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Calcimator

Radiation Dose Calculator

Calculate occupational radiation dose from external gamma sources using inverse square law, shielding HVLs, and compare against OSHA/NRC annual dose limits.

Inputs

Results

Dose rate (µSv/hr)

16.25

Daily dose (µSv)97.5
Annual dose (mSv)24.38
% of OSHA limit (50 mSv/yr)48.8%
2 µSv/hr boundary (m)5.7
0.25 µSv/hr boundary (m)16.12
(%) Icrp Limit121.88%
How to Use This Calculator
  1. Enter Source activity (GBq), Gamma constant (µSv·m²/(GBq·hr)), and Distance from source (m).
  2. Set Shielding (# of HVLs), Exposure hours/day, and Workdays per year.
  3. Review the Dose rate (µSv/hr) result.
  4. Use Daily dose (µSv) and Annual dose (mSv) to inform your decision.

How the result changes with Distance from source (m)

Distance from source (m)Dose rate (µSv/hr)
1000.01
3500
6500
9000

What each input means

Source activity (GBq)
Radioactive source activity in gigabecquerels (1 Ci = 37 GBq).
Gamma constant (µSv·m²/(GBq·hr))
Specific gamma ray constant for the isotope. Cs-137 ≈ 85, Co-60 ≈ 305, Ir-192 ≈ 130.
Distance from source (m)
Distance from the radiation source in metres.
Shielding (# of HVLs)
Number of half-value layers of shielding material between source and worker. Each HVL halves the dose.
Exposure hours/day
Hours per workday spent near the source.
Workdays per year
Number of working days per year for annual dose projection.

What each result means

Dose rate (µSv/hr)
Shielded dose rate at the specified distance in microsieverts per hour.
Daily dose (µSv)
Total daily dose based on hours of exposure.
Annual dose (mSv)
Projected annual occupational dose in millisieverts.
% of OSHA limit (50 mSv/yr)
Annual dose as percentage of the OSHA/NRC 50 mSv/year occupational limit.
2 µSv/hr boundary (m)
Distance at which dose rate drops to 2 µSv/hr (controlled area boundary).
0.25 µSv/hr boundary (m)
Distance for 0.25 µSv/hr (unrestricted/ALARA area boundary).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Source activity (GBq) = 0.5, Gamma constant (µSv·m²/(GBq·hr)) = 130, Distance from source (m) = 2, Shielding (# of HVLs) = 0 = 6 input(s) provided
  2. Calculate Dose rate
    Dose rate = unshieldedDoseRate * shieldingFactor
    16.25 = 16.25
  3. Calculate Daily dose
    Daily dose = shieldedDoseRate * exposureHrsDay
    97.5 = 97.5
  4. Calculate Annual dose
    Annual dose = (dailyDoseUSv * workdaysPerYear) / 1000
    24.375 = 24.375

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