Thomas Faestermann

Isospin symmetry is used to fit the precisely known -values of lighter and -emitters and to extrapolate them up to . For the emitters the half-lives of the pure Fermi decays are calculated and compared with experimentally known values, even for the heaviest cases where the experimental uncertainties are still rather large. For the emitters only the Fermi component of the transitions can be predicted, but with the experimental half-lives the ratio of Gamow–Teller to Fermi strength can be determined.

NUCLEAR REACTIONS 3 He (32 S, α) 31 S, E= 128 MeV; measured reaction products, Eγ, Iγ; deduced γ-ray energies, levels, T 1/2, resonances. Comparison with the shell-model code NuShellX calculations. Modern Markov chain Monte Carlo-based Bayesian statistical techniques. The Doppler Shift Lifetimes (DSL2) facility at the TRIUMF Isotope Separator and Accelerator (ISAC-II) facility.

The efficiency of the weak s process in low-metallicity rotating massive stars depends strongly on the rates of the competing O 17 (α, n) Ne 20 and O 17 (α, γ) Ne 21 reactions that determine the potency of the O 16 neutron poison. Their reaction rates are poorly known in the astrophysical energy range of interest for core helium burning in massive stars because of the lack of spectroscopic information (partial widths, spin parities) for the relevant states in the compound nucleus Ne 21. In this Letter, we report on the first experimental determination of the α-particle spectroscopic factors and partial widths of these states using the O 17 (Li 7, t) Ne 21 α-transfer reaction. With these the O 17 (α, n) Ne 20 and O 17 (α, γ) Ne 21 reaction rates were evaluated with uncertainties reduced by a factor more than 3 with respect to previous evaluations and the present O 17 (α, n) Ne 20 reaction rate is more than 20 times larger. The …

More than 200 states up to 4.1 MeV excitation have been populated in Er 168 with the Er 170 (p, t) reaction at 25 MeV incident energy. About 80 of these states, with 0+ and 2+ assignments, were reported in a previous publication [D. Bucurescu et al., Phys. Rev. C 73, 064309 (2006)]. The present work considerably enriches the knowledge of this nucleus. A multistep coupled-channels analysis of the angular distributions is now presented for all the states observed in this experiment. Spin and parity values between 0+ and 7− are newly assigned for more than 100 states. For the states already reported in the ENSDF database with J π values there is a good agreement with our values. The Er 168 nucleus remains one of the best experimentally known nuclei for states with low and medium spins below 4 MeV excitation energy, representing a challenge for future microscopic structure model calculations aiming to …

In this article we try to summarize all information, gathered in the last three decades, on short-lived (order of Myr) radionuclides found in the Solar System with interstellar origin, most probably due to stellar processes like supernovae. The most important isotope is Fe, but we discuss also information on Al, Pu and Mn. We describe the environment of the Solar System during the past Myr as well as the likely locations where the supernovae occured. Confirming evidence has been found in the composition and energy distribution of galactic cosmic rays. Finally, we discuss the effects that the recent supernova activity might have had on Earth’s climate and biosphere.

As part of a systematic study of the nuclear structure of the Ru isotopes, 98 Ru was investigated via the β-decay of 98 Rh at iThemba LABS, and the 100 Ru (p, t) reaction at the Maier-Leibnitz Laboratory. The combined data results in significant revision of the previous spin assignments and clarification of the nature of levels in 98 Ru, as well as providing insights into the evolution of the structures across the Ru isotopic chain.

Investigations of neutron-rich nuclei, particularly those that lie in regions of the nuclear chart known for a high probability of isomeric states forming, are of vital importance to the understanding of nuclear astrophysical processes. Studies of these nuclei, such as 190 Re, can be used to validate and improve theoretical models of such processes. A polarised-beam experiment has been performed using the Munich Q3D magnetic spectrograph in order to investigate the energy-level structure of 190 Re. An excitation-energy spectrum has been produced, allowing for energies to be assigned to observed states. Through comparison between measured and calculated differential cross-sections and vector analysing powers, the process of assigning spin and parity to newly observed states, and confirming the assignments for previously observed states, is underway.

Globular clusters contain multiple stellar populations, with some previous generation of stars polluting the current stars with heavier elements. Understanding the history of globular clusters is helpful in understanding how galaxies merged and evolved and therefore constraining the site or sites of this historic pollution is a priority. The acceptable temperature and density conditions of these polluting sites depend on critical reaction rates. In this paper, three experimental studies helping to constrain astrophysically important reaction rates are briefly discussed.

We used the Ba 138 (d, α) reaction to carry out an in-depth study of states in Cs 136, up to around 2.5 MeV. In this Letter, we place emphasis on hitherto unobserved states below the first 1+ level, which are important in the context of solar neutrino and fermionic dark matter (FDM) detection in large-scale xenon-based experiments. We identify for the first time candidate metastable states in Cs 136, which would allow a real-time detection of solar neutrino and FDM events in xenon detectors, with high background suppression. Our results are also compared with shell-model calculations performed with three Hamiltonians that were previously used to evaluate the nuclear matrix element (NME) for Xe 136 neutrinoless double beta decay. We find that one of these Hamiltonians, which also systematically underestimates the NME compared with the others, dramatically fails to describe the observed low-energy Cs 136 …

Some observed abundances in globular clusters have suggested the existence of multiple generations of stars within the clusters as the observations require temperature ranges higher than current stars. The 30Si(p,γ)31P reaction plays a key role in the synthesis of the observed abundances. The study of the 30Si(3He,d)31P transfer reaction is a tool for constraining the strengths of low-lying resonances, and the proton partial widths are the main ingredients for calculating those strengths. We present the method used for estimating the proton partial widths and their associated uncertainties.

We use a high-resolution S 32 (d, t) measurement to investigate the claimed existence of a 6401 (3) keV state in S 31 that may affect the P 30 (p, γ) nuclear reaction rate in oxygen-neon (ONe) novae. Our data are shown to exclude the null hypothesis—that the state does not exist—with high significance. Additionally, the data also suggest the existence of a hitherto unreported state at 6648 (4) keV. This state corresponds to a P 30 (p, γ) resonance at 517 (4) keV, located below the higher edge of the Gamow window for peak nova temperatures of about 0.4 GK.

The fission probability of Np was measured as a function of the excitation energy in the energy range of E MeV in order to search for transmission fission resonances. A radioactive Np target was bombarded with deuterons of E = 12 MeV, whereas the energy of the protons was analyzed with a superior resolution of E = 8 keV. The experiment was performed at the Tandem accelerator of the Maier-Leibnitz Laboratory in Garching employing the Np(d,pf) reaction. A group of fission resonances has been observed at excitation energies between E MeV, which could be ordered into three (superdeformed) rotational bands with a rotational parameter of keV, and identified as the first direct observation of transition states composing rotational bands in an odd-odd nucleus as they appear above the top of the outer fission barrier. Nuclear reaction code (talys1.95) calculations were also …

Background: Abundance anomalies in some globular clusters, such as the enhancement of potassium and the depletion of magnesium, can be explained in terms of an earlier generation of stars polluting the presently observed ones. It was shown that the potential range of temperatures and densities of the polluting sites depends on the strength of a few critical reaction rates. The Si 30 (p, γ) P 31 reaction has been identified as one of these important reactions.Purpose: The key ingredient for evaluating the thermonuclear Si 30 (p, γ) P 31 reaction rate is the strength of the resonances which, at low energy, are proportional to their proton width. Therefore, the goal of this work is to determine the proton widths of unbound P 31 states.Method: States in P 31 were studied at the Maier-Leibnitz-Laboratorium using the one-proton Si 30 (He 3, d) P 31 transfer reaction. Deuterons were detected with the high resolution one …

The Coulomb excitation of Ru 102 was performed with beams of C 12 and O 16 ions. The beam particles scattered at forward angles were momentum analyzed with a magnetic spectrograph. The resolution achieved enabled the populations of the 2 1+ state, the unresolved 2 2+/4 1+, and 2 4+/3 1−, doublets of states, and the 3 2− state to be determined as a function of the scattering angle. These populations are compared with gosia calculations, yielding B (E 2; 2 1+→ 0 1+)= 41.5±2.3 Wu, B (E 2; 2 2+→ 0 1+)= 1.75±0.11 Wu, B (E 3; 3 1−→ 0 1+)= 31.5±3.5 Wu, and B (E 3; 3 2−→ 0 1+)= 6.8±0.5 Wu The B (E 3; 3 1−→ 0 1+) value is significantly larger than previously measured. The weakly populated 2 3+ state, presumed to be a member of the band built on the 0 2+ state, was observed clearly for a single angle only, and a fit to its population results in B (E 2; 2 3+→ 0 1+)= 0.053±0.011 Wu Using the known γ-ray …

Abstract Using the reaction 7 Li (7 Li, 10 C) we tried to populate states in the tetraneutron. A peak in the energy spectrum of identified 10 C, which we cannot attribute to a reaction with any other of the target components, corresponds to an excitation of the 10 C+ 4n system of 2.93±0.16 MeV. Under different kinematic conditions an equivalent peak was observed. For a binding energy of the tetraneutron of− 2.93 MeV a much larger width than the observed upper limit of Γ< 0.24 MeV (mainly due to experimental spread) is expected. Therefore, we favor the interpretation that this peak corresponds to 10 C in the first excited state at 3.354 MeV and a tetraneutron with a binding energy of+ 0.42±0.16 MeV.

Coulomb excitation of 102 Ru was performed with beams of 12 C and 16 O ions at the Maier-Leibnitz Laboratory, with the scattered particles momentum analyzed using a Q3D magnetic spectrograph. Both the elastic and inelastically scattered particles were detected, and the resolution achieved enabled the populations of the 2 1+, 2 2+/4 1+ doublet, 2 3+, 2 4+/3 1-doublet, and 3 2-states to be determined as a function of the scattering angle, which were compared with GOSIA calculations. The deduced B (E2; 2 1+→ 0 1+)= 41.5±2.3 Wu is in good agreement with the ENSDF value of 44.7±0.7 Wu, while the B (E2; 2 2+→ 0 1+)= 1.75±0.11 Wu is approximately 40% larger than the ENSDF value. The weakly populated 2 3+ state was observed for a single angle only, and a fit to its population results in B (E2; 2 3+→ 0 1+)= 0.053±0.011 Wu Using the known γ-ray branching ratios, the B (E2; 2 3+→ 0 2+) value is …

The fission probability of Np-238 was measured as a function of the excitation energy in the energy range of E*= 5.4-6.2 MeV in order to search for transmission fission resonances. A radioactive Np-237 target was bombarded with deuterons of Ed= 12 MeV, whereas the energy of the protons was analyzed with a superior resolution of Delta E= 8 keV. The experiment was performed at the Tandem accelerator of the Maier-Leibnitz Laboratory in Garching employing the Np-237 (d, pf) reaction. A group of fission resonances has been observed at excitation energies between E*= 5.5-5.8 MeV, which could be ordered into three (superdeformed) rotational bands with a rotational parameter of (h) over bar (2)/2 (Theta)= 3.507 keV, and identified as the first direct observation of transition states composing rotational bands in an odd-odd nucleus as they appear above the top of the outer fission barrier. Nuclear reaction code (TALYS1. 95) calculations were also performed to extract the multi-humped fission barrier parameters of Np-238 by fitting them to the experimental data of the present (d, pf) and previous (n, f) experiments. The extracted barrier parameters also support the above interpretation of the observed resonances.

In a recent publication an experiment is described which searched for a resonance in the four-neutron system. In a convincing way the knockout of an -particle off He nuclei by protons has been measured and the missing mass of the remaining four neutrons has been calculated from the measured four-momenta of -particles and protons. The missing mass spectrum shows a bump of events corresponding to excitation of the four-neutron system to the continuum. In addition, there is a peak near zero missing mass that is convincingly interpreted as a resonance with excitation energy of the four neutrons E*= 2.37(58) MeV and a width of a Breit-Wigner distribution of =1.75(37) MeV. Unfortunately, in the Duer et al. publication no reference has been made to our paper which had appeared six months earlier, but after the submission of their manuscript to Nature. At least, the corresponding News and Views article should have mentioned our measurement, since that was presumably written after acceptance of the Duer et al. paper. Here, I try to see both results together.

Nucleon-transfer sum rules have been assessed via a consistent reanalysis of cross-section data from neutron-adding (d, p) and-removing (d, t) reactions on well-deformed isotopes of Gd, Dy, Er, Yb, and W, with 92≤ N≤ 108, studied at the Niels Bohr Institute in the 1960s and 1970s. These are complemented by new measurements of cross sections using the (d, p),(d, t), and (p, d) reactions on a subset of these nuclei. The sum rules, defined in a Nilsson-model framework, are remarkably consistent. A single overall normalization is used in the analysis, which appears to be sensitive to assumptions about the reaction mechanism, and in the case of sums using the (d, t) reaction, differs from values determined from reactions on spherical systems.

We have identified an error in the FRESCO calculations described in Ref.[1]. The amplitude of the sequential part of the (p, t) transfer calculation was missing a factor of√{2}. The results from using the correct calculations are shown below in Figs. 1 and 2. Our results and conclusions do not change, given the overall uncertainties.