How to Calculate Dose Rate

by

Radiation Dose Rate Calculator

Cobalt-60 (0.306 mSv·m²/h/GBq) Iridium-192 (0.108 mSv·m²/h/GBq) Cesium-137 (0.077 mSv·m²/h/GBq) Radium-226 (0.033 mSv·m²/h/GBq) Custom Gamma Constant
GBq MBq Curie (Ci)

Calculated Dose Rate:

*Calculation assumes a point source in a vacuum/air without shielding.

How to Calculate Dose Rate

In radiation protection and health physics, calculating the dose rate is essential for ensuring safety around radioactive sources. The dose rate determines how much radiation energy is absorbed by a person per unit of time.

The Dose Rate Formula

The standard formula for calculating the dose rate from a point source is based on the Inverse Square Law:

DR = (Γ × A) / d²
  • DR: Dose Rate (usually in mSv/h).
  • Γ (Gamma): The specific gamma ray dose constant for the isotope.
  • A: The activity of the radioactive source.
  • d: The distance from the source in meters.

Step-by-Step Example

Suppose you have a Cobalt-60 source with an activity of 10 GBq, and you are standing 5 meters away.

  1. Identify the Gamma Constant: For Co-60, Γ is approximately 0.306 mSv·m²/h/GBq.
  2. Apply Activity: Multiply Γ by Activity (0.306 × 10 = 3.06).
  3. Apply Distance: Divide the result by the square of the distance (5² = 25).
  4. Final Result: 3.06 / 25 = 0.1224 mSv/h.

Factors Affecting Dose Rate

While this calculator provides a theoretical value, real-world dose rates are influenced by:

  • Shielding: Lead, concrete, or water barriers significantly reduce the dose rate.
  • Source Geometry: The formula assumes a "point source." Large or complex shapes require different math.
  • Medium: Air attenuates radiation slightly, but dense materials provide much higher protection.
function updateGamma() { var isotopeSelect = document.getElementById("isotope"); var customDiv = document.getElementById("custom-gamma-div"); var gammaInput = document.getElementById("gammaConstant"); if (isotopeSelect.value === "custom") { customDiv.style.display = "block"; } else { customDiv.style.display = "none"; gammaInput.value = isotopeSelect.value; } } function calculateDoseRate() { var gamma = parseFloat(document.getElementById("gammaConstant").value); var activity = parseFloat(document.getElementById("activity").value); var unit = document.getElementById("activityUnit").value; var distance = parseFloat(document.getElementById("distance").value); var resultDiv = document.getElementById("doseResult"); if (isNaN(gamma) || isNaN(activity) || isNaN(distance) || distance <= 0) { alert("Please enter valid positive numbers for activity and distance."); return; } // Convert Activity to GBq for the standard formula var activityInGBq = activity; if (unit === "MBq") { activityInGBq = activity / 1000; } else if (unit === "Ci") { activityInGBq = activity * 37; // 1 Curie = 37 GBq } // Calculation: (Gamma * Activity) / Distance Squared var doseRateMSv = (gamma * activityInGBq) / (distance * distance); var doseRateUSv = doseRateMSv * 1000; // Display results document.getElementById("mSvOutput").innerText = doseRateMSv.toFixed(4) + " mSv/hr"; document.getElementById("uSvOutput").innerText = "(" + doseRateUSv.toLocaleString(undefined, {maximumFractionDigits: 2}) + " µSv/hr)"; resultDiv.style.display = "block"; resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }

Leave a Comment