User stopping tables

Code: lindhard/src/ion/stopping/table.rs (StoppingTable, TableOverride).

Model

A user table gives \( S_e(E) \) for one projectile (atomic number and mass) in one target element, as data the user supplies. Between the tabulated points the cross section is interpolated piecewise linearly in \( \ln S \) against \( \ln E \), which keeps the monotonicity of each segment of the data. Nothing is extrapolated or clamped: a query outside the table’s energy range is an error (OutOfTableRange) that stops the run.

provenance = "Author, Journal vol, page (year), Table N"   # required
ion_z = 5
ion_mass_amu = 11.0093            # optional; default: standard atomic weight
target_z = 14
energy_ev = [1.0e2, 1.0e3, 1.0e4]                 # strictly increasing, eV
stopping_ev_1e15_cm2 = [10.0, 30.0, 60.0]         # eV 1e-15 cm^2 per atom

(The numbers are a format illustration, not data.)

Provenance is mandatory

A table without a non-empty provenance string is rejected at load time: data without an origin is not admitted. The run records each table in summary.json (physics.stopping_tables: the path as written, the resolved path, the SHA-256 of the file’s bytes, the provenance string, the pair and the energy range), and lists it under physics.models as user-table with its provenance as the source.

Do not load SRIM- or ICRU-derived tables into anything committed to a repository. A table is the user’s own data and its terms are the user’s concern; this project’s own tree never contains such tables.

Selecting it

Declare the files under [stopping] tables (see TOML input reference). A table replaces the [physics] stopping model for exactly the (ion_z, target_z) pair it declares, including recoils of that species when recoils are followed; every other pair uses the model. A table cannot be combined with stopping = "equipartition-ls-or", which carries its own Lindhard-Scharff and Oen-Robinson loss.

Assumptions

• The table is tied to the projectile mass it was declared for. A query for a mass that differs by more than a small relative tolerance (tight enough to separate neighbouring isotopes) is an error (TableMassMismatch): the same energy at a different mass is a different speed, and no energy-axis conversion is attempted.
• Compounds are built from element tables by Bragg additivity; a compound table is not a supported input.

Validity

Exactly the table’s energy range. The CLI checks up front that the range contains the beam energy, and for a recoil species that it starts at or below recoil_cutoff_ev; it warns if a table starts above primary_cutoff_ev, because the run fails if a projectile slows below it.

Verification status

The loader, the interpolation and the range and mass checks are unit-tested. The tests use tables generated at test time from our own Lindhard-Scharff model; no table is committed (docs/data-provenance.md).

References

The table’s own provenance string is its reference. The format and the rules are this project’s.