3H-standard Efficiency Tracing Research Articles

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.

Development of a primary standard for calibration of 64Cu activity measurement systems

A 64Cu national primary standard, was developed by the National Institute for Ionising Radiation Metrology (INMRI) of the ENEA (ENEA-INMRI) using the CIEMAT/NIST method of 4 πβ liquid scintillation spectrometry with 3H-standard efficiency tracing. Relatively short 64Cu half-life is required for the work to be performed at the production site. It was produced at the Scanditronix MC40 Cyclotron of the Joint Research Centre (JRC) of the European Commission (Ispra, Italy) through the 64Zn(d,2p) 64Cu reaction. Significant efforts were made to identify and quantify the impurities of 61Cu and 65Zn in the mother solution, which were activated through the 64Zn(d, αn) 61Cu and 64Zn(d,p) 65Zn reactions, respectively. To this purpose, a new procedure for the determination of pure β-emitter impurities by the CIEMAT/NIST method has been applied. A transfer standard portable well-type ionisation chamber was also calibrated with minimum uncertainty.

63Ni, its half-life and standardization: Revisited

Recent liquid scintillation (LS) measurements at the National Institute of Standards and Technology (NIST) and at the Laboratoire National Henri Becquerel (LNHB) on a standardized 63Ni solution that has been tracked for nearly 40 years have resulted in several important findings: (i) a 63Ni half-life value of 101.2±1.5 a has been determined with the present decay data. This value is consistent with a previous specific activity determination and with an earlier value from decay measurements; and it appears to be more satisfactory than a recent data evaluator's recommended value of 98.7 a. (ii) All solution standards of 63Ni as disseminated by NIST for the past 38 + years are internally consistent with past and recent standardizations. (iii) Primary LS standardizations of 63Ni by the triple-to-double coincidence ratio (TDCR) method and by CIEMAT/NIST 3H-standard efficiency tracing (CNET) appear to be comparable, although the latter methodology is believed to be inherently inferior. (iv) There is excellent measurement agreement between NIST and LNHB for 63Ni primary standardizations.

A liquid-scintillation-based primary standardization of 210Pb

A new radioactivity solution standard of 210Pb has been developed and will be disseminated by the National Institute of Standards and Technology (NIST) as standard reference material (SRM) 4337. This new 210Pb solution standard is contained in a 5 mL flame-sealed borosilicate glass ampoule, consists of (5.133±0.002) g of a nominal 1 mol L −1 nitric acid solution, has a density of (1.028±0.002) g mL −1 at 20 °C, has carrier ion concentrations of about 11 μg Pb 2+ and 21 μg Bi 3+ per gram of solution, and is certified to contain a massic activity (9.037±0.22) kBq g −1 as of the reference time 1200 EST, 15 June 2006. All of the uncertainties cited above correspond to standard uncertainties multiplied by a coverage factor k=2. The standardization for the 210Pb content of the solution was based on 4 παβ liquid scintillation (LS) measurements using CIEMAT/NIST 3H-standard efficiency tracing (CNET). Confirmatory determinations were also performed by high-resolution HPGe γ-ray spectrometry, by 2 πα spectrometry with a Si surface barrier detector of separated 210Po, and by 4 πβ(LS)– γ(NaI) anticoincidence counting.

Development of a Primary Standard for Calibration of [18F]FDG Activity Measurement Systems

The 18F national primary standard was developed by the INMRI-ENEA using the 4πβ Liquid Scintillation Spectrometry Method with 3H-Standard Efficiency Tracing. Measurements were performed at JRCIspra under a scientific collaboration between the Institute for Health and Consumer Production, the Amersham Health and the National Institute for Occupational Safety and Prevention (ISPESL). The goal of the work was to calibrate, with minimum uncertainty, the INMRI-ENEA transfer standard portable well-type ionisation chamber as well as other JRC-Ispra and Amersham Health reference Ionising Chambers used for FDG activity measurement.

The standardization of 188W/ 188Re by 4 πβ liquid scintillation spectrometry with the CIEMAT/NIST 3H-standard efficiency tracing method

The massic activity of a solution containing 188W in equilibrium with its daughter, 188Re, has been standardized by the National Institute of Standards and Technology using 4 πβ liquid scintillation counting with efficiency tracing using the CIEMAT/NIST method. Confirmatory measurements were carried out with γ-ray spectrometry using high purity germanium detectors and a 4 πγ NaI(Tl) system. A calibration factor of 1.68 MBq pA −1 ±0.03 MBq pA −1 (expanded, k=2, uncertainty) for the 188W in the solution was determined, along with correction factors for activity determinations using Capintec dose calibrators. A half-life value of 69.78 d±0.05 d (standard uncertainty) was determined by measurement in the NIST 4 πγ ionization chamber and is consistent with currently recommended values.

The standardization of 177Lu by 4 πβ liquid scintillation spectrometry with 3H-standard efficiency tracing

Solutions containing the potential radiotherapy radionuclide 177Lu have been standardized at the National Institute of Standards and Technology (NIST) by 4 πβ liquid scintillation (LS) counting with 3H-standard efficiency tracing using the CIEMAT/NIST method. Confirmatory measurements were made with 4 π NaI(Tl) γ-ray spectrometry. Activity determinations were made on 4 solutions over the course of 10 months with an expanded ( k=2) uncertainty on the activity of 0.8%. Half-life measurements were carried out using the NIST “4 π” γ ionization chamber (IC) and LS counting and gave a new value of 6.65±0.01 d, which is shorter than the current ENSDF-recommended value by 1.3%. Impurity analyses were performed by high-purity germanium (HPGe) γ-ray spectrometry and indicated only the presence of 177mLu at a level of 0.02% that of the 177Lu as of the respective reference times for the four solutions. Calibration factors for the NIST IC and Vinten 671 ionization chambers were developed, as were dial settings for the NIST-maintained Capintec CRC-12.

Calibration of 32P “hot-wall” angioplasty-balloon-catheter sources by liquid-scintillation-spectrometry-based destructive radionuclidic assays

A very quantitative, destructive-analysis procedure was devised for assaying the 32P activity content of “hot-wall” angioplasty-balloon catheters. These sources, developed and under investigation by Radiance Medical Systems, Inc. (Irvine, CA), are intended for use in the prophylactic inhibition of restenosis following balloon angioplasty in heart-disease patients. The assay was based on performing a physicochemical digestion of the balloon catheter to extract the 32P activity followed by liquid-scintillation (LS) spectrometry of the resultant solutions. Measurement-based corrections were applied for the residual activity remaining in the digested balloon debris and in all of the digestion apparatus. The LS spectrometry, with 3H-standard efficiency tracing, utilized a previously-developed method for resolving the always-present 33P impurity. Initial ionization current measurements on the sources prior to the destructive assays led to the establishment of calibration factors that can be used for subsequent non-destructive radionuclidic measurements on similar balloon-catheter sources.

Radioassays and experimental evaluation of dose calibrator settings for 18F

The positron emitter 18F continues to be one of the most important imaging radionuclides in diagnostic nuclear medicine. Assays of radiopharmaceuticals containing this nuclide are often performed in the clinic using commercial reentrant ionization chambers, or “dose calibrators”. Meaningful quantitative clinical studies require accurate knowledge of the injected activity which requires proper calibration of these instruments. Radioassays were performed at the National Institute of Standards and Technology (NIST) on a solution of 18F produced at the National Institutes of Health (NIH) using 4πβ liquid scintillation (fS) counting with 3H-standard efficiency tracing. Cocktails containing water fractions of approximately 0.9 and 9% (both as saline) were used. The massic activity values were measured to be 2.52±0.06 and 2.50±0.03 MBq g −1, respectively, for the 0.9 and 9% water cocktails as of the reference time. The uncertainties on the activity measurements are expanded ( k=2) uncertainties. The largest uncertainty component was found to be the repeatability on a single LS source, with the cocktails containing 0.9% water fraction exhibiting a larger variability by nearly a factor of two. Reproducibility between LS cocktails with the same water fraction was also found to be a large uncertainty component, but with a value less than half that due to measurement repeatability. Radionuclidic impurities consisted of 48V and 46Sc, at levels of 0.11±0.08% (expanded uncertainties) and approximately 2×10 −3% (upper limit) relative to the activity of the 18F, as of the reference time. Dose calibrator dial settings for measuring solutions of 18F were experimentally determined for Capintec CRC-12 and CRC-35R dose calibrators in three measurement geometries: a 5-ml standard NIST ampoule (two ampoules measured), a 12-ml plastic syringe containing 9 ml of solution and a 10-ml Mallinckrodt molded dose vial filled with 5 ml of solution. The experimental dial settings (and the corresponding expanded uncertainties) for these geometries were found to be 477±7, 474±6, 482±6 and 463±7 for the two ampoules, the syringe and the dose vial, respectively, in the CRC-12. The dial settings determined for the CRC-35R were 472±7, 470±7, 464±6 and 456±6 for the two ampoules, the syringe, and the dose vial, respectively. The uncertainties in the dial settings are expanded uncertainties. Comparisons between the empirically determined dial settings and the manufacturer's recommended setting of “439” indicate that use of the manufacturer's setting overestimates the activity by between 3 and 6%, depending upon the geometry used.

On the radioanalytical methods used to assay stainless-steel-encapsulated, ceramic-based 90Sr– 90Y intravascular brachytherapy sources

Very quantitative radiochemical procedures for the destructive assay of stainless-steel-encapsulated, ceramic-based 90Sr– 90Y intravascular brachytherapy sources (termed ‘seeds’) have been devised. These seeds, developed and provided by Bebig Isotopentechnic und Umweltdiagnostik (Berlin, Germany) in collaboration with the Novoste Corporation (Norcross, GA), are intended for use in the prophylactic treatment of restenosis following balloon angioplasty in heart-disease patients. The procedures were applied to the radionuclidic assay of both the bare-ceramic source materials (of proprietary composition) contained within the seeds and to the stainless-steel (SS) sealed sources. The approach consisted of extracting some arbitrary fraction of the 90Sr activity from the ceramic-like material and assaying the resulting solution by 4 πβ liquid scintillation (LS) spectrometry with 3H-standard efficiency tracing. The fraction of extracted activity was determined by ionization current measurements before and after the chemical extraction. All of the ionization current and LS-based activity determinations were made under the experimentally-verified conditional that 90Y was in radioactive equilibrium with 90Sr. For the assay of the SS-jacketed seeds, the encapsulation was initially dissolved and the resultant solution was also assayed by LS spectrometry to determine the amount of activity removed by the SS dissolution step. The developed protocol included provisions for accounting for all possible losses of 90Sr activity in the chemical and source-handling procedures, for the unrecovered activity in the extracted source material and for any residual activity in the solution-transfer and source-handling tools. These destructive assays were required for relating radiochromic-film measurements of the absorbed dose spatial distributions for the seeds to theoretic dose modelling and for establishing calibration factors for subsequent non-destructive radionuclidic measurements on the seeds.

The standardization of 62Cu and experimental determinations of dose calibrator settings for generator-produced 62CuPTSM

The Positron Emission Tomography agent 62Cu Pyruvaldehyde Bis( N 4-methyl)thiosemicarbazone (PTSM) has been standardized by the National Institute of Standards and Technology (NIST) using 4 πβ liquid scintillation counting with 3H-standard efficiency tracing. Using a measurement model developed at NIST for the determination of experimental dose calibrator dial settings for short-lived radionuclides, the correct dial settings for 62CuPTSM in a clinically useful geometry (a 35 ml plastic syringe containing 33 ml of solution) as well as the standard NIST 5 ml glass ampoule have been elucidated. This measurement model is fully described, as is the treatment of associated uncertainties. The correct instrument settings for the NIST Capintec CRC-12 re-entrant ionization chamber (‘dose calibrator’) were found to be ‘499±6’ and ‘489±8’, respectively, for the syringe and ampoule geometries. The stated uncertainties are expanded ( k=2) uncertainties. The expanded uncertainties in the measured activity arising from these new dial settings are ±0.8% and ±1.4%, respectively, for the syringe and ampoule. The measured activities using these settings are lower than those obtained from the manufacture’s recommended setting of ‘448’ by 9.7% for the syringe and 7.7% for the ampoule, and underscore the need for experimental verification of the dose calibrator settings for each radionuclide and each geometry used in the clinic.

Standardisation of 90Sr, 63Ni and 55Fe by the 4πβ liquid scintillation spectrometry method with 3H-standard efficiency tracing

The 4πβ efficiency tracing liquid scintillation spectrometry method was applied with success, at ENEA, to the activity measurement of pure β-emitters ( 90Sr and 63Ni) and electron-capturing nuclides ( 55Fe), using 3H as tracer nuclide. The agreement of these measurements in comparison to other national metrology institutes was checked by means of two comparisons, carried out in 1996–1997. Furthermore a study of the stability of the prepared sources was performed and the dependence of the measured activity concentration on the quenching level was analysed. The radionuclides were standardised to a combined standard uncertainty of 0.14% for 90Sr, 0.55% for 63Ni and 1.18% for 55Fe.

Chemical digestion and radionuclidic assay of TiNi-encapsulated 32P intravascular brachytherapy sources

A very quantitative, destructive assay procedure was devised for accurately measuring the 32P activity content of TiNi-encapsulated intravascular brachytherapy sources and was applied to four different sources (termed `seeds') which were developed and provided by Guidant Intravascular Intervention (formerly NeoCardia). These seeds are intended for use in the prophylactic treatment of restenosis following balloon angioplasty in heart-disease patients. The assays involved the dissolution of the TiNi jacket, extraction of the activity from the internal 32P-containing source material, quantitative solution transfers, and a gravimetrically-based dilution; followed by liquid scintillation (LS) spectrometry of the resulting master solution with 3H-standard efficiency tracing using composition-matched LS cocktails. The LS spectrometry utilized a previously-developed method for resolving the always-present 33P impurity. The protocol included provisions for accounting for all possible losses of 32P in the digestion procedure (based on radiochemical tracing experiments), for any unrecovered activity in the remaining source material, and for any residual activity in the solution-transfer and containing vessels. Sections of the TiNi jackets adjacent to the cut-off active seed portions were also assayed for any contained activity. Such destructive assays were required for relating measurements of the absorbed dose spatial distribution for the seeds to theoretic dose modelling and for establishing calibration factors for subsequent non-destructive radionuclidic measurements on the seeds.

Standardization of 63Ni by 4πβ Liquid Scintillation Spectrometry With 3H-Standard Efficiency Tracing.

The low energy (Eβmax = 66.945 keV ± 0.004 keV) β-emitter 63Ni has become increasingly important in the field of radionuclidic metrology. In addition to having a low β-endpoint energy, the relatively long half-life (101.1 a ± 1.4 a) makes it an appealing standard for such applications. This paper describes the recent preparation and calibration of a new solution Standard Reference Material of 63Ni, SRM 4226C, released by the National Institute of Standards and Technology. The massic activity CA for these standards was determined using 4πβ liquid scintillation (LS) spectrometry with 3H-standard efficiency tracing using the CIEMAT/NIST method, and is certified as 50.53 kBq ·g−1 ± 0.46 Bq · g−1 at the reference time of 1200 EST August 15, 1995. The uncertainty given is the expanded (coverage factor k = 2 and thus a 2 standard deviation estimate) uncertainty based on the evaluation of 28 different uncertainty components. These components were evaluated on the basis of an exhaustive number (976) of LS counting measurements investigating over 15 variables. Through the study of these variables it was found that LS cocktail water mass fraction and ion concentration play important roles in cocktail stability and consistency of counting results. The results of all of these experiments are discussed.

Cocktail mismatch effects in 4πβ liquid scintillation spectrometry: Implications based on the systematics of 3H detection efficiency and quench indicating parameter variations with total cocktail mass (volume) and H 2O fraction

Detection efficiency changes for 3H by 4πβ liquid scintillation (LS) spectrometry cannot be adequately monitored by quench indicating parameters when the quench changes are the result of multiple causal factors (e.g. simultaneously varying cocktail sizes and composition). In consequence, some kinds of cocktail mismatches (between LS counting sources) introduce errors that result from efficiency changes that cannot be fully accounted for by quench monitoring compensations. These cocktail mismatch effects are examined for comparative 3H measurements and for 3H-standard efficiency tracing methods for the assay of other β-emitting radionuclides. Inherent errors can occur in both types of radionuclidic assays, as demonstrated with realistic case examples, unless cocktails are very closely matched. The magnitude of the cocktail mismatch effect (and attendant errors) can range from being virtually negligible (particularly for high-energy β-emitting nuclides and for slight single-variable cocktail composition mismatches) to be being very significant for high-precision metrology and standardizations (particularly with easily quenched, low-energy β emitters and for mismatches due to both varying cocktail constituents and concentrations). The findins presented here support the need to understand fully the quenching systematics of a given LS system (combination of cocktails and spectrometer) and the need for very careful control of cocktail preparations.

Cocktail volume effects in 4πβ Liquid scintillation spectrometry with 3H-standard efficiency tracing for low-energy β-emitting radionuclides

The effect of total liquid scintillation (LS) cocktail volume (or mass) in the 4πβ LS spectrometry of β-emitting radionuclides has been investigated. The magnitude of such possible volume effects on the apparent activity of low-energy β-emitting radionuclides, as determined by the CIEMAT/NIST 3H-standard efficiency tracing method, as well as any systematic trends in the relative detection efficiencies of low-ebergy β-emitters were studied. The radionuclides chosen for the study, 63Ni and 36Cl, were traced against 3H. Detection efficiency losses, as a function of total LS cocktail volume, were found to be energy-dependent. Because of the low E βmax for the decay of 3H and 63Ni, systematic losses in efficiency with increasing cocktail mass, as well as at extremely low (< 5 g) masses were observed. The determination of quench-indicating parameters, even for cocktails of uniform composition, were also found to be volume-dependent. Despite a relatively large (17%) variation in the 3H counting efficiency over the volume range 1–20 mL in 22 mL vials and a corresponding 7% varition in the 63Ni counting efficiency, the CIEMAT/NIST method was able to trace the observed 63Ni activity to about 0.1%. No volume effect on the observed relative efficiency of 36Cl was found. The best condition for repeatability in the determination of the massic activity of a single sample was found to be when the volume is 8–12 mL in a 22 mL vial. The effect of total LS cocktail volume on the efficiency-traced massic activities was found to have no clear, consistent trend and proved difficult to quantify. Nonetheless, two approaches to estimating the magnitude of the effect are presented and indicate that it is extremely small (< 0.1%) and was within the statistical variation of the measurements.

63Ni half-life: a new experimental determination and critical review

The 63Ni half-life has been determined to be 101.06 ± 1.97 a based on three independent measurements, conducted over the past 27 years, of the massic activity of gravimetrically-related 63Ni sources. The 63Ni assays were performed initially (in 1968) by microcalorimetry using an assumed mean β − energy per decay, and subsequently (in 1984 and 1995) by 4πβ liquid scintillation spectrometry with 3H-standard efficiency tracing. The present result is the first and only determination of the 63Ni half-life which is based on actually following the radioactive decay of 63Ni. All previously reported determinations were derived from specific activity evaluations. These earlier determinations have been scutinizingly reviewed as part of this work. Some of these previous values can be revised in lieu of more recent nuclear data and on consideration of the experimental details. Based on a critical evaluation of the extant data set, a 63Ni half-life value of T=101.1 ± 1.4 a is recommended.