Enter Scenario Inputs
Formula Used
Base source rate at 1 meter
Rate1m = ActivityGBq × Gamma Constant
Distance-adjusted unshielded rate
Rateunshielded = Rate1m ÷ d²
Shielding by half-value layer
Attenuation Factor = 0.5(Thickness ÷ HVL)
Shielding by linear attenuation coefficient
Attenuation Factor = e(-μ × Thickness)
Shielded source rate
Rateshielded = Rateunshielded × Attenuation Factor × Buildup Factor × Occupancy Factor
Session and annual dose
Dosesession = Rate × Time and Doseannual = Dosesession × Sessions per Year
All calculations use your supplied gamma constant in µSv·m²/(h·GBq). That keeps the workflow transparent and lets you choose radionuclide-specific data from your own source references.
How to Use This Calculator
1. Enter the source activity.
Choose the correct activity unit, then enter the source strength exactly as recorded on the source label or survey documentation.
2. Add the gamma constant.
Use a gamma or exposure-rate constant that matches the radionuclide, energy, and modeling assumptions you want to apply.
3. Define geometry and work conditions.
Set the working distance, occupancy factor, background level, and time per task to reflect your expected exposure pattern.
4. Add shielding data if applicable.
Pick HVL or linear attenuation mode, enter thickness, then add a buildup factor when scattered radiation is relevant.
5. Review rate, dose, and the chart.
After calculation, inspect the result cards, detailed table, and Plotly graph. Then export the scenario as CSV or PDF.
Example Data Table
| Parameter | Example value | Unit | Why it matters |
|---|---|---|---|
| Activity | 3.2 | GBq | Sets the source strength driving the field. |
| Gamma constant | 84 | µSv·m²/(h·GBq) | Converts source strength into a rate model. |
| Distance | 2 | m | Inverse-square loss reduces intensity quickly. |
| Shielding method | HVL | - | Useful when HVL data is readily available. |
| Shield thickness | 2.5 | cm | More thickness generally means lower transmitted rate. |
| HVL | 1.8 | cm | Shows how fast the shield halves the beam. |
| Buildup factor | 1.1 | ratio | Accounts for scatter contribution behind shielding. |
| Background rate | 0.12 | µSv/h | Adds ambient contribution to the session total. |
| Exposure time | 45 | min | Converts hourly rate into dose per task. |
| Sessions per year | 48 | count | Annualizes the dose estimate for planning. |
Important Use Note
FAQs
1. What does this calculator estimate?
It estimates source-related exposure-equivalent rate, ambient total rate, session dose, annualized dose, and the effect of distance and shielding using your supplied source data.
2. Why does distance change the result so strongly?
The model uses inverse-square behavior. Doubling distance reduces unshielded rate to one quarter, assuming a point-like source and unchanged geometry.
3. When should I use the HVL method?
Use HVL when shielding references are listed as half-value layers for a material and photon energy. It is quick and practical for approximate planning studies.
4. When should I use the linear attenuation coefficient?
Use the μ method when you have a coefficient for the exact material and radiation energy. It often gives a more direct attenuation model for calculations.
5. What does buildup factor do?
Buildup factor adjusts the transmitted field upward to reflect scattered photons that still reach the location behind shielding. Use 1.00 if you do not want that correction.
6. Why add background radiation?
Background rate helps you estimate total ambient conditions during the task. It is added after shielding so you can compare source-only and total session dose.
7. Can I use this for beta or neutron fields?
Not directly. The workflow assumes a photon-style constant and attenuation model. Beta and neutron assessments need different source data, transport assumptions, and shielding treatment.
8. Is this suitable for compliance decisions?
No. Use calibrated instruments, approved source terms, site procedures, and qualified health-physics review for compliance, controlled areas, transport, or licensing decisions.