Photocathodes based on the III-V seminconductor GaAs are used as photo-electron sources to supply spin-polarized electron beams for accelerator applications. In order to achieve a sufficient electron yield, a thin surface layer of cesium combined with an oxidant is applied onto the cathode surface. This process is called the cathode activation and is typically done manually by an experienced...
The rapid development of high-power laser systems in recent decades has sparked significant interest in laser-driven ion acceleration, offering promising characteristics such as high brightness, ultrashort pulse duration, and high particle energies. However, the practical use of laser-accelerated ion beams remains challenging due to their large energy spread and high angular divergence,...
Nuclear reactions of astrophysical interest often concern unstable or even exotic species for which no experimental data exist. Although significant efforts have been devoted in the past decades, experimental information only covers a minute fraction of the data set required for nuclear astrophysics. Moreover, the energy range for which experimental data is available is restricted to the small...
High Purity Germanium (HPGe) detectors are very important tools in nuclear and particle physics, primarily due to their low energy thresholds and exceptional energy resolution, which enables precise measurements across a broad energy spectrum. This study aims to comprehensively characterize the performance of four gamma-ray detectors: two n-type HPGe detectors and two Clover detectors, which...
This work explores the stabilization of key parameters in dual-arm femtosecond laser systems, focusing on improving spatio-temporal control and synchronization to achieve peak powers above 10 PW. In the High-Power Laser System (HPLS) at ELI-NP, pulse energy, spectrum, and temporal "jitter" were analyzed to identify sources of instability and improve overall performance. The ongoing upgrade of...
High-precision experimental data on photon-induced reactions provide an important contribution to the pursuit of a complete microscopic description of the fission process due to their selectivity on excitation of low multipolarity. Unique information can be extracted by using mono-chromatic polarized photons in the entrance channel allowing a determination of transition states through which...
We present a data-driven analysis of dipole strength functions across the nuclear chart, employing an artificial neural network to model and predict nuclear dipole responses. We train the network on a dataset of experimentally measured dipole strength functions for 216 different nuclei. To assess its predictive capability, we test the trained model on an additional set of 10 new nuclei, where...
Dipole polarizabilities are one of several complementary ways to put more narrow constraints on the symmetry energy slope parameter of the nuclear equation of state. Also, precise measurements of dipole polarizabilities present a sensitive benchmark for modern nuclear theory calculations.
In order to derive experimental dipole polarizabilities, nuclear photoabsorption cross sections are...
Electromagnetic response of nuclei plays an important probe in the understanding of nuclear structure. This quantity is also very crucial in the context of nucleosynthesis such as in r-process calculations. R-process studies require calculations of many nuclei and typically the response is extracted by using linear response approaches such as quasiparticle random phase approximation (QRPA)....
Understanding the origin of heavy chemical elements in the Universe remains a fundamental challenge. One of the primary mechanisms for forming such heavy nuclei is the rapid neutron capture process (r-process), which can occur during neutron star mergers [1]. In this process, neutrons are captured at high temperatures, leading to the formation of very neutron-rich nuclei.
In the actinide...
A series of nuclear resonance fluorescence experiments was conducted with bremsstrahlung at $\gamma$ELBE and a quasi-monoenergetic, polarized photon source at HI$\gamma$S.
The acquired experimental data allows for a model-independent determination of the dipole response of the most neutron-rich stable zinc isotope, $^{70}$Zn, which will aid in a better understanding of collective nuclear...
Experimental evidence of the inverse of internal conversion, nuclear excitation by electron capture (NEEC), continues to elude nuclear and plasma physicists alike. Following the reported observation of NEEC in Nature, 2018, using $^{93m}$Mo[1], and its subsequent theoretical disagreement [2], there has been heightened interest in the nuclear excitation mechanism.
Induction and isolation of...
The giant dipole resonance (GDR) represents one of the most fundamental nuclear excitations and dominates the photoresponse of virtually all nuclei. Its geometrical viewing is an isovector oscillation of the proton against the neutron body. This model also provides predictions for the $\gamma$-decay behavior of the GDR in elastic photon and $2^+_1$ Raman scattering reactions.
To rigorously...
The rare-earth region of the nuclear chart is one of the most thoroughly explored in terms of quadrupole deformation, providing a valuable benchmark for studying nuclear structure and collectivity. Two key observables in this context are the energy ratio $R_{4/2}$ and the reduced transition probability $B(E2; 2_1^+ \to 0_1^+)$, which serve as indicators for nuclear structure. Notably, nuclei...
Systematic studies along isotopic and isotonic chains are essential for understanding the characteristics of the low-lying dipole response in atomic nuclei. Such studies can provide valuable insights into the influence of factors such as shell structure and neutron excess on dipole strength. Since photons transfer only small angular momenta, real-photon scattering, commonly denoted as Nuclear...
Laser-based particle sources allow for investigating biological effects of radiation at high instantaneous dose rates. We have run two experiments including the irradiation of monolayer cell cultures at total dose values of 3-12 Gy.
The first one, at the Laser Laboratory for Acceleration and Applications (L2A2), makes use of an X-ray source driven by a 35 fs pulsed laser with 1 mJ pulse...
Photonuclear reactions are a powerful tool to probe the quantum structure of the atomic nucleus by inducing single-particle and collective excitations [1], and also played a significant role in the first moments of our universe or later in stellar nucleosynthesis processes [2]. These reactions are also of great interest because of their many societal applications, such as national security,...
The r-process path of cosmic nucleosynthesis is expected to proceed partly along the $N = 126$ neutron shell closure where it contributes to the third r-process peak [1]. Improved microscopic understanding of cosmic nucleosynthesis calls for more precise and complete data on neutron-rich nuclei in the mass region around the doubly-closed shell nucleus $^{208}$Pb that serve to constrain...
The performance of three different target types—glass slide, polymer film, and liquid sheet—was evaluated for use in plasma mirror Frequency Resolved Optical Gating (PM-FROG) diagnostic of chirped near-infrared laser pulses in the 1–8 ps range. The measurements were conducted at the High Power Laser System (HPLS) of ELI-NP, employing both arms of the laser system in a pump-probe configuration....
Spatio-Temporal Couplings (STC) of ultra-intense laser pulses can significantly impact
relativistic particle acceleration or radiation production, relevant for nuclear photonics applications.
This STC experimental study covers the analysis of residual and induced
spatio-temporal distortions generated with a fs laser oscillator. Complementary, propagation simulations
using real data from...
Laser-accelerated ions typically exhibit an exponential energy spectrum up to a characteristic cut-off energy, which is a signature of target normal sheath acceleration (TNSA) [1]. However, many applications, such as proton therapy [2] or the fast ignition concept in inertial confinement fusion [3] benefit from well defined spectral shapes.
By introducing multiple ion species into the...
Neutral beam injection (NBI) is an established heating method on many existing magnetic confinement fusion devices. Most currently operated NBI systems create neutral Hydrogen, Deuterium, or even Tritium [1] by neutralizing positive or negative ion beams in a gas neutralizer (GN). For ITER a beam energy of 1MeV Deuterium was chosen. It was found that the neutralization yield of positive ions...
This study aims at understanding the dependence of the E1 strength in the transition region from vibrational to rotational nuclei. The chosen method of study is the Nuclear Resonance Fluorescence method, a two-step photonuclear process which consists of the absorption of a photon and the subsequent resonant re-emission of gamma rays.
The experimental data has been acquired using the DHIPS...
In this study, the optimisation of the longitudinal density profile, thickness, and density gradient on the rear side of the gas target formed by a symmetrical and unsymmetrical shock nozzle for the acceleration of proton beams utilising high-repetition kHz lasers has been carried out.
Most of the laser-driven ion acceleration experiments are performed using PW-class lasers focused on the...
The Mössbauer effect allows recoilless resonant nuclear excitation through the interaction of nuclear states with the crystal lattice [1]. This enables energy exchange with vibrational modes (phonons), which can dress the nuclear transition and even allow resonant absorption at slightly detuned photon energies. This process is typically studied using nuclear inelastic scattering. While...
With the advancement of intense laser technology, nonlinear Compton scattering (NCS), in which multiple laser photons are absorbed and a single high energy photon is emitted, has been actively investigated to probe electron and photon dynamics in strong electromagnetic fields [1].
Taira et al. proposed, based on classical electrodynamics calculations, that NCS with circularly polarized...
Since the inception of laser science, one fundamental goal has always been increasing the intensity of laser pulses. One of the techniques used for achieving this goal is Self Phase Modulation (SPM), consisting of pulse propagation through nonlinear media and using nonlinear effects to broaden the spectrum, enabling better compression and shorter pulse lengths. In this presentation, I outline...
To support high-repetition-rate particle production for applications such as radioisotope production, hadron therapy or neutron production, liquid targets are being developed at ELI-NP. With increasing repetition-rates achieved by lasers, liquid targets must regenerate rapidly to ensure consistent interaction conditions. In this study, we investigated the regeneration dynamics of a water...
A new setup for Laser-Compton back-scattering has been installed at the S-DALINAC. Here, the laser beam and the electron beam of the S-DALINAC, both with a width of equal or less than 100 µm, must be stably superimposed over long periods of time. Three systems have been developed, implemented and interconnected to monitor and improve the transverse stability of the electron beam [1]: (i) A...
The advent of intense beams of quasi-monochromatic polarized photons from laser Compton backscattering in the MeV energy range has revolutionized the field of photonuclear reactions [1]. A fourth generation light source comprising laser Compton backscattering from a multi-turn energy-recovery electron linac (ERL) is considered the next technological step. Such a system has not been realized,...
Our research group has been studying isotope CT imaging using nuclear resonance fluorescence with energy-tunable gamma-ray beams generated by laser Compton scattering (LCS) and is currently working on simultaneous imaging of multiple isotopes and their quantitative evaluation. When an incident gamma-ray beam covers two different resonance energies of two nuclides, it is possible to obtain two...
Nanostructured targets can enhance the laser-matter interaction by coupling the laser pulse into the target, by volumetric heating, due to the increased surface area, leading to higher proton energy cut-off, yield, X-ray or gamma ray emission, and terabar pressure. However, enhanced coupling is highly dependent on the correlation of the target parameters to the laser pulse characteristics (as...
Nuclear physics has entered the era of high-precision studies. For light nuclei, modern theories of nuclear forces, such as chiral effective field theory ($\chi$EFT), predict selected electromagnetic transition rates to a few percent accuracy, where they are sensitive to effective two-body currents (2BC). Measurements of decay widths of a few percent or better allow us to test theories [1]. To...
Electron-capture rates on medium-heavy nuclei play a crucial role in the last stage of core-collapse supernovae of massive stars during the deleptonization process. While these rates are highly sensitive to their Gamow-Teller (GT) strength [1], their direct measurement remains experimentally challenging. As an isospin analogue, the isovector spin-flip M1 (IVSM1) response offers an alternative...
Laser-driven photon sources benefit from the inherently small source size and ultrashort duration, resulting in high brilliance beams. Different configurations based on laser-driven electron acceleration have been proposed so far in order to improve the laser-target energy coupling and obtain high energy and high photon flux sources. One method to enhance the number of radiating electrons is...
X-ray sources are of growing importance as a diagnostic tool for High Energy Density (HED) experiments and Inertial Confinement Fusion (ICF) studies as well as the upcoming FAIR facility in Darmstadt. For these applications, so-called x-ray backlighters must meet requirements regarding low divergence, small source size to achieve a sufficient imaging resolution and high brightness to overcome...
