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. 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

 

Publications

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)

A. Göök et al., Particle emission angle determination in Frisch grid ionization chambers by electron drift-time measurements, Nucl. Instr. Meth. A 621, 401 (2010)