Information Notice No. 85-42: Loose Phosphor in Panasonic 800 Series Badge Thermoluminescent Dosimeter (TLD) Elements
SSINS No.: 6835 IN 85-42 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 May 29, 1985 Information Notice No. 85-42: LOOSE PHOSPHOR IN PANASONIC 800 SERIES BADGE THERMOLUMINESCENT DOSIMETER (TLD) ELEMENTS Addressees: All holders of a nuclear power plant operating license (OL) or a construction permit (CP). Purpose: This information notice is provided to alert NRC licensees to a problem noted in some Panasonic 800 series TLD badges that has caused spurious high readings in one of the badges' TLD elements. This information is intended to assist licensees in diagnosing any spurious readings with the Panasonic TLD system. It is expected that recipients will review the information provided for applicability, if appropriate, to their dosimetry programs. However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: The Panasonic 800 series TLD badge contains a card that holds four TLD elements. Each TLD element consists of a thin film of TL phosphor attached to a disk backing with a clear teflon bubble cover. During reading, the phosphor is heated by converging infrared light on the backing. The luminescence from the phosphor (which is proportional to the dose received) radiates through the teflon cover and is read with a photomultiplier tube. Several Panasonic TLD users (including NRC's Region I) have identified badges where crystals of the phosphor have detached themselves from the backing of the element, resulting in high erratic readings in that element. When viewed through a stereoscopic microscope, phosphor crystals can be observed sticking to the teflon cover (presumably by electrostatic charge). In this position, the loose TL material is not in contact with the backing and does not get heated when the badge is read. These TL crystals remain at an elevated energy state and continue to accumulate dose. Apparently erratically high readings result when the loose crystals are shaken back onto the backing surface during a subsequent reading. They are then heated and luminescence proportional to the total doses received during several read cycles is produced. This process can cause the affected element to erroneously read as much as an order of magnitude higher than the other elements in the same card. Although the 8505280181 . IN 85-42 May 29, 1985 Page 2 of 2 frequency of occurrence is small (one licensee found only one problem badge in 30,000), there is evidence that the frequency increases substantially once the badges have been through 100-200- read cycles. Panasonic has a manufacturing quality control (QC) specification on the amount of loose phosphor in an element. However, physical shock and thermal cycles, experienced during badge use, appear to loosen additional material. Panasonic has stated that they have modified their QC program to provide a greater physical challenge to the badge before they are screened. For those badges already in use, licensees can visually inspect any TLD elements suspected of having loose TL crystals. Panasonic has been exchanging badges identified as having excessive loose TL material. No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the Regional Administrator of the appropriate regional office or this office. Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contacts: R. L. Pedersen, IE (301) 492-2967 J. E. Wigginton, IE (301) 492-9425 Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021