their origin is not well understood. Massive stars can produce p-nuclei through photodisintegration of pre-existing intermediate and heavy nuclei. This so-called γ-process requires high stellar plasma temperatures and occurs mainly in explosive O/Ne burning during a core-collapse supernova. Although the γ-process in massive stars has been successful in producing a large range of p-nuclei, significant deficiencies remain. An increasing number of processes and sites has been studied in recent years in search of viable alternatives replacing or supplementing the massive star models. A large number of unstable nuclei, however, with only theoretically predicted reaction rates are included in the reaction network and thus the nuclear input may also bear considerable uncertainties. The current status of astrophysical models, nuclear input and observational constraints is reviewed. After an overview of currently discussed models, the focus is on the possibility to better constrain those models through different means. Meteoritic data not only provide the actual isotopic abundances of the p-nuclei but can also put constraints on the possible contribution of proton-rich nucleosynthesis. The main part of the review focuses on the nuclear uncertainties involved in the determination of the astrophysical reaction rates required for the extended reaction networks used in nucleosynthesis studies. Experimental approaches are discussed together with their necessary connection to theory, which is especially pronounced for reactions with intermediate and heavy nuclei in explosive nuclear burning, even close to stability.

Discovery and cross-section measurement of neutron-rich isotopes in the element range from neodymium to platinum with the FRS

Abstract:Using the high-resolution performance of the fragment separator FRS at GSI we have discovered 60 new neutron-rich isotopes in the atomic number range of 60⩽Z⩽78. The new isotopes were unambiguously identified in reactions with a

High-resolution measurement of the time-modulated orbital electron capture and of the β+ decay of hydrogen-like 142Pm60+ ions

Abstract The periodic time modulations, found recently in the two-body orbital electron capture (EC) decay of both, hydrogen-like 140Pr58+ and 142Pm60+ ions, with periods near to 7 s and amplitudes of about 20%, were re-investigated for the case of 142Pm60+ by using a 245 MHz resonator cavity with a much improved sensitivity and time resolution. We observed that the exponential EC decay is modulated with a period T = 7.11 ( 11 ) s , in accordance with a modulation period T = 7.12 ( 11 ) s as obtained from simultaneous observations with a capacitive pick-up, employed also in the previous experiments. The modulation amplitudes amount to a R = 0.107 ( 24 ) and a P = 0.134 ( 27 ) for the 245 MHz resonator and the capacitive pick-up, respectively. These new results corroborate for both detectors exactly our previous findings of modulation periods near to 7 s , though with distinctly smaller amplitudes. Also the three-body β + decays have been analyzed. For a supposed modulation period near to 7 s we found an amplitude a = 0.027 ( 27 ) , compatible with a = 0 and in agreement with the preliminary result a = 0.030 ( 30 ) of our previous experiment. These observations could point at weak interaction as origin of the observed 7 s -modulation of the EC decay. Furthermore, the data suggest that interference terms occur in the two-body EC decay, although the neutrinos are not directly observed.

OPPORTUNITIES TO CONSTRAIN ASTROPHYSICAL REACTION RATES FOR THE s-PROCESS VIA DETERMINATION OF THE GROUND-STATE CROSS-SECTIONS

Modern models of s-process nucleosynthesis in stars require stellar reaction rates of high precision. Most neutron-capture cross-sections in the s-process have been measured, and for an increasing number of reactions the required precision is achieved. This does not necessarily mean, however, that the stellar rates are constrained equally well, because only the capture of the ground state of a target is measured in the laboratory. Captures of excited states can contribute considerably to stellar rates that are already at typical s-process temperatures. We show that the ground-state contribution X to a stellar rate is the relevant measure to identify reactions that are or could be well constrained by experiments and apply it to (n,{gamma}) reactions in the s-process. We further show that the maximum possible reduction in uncertainty of a rate via determination of the ground-state cross-section is given directly by X. An error analysis of X is presented, and it is found that X is a robust measure with mostly small uncertainties. Several specific examples (neutron capture of {sup 79}Se, {sup 95}Zr, {sup 121}Sn, {sup 187}Os, and {sup 193}Pt) are discussed in detail. The ground-state contributions for a set of 412 neutron-capture reactions around the s-process path are presentedmorexa0» in a table. This allows identification of reactions that may be better constrained by experiments and that cannot be constrained solely by measuring ground-state cross-sections (and thus require supplementary studies). General trends and implications are discussed.«xa0less

First Measurement of Several β-Delayed Neutron Emitting Isotopes Beyond N=126

The β-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N≳126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β-decay strength distribution. This provides important constraints on global theoretical models currently used in r-process nucleosynthesis.

Between atomic and nuclear physics: radioactive decays of highly-charged ions

Highly charged radioactive ions can be stored for extended periods of time in storage rings which allows for precision measurements of their decay modes. The straightforward motivation for performing such studies is that fully ionised nuclei or few-electron ions can be viewed as clean quantum-mechanical systems, in which the interactions of the many electrons can be either excluded or treated precisely. Thus, the influence of the electron shell on the decay probability can be investigated. Another important motivation is stellar nucleosynthesis, which proceeds at high temperatures and the involved atoms are therefore highly ionised. Presented here is a compact review of the relevant experiments conducted at heavy-ion storage rings. Furthermore, we outline the perspectives for future experiments at new-generation storage-ring facilities.

Beta decay of highly charged ions

Ion storage rings and ion traps provide the very first opportunity to address nuclear beta decay under conditions prevailing in hot stellar plasmas during nucleosynthesis, i.e. at high atomic charge states. Experiments are summarized that were performed in this field during the last decade at the ion storage-cooler ring ESR in Darmstadt. Special emphasis is given to the first observation of bound-state beta decay, where the created electron remains bound in an inner orbital of the daughter atom. The impact of this specific ‘stellar’ decay mode for s-process nucleosynthesis as well as for nuclear ‘eon clocks’ is outlined. Finally, a new technique, single-ion decay spectroscopy, is presented, where one observes two-body beta decay characteristics (i.e. orbital electron capture or bound-state beta decay) of highly charged, single ions for well-defined nuclear and atomic quantum states of both the mother – and the daughter – ion.

KADoNiS-

Abstract The KADoNiS-p project is an online database for cross sections relevant to the p-process. All existing experimental data was collected and reviewed. With this contribution a user-friendly database using the KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) framework is launched, including all available experimental data from (p,γ), (p,n), (p,α), (α,γ), (α,n) and (α,p) reactions in or close to the respective Gamow window with cut-off date of August 2012 ( http://www.kadonis.org/pprocess ).

p

The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) project is an online database (www.kadonis.org) for cross sections relevant for s-process and the p-process nucleosynthesis. Recently, the p-process part of the KADoNiS database has been extended, and now includes almost all available experimental data from (p, γ), (p, n), (p, α), (α, γ), (α, n) and (α, p) reactions in or close to the respective Gamow window.

: The astrophysical

The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the nmain decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208Hg to 218Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. nThe impact of the uncertainties connected with the eta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to nobtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA, ncommonly used in r-process model calculations. Further measurements around N 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations.