Massic activity ratios of the NBS/NIST tritiated-water standards issued between 1954 and 1999

As part of the preparation and calibration of three new National Institute of Standards and Technology (NIST) tritiated-water radioactivity Standard R eference Materials (SRMs), the massic-activity (activity of the sample divi ded by the mass of the sample) ratios of all of the available NBS/ NIST tri tiated-water SRMs issued between 1954 and 1999 were measured using liquid-s cintillation (LS) counting. Four of the tritiated-water standards (SRMs 436 1, 4926B, 4927C, and 4927D) were not available for measurement. All of the other tritiated-water standards (SRMs 4361B, 4361C, 4926, 4926C, 4926D, 492 6E, 4927, 4927B, 4927E, and 4927F) were available, having been stored in fl ame-sealed glass ampoules. Where possible, massic-activity ratios measured by liquid-scintillation counting are compared with massic-activity ratios c alculated from gravimetric dilution factors. The agreement is well within t he stated uncertainties. For two of the tritiated-water standards that were not available for measurement (SRMs 4361 and 4926B), massic-activity ratio s calculated from gravimetric dilution factors are available.