No abstract available

[en] Massic activity values obtained for NBS/NIST tritiated water SRMs 4927 and 4927E, using internal gas-proportional counting, are reported. The massic activity ratios of all of the available NBS/NIST tritiated water SRMs and samples of the Level 1 and Level 3 tritiated water standards produced by the National Physical Laboratory (NPL) in 1996 were measured using an extensive series of liquid-scintillation intercomparisons. New massic activity values obtained for the NPL standards, using the gas counting results for SRM 4927E and the results of the liquid-scintillation intercomparison, are also reported. A new determination of the half-life of tritium was made using massic activity data for SRM 4927 over a period of 38 years. The new value is (4504±9) (one standard deviation) days. This value differs significantly from the previous NBS/NIST value but is in good agreement with the value recommended in the Evaluated Nuclear Structure Data File (ENSDF)

[en] As reported at the ICRM 2011, it was discovered that the source holder used for calibrations in the NIST 4πγ ionization chamber (IC) was not stable. This has affected a large number of half-life measurement results previously reported and used in compilations of nuclear data. Corrections have been made on all of the half-life data based on the assumption that the changes to the ionization chamber response were gradual. The corrections are energy dependent and therefore radionuclide specific. This presentation will review our results and present the recommended changes in half-life values and/or uncertainties. - Highlights: • The NIST half-life data is corrected for sample positioning variations and refitted. • These results are reported and increased errors in the reported values are given. • Longer lived radionuclides are discussed

[en] For nearly half a century, the half-lives of many radionuclides have been measured with increasing precision. The results of these measurements for many long-lived radionuclides, such as ⁶⁰Co, ¹³⁷Cs, ⁸⁵Kr, ¹³³Ba, ²⁰⁷Bi, ¹⁵²Eu, ¹⁵⁴Eu, and ¹⁵⁵Eu, have been updated recently by the Radioactivity Group of NIST. These long-lived radionuclides are used extensively to calibrate various nuclear counting and monitoring systems. The long-term precision of these calibrations can be greatly affected by the uncertainties in the calibrant half-lives. Results for the half-lives of many radionuclides measured over the last four decades are tabulated. In addition, values of the half-lives of several short-lived radionuclides used in nuclear medicine are addressed, which are critical in determining the correct dosage given in patient treatment, are addressed. Comparisons with the recommended values from the International Atomic Energy Agency Coordinated Research Program and the Evaluated Nuclear Structure Data File from Brookhaven National Laboratory are presented and any apparent disagreements noted

[en] Samples of ²⁴Na, ⁴²K, ⁷⁶As and ¹⁹⁸Au were produced by irradiation in the National Institute of Standards and Technology (NIST) reactor, and examined for impurities before and after measurement. Half-life measurements were carried out in the NIST 4πγ pressurized ionization chamber. The results are compared to presently accepted values and previous NIST measurements

[en] Solutions containing the potential radiotherapy radionuclide ¹⁷⁷Lu have been standardized at the National Institute of Standards and Technology (NIST) by 4πβ liquid scintillation (LS) counting with ³H-standard efficiency tracing using the CIEMAT/NIST method. Confirmatory measurements were made with 4π NaI(Tl) γ-ray spectrometry. Activity determinations were made on 4 solutions over the course of 10 months with an expanded (k=2) uncertainty on the activity of 0.8%. Half-life measurements were carried out using the NIST ''4π'' γ ionization chamber (IC) and LS counting and gave a new value of 6.65±0.01 d, which is shorter than the current ENSDF-recommended value by 1.3%. Impurity analyses were performed by high-purity germanium (HPGe) γ-ray spectrometry and indicated only the presence of ^177mLu at a level of 0.02% that of the ¹⁷⁷Lu as of the respective reference times for the four solutions. Calibration factors for the NIST IC and Vinten 671 ionization chambers were developed, as were dial settings for the NIST-maintained Capintec CRC-12

[en] The massic activity of a solution containing ¹⁸⁸W in equilibrium with its daughter, ¹⁸⁸Re, has been standardized by the National Institute of Standards and Technology using 4πβ liquid scintillation counting with efficiency tracing using the CIEMAT/NIST method. Confirmatory measurements were carried out with γ-ray spectrometry using high purity germanium detectors and a 4πγ NaI(Tl) system. A calibration factor of 1.68 MBq pA^-1±0.03 MBq pA^-1 (expanded, k=2, uncertainty) for the ¹⁸⁸W in the solution was determined, along with correction factors for activity determinations using Capintec dose calibrators. A half-life value of 69.78 d±0.05 d (standard uncertainty) was determined by measurement in the NIST 4πγ ionization chamber and is consistent with currently recommended values

[en] The measurement of ¹⁶⁶Ho, both as a chloride solution and as [¹⁶⁶Ho]-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylenephoonic acid (DOTMP), was examined for four models of radionuclide calibrators: Capintec CRC-35R (two chambers), Capintec 712MX, AtomLab 100 (two chambers), and a Capintec CRC-12. Holmium-166 chloride was measured as 16 ml in 20-ml glass dose vials. Diagnostic imaging level [¹⁶⁶Ho]DOTMP solutions, nominally 400 MBq g^-1, were measured as 12 ml in 20-ml dose vials. Finally, therapeutic level [¹⁶⁶Ho]DOTMP solutions, nominally 9 GBq g^-1, were measured as aliquots of 100-500 μl in sealed plastic vials of 10-ml saline. Single calibration factors for each instrument manufacturer are recommended for 12-16-ml of either solution in 20-ml glass dose vials, (673±9)x10 and 72.7±0.7, for the Capintec and AtomLab models, respectively. Calibration factors recommended for the therapeutic dose geometry are (706±6)x10 and 68.7±1.3, for the Capintec and AtomLab models, respectively. The calibration factors recommended for an NIST 5-ml ampoule are (686±5)x10 and 70.9±0.4 for the Capintec and AtomLab models, respectively

[en] Assays of radioactive noble gases, in particular reactor gaseous effluents, are routinely made with Ge(Li) gamma-ray spectrometers. In the past, significant uncertainties in these assays have been associated with the calibration of the detector, that is, with the preparation of a curve showing full-energy-peak efficiency as a function of gamma-ray energy. A method of preparing such a curve, based on measurements made with gamma-ray point-source standards, is given here. An expression is presented that relates the full-energy-peak efficiency for a point source, centered above a glass hemisphere, to that of a gaseous source in a spherical ampoule, for a given gamma-ray energy. Measurements made with standards of ⁸⁵Kr, ¹²⁷Xe, sup(131m)Xe, and ¹³³Xe demonstrate that the method is suitable for the intended purpose. (author)

[en] The National Bureau of Standards gas-counting equipment is described. This consists of matched, length-compensated copper and stainless steel internal gas counters, which can be used in the proportional or Geiger-Mueller regions. The data acquisition and processing is by means of a computer-based multichannel analyzer. Methods for preparing relative standards based on measurements with ion chambers and fixed-geometry solid-state detectors are discussed. Noble-gas standards for argon-37, krypton-85, xenon-131m, and xenon-133 have so far been prepared, the last involving purification on the NBS isotope separator