Francis J. Schima

Preparation and calibration of the 1978 National Bureau of Standards tritiated-water standards

Abstract The National Bureau of Standards activity standards for tritiated water, SRM 4926 and SRM 4927, have been recalibrated by the method of internal gas-proportional counting, and a new series of standards has been prepared. These standards are used in measurements made by the International Atomic Energy Agency and the World Meteorological Organization (IAEA/WMO) Tritium Monitoring Network. The agreement between the 1961 and 1978 gas counting measurements is 0.7%, assuming the adopted half-life of 12.35 yr. The results are, however, in complete agreement if, instead, a half-life of 12.44 yr is used. A half-life of 12.43 ± 0.05 yr, based on measurements of the NBS tritiated-water standards over a span of 18 yr, is suggested.

New and revised half-life measurements results

Abstract The half-lives of many radionuclides have been measured in the Radioactivity Group of NIST over the last three decades. The results of these measurements for many long-lived radionuclides such as 60Co, 137Cs, 85Kr, 22Na, 133Ba, 207Bi, 152Eu, 1 33Eu, 134Eu, 135Eu, and 125Sb have been recently revised. The results for the half-lives of the many radionuclides measured over the last three decades are tabulated. Comparisons with the recommended values from the International Atomic Energy Agency Coordinated Research Program (IAEA-CRP) are given for the long-lived radionuclides.

Tables for cascade-summing corrections in gamma-ray spectrometry

Abstract Calculations of the spectral distortion caused by the simultaneous detection of cascade radiations in gamma-ray spectrometry involve terms containing the relative probability for the coincident emission of the radiations involved. Here we present tables of these probabilities (“summing coefficients”) for the most probable gamma rays of some frequently encountered radionuclides, to be combined with measured full-energy-peak or total efficiencies of a particular system to calculate emission rates that would be measured without cascade summing.

The standardization and decay scheme of rhenium-186

Abstract Rhenium-186 has been standardized for activity by the CIEMAT/NIST method of 4πβ liquid-scintillation efficiency tracing with tritium, with an uncertainty (equivalent to 1 SD) of 1.61%. Half-life measurements with a pressurized ionization chamber give a T 1 2 = 89.25 ± 0.07 h . Photon emission rates were measured with semiconductor detectors, and the probability of emission of the principal γ-ray at 137 keV was found to be P7 = 0.0945 ± 0.0016.

Liquid-scintillation counting techniques for the standardization of radionuclides used in therapy

Abstract Radionuclides are increasingly used in therapeutic nuclear medicine. The CIEMAT/NIST method of standardizing high-energy beta-particle emitters is being applied to a list of candidate radionuclides developed by the US nuclear medicine community. Standards and standard methods are needed by the pharmaceutical manufacturers in North America before these nuclides can be widely distributed. Solutions standardized by liquid-scintillation counting are used to establish counting efficiencies for Cerenkov counting and NaI(T1) well crystals, and potentiometer settings for commercial radionuclide calibrators. Results are presented for a number of beta-particle-emitting radionuclides.

The standardization of samarium-153

Samarium-153 has been standardized by 4 pi beta liquid-scintillation counting, with an uncertainty of 0.4%. The probability per decay for the 103.2-keV gamma ray was measured, using two germanium detectors, to be 0.298 +/- 0.004. The half life, based on liquid-scintillation measurements over 6.4 half lives and pressurized-ionization-chamber measurements over four half lives, was found to be 46.27 +/- 0.02 h. The uncertainties given are one estimated standard deviation (of the mean when applicable) for random and non-random components.

The standardization of the potential bone palliation radiopharmaceutical 117mSn(+4)DTPA

Solutions containing the potential bone pain palliation radionuclide 117mSn, in chloride form and as a diethylenetriaminepentaacetate (DTPA) complex, have been standardized by 4 pi beta liquid scintillation (LS) spectrometry and 4 pi gamma-ray spectrometry. Massic activities of the stock solutions were measured in order to determine dose calibrator settings for the solutions using commercial dose calibrators. Excellent agreement in the measurement of solution massic activity between the two techniques was achieved. The massic activity of 117mSnCl4 stock solution was found to be 38.62 +/- 0.23 MBq g-1 and 38.81 +/- 0.94 MBq g-1 with LS spectrometry and 4 pi gamma-ray spectrometry respectively. The respective values of the massic activity of the 117mSnDTPA stock solution with LS spectrometry and 4 pi gamma-ray spectrometry were 39.35 +/- 0.23 MBq g-1 and 39.70 +/- 0.96 MBq g-1. Impurities were analyzed in several solutions and found to have emission rates on the order of 10(-4) to 10(-6) of the rate of the 117mSn emission at the end-of-bombardment. The largest impurities came from 113Sn and 125Sn, the activation products of isotopic impurities present in the 117Sn target. The relative proportions of the various impurities were found to be highly dependent upon the source of 117Sn target material. The implications of choice of half-life used in the decay correction of 117mSn are discussed.

Determination of the photon emission rates of the NBS long-lived mixed-radionuclide standard

Abstract A mixture of 125 Sb, 154 Eu, and 155 Eu has been used to prepare gamma-ray emission-rate standards with a functional life of over 10 years and with useful photon emissions at over 18 energies between 25 and 1600 keV. The standards are useful for the calibration of the efficiency of germanium gamma-ray detectors in this energy range. Correlated summing corrections are moderate, compared to many radionuclides which provide multiple calibration points. Photon-emission rates for the major radiations have been measured, for sources quantitatively related to the standards, with four germanium spectrometer systems especially calibrated for the purpose. For two coaxial detectors, efficiency values were established at 28 energies between 88 and 2800 keV, with an average total uncertainty, estimated at a level corresponding to a standard deviation of the mean, of about 0.6%. At lower energies, the most reliable calibration points were given by X- or gamma-rays directly measured with defined-geometry NaI(Tl) systems. Calculated efficiency curves were used for interpolation between these points. Significant efficiency changes of the coaxial detectors with time were monitored and accounted for. The emission rates of selected X-rays and gamma-rays from the standards are specified with total uncertainties of from 0.6% to 1.3%, estimated to correspond to one standard deviation of the mean.

Low-level radioactivity ocean sediment standard reference material

Abstract The National Institute of Standards and Technology (NIST), in cooperation with experienced international laboratories, will issue a low-level radioactivity Ocean Sediiment Standard Reference Material (SRM) 4357 in 1996. The Ocean Sediment joins the NIST suite of six other ‘natural matrix’ environmental radioactivity Standard Reference Materials. This family of natural matrix materials have already been used: (1) to develop radiochemical procedures; (2) to test radiochemical procedures already in use for environmental and biokinetic evaluations; (3) to calibrate instruments; (4) to intercompare and evaluate radiochemical methods; (5) to test competency of technicians to do radiochemical assays; and (6) to demonstrate that data output is reliable. The participating laboratoires provided data for the radionuclides are of sufficient quality to establish certified values and reanonable uncertainty limits given the relatively low concentrations of the radionuclides. The uncertainties for a number of certified radionuclides are non-symmetrical and large because of the non-normal distribution of reported values.

Measurement standards for strontium-89 for use in bone palliation

Strontium-89 standards have been prepared for use in calibrating instruments in the measurement chain from production in reactors to administration in the clinic or radiopharmacy. Alternate reactor production schemes were evaluated to yield high purity 89Sr with minimum 85Sr impurity. Following purification to remove radionuclidic impurities, samples of 89Sr were standardized by high-efficiency liquid-scintillation counting with a relative expanded uncertainty (intended to approximate two standard deviations) of 0.48%. A Standard Reference Material, SRM 4426A, was prepared and distributed to radiopharmaceutical manufacturers and other customers. The standard sources of 89Sr were used in different geometries to calibrate high purity Ge semiconductor detectors, re-entrant ionization chambers and commercial radionuclide calibrators. The latter included Capintec dose calibrators and the Capintec beta C NaI(Tl) scintillation counter.