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INAA: Sample Preparation

In preparing samples for Instrumental Neutron Activation Analysis, great care must be taken to prevent contamination of the sample container. Since the sample to be analyzed is almost always counted in the container in which it was irradiated, any foreign material on the container or in the container will appear as a constituent of the sample and be so considered during the analysis of the sample. Handling sample containers with bare hands will add appreciable amounts of both sodium and chlorine to the container surface. Identifying samples by writing on them with inks or grease pencils also introduces unknown impurities into the analysis process. Consecutive Arabic numerals (not to exceed 65,000) scribed (with an engraving tool or diamond point) on the side of the container provide an efficient means of identification of samples. (It is also possible to enclose the sample to be irradiated in an outer container which can be identified by marking it with ink or marking pencil, however this method introduces another area where error can occur if the samples are spilled.) If non-numeric sample identification is needed, alphanumeric identifiers may be used instead, but total identification width may not exceed 15 ASCII characters.

Samples should be submitted to UWNR pre-weighed in standard UWNR irradiation vials (available on request in 2/5 or 4 dram sizes). (Other sample sizes can be used by special arrangement, but only the indicated sizes fit the automatic sample changers.) Bulk materials may be submitted for analysis. In this case, UWNR staff will prepare the samples for irradiation, at additional expense.

When presenting pre-weighed and packaged samples, the vials should be no more than half full (0.5 ml for 2/5 dram vial, 5 ml for 4 dram vial). Vials are sealed at the Reactor Laboratory by friction welding (spinning the cap within the vial). Sample material trapped between the sides of the vial and the cap will cause failures in the friction-welded seals and, consequently, the samples will leak. Therefore, when handling and transporting filled vials, keep them upright to prevent sample material from contaminating the weld area. Note that liquid samples may contaminate the sealing area by condensation if the vials are kept closed for long periods.

Samples must be individually identified and accompanied by the standard UWNR NAA Information Sheet (copy attached). The top one-third of this sheet should be completed by the person submitting the samples for irradiation. If you can make sample identification and weights available on disk (in DOS text files, comma-delimited text files, or spreadsheet files which can be imported into QuattroPro), this will eliminate a possible source or transcription errors. Otherwise, provide sample number and sample mass information on applicable portions of the back of the form. New NAA service users will also be asked to complete a form supplying information needed for reporting of laboratory activities.

If you wish to provide standards to be used in the analysis process, ensure that:

  1. Standards approximate the unknowns in both volume and major element composition.
  2. Standards are identical unless the concentration of element(s) standardized remains constant and the weight of standard material is varied to satisfy 1..
  3. Standards are identified by number, but these numbers must not be included in the sequential sample numbering system chosen. (Our program assigns "standard" as identification for all standards.)
  4. Standard composition must be specified.
  5. Standards must be provided in a 1:8 ratio to samples for the small vials. See the back of the submittal form for standardization information for the large vials.
  6. Standards should contain elements to be measured in approximately the same range as is expected in the unknown sample.
If it is possible to supply UWNR with one or two extra samples in an initial batch of unknowns, gross errors in irradiation and counting times can be avoided, and standards can be adjusted to more nearly duplicate the sample composition.

Finally, the more information you can provide regarding the unknown sample composition, elements of interest, and expected levels of these elements, the better and more economical our analysis can be.


For questions or further information:
    Telephone: 608-262-3392
    Email: reactor "at" engr.wisc.edu
Mailing Address:  
    Nuclear Reactor Laboratory
    1513 University Avenue
    Madison, WI 53706-1572
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