Reporting without context
The significance of radiation measurement data is often only understood by technicians or experts with experience, which means those who are unfamiliar with the context of measurement may not understand the significance.
Some examples of where radiation measurements have been reported without context:
- Staff perform the same cleaning actions for high readings as low readings, leading to extremity doses above statutory limits.
- Reviewers do not act on readings performed by other staff as they are expecting to see different units (μSv vs mSv).
- Instrument readings recorded were not compared with a standard or action level and therefore staff cannot tell whether the sample has passed or failed. Further details such as detector details/response and efficiency, method of collection, area sampled etc. are not available for the staff member, therefore a judgement cannot be made.
Why context is missing
Radiation equipment can give readings in many different formats, ranges, and radiation type (α/β/γ). Readings can be instrument readings such as counts per second (CPS), SI radiation quantities such as sieverts (Sv), becquerels (Bq), and derived units such as Bq/cm2 or mSv/hour. There are also non-SI units which can cause confusion, for example working levels, roentgen equivalent man (REM), dose/kerma area product (DAP/KAP).
In addition, readings can be instrument specific, be energy or radionuclide dependant. If a generic template is used, it might not have the correct context if it is made for a specific radionuclide or radiation type. For example, there could be different exemption or action levels for gross alpha/gamma or Co-60. People may feel it is ‘safer’ not to put context onto a form because they are worried it might not be correct if it is used in a different situation. However, without an indication of the range expected, unsafe situations can arise as described above.
Providing an expected range and context can help the transfer of information/communication between staff. This can draw attention to results outside the expected range for all staff and help reviewers/experts make a judgement on the meaning of what is recorded. For example, when receiving a medical result such as a blood test the reading is printed next to the expected range (e.g. TSH 1.69 mIU/L [0.4-3.5]) which is then interpreted by the doctor to infer normal thyroid function. Similarly, in radiation, a reading with context helps to focus attention, but interpretation typically requires expert analysis.
Where possible a reading should be related to a limit, typical range, detection level or action level. Possible context for radiation measurements include:
- 20 cps [limit of detection ~ 3cps (~10 Bq/cm2)]
- 400,000 Bq [exemption limit 1,000 Bq]
- 0.5 Bq/g [exemption limit 1 Bq/g]
- 10 μSv/hr [typical working range 1-20 μSv/hr]
- 1 Bq/cm2 [limit for clearance 4 Bq/cm2]
- 3 Bq/m3 [DAC (I-131): 400 Bq/m3] (Derived Air Concentration limit)
- 2.1 mSv/year [Natural Background 1.5mSv, CT scan 5mSv, Occupational Limit 20 mSv]
Where instrument-specific units are used geometric efficacy should be provided for specific radionuclides or radiation types to ensure that the readings are interpretable at a later date.