Live-timed Anticoincidence Counting Research Articles

Activity standard and calibrations for 227Th with ingrowing progeny

Thorium-227 was separated from its progeny and standardized for activity by the triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting. Confirmatory liquid scintillation-based measurements were made using efficiency tracing with 3H and live-timed anticoincidence counting (LTAC). The separation time and the efficiency of the separation were confirmed by gamma-ray spectrometry. Calibrations for reentrant pressurized ionization chambers, including commercial radionuclide calibrators, and a well-type NaI(Tl) detector are discussed.

Liquid scintillation efficiencies, gamma-ray emission intensities, and half-life for Gd-153

Gadolinium-153 was standardized for activity by live-timed anticoincidence counting and an ampoule was submitted to the international reference system (SIR). Absolute emission intensities for the main γ rays were determined with calibrated high-purity germanium (HPGe) and lithium-drifted silicon (Si(Li)) detectors. A revised decay scheme is indicated, with no probability of direct electron capture to the 153Eu ground state. Triple-to-double coincidence ratio (TDCR) efficiency curves indicate that the revised decay scheme is consistent with experiment. Half-life measurements agree with a previous NIST determination and show no sensitivity to chemical environment.

Measurement of the absolute gamma emission intensities from the decay of Th-229 in equilibrium with progeny

There are few long-lived radionuclides yielding high intensity gamma-rays emission with energies ranging from 100 keV to 500 keV that can be applied as radioactive gamma standard to calibrate HPGe detectors. Furthermore, this energy range represents the main emitted energies of the majority of radionuclides used in nuclear medicine. The Brazilian National Laboratory for Ionizing Radiation Metrology (LNMRI/IRD/CNEN) has attempted to identify radionuclides that have the potential to be used as a calibration source due to their long half-life as well as their emission spectrum. Hence, LNMRI promotes standardization studies of gamma-emitting radionuclides that meet these criteria on order to disseminate them. Thorium-229, with its well-defined energies and relatively high intensities, is one such candidate radionuclide for the energy and full-energy peak efficiency calibration of high-purity gamma spectrometers. Thorium-229 was standardized by the method of 4παβ(LS)-γ(NaI(Tl)) live timed anticoincidence counting. The emission intensities of gamma-rays associated with the decay of 229Th have been determined by HPGe gamma ray spectrometry with accuracy and precision. The results are in agreement with current literature data.

Sum-peak method with two NaI(Tl) crystals: 68(Ge+Ga) standardization

A 68(Ge+Ga) commercial solution has been standardized in LNMRI in Brazil, by sum-peak method, in which a 3”x3” NaI(Tl) gamma-ray detector is positioned at the top of a well-type 5”x5” NaI(Tl) gamma-ray detector, resulting in a set up approximately 4p geometry. In this work the known germanium volatility was tested using three dried sources and three liquid sources in the sum-peak method measurements and the activity results showed a standard deviation of 0.41%. The activities were compared with another primary method: 4pb-g live-timed anti-coincidence counting. The two methods gave activity concentration values with differences from the certified value of +0.8 % (anticoincidence method) and -3.4% (sum-peak method).

134Cs activity standardization by 4πβ(LS)-γ(NaI-Tl) anticoincidence counting and submission to international reference system

From a commercial supplier a solution containing 134Cs has been standardized at National Laboratory for Ionizing Radiation Metrology (LNMRI) for the first time using three Liquid scintillation based measurement. These measurement methods are 4πβ-γ live-timed anticoincidence counting, 4πβ-γ coincidence counting and 3H-standard efficiency tracing with the CNET methods. The results obtained by anticoincidence counting was adopted as reference value and its combined uncertainty was 0.38%. The agreement of this reference value with coincidence counting and CNET methods were 0.39% and 0.34% respectively and were in consistency with each uncertainty method. The weighted mean results coincidence counting and CNET methods are also in close agreement 0.03% with anticoincidence counting method and meets the requirement of primary and national standard.This standardization was made in order to reduce the uncertainty in 134Cs measurement in Brazil and also following a request made by Bureau International des Poids and Mesures for new submission to International Reference System. The LNMRI last submission was made in 1987. Therefore from a 134Cs master solution a NIST ampoules was prepared and LNMRI/IRD submitted it to the International Reference System, Bureau International of Poids and Measures (SIR/BIPM). In this paper will be analyzed the LNMRI measurement and performance each measurement methods and also take into account the reference value of KCDB, we determined also the 134Cs gamma emission probabilities of main energy.

Standardization of 106Ru/Rh by live-timed anticoincidence counting and gamma emission determination

The absolute activity standardization measurement system of radionuclide by live-timed anticoincidence counting was implemented at LNMRI in 2008 to reduce the effects of some correction factors on the determination of activity with coincidence counting technique used for decades in the laboratory, for example, the corrections of dead time and resolution.With the live-timed anticoincidence system, the variety of radionuclides that can be calibrated by LNMRI was increased in relation to the type of decay. The objective of this study was to standardize the 106Ru activity, determine gamma emission probabilities by spectrometric method for some energies, and estimate measurement uncertainties.

Long-term stability of carrier-added 68Ge standardized solutions

Tests for chemical stability were carried out on carrier-added 68Ge solutions prepared and calibrated in 2007 and 2011 to evaluate the suitability of the specific composition as a potential Standard Reference Material. Massic count rates of the stored solutions were measured using a NaI(Tl) well counter before and after gravimetric transfers. The present activity concentration of the 2007 solution was also measured using live-timed anticoincidence counting (LTAC) and compared to the 2007 calibrated value. The well counter data indicated no change in massic count rate to within uncertainties for either solution. The LTAC measurements gave a difference of −0.49% in the activity concentration 2007 solution over 7 years. However, the uncertainty in the decay correction over that time, due to the uncertainty in the 68Ge half-life, accounted for the majority (0.67% out of 0.83%) of the standard uncertainty on the activity concentration. The results indicate that these carrier-added solutions are stable with regard to potential activity losses over several half-lives of 68Ge.

Revision of the NIST Standard for (223)Ra: New Measurements and Review of 2008 Data.

After discovering a discrepancy in the transfer standard currently being disseminated by the National Institute of Standards and Technology (NIST), we have performed a new primary standardization of the alpha-emitter 223Ra using Live-timed Anticoincidence Counting (LTAC) and the Triple-to-Double Coincidence Ratio Method (TDCR). Additional confirmatory measurements were made with the CIEMAT-NIST efficiency tracing method (CNET) of liquid scintillation counting, integral γ-ray counting using a NaI(Tl) well counter, and several High Purity Germanium (HPGe) detectors in an attempt to understand the origin of the discrepancy and to provide a correction. The results indicate that a −9.5 % difference exists between activity values obtained using the former transfer standard relative to the new primary standardization. During one of the experiments, a 2 % difference in activity was observed between dilutions of the 223Ra master solution prepared using the composition used in the original standardization and those prepared using 1 mol·L−1 HCl. This effect appeared to be dependent on the number of dilutions or the total dilution factor to the master solution, but the magnitude was not reproducible. A new calibration factor (“K-value”) has been determined for the NIST Secondary Standard Ionization Chamber (IC “A”), thereby correcting the discrepancy between the primary and secondary standards.

Standardization of 166mHo and 243Am/239Np by live-timed anti-coincidence counting with extending dead time

The National Laboratory for Metrology of Ionizing Radiation (LNMRI)/Brazil acquired 166mHo and 243Am/239Np solutions from commercial suppliers in order to realize primary standardization and therefore reducing the associated uncertainties. The method used in the standardization was the live-timed 4πβ(LS)-γ(ΝaI(Tl)) anticoincidence counting. The live-timed anticoincidence system is operated since 2006 in LNMRI and is composed of two MTR2 modules donated by Laboratoire National Henri Becquerel (LNE-LNHB)/France. The data acquisition system uses a homemade LabView program and an Excel file for calculus. These systems have been used for primary standardization at LNMRI for many radionuclides and recently took part in the 124Sb and 177Lu International Key Comparisons with good performance.

Standardization of 241Am, 124Sb and 131I 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 131I, 124Sb and 241Am have been standardized. In this work the measurement method, the results and the associated uncertainties are described and discussed.

Standardization of 67Ga, 51Cr and 55Fe by live-timed anti-coincidence counting with extending dead time

In this work, the activity standardization of 51Cr, 55Fe and 67Ga by live-timed anti-coincidence counting with extending dead time is described. The difficulties of the method, the uncertainties of the results of the measurements and the comparison of these results with others measurement methods are discussed.