Dale D. Hoppes

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.

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.

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.

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.

The needs for brachytherapy source calibrations in the United States

Abstract Brachytherapy sources of beta and gamma radiation (“brachy” is from the Greek, meaning “near”) have a long history of use in interstitial, intracavitary, intraluminal, and ocular radiation therapy. In the past the US national standards for these sources were often specified in activity or milligram radium equivalent. With the introduction of new radionuclide sources to replace radium, source strength calibrations are now expressed as air kerma rate at a meter. In this paper, we review the NIST standards for brachytherapy sources, list some of the common radionuclides and source encapsulations in use in the US radiology community, and describe the latest NIST work, in collaboration with several US medical institutions, on a method of two- and three-dimensional dose mapping of brachytherapy sources using radiochromic films.

Liquid-scintillation standardization of 123mTe

Abstract A commercial liquid-scintillation system and calibrated germanium gamma-ray spectrometers were used to confirm the use of the 159-keV gamma ray of 123m Te as a primary efficiency calibrant for which the activity measurement is simple. The evaluated gamma-ray probability per decay is 0.840 ± 0.004. Liquid-scintillation spectra confirm that conversion electrons greater than 50 keV can be detected in at least 99.5% of the decays. The half-life was measured as 119.2 ± 0.1 days.

International committee for radionuclide metrology : guidelines for international acceptance of radioactivity calibration sources

Abstract These Guidelines for the International Acceptance of Radioactivity Calibration Sources were written in response to a request from the International Committee for Radionuclide Metrology (ICRM). They outline the common basis for the quality control of the production of national standard samples of radioactivity. The members of ad hoc committee were: D. Bek-Uzarov Belgrade, Yugoslavia C. Ballaux † Brussels, Belgium P. Christmas † Teddington, England K. Debertin † Braunschweig, Germany D. D. Hoppes † Gaithersburg, MD, U.S.A. J. M. R. Hutchinson, Chairman † Gaithersburg, MD, U.S.A. T. Radoszewski Otwock Swierk, Poland A. Szorenyi Budapest, Hungary H. Volchok, deceased New York, NY, U.S.A.

Standardization and decay scheme of 201Tl

Abstract An intercomparison exercise was conducted among three national standards laboratories and a commercial supplier to determine the degree of agreement between directly determined values of the activity concentration of a solution of 201 Tl. The γ-ray emission probabilities of 201 Tl were also determined, providing an emission probability for the 167.4 keV γ ray of 0.1000 ± 0.0006.

National Bureau of Standards decay-scheme investigations of strontium-82-rubidium-82

Abstract An unweighted average of photon- and positron-emission rates from 82 Rb sources measured under eight different circumstances yields a probability per decay for the 776-keV γ ray of 0.149, with an estimated standard deviation of 0.004. However, separate consideration of positron measurement by liquid-scintillation counting and by annihilation-radiation spectrometry gives emission rates differing by five times the total uncertainty of either. The half life of 82 Sr was measured as 25.36 ± 0.03 d by following the decay with a γ-ray spectrometer. Methods for measuring a 85 Sr impurity by γ-ray spectrometry and by liquid scintillation counting have been developed.