The Surface contamination sector of the Radiation Metrology Laboratory is involved in calibration activities for the surface contamination detectors.
The surface contamination measurement is required by the radiation protection law in many different operating conditions, with the aim of worker and environment safeguard. The calibration of these detectors is quite complex: the experimental condition variety that can be found does not allow setting up standard procedures.
For this reason, surface contamination measurements are one of the less accurate in the radiation protection field. Also concerning the calibration and the reference instruments, these measurements result unsatisfying. To deal with this issue, a Working group named “Surface contamination measurements” has been established in 2006 and our laboratory took part in this project. The aim was to define and develop calibration procedures that are harmonized and shared by different calibration centers.
Thanks to this work, it was written an ACCREDIA Technical Document (DT-07-DT, 2017, only in Italian).
Procedures created by our Surface Contamination Sector consist in certificated and referenced methodologies for surface contamination measurement, with direct calibration of the instruments using flat sources, as described by the norm ISO 8769 (2016) “Reference sources-Calibration of surface contamination monitors-Alpha-, beta- and photon emitters”. The procedures follow the sector norm ISO 7503-1,2,3 (2016) “Measurement of radioactivity – Measurement and evaluation of surface contamination”.
Currently available sources are reported in the following table. With these sources, it is possible to verify for every instrument the energy dependence on the efficiency and the efficiency dependence on the source-detector distance (rate measurement with the same source at different distances).
Table of the available sources:
| Source code | Radionuclide | Energy (keV) | Radiation type | Activity* (Bq) | Emission rate* (s-1) | Geometry | Active Surface (cm2) |
| AM241 | Am-241 | 5400 | alfa | 2314 | 1107 | flat | 300 |
| C14 | C-14 | 49 | beta | 3589 | 1340 | flat | 300 |
| TC99 | Tc-99 | 95 | beta | 3310 | 1610 | flat | 300 |
| CO60 | Co-60 | 96 | beta | 2267 | 1209 | flat | 300 |
| CS137 | Cs-137 | 171 | beta | 2328 | 1510 | flat | 300 |
| CL36 | Cl-36 | 250 | beta | 3150 | 1960 | flat | 300 |
| SR90 | Sr-90/Y-90 | 567 | beta | 2936 | 3771 | flat | 300 |
(*) Data evaluated in November 2019
Flat sources available in the calibration center
Information and contacts
For information about our activities, please do not hesitate to contact us by email to the following address: metrologia-radiazioni@polimi.it