Neutron ToF Spectrometer NeuLAND

NeuLAND (new Large-Area Neutron Detector) is the next-generation neutron detector designed for R³B which meets all requirements defined by the ambitious physics program proposed for the R³B facility. NeuLAND features a high detection efficiency, a high resolution, and a large multi-neutron-hit resolving power. This is achieved by a highly granular design of plastic scintillators, avoiding insensitive converter material. The detector will consist of 3000 individual submodules with a size of 5x5x250 cm³, arranged in 30 double planes with 100 submodules providing an active face size of 250x250 cm² and a total depth of 3 m. NeuLAND can be divided into two detectors for special applications and can be placed at different distances from the target, in order to meet specific experimental demands.

A momentum resolution of Δp/p of 10^-3 similar to that for the charged particles is desired, resulting in resolution requirements for the time of flight of σ(t) < 150 ps and a position resolution of σ(x,y,z) ≈ 1.5 cm for given flight paths in the range from 10 to 35 m. For an experiment on a medium mass nucleus at about 600 MeV/nucleon, invariant-mass resolutions of about ΔE =20 keV at 100 keV above the neutron threshold will be reached using the maximum flight path. Apart from the excellent energy resolution of NeuLAND, the enhanced multi-neutron recognition capability with efficiencies of 50 to 70% (depending on the physics scenario and settings) for the 4-neutron multiplicity  will constitute a major step  in neutron detection.

The table below shows the neutron separation matrices for multiplicities of 1 to 4 neutrons. Columns display the neutron multiplicity simulated at the target position, rows the neutron multiplicity derived from the calorimetric algorithm. Values are given in percent. Neutrons were simulated with 200 (left), 600 (center) and 1000 MeV (right matrix). NeuLAND with 30 doubleplanes was located at a distance of 15 m to the target. Neutrons were generated with a relative energy of 500 keV with respect to a medium heavy projectile fragment. The distance between target and NeuLAND was filled with air and a 4mm steel window. Simulations have been performed with Geant4 using the QGSP_INCLXX_HP physics list. Note, that the details of the separation matrices strongly depend on the possible maximum neutron multiplicities and of the detailed settings. In the case simulated here, we assume an experiment with a maximum multiplicity of four neutrons impinging on the detector. As a consequence the probability to find a 4-neutron event in the correctly reconstructed neutron multiplicity is larger than for 2 or 3 neutrons.

The final design, containing details of the technical realization of NeuLAND, including mechanics, readout electronics, submodules tests, calibrations, and the construction procedure are described in the NeuLAND Technical Report , summarizing the result of several years of R&D efforts. Different design concepts have been investigated, including converter-based solutions, e.g., a detector based on steel converter plus charged-particle detection with resistive-plate chambers (RPC). The RPC concept has been ruled out mainly because of its insufficient multi-neutron detection capability. A fully active detector with calorimetric properties has turned out to be the best solution. The NeuLAND Technical Design Report has been finalized in 2011 and accepted by FAIR on January 18, 2013.