Nukleare Photonik

Nuclear Photonics

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.

https://www.ikp.tu-darmstadt.de/nuclearphotonics

Laser-Compton-Backscattering Soruce at S-DALINAC

Figure: Simulation of the x-Ray spectra from the designed LCB-Source at the S-DALINAC. The simulation Code is used from: Volz, Paul, & Meseck, Atoosa (2018). Analytical Calculations for Thomson-Backscattering. Verhandlungen der Deutschen Physikalischen Gesellschaft, (Wuerzburg2018issue).
Figure: Simulation of the x-Ray spectra from the designed LCB-Source at the S-DALINAC. The simulation Code is used from: Volz, Paul, & Meseck, Atoosa (2018). Analytical Calculations for Thomson-Backscattering. Verhandlungen der Deutschen Physikalischen Gesellschaft, (Wuerzburg2018issue).

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.

Figure: Picture of the dummy “parabolic mirror” for electron beam test, to fit the electrons through the hole.
Figure: Picture of the dummy “parabolic mirror” for electron beam test, to fit the electrons through the hole.

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).

Instrumentation

Spalt-Ionisationskammer im ELIGANT Set-up an ELI-NP
Figure: CAD-drawing of the ionization chamber implemented in the ELIGANT-array at ELI-NP.

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.

Pulshöhendefekt in einem 80:20 Ar+CF4 Gasgemisch
Figure: Mean pulse height defect measured in a 80:20 Ar+CF4 mixture.

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.

 

Collaboration partners

 

Funding

  • 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).

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  • 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.

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Recent publications

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)