Standardization of (241)Am, (124)Sb and (131)I by live-timed anti-coincidence counting with extending dead time.

The National Metrology Laboratory for Ionizing Radiation (LNMRI)/Brazil has implemented a live-timed anti-coincidence system with extending dead time to complement the existing systems in its Radionuclide Laboratory for activity measurements of radioactive sources. In this new system, the proportional counter has been replaced by a liquid-scintillation-counter for alpha and beta detection. In order to test the performance of the new system, radioactive solutions of (131)I, (124)Sb and (241)Am have been standardized. In this work the measurement method, the results and the associated uncertainties are described and discussed.

Measurements of photon emission probabilities from the decay of 226Ra and daughters.

X- and gamma-rays spectrometric techniques have been used to determine and improve the photon emission probability data of 226Ra. These values were obtained from 226Ra spectra in radioactive equilibrium with daughters such as 222Rn, 214Bi and 214Pb in the 50-2500 keV energy range. The efficiency calibration of the coaxial and planar Ge detectors took into account correction factors for pile-up losses, attenuation and source geometry effects, and gamma-gamma and gamma-X summation losses. XK emission probabilities were successfully resolved and determined more precisely because of the ability to de-convolute complex regions of the spectrum below 90 keV combined with spectral knowledge of the interferring Pb-XK-rays. The resulting absolute intensities of the main photon emissions of 226Ra and daughters exhibit improvements (+/-0.7% for the smallest uncertainty estimated to one standard deviation) or agree with published data.

Absolute determination of activity per mass and half-life measurements of 152Eu.

A solution of 152Eu was absolutely standardized by the 4pi beta (PPC)-gamma (HPGe) coincidence counting method as part of an intercomparison program coordinated by Bureau International des Poids et Mesures. The measured activity has been used to determine the calibration factor of the LNMRI reference ionization chamber for 152Eu. The half-life of 152Eu was also determined by means of a 4pi gamma ionization chamber to be (4963.6+/-15.3) days, and compared with others published values.

Measurements of nuclear data parameters of 201Tl by gamma-ray spectrometry.

201Tl is frequently used in radiopharmaceutical applications, and therefore the gamma-ray emission probabilities and half-life have been re-determined by means of gamma-ray spectroscopy. While the activity was calibrated using the sum-peak coincidence method, the half-life was obtained by the reference source method based on simultaneous counting of a reference source and the sample. Both the measurement techniques and assignment of uncertainties are presented and discussed, and the resulting data are shown to be in good agreement with previously published studies.

Use of the reference source method to determine the half-lives of radionuclides of importance in nuclear medicine.

The reference source method associated with HPGe gamma-ray spectrometric techniques has been applied to half-life determinations of radionuclides used in nuclear medicine. Simultaneous measurements were undertaken for radiopharmaceutical nuclides such as 67Ga, 99Tcm, 123I, 131I and another radionuclide as reference. Besides optimizing the analysis time, this procedure was shown to be independent of the instrumental technique, environmental and radiochemical impurity interferences for most radionuclides. However, some restrictions were observed in samples that contained impurities with the same emission energy or an energy that was very close to the energy of the radionuclide to be measured. The measurement conditions improved the quoted accuracy of the half-life by reducing the type B component uncertainty.

166mHo: a multi-gamma standard for the calibration of Ge spectrometers.

Efficiency calibration curves for germanium detectors are usually established by using a large number of standard gamma-ray sources of specific radionuclides, that decay with few gamma-rays, or radionuclides with complex decay schemes, such as 133Ba or 152Eu. But these multi-gamma radionuclides cannot be used alone, because the gamma-rays of high intensity are irregularly distributed across the energy spectrum. 166mHo is a more suitable single source for such calibrations, because this radionuclide decays by beta(-)emission to the excited states of 166Er with the subsequent emission of about 20 strong and well distributed gamma-rays ever the energy range 50-1000 keV. Moreover, with a relatively long half-life (1200 yr) and characteristic X-rays between 40 and 50 keV, this nuclide is a good standard for the calibration of germanium detectors. The X- and gamma-ray emission probabilities of their main lines need to be known with good accuracy in order to resolve the discrepancies found in the literature. A combination of 4pi beta-gamma coincidence and X- and gamma-ray spectrometric techniques have been used to determine 50 photon emission probabilities.

Calibration of ionization chamber for ¹8F and 68Ga.

In order to maintain the results of primary activity standardizations carried out in 2011 the LNMRI has determined the calibration factors for a pressurized 4π-ionization chamber for the nuclides (18)F and (68)Ga. This ionization chamber is coupled to a 6517A Keithley electrometer which is controlled by a homemade LabVIEW program. This paper will describe the main issues related to the calibration of an ionization chamber system for positron emitters and short half-life radionuclides such as timing, current measurement, background, decay, and (226)Ra check source measurements.