D. Savran
23 shared publications
Volker Werner
Technische Universität Darmstadt
18 shared publications
Johann Isaak
Technische Universität Darmstadt
17 shared publications
Philipp Scholz
University of Cologne, Institute for Nuclear Physics, 50937 Köln, Germany
17 shared publications
N. Pietralla
Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany
15 shared publications
Jan Mayer
Universität zu Köln
14 shared publications

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- 2 October 2026
- Published by MDPI AG in Journal of Manufacturing and Materials Processing
Manufacturing Methodology for Single- and Multilayer Square Scintillating Fiber-Based Ribbons for Direct Coupling to Linear Photosensor Arrays
by P. Garcia Gil, I. Brandherm, M. Heil, D. Savran, C. Caesar, J. Weinert, S. Schwab, T. Aumann, E. Casarejos, C. J. Schmidt, et al.
High-Energy and Nuclear Physics research facilities around the world demand cutting-edge instruments dedicated to exploring the signatures of particles knocked out by collisions at ultra-relativistic energies. Each instrument is a class of its own, but shares underlying technologies proven to solve specific challenges. Polymer-based scintillating fibers (cross sections typically below 1 mm²) are sensitive to a large range of particle types and broad energy ranges and provide a fast response, fine spatial segmentation, and a low material budget, making them suitable for particle tracking, beam monitoring, and timing applications. Indeed, scintillating fibers can cover a large variety of shapes and sizes when assembled as ribbons, also allowing for multilayer designs. While most multilayer fiber detectors employ round-section fibers in staggered layers configuration, the square cross section permits regular arrangements with gapless fully packed ribbons and a quasi-uniform distribution of sensitive material. This work presents the manufacturing process developed at the Detector Laboratory of GSI Helmholtzzentrum für Schwerionenforschung (Germany) for manufacturing single- and multilayer ribbons made of scintillating square fibers. The complete production sequence is described, including fiber winding and positioning, bonding of layers, stacking and alignment of multilayer ribbons, integration of mechanical interfaces, machining and surface finishing of the optical couplings, and quality control procedures. Dedicated tooling was developed for each production stage to provide mechanical reproducibility and scalability. The process can be fully adapted to different fiber sizes, ribbon widths and lengths, and layer configurations, enabling the production of both small prototypes and large-format modules. This technology, already validated in operative instruments, is being deployed in a new generation of experiments for the international Facility for Antiproton and Ion Research (FAIR) research center.
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- 2 October 2026
- Published by MDPI AG in Journal of Manufacturing and Materials Processing
Open Access
Manufacturing Methodology for Single- and Multilayer Square Scintillating Fiber-Based Ribbons for Direct Coupling to Linear Photosensor Arrays
by P. Garcia Gil, I. Brandherm, M. Heil, D. Savran, C. Caesar, J. Weinert, S. Schwab, T. Aumann, E. Casarejos, C. J. Schmidt, et al.
High-Energy and Nuclear Physics research facilities around the world demand cutting-edge instruments dedicated to exploring the signatures of particles knocked out by collisions at ultra-relativistic energies. Each instrument is a class of its own, but shares underlying technologies proven to solve specific challenges. Polymer-based scintillating fibers (cross sections typically below 1 mm²) are sensitive to a large range of particle types and broad energy ranges and provide a fast response, fine spatial segmentation, and a low material budget, making them suitable for particle tracking, beam monitoring, and timing applications. Indeed, scintillating fibers can cover a large variety of shapes and sizes when assembled as ribbons, also allowing for multilayer designs. While most multilayer fiber detectors employ round-section fibers in staggered layers configuration, the square cross section permits regular arrangements with gapless fully packed ribbons and a quasi-uniform distribution of sensitive material. This work presents the manufacturing process developed at the Detector Laboratory of GSI Helmholtzzentrum für Schwerionenforschung (Germany) for manufacturing single- and multilayer ribbons made of scintillating square fibers. The complete production sequence is described, including fiber winding and positioning, bonding of layers, stacking and alignment of multilayer ribbons, integration of mechanical interfaces, machining and surface finishing of the optical couplings, and quality control procedures. Dedicated tooling was developed for each production stage to provide mechanical reproducibility and scalability. The process can be fully adapted to different fiber sizes, ribbon widths and lengths, and layer configurations, enabling the production of both small prototypes and large-format modules. This technology, already validated in operative instruments, is being deployed in a new generation of experiments for the international Facility for Antiproton and Ion Research (FAIR) research center.
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- 19 June 2025
- Published by Springer Nature in The European Physical Journal A
Total cross sections of the ${^{87}\hbox {Rb}}(\hbox {p},\gamma ){^{88}\hbox {Sr}}$ reaction measured via in-beam gamma-ray spectroscopy
by Svenja Wilden, Benedikt Machliner, Martin Müller, Andreas Zilges
The $${^{87}\hbox {Rb}}(\hbox {p},\gamma ){^{88}\hbox {Sr}}$$ $^{87} Rb (p, γ)^{88} Sr$ reaction was measured for the first time at astrophysically relevant energies in an in-beam experiment at the high-efficiency HPGe $$\gamma $$ $γ$ -ray spectrometer HORUS at the University of Cologne. To determine total cross sections of the $${^{87}\hbox {Rb}}(\hbox {p},\gamma ){^{88}\hbox {Sr}}$$ $^{87} Rb (p, γ)^{88} Sr$ reaction, proton beams at six different energies between E $$_p$$ $_{p}$ = $${2.0}\hbox { MeV}$$ $2.0 MeV$ and $${5.0}\hbox { MeV}$$ $5.0 MeV$ were provided by a 10 MV FN tandem accelerator, spanning nearly the entire Gamow window relevant for the astrophysical $$\gamma $$ $γ$ -process. These total experimentally obtained cross sections were then compared to calculations performed using the talys 2.0 code. In comparison, the measured total cross-sections are found to be lower than those predicted by different models used as input parameters for the talys 2.0 code for $$\hbox {E}_{p} = {2.0}\hbox { MeV}$$ $E_{p} = 2.0 MeV$ to $${3.5}\hbox { MeV}$$ $3.5 MeV$ .
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- 19 June 2025
- Published by Springer Nature in The European Physical Journal A
Open Access
Total cross sections of the ${^{87}\hbox {Rb}}(\hbox {p},\gamma ){^{88}\hbox {Sr}}$ reaction measured via in-beam gamma-ray spectroscopy
by Svenja Wilden, Benedikt Machliner, Martin Müller, Andreas Zilges
The $${^{87}\hbox {Rb}}(\hbox {p},\gamma ){^{88}\hbox {Sr}}$$ $^{87} Rb (p, γ)^{88} Sr$ reaction was measured for the first time at astrophysically relevant energies in an in-beam experiment at the high-efficiency HPGe $$\gamma $$ $γ$ -ray spectrometer HORUS at the University of Cologne. To determine total cross sections of the $${^{87}\hbox {Rb}}(\hbox {p},\gamma ){^{88}\hbox {Sr}}$$ $^{87} Rb (p, γ)^{88} Sr$ reaction, proton beams at six different energies between E $$_p$$ $_{p}$ = $${2.0}\hbox { MeV}$$ $2.0 MeV$ and $${5.0}\hbox { MeV}$$ $5.0 MeV$ were provided by a 10 MV FN tandem accelerator, spanning nearly the entire Gamow window relevant for the astrophysical $$\gamma $$ $γ$ -process. These total experimentally obtained cross sections were then compared to calculations performed using the talys 2.0 code. In comparison, the measured total cross-sections are found to be lower than those predicted by different models used as input parameters for the talys 2.0 code for $$\hbox {E}_{p} = {2.0}\hbox { MeV}$$ $E_{p} = 2.0 MeV$ to $${3.5}\hbox { MeV}$$ $3.5 MeV$ .
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Cited by 7
- 20 May 2025
- Published by American Physical Society (APS) in Physical Review Letters
Deviations from the Porter-Thomas distribution due to non-statistical $γ$ -decay below the $^{150}$ Nd neutron separation threshold
by O. Papst, J. Isaak, V. Werner, D. Savran, N. Pietralla, G. Battaglia, T. Beck, M. Beuschlein, S. W. Finch, U. Friman-Gayer, et al.
We introduce a new method for the study of fluctuations of partial transition widths based on nuclear resonance fluorescence experiments with quasimonochromatic linearly polarized photon beams below particle separation thresholds. It is based on the average branching of decays of J = 1 states of an even-even nucleus to the 2 1 + state in comparison to the ground state. Between 5 and 7 MeV, a constant average branching ratio for γ decays from 1 − states of 0.490(16) is observed for the nuclide Nd 150 . Assuming χ 2 -distributed partial transition widths, this average branching ratio is related to a degree of freedom of ν = 1.93 ( 12 ) , rejecting the validity of the Porter-Thomas distribution, requiring ν = 1 . The observed deviation can be explained by nonstatistical effects in the γ -decay behavior with contributions in the range of 9.4(10)% up to 94(10)%.
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- 20 May 2025
- Published by American Physical Society (APS) in Physical Review Letters
Open Access
Deviations from the Porter-Thomas distribution due to non-statistical $γ$ -decay below the $^{150}$ Nd neutron separation threshold
by O. Papst, J. Isaak, V. Werner, D. Savran, N. Pietralla, G. Battaglia, T. Beck, M. Beuschlein, S. W. Finch, U. Friman-Gayer, et al.
We introduce a new method for the study of fluctuations of partial transition widths based on nuclear resonance fluorescence experiments with quasimonochromatic linearly polarized photon beams below particle separation thresholds. It is based on the average branching of decays of J = 1 states of an even-even nucleus to the 2 1 + state in comparison to the ground state. Between 5 and 7 MeV, a constant average branching ratio for γ decays from 1 − states of 0.490(16) is observed for the nuclide Nd 150 . Assuming χ 2 -distributed partial transition widths, this average branching ratio is related to a degree of freedom of ν = 1.93 ( 12 ) , rejecting the validity of the Porter-Thomas distribution, requiring ν = 1 . The observed deviation can be explained by nonstatistical effects in the γ -decay behavior with contributions in the range of 9.4(10)% up to 94(10)%.
Cited by 7
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Cited by 7
- 15 April 2024
- Published by American Physical Society (APS) in Physical Review C
Low-lying dipole response of ${}^{64}{Ni}$
by M. Müscher, E. Litvinova, R. Schwengner, T. Beck, D. Bemmerer, F. Fiedler, S. W. Finch, U. Friman-Gayer, S. Hammer, J. Isaak, et al.
Two complementary real-photon scattering experiments were conducted on the proton-magic ${}^{64}{Ni}$ nucleus to study the dipole response up to its neutron-separation energy of $S_{n} = 9.7 MeV$ . By combining both measurements, 87 $E 1$ and 23 $M 1$ transitions were identified above 4.3 MeV. The results of the observed $M 1$ transitions were compared to shell-model calculations using two different model spaces. It was found that the inclusion of excitations across the $Z = 28$ shell gap in the calculations has a large impact. Furthermore, average cross sections for decays to the ground state (elastic transitions) as well as to lower-lying excited states (inelastic decays) were determined. The corresponding $E 1$ channel was compared to calculations within the relativistic equation of motion (REOM) framework. Whereas the calculations of highest possible complexity reproduce the fragmentation and overall behavior of the $E 1$ average elastic cross section well, the predicted absolute cross sections are approximately twice as high as the experimental upper limits even though the latter also include an estimate of the inelastic-decay channel.
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- 15 April 2024
- Published by American Physical Society (APS) in Physical Review C
Low-lying dipole response of ${}^{64}{Ni}$
by M. Müscher, E. Litvinova, R. Schwengner, T. Beck, D. Bemmerer, F. Fiedler, S. W. Finch, U. Friman-Gayer, S. Hammer, J. Isaak, et al.
Two complementary real-photon scattering experiments were conducted on the proton-magic ${}^{64}{Ni}$ nucleus to study the dipole response up to its neutron-separation energy of $S_{n} = 9.7 MeV$ . By combining both measurements, 87 $E 1$ and 23 $M 1$ transitions were identified above 4.3 MeV. The results of the observed $M 1$ transitions were compared to shell-model calculations using two different model spaces. It was found that the inclusion of excitations across the $Z = 28$ shell gap in the calculations has a large impact. Furthermore, average cross sections for decays to the ground state (elastic transitions) as well as to lower-lying excited states (inelastic decays) were determined. The corresponding $E 1$ channel was compared to calculations within the relativistic equation of motion (REOM) framework. Whereas the calculations of highest possible complexity reproduce the fragmentation and overall behavior of the $E 1$ average elastic cross section well, the predicted absolute cross sections are approximately twice as high as the experimental upper limits even though the latter also include an estimate of the inelastic-decay channel.
Cited by 7
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Cited by 9
- 1 November 2023
- Published by American Physical Society (APS) in Physical Review C
Direct demonstration of the two-phonon structure of the $J^{π} = 1_{4742 keV}^{-}$ state of ${}^{88}{Sr}$
by J. Isaak, D. Savran, N. Pietralla, N. Tsoneva, A. Zilges, K. Eberhardt, C. Geppert, C. Gorges, H. Lenske, D. Renisch
We have studied the decay pattern of the $J^{π} = 1_{4742 keV}^{-}$ state of ${}^{88}{Sr}$ to probe its quadrupole-octupole coupled two-phonon structure. In particular, a unique fingerprint to prove the two-phonon nature is the $E 2$ decay strength of the $1_{4742 keV}^{-} \to 3_{1}^{-}$ transition into the one-octupole-phonon state. $γ$ -ray spectroscopy was performed after the $β$ decay of ${}^{88}{Rb}$ to obtain the necessary sensitivity for this weak-intensity decay branch. Sufficient amounts of ${}^{88}{Rb}$ $(T_{1 / 2} = 17.8 \min)$ were produced by neutron activation of natural Rb in the TRIGA Mark II reactor. The results show that the $B (E 2)$ value of the $1_{4742 keV}^{-} \to 3_{1}^{-}$ transition is equal to the $B (E 2)$ of the $2_{1}^{+} \to 0_{1}^{+}$ transition, directly demonstrating the quadrupole-octupole coupled two-phonon nature of the $1^{-}$ state. A comparison of the results with energy-density functional plus quasiparticle-phonon model calculations shows remarkable agreement, corroborating this assignment.
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- 1 November 2023
- Published by American Physical Society (APS) in Physical Review C
Direct demonstration of the two-phonon structure of the $J^{π} = 1_{4742 keV}^{-}$ state of ${}^{88}{Sr}$
by J. Isaak, D. Savran, N. Pietralla, N. Tsoneva, A. Zilges, K. Eberhardt, C. Geppert, C. Gorges, H. Lenske, D. Renisch
We have studied the decay pattern of the $J^{π} = 1_{4742 keV}^{-}$ state of ${}^{88}{Sr}$ to probe its quadrupole-octupole coupled two-phonon structure. In particular, a unique fingerprint to prove the two-phonon nature is the $E 2$ decay strength of the $1_{4742 keV}^{-} \to 3_{1}^{-}$ transition into the one-octupole-phonon state. $γ$ -ray spectroscopy was performed after the $β$ decay of ${}^{88}{Rb}$ to obtain the necessary sensitivity for this weak-intensity decay branch. Sufficient amounts of ${}^{88}{Rb}$ $(T_{1 / 2} = 17.8 \min)$ were produced by neutron activation of natural Rb in the TRIGA Mark II reactor. The results show that the $B (E 2)$ value of the $1_{4742 keV}^{-} \to 3_{1}^{-}$ transition is equal to the $B (E 2)$ of the $2_{1}^{+} \to 0_{1}^{+}$ transition, directly demonstrating the quadrupole-octupole coupled two-phonon nature of the $1^{-}$ state. A comparison of the results with energy-density functional plus quasiparticle-phonon model calculations shows remarkable agreement, corroborating this assignment.
Cited by 9
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Cited by 20
- 10 July 2023
- Published by American Physical Society (APS) in Physical Review C
Experimental study of excited states of ${}^{62}{Ni}$ via one-neutron $(d, p)$ transfer up to the neutron-separation threshold and characteristics of the pygmy dipole resonance states
by M. Spieker, L. T. Baby, A. L. Conley, B. Kelly, M. Müscher, R. Renom, T. Schüttler, A. Zilges
The degree of collectivity of the pygmy dipole resonance (PDR) is an open question. Recently, Ries et al. suggested the onset of the PDR beyond $N = 28$ based on the observation of a significant $E 1$ strength increase in the Cr isotopes and proposed that the PDR has its origin in a few-nucleon effect. Earlier, Inakura et al. had predicted by performing systematic calculations using the random-phase approximation (RPA) with the Skyrme functional SkM* that the $E 1$ strength of the PDR strongly depends on the position of the Fermi level and that it displays a clear correlation with the occupation of orbits with orbital angular momenta less than $3 ℏ (l \leq 2)$ . To further investigate the microscopic structures causing the possible formation of a PDR beyond the $N = 28$ neutron shell closure, we performed a ${}^{61}{Ni} (d, p) {}^{62}{Ni}$ experiment at the John D. Fox Superconducting Linear Accelerator Laboratory of Florida State University. To determine the angular momentum transfer populating possible $J^{π} = 1^{-}$ states and other excited states of ${}^{62}{Ni}$ , angular distributions and associated single-neutron transfer cross sections were measured with the Super-Enge Split-Pole Spectrograph. A number of $J^{π} = 1^{-}$ states were observed below the neutron-separation threshold after being populated through $l = 2$ angular momentum transfers. A comparison to available $(γ, γ^{'})$ data for ${}^{58, 60}{Ni}$ provides evidence that the $B (E 1)$ strength shifts further down in energy. The $(d, p)$ data clearly prove that $l = 0$ strength, i.e., the neutron ${(2 p_{3 / 2})}^{- 1} {(3 s_{1 / 2})}^{+ 1}$ one-particle–one-hole configuration, plays only a minor role for $1^{-}$ states below the neutron-separation threshold in ${}^{62}{Ni}$ .
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- 10 July 2023
- Published by American Physical Society (APS) in Physical Review C
Experimental study of excited states of ${}^{62}{Ni}$ via one-neutron $(d, p)$ transfer up to the neutron-separation threshold and characteristics of the pygmy dipole resonance states
by M. Spieker, L. T. Baby, A. L. Conley, B. Kelly, M. Müscher, R. Renom, T. Schüttler, A. Zilges
The degree of collectivity of the pygmy dipole resonance (PDR) is an open question. Recently, Ries et al. suggested the onset of the PDR beyond $N = 28$ based on the observation of a significant $E 1$ strength increase in the Cr isotopes and proposed that the PDR has its origin in a few-nucleon effect. Earlier, Inakura et al. had predicted by performing systematic calculations using the random-phase approximation (RPA) with the Skyrme functional SkM* that the $E 1$ strength of the PDR strongly depends on the position of the Fermi level and that it displays a clear correlation with the occupation of orbits with orbital angular momenta less than $3 ℏ (l \leq 2)$ . To further investigate the microscopic structures causing the possible formation of a PDR beyond the $N = 28$ neutron shell closure, we performed a ${}^{61}{Ni} (d, p) {}^{62}{Ni}$ experiment at the John D. Fox Superconducting Linear Accelerator Laboratory of Florida State University. To determine the angular momentum transfer populating possible $J^{π} = 1^{-}$ states and other excited states of ${}^{62}{Ni}$ , angular distributions and associated single-neutron transfer cross sections were measured with the Super-Enge Split-Pole Spectrograph. A number of $J^{π} = 1^{-}$ states were observed below the neutron-separation threshold after being populated through $l = 2$ angular momentum transfers. A comparison to available $(γ, γ^{'})$ data for ${}^{58, 60}{Ni}$ provides evidence that the $B (E 1)$ strength shifts further down in energy. The $(d, p)$ data clearly prove that $l = 0$ strength, i.e., the neutron ${(2 p_{3 / 2})}^{- 1} {(3 s_{1 / 2})}^{+ 1}$ one-particle–one-hole configuration, plays only a minor role for $1^{-}$ states below the neutron-separation threshold in ${}^{62}{Ni}$ .
Cited by 20
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Cited by 2
- 20 March 2023
- Published by American Physical Society (APS) in Physical Review C
Determination of $^{170, 172} Yb {(α, n)}^{173, 175} Hf$ reaction cross sections in a stacked-target experiment
by M. Müller, F. Heim, Y. Wang, S. Wilden, A. Zilges
Background: For understanding the synthesis of elements in the universe, precise knowledge of reaction rates and cross sections is paramount. This is especially true for the $p$ process because its study requires large network calculations including thousands of nuclei and nuclear reactions with little room for simplification. Therefore, robust theoretical methods for predicting cross sections are needed which are usually based on Hauser-Feshbach calculations. These calculations use physics input in the form of $γ$ -ray strength functions, nuclear level densities, and particle $+$ nucleus optical-model potentials. These have to be constrained using experimental results.
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- 20 March 2023
- Published by American Physical Society (APS) in Physical Review C
Determination of $^{170, 172} Yb {(α, n)}^{173, 175} Hf$ reaction cross sections in a stacked-target experiment
by M. Müller, F. Heim, Y. Wang, S. Wilden, A. Zilges
Background: For understanding the synthesis of elements in the universe, precise knowledge of reaction rates and cross sections is paramount. This is especially true for the $p$ process because its study requires large network calculations including thousands of nuclei and nuclear reactions with little room for simplification. Therefore, robust theoretical methods for predicting cross sections are needed which are usually based on Hauser-Feshbach calculations. These calculations use physics input in the form of $γ$ -ray strength functions, nuclear level densities, and particle $+$ nucleus optical-model potentials. These have to be constrained using experimental results.
Cited by 2
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Cited by 1
- 8 December 2022
- Published by Springer Nature
Pygmy Dipole Resonance: Experimental Studies by Different Probes
by Andreas Zilges, Deniz Savran
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- 8 December 2022
- Published by Springer Nature
Pygmy Dipole Resonance: Experimental Studies by Different Probes
by Andreas Zilges, Deniz Savran
Cited by 1
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Cited by 12
- 17 March 2022
- Published by American Physical Society (APS) in Physical Review C
Lifetime analysis of ${}^{128, 130}{Te}$ via the Doppler-shift attenuation method
by Sarah Prill, Anna Bohn, Vera Everwyn, Guillaume Häfner, Felix Heim, Mark Spieker, Michael Weinert, Julius Wilhelmy, Andreas Zilges
Background: The $Z = 52$ nuclei ${}^{128}{Te}$ and ${}^{130}{Te}$ are interesting candidates to study nuclear-structure properties close to the $Z = 50$ shell. The knowledge of lifetimes of low-lying states in those nuclei is still scarce.
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- 17 March 2022
- Published by American Physical Society (APS) in Physical Review C
Lifetime analysis of ${}^{128, 130}{Te}$ via the Doppler-shift attenuation method
by Sarah Prill, Anna Bohn, Vera Everwyn, Guillaume Häfner, Felix Heim, Mark Spieker, Michael Weinert, Julius Wilhelmy, Andreas Zilges
Background: The $Z = 52$ nuclei ${}^{128}{Te}$ and ${}^{130}{Te}$ are interesting candidates to study nuclear-structure properties close to the $Z = 50$ shell. The knowledge of lifetimes of low-lying states in those nuclei is still scarce.
Cited by 12
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Cited by 205
- 1 January 2022
- Published by Elsevier in Progress in Particle and Nuclear Physics
Photonuclear reactions—From basic research to applications
by A. Zilges, D.L. Balabanski, J. Isaak, N. Pietralla
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- 1 January 2022
- Published by Elsevier in Progress in Particle and Nuclear Physics
Top Cited Papers
Photonuclear reactions—From basic research to applications
by A. Zilges, D.L. Balabanski, J. Isaak, N. Pietralla
Cited by 205

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