arXiv subjects

Carsten Brandau

Publications and source records attributed to Carsten Brandau.

7 recordsLinked to original sources

arXiv2026

Precision masses of neutron-rich platinum and gold nuclei reveal enhanced $N=126$ shell strength below doubly-magic $^{208}$Pb

The heaviest stable nuclei in the universe owe their existence to quantum shell structure, the grouping of protons and neutrons into discrete energy levels separated by gaps. The largest known neutron shell gap in stable nuclei, at $N=126$, stabilizes doubly-magic $^{208}$Pb and is responsible for the characteristic abundance peak of heavy elements near gold and platinum produced by the rapid neutron-capture process (r-process). Whether this shell gap persists as protons are removed from lead is a question central to both nuclear structure and the modeling of heavy-element synthesis, yet it has remained unanswered due to the extraordinary difficulty of producing the relevant neutron-rich nuclei. Direct experimental knowledge in this region was essentially absent. Here we report the first precision mass measurements of $^{203,204}$Pt and $^{204,205,206}$Au, performed at GSI using a novel combination of Schottky and isochronous mass spectrometry in a heavy-ion storage ring. The $N=126$ isotones $^{204}$Pt and $^{205}$Au are more strongly bound than the extrapolated trend of the previously known mass surface by 403 and 464~keV, respectively, revealing an unexpectedly enhanced $N=126$ shell strength below doubly-magic $^{208}$Pb. Furthermore, the proton-neutron interaction strength exhibits a hitherto unobserved bifurcation at $N=126$ as protons are removed from $^{208}$Pb. Our results redefine the nuclear mass surface in the neutron-rich heavy-element region and provide direct experimental benchmarks for theoretical models whose extrapolations toward more exotic nuclei are essential for r-process nucleosynthesis calculations.

nucl-ex↗

arXiv2019

Lifetimes and g-factors of the HFS states in H-like and Li-like bismuth

The LIBELLE experiment performed at the experimental storage ring (ESR) at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, has successfully determined the ground state hyperfine (HFS) splittings in hydrogen-like ($^{209}\rm{Bi}^{82+}$) and lithium-like ($^{209}\rm{Bi}^{80+}$) bismuth. The study of HFS transitions in highly charged ions enables precision tests of QED in extreme electric and magnetic fields otherwise not attainable in laboratory experiments. Besides the transition wavelengths the time resolved detection of fluorescence photons following the excitation of the ions by a pulsed laser system also allows to extract lifetimes of the upper HFS levels and g-factors of the bound 1s and 2s electrons for both charge states. While the lifetime of the upper HFS state in $^{209}\rm{Bi}^{82+}$ has already been measured in earlier experiments, an experimental value for lifetime of this state in $^{209}\rm{Bi}^{80+}$ is reported for the first time in this work.

physics.atom-ph↗

arXiv2015

First Measurement of the $^{96}$Ru(p,$γ$)$^{97}$Rh Cross Section for the p-Process with a Storage Ring

This work presents a direct measurement of the $^{96}$Ru($p, γ$)$^{97}$Rh cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating $^{96}$Ru ions interacted repeatedly with a hydrogen target. The $^{96}$Ru($p, γ$)$^{97}$Rh cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the $γ$-ray strength function as well as the level density model can be pinned down with the measured ($p, γ$) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the $γ$-ray strength function and the level density have been removed. As a result, a constrained $^{96}$Ru($p, γ$)$^{97}$Rh reaction rate over a wide temperature range is recommended for $p$-process network calculations.

nucl-ex↗

arXiv2011

Differential energy measurement between He- and Li-like uranium intra-shell transitions

We present the first clear identification and highly accurate measurement of the intra-shell transition $1s2p\, ^3P_2 \to 1s2s\, ^3S_1$ of He-like uranium performed via X-ray spectroscopy. The present experiment has been conducted at the gas-jet target of the ESR storage ring in GSI (Darmstadt, Germany) where a Bragg spectrometer, with a bent germanium crystal, and a Ge(i) detector were mounted. Using the ESR deceleration capabilities, we performed a differential measurement between the $1s2p\, ^3P_2 \to 1s2s\, ^3S_1$ He-like U transition energy, at 4510 eV, and the $1s^22p\ ^2P_{3/2} \to 1s^22s\, ^2S_{1/2}$ Li-like U transition energy, at 4460 eV. By a proper choice of the ion velocities, the X-ray energies from the He- and Li-like ions could be measured, in the laboratory frame, at the same photon energy. This allowed for a drastic reduction of the experimental systematic uncertainties, principally due to the Doppler effect, and for a comparison with the theory without the uncertainties arising from one-photon QED predictions and nuclear size corrections.

physics.atom-ph↗

arXiv2009

Observation of the 2p3/2 -> 2s1/2 intra-shell transition in He-like uranium

We present the first observation of the 1s2p 3P2 ? 1s2s 3S1 transition in He-like uranium. The experiment was performed at the internal gas-jet target of the ESR storage ring at GSI exploiting a Bragg crystal spectrometer and a germanium solid state detector. Using the 1s2 2p 2P3/2 ? 1s2 2s 2S1/2 transition in Li-like uranium as reference and the deceleration capabilities of the ESR storage rings, we obtained the first evaluation of the He-like heavy ion intra-shell transition energy.

physics.atom-ph↗

arXiv2008

Nuclear excitation by electron capture followed by fast x-ray emission

The resonance strength of the two-step process of nuclear excitation by electron capture followed by $γ$ decay of the nucleus can be significantly increased in highly charged ions if the resonant capture proceeds via an excited electronic state with subsequent fast x-ray emission. For fully ionized $^{238}_{92}\mathrm{U}$ and $^{232}_{90}\mathrm{Th}$, the {x-ray} decay stabilizes the system against internal conversion of the captured electron, with an increase of both nuclear lifetimes and resonance strengths of up to two orders of magnitude compared with the case when occupied atomic orbitals prevent the x-ray de-excitation. Applications of this effect to the measurement of the not yet experimentally observed nuclear excitation by electron capture and to dense astrophysical plasmas are discussed.

nucl-th↗

arXiv2000

Dielectronic recombination of lithium-like Ni25+ ions - high resolution rate coefficients and influence of external crossed E and B fields

Absolute dielectronic recombination (DR) rates for lithium-like Ni$^{25+}$($1s^2 2s$) ions were measured at high-energy resolution at the Heidelberg heavy-ion storage ring TSR. We studied the center-of-mass energy range 0--130 eV which covers all $Δn$=0 core excitations. The influence of external crossed electric (0--300 V/cm) and magnetic (41.8--80.1 mT) fields was investigated. For the measurement at near-zero electric field resonance energies and strengths are given for Rydberg levels up to n$=$32; also Maxwellian plasma rate coefficients for the $Δn$=0 DR at electron temperatures between 0.5 and 200 eV are provided. For increasing electric field strength we find that for both the $2p_{1/2}$ and the $2p_{3/2}$ series of Ni$^{24+}$($1s^2 2p_j n\ell$) Rydberg resonances with n>30 the DR rate coefficient increases approximately linearly by up to a factor of 1.5. The relative increase due to the applied electric field for Ni$^{25+}$ is remarkably lower than that found in previous measurements with lighter isoelectronic Si$^{11+}$, Cl$^{14+}$ and also Ti$^{19+}$ ions, [T. Bartsch et al, Phys. Rev. Lett. {\bf 79}, 2233 (1997); {\bf 82}, 3779 (1999) and to be published] and in contrast to the results for lighter ions no clear dependence of the electric field enhancement on the magnetic field strength is found. The Maxwellian plasma rate coefficients for $Δn$=0 DR of Ni$^{25+}$ are enhanced by at most 11% in the presence of the strongest experimentally applied fields.

physics.atom-ph↗