User Guide
webdedx calculates the stopping power (dE/dx) and range of charged particles in matter. There is nothing to install — every calculation runs locally in your browser, and the page works on both phones and desktops.
Two-minute tour below. Jump to a section:
1. Calculate stopping power & range
Open the Calculator tab to get the stopping power and CSDA range for a particle in a material, at one energy or a list of energies.
- Pick a particle, material, and program. Choose e.g. proton, Water (liquid), and a program. Leaving the program on Auto lets webdedx pick a compatible one (here, ICRU 49).
- Enter an energy. Type a value into the Energy field — results update instantly. A 100 MeV proton in liquid water gives 0.7286 keV/µm and a 7.721 cm range.
- Add more rows. Use + Add row to compare several energies side by side.
- Go Advanced when you need more. The Basic / Advanced switch (top right) unlocks density and I-value overrides, inverse lookups (find the energy for a given range or stopping power), and multi-entity comparisons.
- Export or share. Export PDF / CSV, or use Share URL — the entire app state lives in the link, so it reproduces exactly what you see.
Choosing a program (data source)
The program is the source of the numbers — the same particle in the same material gives slightly different stopping power and range depending on which dataset or model you pick. That is why the picker calls it a "data source". Leave it on Auto-select to let webdedx choose a compatible one, or pick explicitly. Programs that have no data for the current particle/material are greyed out.
Programs come in three kinds, shown as a small badge:
- ▦ DATA (tabulated) — values interpolated from published tables: PSTAR (protons, NIST/ICRU 49), ASTAR (alpha particles), ESTAR (electrons), ICRU 73 and MSTAR (heavier ions).
- ∫ FN (analytical) — computed from a formula (Bethe). Use when no tabulated data exists for your case.
- 🔗 EXT (external) — loaded from a
.webdedxfile you supply (see External data below).
Rule of thumb: prefer the tabulated program validated for your particle and energy range, and fall back to the analytical Bethe model only when nothing tabulated covers it.
Quantities & units
Every result is one of two quantities. Both are reported side by side — range is a distinct physical quantity, not an afterthought.
- Stopping power — the rate of energy loss per unit path length. It is the sum of an electronic component (collisions with atomic electrons, dominant at most energies) and a nuclear component (elastic collisions with nuclei, dominant only at very low energy).
- CSDA range — the Continuous-Slowing-Down-Approximation range: the total path length a particle travels before coming to rest, obtained by integrating 1 / stopping power over energy. The Bragg peak — the sharp dose maximum at the end of the track — sits just before the CSDA range.
Units
- Stopping power. MeV·cm²/g is the mass stopping power (stopping power ÷ density) — geometry-independent, so values are comparable across materials. keV/µm and MeV/cm are linear units (energy lost per unit length) and need the material density to convert.
- CSDA range. g/cm² is the geometry-independent mass range; cm is the physical depth, obtained by dividing by the density (Rcm = Rg/cm² / ρ).
- Energy. For ions, energy is normalised by mass: MeV/nucl divides by the integer mass number A, while MeV/u divides by the actual atomic mass in unified mass units — the two differ by ~0.8% for a proton but are equal for carbon-12. Electrons (ESTAR) use plain MeV, since per-nucleon energy is undefined for leptons.
2. Plot curves
The Plot tab draws stopping power (or range) versus energy as an interactive curve, so you can see the whole picture at a glance.
- Choose the particle and material just like in the calculator.
- Switch the Y unit (keV/µm, MeV/cm, MeV·cm²/g) and toggle log / linear axes with the buttons above the chart.
- Use + Add Series to overlay several particles or materials for comparison.
- Export the chart as an image with Export image.
Advanced mode
The Basic / Advanced switch in the top bar controls how much of the app is shown. Basic keeps the essentials — one program, an energy table, and export. Advanced unlocks multi-program comparison, the inverse lookups described below, custom compounds, MSTAR modes, and density / I-value overrides. The choice is remembered and travels in shared links.
Overrides & options
- Aggregate state (Gas / Condensed). The same substance has a different mean excitation energy (I-value) as a gas versus condensed matter, which shifts stopping power by a few percent at intermediate energies. It also sets the default stopping-power unit (gas → MeV·cm²/g, condensed → keV/µm).
- Density override (g/cm³). Affects only the conversion between mass units (MeV·cm²/g, g/cm²) and linear units (keV/µm, MeV/cm, cm) — the underlying mass stopping power is unchanged. Useful for gases at non-standard pressure/temperature or for powders and pressed pellets.
- I-value override (eV). The mean excitation energy appears in the Bethe formula; a higher I-value gives a lower electronic stopping power. Leave blank to use the tabulated material constant, or enter a measured value for your sample.
- Interpolation. Controls how values between tabulated points are computed: the axis scale (log-log vs lin-lin) and the method (linear vs spline). The setting applies to every data source; mixing settings across compared series is not supported.
MSTAR modes (heavy ions)
When MSTAR is the active program, a mode selector chooses its calculation variant. B (auto special) is the recommended default.
| Mode | Meaning |
|---|---|
| A | Auto base: C for condensed targets, G for gaseous |
| B | Auto special: D for condensed, H for gaseous (default) |
| C | Condensed standard |
| D | Condensed special (downgrades to C for target Z ≤ 3) |
| G | Gas standard |
| H | Gas special (projectile Z = 3–11 and 16–18; downgrades to G otherwise) |
Inverse lookups
The forward table goes energy → stopping power and range. Advanced mode adds two reverse tabs that solve for the energy instead:
- Range →. Enter a target CSDA range; the app returns the energy that produces it, plus the stopping power at that energy. The mapping from range to energy is one-to-one.
- STP →. Enter a target stopping power; the app returns the energy. Because stopping power rises to a maximum at the Bragg peak and falls off on either side, two energies can give the same value — a low-energy and a high-energy branch — so both are shown. A target above the Bragg-peak maximum has no solution.
Custom compounds
Define your own material from its elemental composition and density. Stopping powers are then computed from the elements using the Bragg additivity rule (a weight-fraction-weighted sum of the elemental mass stopping powers).
- Composition. Enter it either as atom counts per formula unit (Formula mode) or as weight fractions in % (Weight fraction mode). The two views are kept in sync; weight fractions must total 100%.
- Phase. Gas or condensed — the same aggregate-state choice as above, used for I-value selection and the default display unit.
- I-value (optional). Leave it blank to derive an effective value from the elements via Bragg additivity, or enter a measured mean excitation energy in eV.
Good to know
- Everything is in the URL. Bookmark or send a link and it restores the particle, material, program, energies, units, and advanced options.
- Units convert on the fly. Change stopping-power or energy units from the column headers / axis toggles — the underlying calculation does not re-run.
- Works offline. Once the page has loaded, calculations run entirely in your browser.
Loading your own datasets
External stopping-power tables can be loaded by opening Calculator or Plot with an extdata query parameter, in the form extdata=<label>:<encoded dataset URL>, where the URL points to the root of a hosted .webdedx directory.
After loading, the source appears in a collapsible External Data Sources panel below the entity selectors. Its programs show up in the Program selector under an External group (🔗 prefix, (ext) suffix); external-only
particles and materials appear in their own External groups.
Calculator with the SRIM reference dataset
Proton in liquid water, ICRU 49, single 100 MeV row:
http://sveltekit-prerender../calculator?urlv=3&extdata=srim:https%3A%2F%2Fs3p.cloud.cyfronet.pl%2Fdedxweb%2Fdedxweb%2Fsrim-gui.webdedx%2F&particle=1&material=276&program=7&energies=100&eunit=MeVKeyboard shortcuts
The entity picker (Particle / Material / Program) is built for keyboard-first navigation:
| Key | Action |
|---|---|
| / | Focus the search field (expands the panel if collapsed) |
| ↑ / ↓ | Move the highlight up / down through the list |
| ↵ Enter | Select the highlighted item; jumps to the next empty field |
| Escape | Blur focus and collapse the picker (on the Calculator page) |
| ← / → | Cycle Particle / Material / Program tabs (when a tab is focused) |
Tip: press /, type to
filter, use ↑↓ to highlight, then ↵ to confirm and move to the next field.