The CASCADE neutron detector concept

It is a GEM-based hybrid solid converter gas detector for efficient and position sensitive detection of thermal and cold neutrons on large areas. The detector concept is based on using solid neutron converter layers in a common gas detector system, which guarantees sub-microsecond absolute time resolution and insensitivity to Gamma-rays. GEM-technology  provides inherently a rate capacity on the order of 10^7 n/cm^2s. The GEM (= Gas Electron Multiplier) was developed by F. Sauli at CERN's gas detectors developement group (GDD) in 1997. In the CASCADE detector, the GEM is operated in a mode transparent for charges. It serves as the perfect substrate for the solid 10-Boron converter, allowing to cascade several converter layers one behind the other without loss of position [1].

 

Sketch of the detector: a cascade of GEM-foils coated on both sides with 10-Boron and 10-Boron-coated driftelectrodes. Primary electrons, produced by the escaping charged particle of the neutron conversion, are guided undistorted through all of the GEMs onto an arbitrary readout-structure.

 

This concept results in an entirely disentangled neutron detection scheme: Neutron conversion, charge transport and amplification as well as charge collection result to be entirely independent processes. In consequence, an enormous technical advantage over current detector technology is at free universal disposition for specialized applications.

The detector works with ordinary counting gases under normal pressure. So lightweight, easy to handle and in particular large area detectors can be constructed. Cleaning by constant throughput of fresh counting gas avoids ageing effects, which guarantees long term stability and long lifetime of the detector.

 

The neutron detection bottleneck shifts to data read-out electronics and its bandwidth. High energy physics has already been there, and we can learn how to approach and solve this challenge: Highly integrated ASIC-technology allows to realize thousands of individual detection channels at non-proportional cost. We have transferred ASIC-technology from high energy physics to neutron detection. Rate capacity can be realized according to needs through the ASIC electronic front-end paired with an adaptable integrated FPGA data processing unit. Here, data histograming can in principle be realized on line within the module on many million freely configurable counters (local RAM on board).

 


 [1] Any use of GEM foils in detectors is protected by patents owned by CERN and requires a written license from CERN. Such a licence is free of charge for R&D purposes. Commercial licenses can be granted on conditions to be agreed with CERN. More information about GEM licencing can be found at http://cern.ch/gem.