| Case | Mode | Fluence | Key coefficient | B | f | Notes |
|---|---|---|---|---|---|---|
| Example A | Charged | 2.5×108 1/cm² | S/ρ = 1.8 MeV·cm²/g | 1.0 | 1.0 | Monoenergetic charged field, full deposition. |
| Example B | Photon | 1.2×1010 1/m² | E = 0.662 MeV, μen/ρ = 0.0032 m²/kg | 1.1 | 1.0 | Photon field with modest buildup correction. |
| Example C | Photon | 5.0×106 1/cm² | E = 80 keV, μen/ρ = 0.12 cm²/g | 1.0 | 0.7 | Lower energy photons, partial deposition modeled. |
Charged particles (stopping power)
When mass stopping power is available, absorbed dose is estimated by:
D(Gy) = Φ(1/cm²) · (S/ρ)(MeV·cm²/g) · 1.602×10⁻¹⁰ · B · f
- Φ is particle fluence.
- S/ρ is mass stopping power in the target medium.
- 1.602×10⁻¹⁰ converts MeV/g to J/kg.
- B is an optional buildup correction; f is deposition fraction.
Photons (energy-absorption coefficient)
For photons using the mass energy-absorption coefficient:
D(Gy) = Φ(1/m²) · E(MeV) · 1.602×10⁻¹³ · (μen/ρ)(m²/kg) · B · f
- E is mean photon energy.
- μen/ρ maps energy fluence to absorbed dose.
- Equivalent dose uses H = D · wR.
- Select the correct model: charged particles or photons.
- Enter fluence and choose the matching area unit.
- Provide either stopping power (charged) or energy and μen/ρ (photons).
- Optionally add buildup factor and deposition fraction.
- Set wR if you want equivalent dose in sievert.
- Add exposure time to get dose and equivalent dose rates.
- Press Compute Dose to show results above the form.
Professional context for converting fluence to absorbed dose and equivalent dose.
1) Why fluence is a useful starting metric
Fluence counts how many particles or photons cross a unit area. It comes directly from beam monitors, simulations, or survey tallies. Converting fluence to dose links field strength to energy deposited for planning, optimization, and documentation.
2) Dose and unit relationships
Absorbed dose is energy per mass: 1 Gy = 1 J/kg and 1 rad = 0.01 Gy. Equivalent dose is H = D · wR in sievert. For photons and electrons, wR is often 1, while heavy ions can require larger values.
3) Photon pathway using mass energy-absorption
Photon dose can be estimated using fluence, mean energy, and μen/ρ. The calculator applies 1.602×10⁻¹³ J/MeV and supports μen/ρ in m²/kg or cm²/g. As energy increases, coefficients in soft tissue commonly drop, so dose per fluence can decrease.
4) Charged-particle pathway using mass stopping power
For charged particles, mass stopping power S/ρ links fluence to energy loss in the medium. The constant 1.602×10⁻¹⁰ converts MeV/g to J/kg. Because S/ρ depends strongly on energy, local dose can rise near the end of range for many ions.
5) Typical magnitudes and practical inputs
Fluence may range from 10³–10⁶ 1/cm² in low fields up to 10⁸–10¹² 1/cm² in intense beams. Always match coefficients to the same material (water, air, silicon, tissue-equivalent) and to the closest representative energy or spectrum. For X-rays near 60–120 keV, μen/ρ for water is often about 0.02–0.2 cm²/g, while MeV gammas are typically much smaller.
6) Buildup factor and scatter corrections
The buildup factor B approximates scatter that increases fluence at a point. Thin geometries often use B ≈ 1. Broader fields and thicker shielding can justify B > 1 based on measurements or validated references.
7) Deposition fraction and geometry effects
The deposition fraction f accounts for incomplete energy deposition in the sensitive mass. Values below 1 occur in thin layers, small detectors, or near boundaries. If uncertain, start with f = 1 and refine using geometry or simulation.
8) Uncertainty and reporting
Practical uncertainty often comes from fluence calibration and coefficient selection. Optional percent inputs are combined in quadrature to give an overall 1σ dose uncertainty. For defensible reporting, record units, material, energy assumptions, and any corrections (B, f), plus dose rate when time is provided.
1) What is the difference between fluence and flux?
Fluence is the total number crossing an area. Flux (or fluence rate) is fluence per time. If you enter exposure time, the calculator reports dose rate derived from dose divided by time.
2) When should I use the photon model?
Use it when radiation is primarily photons and you have mean photon energy plus μen/ρ for the same material. This approach is common for X-ray and gamma fields.
3) When should I use the charged-particle model?
Use it for electrons, protons, alphas, or ions when a mass stopping power is available for the target medium. It is especially useful when charged-particle equilibrium is expected.
4) Why do I see both 1/cm² and 1/m²?
The two dose formulas use different reference area units. The calculator converts internally so you can enter fluence in either unit while keeping the conversion constants consistent.
5) What does the buildup factor represent?
B approximates scatter contributions that increase fluence at the point of interest. If you do not have a justified buildup correction, set B = 1 to avoid overstating dose.
6) How do I choose the deposition fraction?
f captures incomplete energy deposition due to geometry, leakage, or lack of equilibrium. Use f = 1 for conservative full deposition, or apply a smaller value based on measurements or simulation.
7) Are the results acceptable for regulatory reporting?
The calculator is a physics estimator. For compliance, use validated coefficients, documented assumptions, and calibration traceability. Confirm results with standards-based methods or accredited dosimetry when required.