Unmasking neutrons with NeuLAND
GSI detector test for FAIR
How are very neutron rich nuclei build up? To answer this question scientists at GSI Helmholtzzentrum für Schwerionenforschung GmbH build the neutron detector NeuLAND. Now the first double plane of the neutron detector was tested. NeuLAND will be part of the R3B experiment at the future particle accelerator facility FAIR. With NeuLAND scientists can correlate multiple neutrons to one nuclear reaction as effective as never before. The aim: To understand the formation of elements in supernovae.
Three meters long, 2,50 meters high and broad – this is how big the completed detector NeuLAND is going to be. It consists of 3000 measuring instruments, so-called scintillator made of plastic bars. They produce light as soon as a neutron passes through them and interacts with the scintillator. It gets transformed into an electrical signal which delivers information on the neutron to the scientists.
The neutrons originate from a fragmentation reaction: When accelerated neutron rich nuclei hit a foil, they get excited and emit one or several neutrons. Researchers want to measure these neutrons and very precisely register the number of neutrons passing through the detector. This reveals information on neutron rich nuclei which play an important role in the natural formation of elements like gold or lead in supernovae, huge stellar explosions. It is planned to produce these nuclei at the future particle accelerator facility FAIR. Apart from that scientists are especially interested in exotic systems which almost only consist of neutrons and have to be artificially produced. They only exist for a very short period of time. When they decay the motion of the neutrons provides information on their specific properties.
To measure neutrons is a special challenge for physicists. They are neutral, as their name indicates, and therefore not electrcally charged. Thus they hardly interact with matter. Almost unnoticed they scurry through the measuring instruments. „This is why the NeuLAND cube is so big“, Dr. Konstanze Boretzky, head of the NeuLAND working group, explains. „The farther the distance the neutrons have to cover the more likely they reveal themselves. When they pass NeuLAND they emit their energy completely. Beside the time of their impact this amount of energy is an important information“, Boretzky explains. „From measuring the neutrons we want to deduce the original neutron rich nucleus which decayed in a nuclear reaction. This is why we have to know if several neutrons hit the detector close together. This is only possible if we measure their energy and correlate it with the hits.“
Currently the fifth NeuLAND double plane is under construction at GSI. In September one fifth is supposed to be tested in the GSI beam. Until 2017 all 30 double planes should be completed.
NeuLAND is built under the technical supervision of the GSI project area Rare Isotope Beams within the FAIR@GSI project and the NUSTAR collaboration. The experiment will be part of the high energy branch of the Super Fragment Separator at the new particle accelerator facility FAIR. Next to GSI the following institutes were significantly involved in NeuLANDs construction: Technische Universität Darmstadt, University of Cologne, Goethe University in Frankfurt and Petersburg Nuclear Physics Institute.