What does "NIST Traceability" really mean?

[dj_strom@ccmail.pnl.gov (Daniel J Strom)]

All,

I'd like to find out what "NIST traceability" of standards really means 
in the context of ANSI/HPS N13.30-1996, "Performance Criteria for 
Radiobioassay.  An American National Standard."  NIST Traceability is 
not defined in N13.30, but it is defined, at least for manufacturers, in 
ANSI N42.22-1995.

My understanding is that a standard radionuclide solution bought from 
NIST is a "certified source" (at least until one opens the flame-sealed 
glass ampoule and it begins to evaporate).  One can prepare "derived 
traceable sources" from certified sources, such as dilutions, etc.  
However, to be "NIST traceable," one must participate in a Measurements 
Assurance Program (MAP) with NIST, a two-way exchange of samples and 
unknowns.  One's measurement program must get the right answer for 
samples supplied to it by NIST, and NIST must agree, after it makes 
measurements on them, that samples supplied by one's program have the 
activity, concentration, etc. that one claimed they had.

My colleague at PNNL, Jay MacLellan, points out that N42.22 section 
6.3.d. addresses traceability of derived sources.  That section states, 
"NIST verification of derived sources (e.g., charcoal cartridges, 
solids, water equivalent sources, filters, etc.) is recommended.  
However, due to the diversity of secondary sources, opportunities for 
verification with NIST may be limited due to the costs and extra 
resources necessary for special calibrations.  In this case, the derived 
sources may be termed traceable provided the procedures subsequent to 
establishment of traceability are subjected to an internal MAP that has 
been examined and approved by qualified individuals.  (Although the term 
traceable is applied to derived sources, NIST does not accept 
responsibility for the accuracy of the procedures used to prepare such 
sources.)"

I'd like to know what in-house and commercial "service laboratories" (in 
the N13.30 sense of the lab that analyzes bioassay samples) are actually 
doing, and what customers of service labs are accepting as "NIST 
traceability" for purposes of N13.30.

Thanks.

References

American National Standards Institute (ANSI).  Traceability of 
Radioactive Sources to the National Institute of Standards and 
Technology (NIST) and Associated Instrument Quality Control.  ANSI 
N42.22-1995.  New York: Institute of Electrical and Electronics 
Engineers, Inc. 1995.

Health Physics Society (HPS).  Performance Criteria for Radiobioassay.  
An American National Standard. HPS N13.30-1996.  McLean, Virginia: 
Health Physics Society; 1996.

The opinions expressed above are my own, and have not been reviewed or 
approved by Battelle, the Pacific Northwest National Laboratory, or the 
U.S. Department of Energy.

Daniel J. Strom, Ph.D., CHP
Staff Scientist
Health Protection Department K3-56
Pacific Northwest National Laboratory
Battelle Boulevard, P.O. Box 999
Richland, WA 99352-0999 USA
(509) 375-2626
(509) 375-2019 fax
dj_strom@pnl.gov