Low background facility for ionizing radiation at LNE LNHB: Design and traceability

This paper presents the set up of a low background calibration facility aimed at calibrating environment survey meter. The facility is a lead box 100 cm x 100 cm x 125 cm with 2.5 cm thickness walls, the Caesium 137 source is located in a conical collimator including an internal cavity for the source. The ambient dose equivalent rate in the beam of this facility varies between 300 and 80 nSv/h. This quantity is traceable to the air kerma national references of LNE-LNHB. The standard uncertainty for the ambient dose equivalent rate is about 2% and the uncertainty of the calibration coefficient od a survey meter, depending meanly on the uncertainty if the background measure, is estimated between 5% and 10%.