Builds a pre-processed lookup table from the active ComptoxR::pt isotope
data for use by expand_isotope_shortcodes(). Cached to RDS to avoid
rebuilding on every run. If a WQX dictionary cache is already present, missing
radiochemical isotope shortcodes are added without live CAS lookups.
Usage
load_isotope_lookup(cache_dir)
Arguments
- cache_dir
Directory for cache files (e.g., "data/reference_cache")
Value
List with components: lookup (tibble), elem_alt_names (named character vector)
Details
The lookup contains shortcode->canonical mappings (e.g. "u234" -> "Uranium-234"),
element name->canonical mappings for spelled-out normalization, and alternate
element name spellings (American vs IUPAC).
