The picture shows the NEPTUN tagging magnet with the focal plane chamber and the attached photo multiplier tubes.

Reaction rates for photon induced nuclear reactions are measured in various experimental setups for the study of nuclear structure.

Different facilities offer different advantages, while most lack a good or even any resolution for the excitation energy.

NEPTUN is capable to measure reaction rates as a function of excitation energy with the help of tagged photons. The energy resolution of 50 keV and better is excellent.

The photons are produced by the effect of bremsstrahlung. The monoenergetic electrons from the S-DALINAC impinge onto a thin radiator target made from gold. Here, bremsstrahlung is induced. The thickness of the radiator target is chosen accordingly to let the electrons produce at most one photon. The scattered electrons are analyzed by a large dipole magnet. They are focussed to different positions according to their momentum in the focal plane of the magnet. An array of detectors with a high spatial granularity detects the electrons and therefore determines their energy.

The related photons continue to the experimental target and can induce nuclear reactions. The reaction products are detected by corresponding detector arrays. By making use of the time relation, the induced reaction products are assigned to the related electron.

The energy of the photon which induced the reaction can easily be calculated as the difference of the incoming electron beam energy minus the scattered electron's energy.

For the measurement of (g,n) reaction rates a neutron detector array is in operation.

For the measurement of (g,g') reaction rates a LaBr3 scintillator array is currently under construction.

For both arrays we pursue a digital data acquisition, which is being developed at the moment.

NEPTUN is also well suited for the characterization of gamma detectors. It can be considered as a monoenergetic gamma source with tunable intensity and energy. The beam current can be adjusted to arbitrarily low values.

We always look for motivated students to reinforce our team! If you are interested, please contact for a tour and information without obligation.

Previous campaigns:

  • extended detector characterization campaign including the materials HPGe, LaBr3 and CsI:(Tl) . A prototype detector for the CALIFA calorimeter barrel has been investigated, which will be used at the future FAIR facility.