# Proton range in polyethylene

This is a source-traceable redraw of the NIST PSTAR calculated projected-range table for protons in its Polyethylene preset (material 221). The site retains the complete NIST output and the figure-generation script. PSTAR's projected-range field is mass range in g/cm². The figure uses NIST's 133 default energy rows; it does not trace the NASA report's SRIM curve.

NIST identifies polyethylene density as 0.94 g/cm³ at 20 °C and 101,325 Pa. For the four-reader comparison, geometric-equivalent depth in centimetres is mass projected range divided by this density. This is a density-specific conversion, not recommended shielding thickness.

## NASA report cross-check

NASA/TP-2020-220514, printed p. 4, footnote 7 prints approximate polyethylene ranges at 1, 10, 100 and 1,000 MeV as 0.2 mm, 1.2 mm, 7.7 cm and 330 cm. The same page captions Figure 4 as an SRIM result and footnote 8 gives the NIST projected-range/density conversion. The four report values are preserved separately in nasa-report-cross-check.csv, not substituted into the NIST series. At 1 MeV, the retained NIST table converts to 0.0227 mm, about 8.8 times shorter than the NASA footnote value. At 10, 100 and 1,000 MeV, values agree to the shown rounding. The SRIM run settings/raw coordinates have not been recovered, so this discrepancy is unresolved.

## Limitations

Projected range is the average depth in the initial direction as particles slow to rest. It is not a sharp stopping boundary, a range distribution, or a shield-performance measure. No fluence, mixed space spectrum, secondary-particle cascade, spacecraft geometry, mass trade, absorbed/equivalent dose, biological effect, or shielding performance is computed. The graph supports no safe-thickness recommendation.

## Reproduction

Run python generate.py using the Python standard library. It parses the retained NIST text response, writes the data CSVs and desktop/mobile SVGs, and checks 133 ordered unique rows, the four exact NIST cross-check values, the density conversion, the unresolved 1 MeV ratio, and the other three rounding comparisons. The table and all generated SVGs are parsed/checked. Reproduction validates this deterministic transformation of published calculator output, not the underlying proton-transport model.

## Attribution

NIST PSTAR: https://physics.nist.gov/PhysRefData/Star/Text/PSTAR.html
NIST quantities and method: https://physics.nist.gov/PhysRefData/Star/Text/programs.html
NIST projected range definition: https://physics.nist.gov/PhysRefData/Star/Text/appendix.html
NIST polyethylene material 221: https://physics.nist.gov/cgi-bin/Star/compos.pl?matno=221&mode=text
NASA/TP-2020-220514: https://ntrs.nasa.gov/citations/20200003125

NIST's download page permits redistribution/modification with notice that derivatives are derived from NIST and modified versions are identified as modified: https://physics.nist.gov/PhysRefData/Star/Text/download.html. This original redrawn graphic is derived from the NIST PSTAR table; DMGB Systems is responsible for its presentation and does not imply agency endorsement.