Porträt Prof. Dr. Bemmerer, Daniel; FWKK

Prof. Dr. Daniel Bemmerer

Group lea­der Nuclear Astrophysics, Technical Director Felsenkeller accelerator
Nuclear Physics
Phone: +49 351 260 3581
+49 351 260 3901
Fax: +49 351 260 13581

Detector development for CBM at FAIR

Detector development for NeuLAND at FAIR

Detector Development for basic research

For basic research, detectors with very high time resolution and excellent sensitivity are required. This is particularly true for the experiments HADES, CBM, and R3B at GSI and FAIR in Darmstadt, Germany. A long-standing, sustained effort has been mounted at HZDR to support these experiments by developing and testing the best detectors, especially for timing purposes. This work has been greatly accelerated due to the fact that the HZDR 40 MeV ELBE electron beam offers ideal conditions for testing such detectors. 

Single-electron mode of the ELBE 40 MeV electron beam

For timing detector tests, it is sometimes of benefit to inject only a very small amount of ionization into an ionization-based detector. This can be done exceedingly well using the single-electron mode of ELBE, where one or just a few electrons are accelerated in one bunch.

The plot shows the charge spectrum, as observed in a thin plastic scintillator serving as efficiency reference. Two different modes of operation of ELBE are shown, as controlled by the electron gun gate voltage:

  • In the top panel, the peaks due to 1–6 electrons per bunch are visible, as well as some low-charge background that is not correlated in time.
  • In the bottom panel, just the peak due to one electron per bunch survives, due to the lower gate voltage and additional screens restricting the beam envelope.

Both the single-electron (bottom panel) and the multi-electron (top panel) modes of operation have been used for detector tests. The single-electron mode was patented (Kotte et al. 2010).

Please see also our separate page on the electron beam at ELBE, with information for potential external users.

  ELBE, single-electron mode

High-rate capability of RPC detectors tested at ELBE

Using the scalability of the electron flux in single-electron mode, ceramic RPC detectors that are capable of sustaining fluxes up to several times 105 electrons / cm2 s have been proven to show satisfactory efficiency and time resolution (Naumann et al. 2011).

This high rate capability represents the current world record for ceramic RPCs.

See also Akindinov et al. 2017.

  Ceramic RPC with ultra-high rate capability

Large neutron time of flight detector NeuLAND for the R3B experiment at FAIR

The rare-ion beam experiment R3B (Reactions with Relativistic Radioactive Beams) at the future FAIR facility aims for kinematically complete measurements of fast radioactive ions. One particularly important component of the R3B setup is the neutron detector, called NeuLAND after the existing LAND (Large Area Neutron Detector).

The HZDR group has deeply studied one option for the implementation of such a detector, based on steel converters to convert the energetic neutrons to charged particles and multigap resistive plate chambers (MRPCs) to detect the charged particles with high efficiency and 0.1 ns time resolution. This work culminated in the construction and successful test of a 2 m x 0.5 m large prototype, complemented by extensive Monte Carlo simulations and test experiments at the HZDR electron beam (for the time resolution) and at the TSL Uppsala quasi-monochromatic neutron beam (for the neutron response):

2m long NeuLAND prototype HZDR201b/HZDR202 for FAIR in the detector test cave at ELBE

After the R3B collaboration decided to construct NeuLAND following a different approach using plastic scintillators, the HZDR/TU Dresden group showed experimentally for the first time that these large, wide plastic scintillator bars (270 x 5 x 5 cm3) can be successfully read out by novel silicon photomultipliers (SiPMs) while maintaining efficiency and time resolution. The picture shows a time-over-charge plot for one side of the long NeuLAND bar. After subtraction of the size of the electron beam, a time resolution of σ = 138 ps is found, in keeping with the NeuLAND design criteria. 

Follow-up studies showed excellent linearity and saturation behaviour over the required range of NeuLAND.

 Time resolution of a NeuLAND scintillator, read out by SiPMs (Reinhardt et al. Nucl. Inst. Meth. A 2016)