Libisis and Homer algorithms

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Instrument operations and the description of the data processing algorithm

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A neutron detection instrument we are talking about (e.g. [1]) consists of number of long helium filled tubes with a wire passing through their center. High voltage is applied between the tube and the central wire which makes the system as a long Geiger counter, sensitive to a neutron arrival. The electronics connected to the tube measures resistivity between the tube and the central wire and can establish the position of the neutron caused discharge by calculating the ratio of the resistivities between two parts of the tube around the discharge.

When the Libisis and Homer transform the raw detector data into the spectrum data they are using the following auxiliary files

  • file "Spectra.dat" is located on data acquisition electronics maps physical detectors to "spectrum" 4-1 mapping because of the electronics limitations (balance between the time resolution and the spacial resolution). Processed by hardware. Its influence to the data in the number of spatial and temporal channels.
  • file "Detector.dat" provides physical position of the detectors on the instrument. Detectors are recognized by their label. Libisis uses it to restore real position of the detectors from their label while producing a "spectra file"
  • "white beam file" helps identify the position and sensitivity of the detectors more precisely (instrument specific?)
  • "mask file" is created by Libisis diagnose function and used to mask detectors which are identified as bad.
  • "map file" is used by Homer to combine physical detectors into logical bigger logical units.