United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. NO. 93-30: NRC Requirements for Evaluation of Wipe Test Results; Calibration of Count Rate Survey Instruments

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C. 20555

                                April 12, 1993

                                    TEST RESULTS; CALIBRATION OF COUNT RATE 
                                    SURVEY INSTRUMENTS


All U.S. Nuclear Regulatory Commission Licensees


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert NRC licensees to the following:

      a.    NRC requirements for evaluation of wipe test results

      b.    Calibration of count rate survey instruments based on the use of   
            the instrument. 

It is expected that recipients will review this information for applicability
to their facilities and consider actions, as appropriate, to ensure
instruments used for contamination surveys are properly calibrated.  However,
suggestions contained in this information notice are not new NRC requirements;
therefore, no specific action or written response is required.

Description of Circumstances

Licensees have recently been cited for failure to properly calibrate
instruments used to evaluate wipe tests and survey instruments used for
contamination surveys.

Some licensees are evaluating wipe samples with wipe test counters without
determining the instrument sensitivity or efficiency.  The licensee must
demonstrate that the instrument is calibrated to make measurements and
sufficiently sensitive to meet the applicable regulatory requirements in 
10 CFR Parts 20, 34 and 35.

Also, NRC inspections have revealed that many count rate survey instruments
used exclusively with pancake probes for measuring surface contamination are
not being calibrated with procedures established for this use.  The
instruments have been calibrated following the procedures outlined in 
Appendix B of Regulatory Guide 10.8, Revision 2, "Model Procedure for
Calibrating Survey Instruments."  This procedure provides guidance for
calibrating survey instruments used for dose rate measurements, not
contamination levels.


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The following provide examples of NRC regulations that include specific
performance criteria:  10 CFR 20.205(b)(2) requires a minimum detection limit
of 0.01 microcurie per 100 square centimeters of package surface, when
monitoring the external surfaces of incoming packages; 10 CFR 34.25(c) and 
10 CFR 35.59 (c)(3) require that a leak test be capable of detecting the
presence of 0.005 microcurie of removable contamination on a sealed source; 
10 CFR 35.70(f) requires that a medical use licensee conduct the surveys
required by 10 CFR 35.70(e) so as to be able to detect contamination on each
wipe sample of 2000 disintegrations per minute (dpm), 9.01E-4 microcurie; 
10 CFR 35.315(a)(7) requires that rooms used by patients undergoing
radiopharmaceutical therapy not be reassigned until removable contamination
levels are less than 200 dpm per 100 square centimeters; and 10 CFR 35.70(h)
requires that survey records for removable contamination in each area be
expressed in dpm per 100 square centimeters.

Calibration information can be found in the instrument manufacturer's guidance
or the following references for calibrating instruments to detect surface

      1)    National Council on Radiation Protection and Measurements (NCRP)   
            Report No. 112, Calibration of Survey Instruments used in          
            Radiation Protection for the Assessment of Ionizing Radiation      
            Fields and Radioactive Surface Contamination (see Attachment 1 for 

      2)    American National Standards Institute, Inc. (ANSI) ANSI N323-1978, 
            Radiation Protection Instrumentation Test and Calibration (see     
            Attachment 1 for address)

      3)    NUREG-1156, Accuracy and Detection Limits for Bioassay             
            Measurements in Radiation Protection, Statistical Consideration    
            (see Attachment 1 for address)

      4)    NUREG/CR-4007, Lower Limit of Detection:  Definition and           
            Elaboration of a Proposed Position for Radiological Effluent       
            Environmental Measurements, September 1984 (written by the
            National Bureau of Standards, now the National Institute of
            Standards and Technology) (see Attachment 1 for address)

I.  Wipe Test Counters

    The licensee, not the instrument manufacturer, is responsible for          
    demonstrating that the instrument and method used are sensitive enough to  
    meet NRC regulatory requirements.

    The efficiency and sensitivity of the instrument are a function not only   
    of the physical components of the device, but also of the methodology of.

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    the survey and the counting procedures.  The counting procedures need to   
    address the time of counting, the background count, the energy spectrum    
    and emission rates of the isotope, and the desired accuracy of the         

    An efficiency must be determined for each isotope used, and normally the   
    isotope with the lowest efficiency is assumed to be the isotope detected   
    until the emission spectrum of the sample can be analyzed.

    The sensitivity, or minimum detectable activity (MDA), defines the minimum 
    activity which will produce counts above the background for a specific     
    counting time that will yield the true count rate within a predetermined   
    degree of accuracy.  

    The MDA may be set by the regulations governing the licensed activity, for 
    example, 2000 dpm may be chosen to comply with 10 CFR 35.70(f).  Licensees 
    must, at a minimum, choose a measurement system with an MDA equal to, or   
    less than, that required by applicable NRC regulations.  Licensees may     
    either develop their own procedure or follow the manufacturer's            
    instructions for the calibration of the wipe test counter and the check of 
    the MDA. 

    If the background is too high to accurately count the required MDA, the
    instrument may need to be moved to a lower background area or serviced.

II. Count Rate Survey Instruments

    Count rate survey instruments (those with a counts per minute (cpm) scale) 
    using pancake probes are routinely used to detect and measure surface      
    contamination.  Pancake probes are thin window Geiger-Mueller probes which 
    typically have an active face area of about 15 square centimeters.         
    Pancake probes are most efficient for detecting and measuring energetic    
    beta radiation from radioactively contaminated surfaces.  The measured     
    activity is commonly expressed in units of disintegrations per minute      

    To obtain uniform radiation fields, calibrations are commonly made with    
    the detector window nearly in contact with large area, flat, uniformly     
    distributed sources such as planchet sources.  The American National       
    Standard Institute (ANSI) N323-1978, Radiation Protection                  
    Instrumentation Test and Calibration, specifies that calibration           
    shall be performed with a standard source or sources providing radiation   
    fields similar to those for which the instrument is used (Section 4.3.2).  
    For example, the proper beta radiation response of an instrument would be  
    determined with a source of beta radiation of similar properties to the    
    radioisotopes in use.

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This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
the technical contacts listed below or the appropriate regional office.

                                   ORIGINAL SIGNED BY

                              Richard E. Cunningham, Director
                              Division of Industrial and
                                Medical Nuclear Safety
                              Office of Nuclear Material Safety
                                and Safeguards

Technical contacts:  Jim Smith, NMSS
                     (301) 504-2613

                     Torre Taylor, NMSS
                     (301) 504-2611

1.  Addresses of Organizations
2.  List of Recently Issued NMSS Information Notices
3.  List of Recently Issued NRC Information Notices

                                                            Attachment 1
                                                            IN 93-30
                                                            April 12, 1993
                                                            Page 1 of 1

                          ADDRESSES OF ORGANIZATIONS

    1.      NUREG Documents:

            The NRC Public Document Room
            2120 L Street, N.W., Lower Level
            Washington, D.C. 20555

    2.      NCRP Publications
            P.O. Box 30175
            Washington, D.C.  20014

    3.      ANSI
            1430 Broadway 
            New York, NY  10018

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