Nuclear photonics is an emerging field of research and combines nuclear physics and high-density matter physics by using unique characteristics of new high-intensity laser-beam facilities for the first time.
LOEWE Initiative – International Center for Nuclear Photonics
On January 1, 2019, the Hessian Ministry for Higher Education, Research and the Arts has established the International Center for Nuclear Photonics at TU Darmstadt in the framework of the LOEWE initiative as a new research cluster.
Laser-Compton-Backscattering Soruce at S-DALINAC
For a wide range of applications in nuclear photonics it is necessary to have a brilliant quasi-monochromatic high energy photon beam. Hence, the development of artificial γ-sources is important. While bremsstrahlung produced by an electron linear accelerator (LINAC) has a broadband spectrum, novel γ-ray sources use Laser Compton Backscattering (LCB). At this point the energy recovery linac comes into account. While generating bremsstrahlung destroys the electron beam, Laser Compton Backscattering is a suitable in beam experiment for multi turn ERLs. Due to the negligible recoil of the electron. Also the expected energy spread of the scattered photons produced in a LCB Source within an ERL is currently the best reachable. In the LOEWE Nuclear Photonics research cluster, the conditions are excellent for the further advancement of this technology.
The concept of laser Compton backscattering is given by the Inverse Compton Effect. When a photon collides antiparallel with an electron, the photon is backscattered. Thereby the photon gains energy, it is boosted in a cone proportional to 1/γ. This characteristic of the distribution can be seen in the simulation, see figure, of the planned LCB-Source, with the basic parameters, using the simulation code developed by P. Volz and A. Meseck.
To keep it as this simple, in the LCB source at S-DALINAC, a laser beam is coupled into the accelerator antiparallel to the direction of electrons flight path and collides at an focus point with the electron beam. The coupling is solved by an off-axis parabolic mirror, which brings the laser beam onto the path of the electrons and at the same time lets the electrons pass through a hole in itself. This concept for the electron beam was tested successfully with a dummy mirror, see picture, inside the S-DALINAC during operation. The overall design of the LCB-Source, with necessary components, was concretized and completed this year. And have been incorporated into the applied funding within the FUGG program for major research instrumentation by the DFG.
Furthermore, concepts and components for measuring and processing the scattered photons were created and characterized. Next year we expect to be able to start the construction of the LCB source at S-DALINAC. Simulations predict for the LCB source, a good beam quality and accordingly a promising accuracy in the characterization of the electron beam parameters. With which we would be able to investigate the interaction of laser and accelerator for a much more brilliant LCB source.
Experiments within the framework of nuclear photonics
In our research group we focus our activities in nuclear photonics on the nuclear fission process. Our main investigations concern fission induced by gamma rays. We use gamma rays – in the near future from the unique gamma-ray source at the Extreme Light Infrastructure – Nuclear Physics in Romania – to excite heavy nuclei like 238U with gamma rays into intermediate states at 5-10 MeV excitation energy. If the excited nuclei undergo fission, the fission fragments are being measured using an ionization chamber. Our studies are aimed at determining fragment properties in a large number of nuclei in order to facilitate a detailed theoretical description of the highly complex fission process. Such advanced model descriptions are, among others, relevant for nuclear astrophysics (as the r-process) or technical aspects (like transmutation).
The structure of intermediate states of fissioning nuclei can be studied by measuring properties in nuclear fission. Mass, kinetic energy and angular distributions of fission fragments are detected using ionization chambers. Additional LaBr3- and HPGe-detectors allow the prompt gamma- and neutron-evaporation to be measured simultaneously. In the figure a newly developed ionization chamber, implemented in the ELIGANT detector array located at the Extreme Light Infrastructure – Nuclear Physics (ELI-NP), is shown. In this future experiment fission fragment mass-, kinetic energy- and angular-distribution as well as gamma- and neutron-evaporation distribution will be measured simultaneously with a monochromatic, polarized gamma-beam.
In order to build more compact ionization chamber, a study on electron mobility and pulse-height defect in different counting gas mixtures of Ar+CF4 was carried out in collaboration with the European Commission's Joint Research Centre in Geel (JRC). The fissioning system 252Cf(sf) was studied by using a twin Frisch-grid ionization chamber and various detector gases. In the graph the extracted mean pulse-height-defect distribution for 80% Argon and 20% CF4 is shown. The calculated fission fragment pre-neutron properties were in excellent agreement with established data.
Str. Reactorului no.30, P.O.BOX MG-6, Bucharest – Magurele, Romania
ELI-NP is going to be the most advanced research facility in the world focusing on the study of photonuclear physics and its applications, comprising a very high intensity laser of two 10PW ultra-short pulse lasers and the most brilliant tunable gamma-ray beam. This unique experimental combination will enable ELI-NP to tackle a wide range of research topics in fundamental physics, nuclear physics and astrophysics, and also applied research in materials science, management of nuclear materials and life sciences.
Since 1962, the JRC facility in Geel brings together multi-disciplinary expertise for developing new measurement methods and tools such as reference materials, promoting standardisation and harmonisation across the European Union to stimulate innovation and to protect consumers and citizens.
Joint Research group of Prof. J. Enders, T. Kröll, N. Pietralla and M. Roth.
BMBF Integrated Research ELI-NP between the University of Cologne (Prof. Zilges), the TU Darmstadt (Prof. Enders, Prof. Kröll, Prof. Pietralla) and the LMU Munich (PD Thirolf).
The International Center for Nuclear Photonics at TU Darmstadt is funded by the Hessian HMWK within the LOEWE initiative. The projects described on these web pages are financially supported by the LOEWE research cluster. As a LOEWE research cluster, the International Center for Nuclear Photonics is member of the Hessian proLOEWE network.
M. Peck et al., Performance of a twin position-sensitive Frisch-grid ionization chamber for photofission experiments, EPJ Web Conf. 239, 05011 (2020)
M. Peck et al., Pulse-height defect of Ar+CF4 mixtures as a counting gas for fission-fragment detectors, NIM A 919, 105 (2019)
A. Göök et al., Correlated mass, energy, and angular distributions from bremsstrahlung-induced fission of 234U and 232Th in the energy region of the fission barrier, Phys. Rev. C 96, 044301 (2017)