Preparation of 1100 60Co calibration sources : JRC-Geel contribution to WP5 Task 1 deliverable 5.1.1. of the MetroDecom project

JRC-Geel is a partner in the EMRP project named MetroDecom, Metrology for decommissioning nuclear facilities. The project focusses on the different aspects of metrology applied in the field of decommissioning of nuclear facilities. The commitments of the Radionuclide Metrology Sector of JRC-Geel (RN) were to conduct part of the work to be carried out in WP5 Development of reference materials and standard sources. In Task 1 reference materials and standard sources for segregation of materials and for free release measurements needed to be produced and characterised. From a standard solution a mother dilution was made to obtain a solution with an activity concentration of around 100 Bq per 20 μL. The solution was dispensed in the cavity of 1120 metallic source holders making use of a precision pattern dispenser. After evaporation of the liquid, the cavity of the CMI source holders was mechanically closed. Before and during the source preparation, check sources in the shape of aluminium pills were produced in order to monitor the stability of the activity concentration of the mother solution. The activity of all the sources was determined by gamma-ray spectroscopic measurements using a NaI-well detector. Some outliers were identified and 1100 sources with certified activity content were selected and made available for further use in Work Package 2 of the project. On the basis of the activity calculations it can be stated that sources were successfully prepared according to the specifications and will be used as calibration standards for the calibration of a free release measurement facility to measure radioactive waste. They can also be used as calibration standard for the calibration of waste segregation facilities. One of the deliverables in the task was to develop a reference material for the calibration of a free release facility and testing facility for segregation of waste. The sources are in the form of 1100 steel and 1100 plastic balls with point sources of 152Eu and 60Co inside. The task of RN was to produce and standardise the 1100 60Co point sources in a form of metal holders containing around 100 Bq of 60Co each. These metallic source holders can be inserted in metallic or plastic balls in order to simulate contaminated waste. The sources were successfully produced using an precision pattern dispenser, and standardised by measuring them in the 20.3 X 20.3 cm NaI-well detector. The standardised sources together with the certificate stating their activities were made available for further use in the project.