United States Nuclear Regulatory Commission - Protecting People and the Environment

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  

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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 

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