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.

Activity standardization and half-life measurement of 177Lu

The activity of the 177Lu solution has been measured by means of the CIEMAT/NIST efficiency tracing method. This result has been compared to the previous obtained results received from 4πβ(LS)–γ coincidence and anticoincidence counting. The activities determined with various methods have been found to be consistent.The decay curve of the 177Lu solution has been followed in the TDCR counter to determine the half-life of this isotope. The half-life has been separately determined for double and triple coincidence events. The arithmetic mean value of these two results has been found to be T1/2 = 6.6489(52) d.

International comparison of activity measurements of a solution of 51Cr

Main textA bilateral comparison between LNE-LNHB, France and the RC POLATOM, Poland on activity measurements of the 51Cr solution was organized in 2022 as the EURAMET project No 1554 and registered as EURAMET.RI(II)-K2.Cr-51 key comparison. In both laboratories, primary activity measurements techniques based on 4π(LS)-γ coincidence and anti-coincidence counting methods were used. LNE-LNHB also performed indicative measurements in a large-well NaI(Tl) detector using the 4πγ method. The final result of the comparison in RC POLATOM was the weighted mean of the results of the 4π(LS)-γ coincidence method and the 4π(LS)-γ anti-coincidence method, and in the LNE-LNHB - the value obtained by the 4π(LS)-γ anti-coincidence method. The power-moderated mean of the final results values was calculated. An additional ampoule containing the same 51Cr solution was sent to the BIPM in order to link the results achieved in the bilateral comparison to the BIPM SIR reference system.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Primary standardization of 212Pb activity by liquid scintillation counting

An activity standard for 212Pb in equilibrium with its progeny was realized, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. A Monte Carlo-based approach to estimating uncertainties due to nuclear decay data (branching ratios, beta endpoint energies, γ-ray energies, and conversion coefficients for 212Pb and 208Tl) led to combined standard uncertainties ≤ 0.20 %. Confirmatory primary measurements were made by LS efficiency tracing with tritium and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting. The standard is discussed in relation to current approaches to 212Pb activity calibration. In particular, potential biases encountered when using inappropriate radionuclide calibrator settings are discussed.

Standardization of 177Lu by means of 4π(LS)β-γ coincidence and anti-coincidence counting

Standardization of 177Lu by means of 4π(LS)β-γ coincidence and anti-coincidence counting

Standardization of 223Ra by live-time anticoincidence counting and gamma-ray emission determination

From a commercial supplier, three independent lots of an aqueous solution containing 223Ra in equilibrium with its deteriorating progeny were considered for standardization, by using live-time anticoincidence counting (LTAC) in the Laboratório Nacional de Metrologia das Radiações Ionizantes (LNMRI) Brazil. The ionization chamber calibration factors were obtained using measurements of independent lots of 223Ra in LTAC considering the absolute method in order to evaluate the constancy and reproducibility of the standardization. The calibration factors of three high-performance well-type ionization chamber systems and four commercial well-type ionization chambers were determined. The LTAC results showed that lots 2 and 3 were 1069.88 and 1097.44 kBq/kg, with corresponding relative standard uncertainties 0.12% and 0.20%, respectively. The spectrometry method results of each lot value were classified as positive by ANOVA hypothesis testing. The emission probabilities relating to the X- and γ-rays in region from 81 to 830 keV ware determined.Hence, LNMRI can provide calibration services for 223Ra.

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.

Accurate integral counting using multi-channel analyzers

Many techniques in radionuclide metrology rely on accurate measurement of the total count rate, that is integral counting, from a detector. We present the design and results from integral counting using a live-timed multi-channel analyzer (MCA) based on a list-mode digitizer and a live-timed scalar, both with imposed, extending dead times. These systems were benchmarked against an existing NIST anti-coincidence counting system. Both systems were used to determine correction factors to an MCA that uses Gedcke-Hale dead-time corrections. Tests were performed for a large-area gas-flow proportional counter and a NaI(Tl) detector for count rates up to 80 000 s−1. The results were used to create correction factors suitable for alpha- and beta-particle emission rate calibrations.

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).

Primary standardization of 224Ra activity by liquid scintillation counting

A standard for activity of 224Ra in secular equilibrium with its progeny has been developed, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. The standard was confirmed by efficiency tracing and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting, as well as by 4πγ ionization chamber and NaI(Tl) measurements. Secondary standard ionization chambers were calibrated with an expanded uncertainty of 0.62% (k = 2). Calibration settings were also determined for a 5 mL flame-sealed ampoule on several commercial reentrant ionization chambers (dose calibrators).

Production of a carrier-free standard 56Mn source for the NRC manganese salt bath

The National Research Council (NRC) of Canada's primary method for emission rate for radionuclide neutron sources utilizes a manganese salt bath which was last calibrated in the 1960s. At that time, an NRC RaBe neutron source was used to irradiate a solution of calcium permanganate to take advantage of the Szilard-Chalmers effect in producing the bulk 56Mn material for standardization and calibration of the bath. When attempting to repeat this exercise, a small amount (~100 kBq) was produced. This amount was sufficient for the standardization process but did not yield enough material to calibrate the bath to a sufficient level of precision.Improvements upon the previous separation scheme adopted at NRC for the separation of the 56Mn from the bulk irradiated material included the rinsing of the 56Mn dioxide precipitate using a mixture of sulfuric acid and hydrogen peroxide. While these improvements made in the separation chemistry improved the yield of 56Mn extraction from 60% to above 95% the maximum amount of activity was still quite low. Hence in March of 2018, the SLOWPOKE-2 Facility at the Royal Military College in Kingston, ON, was used to irradiate three vials of KMnO4 in solution. An estimated 2 GBq was produced and sent to NRC, from which the extraction procedure recovered essentially all of the available 56Mn.The 56Mn was standardized using the 4πβ−γ anti-coincidence counting system and confirmed using the CIEMAT/NIST primary method. The resulting bulk material was certified with an uncertainty of 0.8% (k = 2). Minor quantities of 65Zn, 69mZn and 42K were unexpectedly observed but were in minute quantities so as not to affect the results of the standardization or calibration. The standardized 56Mn artifact was used to calibrate the Secondary Standard Ionizing Radiation Chamber System (SSIRCS) for a more rapid deployment of the calibrant in the future.

Application of Digital Anti-Coincidence Counting Method for Primary Activity Determination of <sup>59</sup>Fe

As a radiopharmaceutical, the use of 59 Fe is classified as a high pharmaceutical risk product. Therefore, a standard reference for activity measurement of 59 Fe is necessary to ensure its metrological aspect. This paper describes an alternative method for primary activity determination of 59 Fe for establishing a standard reference. The 59 Fe solution was prepared using two different cocktails and measured by the 4 p b (LS)- g counting system using a digital anti-coincidence counting method with emulated live-time of the extending dead-time. A final activity results at the reference time for the two samples series are (473.32 ± 2.55) kBq/g and (477.14 ± 2.42) kBq/g with quoted uncertainty evaluated at k = 1. The final activity was compared to the value obtained from the other two coincidence counting method and found to be in a good agreement within its uncertainty value.

Standardization of I-124 by three liquid scintillation-based methods

A solution of 124I was standardized for activity by 4πβ(LS)-γ(NaI) live-timed anticoincidence (LTAC) counting, with confirmatory measurements by triple-to-double coincidence ratio (TDCR) and CIEMAT-NIST efficiency tracing (CNET) liquid scintillation counting. The LTAC-based standard was shown to be in agreement (within k = 1 uncertainties) with previous measurements at NIST and elsewhere. Calibration settings for radionuclide calibrators were determined and a discrepancy with literature values, partially due to a calibration methodology dependent upon an erroneous setting for 18F, was identified and explained.

Standardisation of 85Sr with digital anticoincidence counting and half-life determination of the 514 keV level of 85Rb

The activity of a 85Sr solution was determined by means of fully digital 4πβ(LS)-γ anticoincidence counting. The measurements were carried out in a custom-built, combined TDCR / 4πβ(LS)-γ coincidence system, utilising a commercially available CAEN N6751C digitizer. The analysis of the experimental data, collected in list-mode format, was performed off-line by using the SoftKAM computer code developed at PTB. The data were also used to determine the half-life of the 514 keV level of 85Rb which was found to be (1020.2 ± 6.0) ns.

INAA with anticoincidence counting significantly reduces interferences from the 554.3-keV photopeak of 82Br to allow reliable measurements of nanogram levels of arsenic in solid biological materials via the 559.1-keV photopeak of 76As

It is rather difficult to measure low levels of arsenic by instrumental neutron activation analysis (INAA) in biological materials containing high levels of bromine and antimony in particular, as well as sodium and potassium. The 559.1-keV photopeak of 76As is interfered with by the 554.3- and 564.1-keV photopeaks of 82Br and 122Sb, respectively. The use of INAA in conjunction with anticoincidence spectrometry (INAA-AC) was found to reduce the background under the 559.1-keV photopeak by factors of 4–16 for the biological reference materials analyzed and to decrease the detection limit to 0.35 µg kg−1 making the measurement of nanogram amounts arsenic in them possible.

PRIMARY STANDARDIZATION OF THE MASSIC ACTIVITY OF A PROTACTINIUM-233 SOLUTION.

Protactinium-233 (233Pa) is used as a tracer for radiochemical analysis and is of particular interest as an isotope dilution mass spectrometry (IDMS) spike for 231Pa/235U radio-chronometry. To this end, we present massic activity determinations by two methods for a 233Pa solution, which was prepared at Lawrence Livermore National Laboratory (LLNL) and is being characterized at multiple labs as part of a 231Pa reference material production project. One activity determination method was 4πβ-γ anti-coincidence counting in a multi-dimensional extrapolation model, with Monte Carlo corrections. An independent massic activity determination was completed by γ-ray spectrometry using 5 HPGe detectors using 5 γ-ray lines. The anti-coincidence and γ-ray spectrometry results agree and have combined standard uncertainties of about 0.33 % and 1.0 % respectively. In addition, the two methods were combined to derive γ-ray emission probabilities from 233Pa decay.

An analytical figure of merit term to assess the practical advantages of anticoincidence gamma-ray spectrometry in INAA and its application to the determination of low levels of magnesium in biological reference materials

One of the advantages of anticoincidence counting is the substantial decrease of background activity leading to improved detection limits. A disadvantage is the reduction of a gamma-ray peak area. We defined an analytical figure of merit (AFOM) term for assessing the practical advantages of anticoincidence counting in instrumental neutron activation analysis (INAA). This term takes into account parameters such as peak resolution, peak area, background, dead time, counting time, and counting statistics and represents changes in the sample matrix composition. The effectiveness of the AFOM term was evaluated by analyzing 16 NIST and IAEA biological reference materials for Mg by INAA.

Standardization of 59Fe by efficiency extrapolation 4πβ-γ anticoincidence method

A solution of 59Fe was standardized in the frame of a Bureau International des Poids et Mesures (BIPM) international key-comparison piloted by Asian Pacific Metrology Program (APMP) regional metrology organization. The method used was the live-timed 4πβ-γ anticoincidence counting with extended dead-time with efficiency extrapolation method. The confirmation of these results was performed by conventional 4πβ-γ coincidence counting with efficiency extrapolation and CIEMAT/NIST liquid scintillation counting methods. The value of the evaluated anticoincidence measurement was used to calibrate the LNMRI second standard ionization chambers for providing 59Fe solutions to nuclear medicine canters in the procedures of anaemia diagnosis. Besides this value was adopted as the comparison value of LNMRI and sent to APMP organization. The half-life of 59Fe was determined following the decay of one ampoule sample with 59Fe solution in an ionization chamber (Centronic model IG12).

Standardization of 64Cu activity

The complex decay scheme that makes 64Cu promising as both an imaging and therapeutic agent in medicine also makes the absolute measurement of its activity challenging. The National Institute of Standards and Technology (NIST) has completed a primary activity standardization of a 64CuCl2 solution using the 4πβ(LS)-γ(NaI) live-timed anticoincidence (LTAC) counting method with a combined standard uncertainty of 0.51 %. Two liquid scintillation (LS) counting methods were employed for confirmatory measurements. Secondary measurements were made by high-purity germanium detectors, pressurized ionization chambers (IC), and a well-type NaI(Tl) counter. Agreement between the LTAC-based standard and standards from other laboratories was established via IC calibration factors. Poor agreement between methods and with theoretical IC responses may indicate a need for improved β+/- branching probabilities and a better treatment of β+/- spectra.