Summary report of fax provided by State of
California
On August 2, 2004 at 5:00 pm PDT, a licensee employee was irradiating electrical parts using the Low Dose 142-MA Self Contained, Shielded Panoramic Irradiator. This device uses a Cobalt- 60 (Co-60) source with an activity of 2 Curies. The licensee employee was able to bypass the interlock to the chamber while the chamber was irradiating. The employee was wearing a film badge and holding his ring badge in his hand (not on finger) while working with the chamber. The film badge was first used on August 2, 2004. The ring and film badges were collected and immediately shipped for analysis.
The source of radiation within the chamber is a sealed Co-60 (2 Curies) source and is exposed by raising and lowering the source rod. Raising the rod activates the door interlock and exposes the source within the chamber. The licensee intended to place a product into the chamber and failed to notice that the source rod was up, and pulled open the door while the interlock was activated. The safety interlock failed and was unsuccessful in keeping the doors locked. The door was immediately closed (exposure time approximately 3 seconds)
On August 4, 2004, the licensee contacted a Health Physics consultant and performed a calculation to estimate the possible exposure level. They used the Gamma Constant for Co-60, the exposure time, distance, and activities that were involved.
During the afternoon of August 4, 2004, J. L. Shepherd inspected the equipment and determined that the interlock was defective and advised that they install an alternate interlock that is sturdier. They returned on August 5, 2004 and installed the new interlock.
Wear on the interlock arm caused the ultimate failure on August 4, 2004, and was most probably caused by repeated attempts by the operators of the irradiator to forcibly open the cavity lids while the source was in the "Irradiate" position. The replacement arm has been redesigned and strengthened to avoid the recurrence of a problem of this nature in the future.
California preliminary exposure estimate to the operator's hands is less than 200 millirem while licensee calculation showed exposure received to be approximately 2-3 millirem.
Incident remains open until receipt of documentation of monitoring device exposure and copies of the physicist's calculations.