Dose limits and Annual Dose Estimation
Dose Limits
- Radiation workers (occupational exposure)
- Whole body - 50 mSv in any one year
20 mSv/year (averaged over a period of 5 consecutive calendar years)
Dose rate of 10 µSv/hour equates to a dose of 20 mSv in a working year - Member of the public
- Whole body - 1 mSv/year
Dose rate of 0.5 µSv/hour equates to a dose of 1 mSv in a working year
Details of local working rules are detailed in each PSP, and should include requirements for storage, shielding, PPE, personal and area monitoring, decontamination and emergency procedures, equipment calibration and testing, and waste disposal procedures as applicable.
Annuld Dose Estimation
An estimation of the total annual effective external dose can be made using data sheets available in an extract from the Radionuclide and Radiation Protection Data Handbook (2002) . The values provided in the ‘External Exposure’ section of the data sheets cover several exposure routes, and by adjusting for the estimated contact hours and the source size, an approximate annual dose can be calculated.
Example of dose estimation - exposure to a 37MBq Co-57 source for 25 hours.• Choose the most likely exposure type: a point source at 30cm
• Source size = 37MBq
• Exposure hours = 25
• Value from data sheet for point source exposure at 30cm for a 1MBq Co-57 is 2.52 x 10-4mSv/hr
Calculation: (2.52 x 10-4) x 37 x 25 = 0.2331mSv
When estimating a dose the worst-case should be assumed (ie. choose high values). If your estimated dose exceeds the limit listed above please contact the RSO
