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calibration.md

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Calibration sources

legend-pygeom-l200 can easily be used to include the calibration sources deployed with the SIS.

As the position and types of sources frequently change, they are not hard-coded in the python code, but can be configured in a runtime configuration file.

TL;DR: a working example:

sis:
  "1":
    sis_z: 8250
    sources: ["Th228", null, null, "Th228"]
  "2": null
  "3": null
  "4": null

Warning

With all parameters mentioned on this page, it is very easy to produce "overlaps" in the resulting geometry (i.e. the source being in the same spot as another part of the geometry). Overlaps will lead to unpredictable problems while simulating. It is very important that you run a remage-based overlap check at least once for any set of parameters.

calibration source configuration

The sis config object contains objects describing the deployed sources in each of the four SIS tube (or null, if no sources are deployed in that tube). The numbering equals the "official" SIS numbering scheme.

The sis_z coordinate is the SIS reading of the deployed SIS strings. The coordinate is transformed into simulation coordinates as described on the Confluence page.

Each SIS string has four slots for sources, that can be filled differently with this tool. The sources array contains the four slots from the top to the bottom. The bottom source is seated on top of the tantalum absorber.

Different types of sources can be included in the slots:

  • Th228 — a normal LEGEND calibration source (as described in L. Baudis et al 2023 JINST 18 P02001).
  • Ra — a special calibration source.
  • ...+Cu — add a copper absorber cap to any other source. The dimensions of the cap can be seen in the code.
  • null — no source in this slot. The tantalum absorber is placed irrespective of whether a source is placed inside in the slot.

Note

The generated geometry does not contain the requested source material. The decaying isotope has to be configured in the user's Geant4/remage macro file.

The volumes named source_inner_sis{SIS number}_source{slot} can be used as the confinement volumes in remage (i.e. with a regex ^source_inner_.*, if all sources share an isotope).

extra source outside SIS

It is also possible to add an extra source, that is not part of any SIS string, via a config file. all notes on SIS sources above also apply to this extra source.

extra_source:
  # x, y, z coordinates. z extends positively downwards, z = 0 is a source
  # "screwed into the top plate" (i.e. z is the coordinate of the top face of the
  # volume the source wopuld normally be screwed into.
  position_in_mm: [0, 0, 700]
  # to identify in geometry, this produces a volume `source_inner{name}`
  name: "_central"
  source: "Th228+Cu"

copper absorber

The dimensions of the optional copper absorber can be adjusted in the runtime config, as this part is often replaced. It is the users responsibility to make sure that the absorber does not overlap with any other part of the geometry, and is in the right position.

cu_absorber:
  height: 13.6
  inner_height: 10.6
  inner_radius: 3.2
  outer_radius: 6.2