Activity measurements and calibrations for Ac in radioactive equilibrium with its progeny.

The massic activity of Ac in 0.1 mol/L HCl was measured by multiple primary methods over four consistent measurement campaigns. Results from the triple-to-double coincidence ratio (TDCR) method of liquid scintillation (LS) counting were in accord with other LS-based primary methods.

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 Eu ground state.

The international reference system for beta-particle emitting radionuclides: Validation through the pilot study CCRI(II)-P1.Co-60.

The Bureau International des Poids et Mesures (BIPM) is developing a new transfer instrument to extend its centralized services for assessing the international equivalence of radioactive standards to new radionuclides. A liquid scintillation counter using the triple/double coincidence ratio method is being studied and tested in the CCRI(II)-P1.Co-60 pilot study.

Primary standardization of Pb activity by liquid scintillation counting.

An activity standard for Pb 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 Pb and Tl) led to combined standard uncertainties ≤ 0.20 %.

Ra-224 activity, half-life, and 241 keV gamma ray absolute emission intensity: A NIST-NPL bilateral comparison.

The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of RaCl were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry.

Radionuclide calibrator responses for Ra in solution and adsorbed on calcium carbonate microparticles.

A suspension of Ra adsorbed onto CaCO microparticles shows promise for α-therapy of intracavitary micro-metastatic diseases. To facilitate accurate activity administrations, geometry-specific calibration factors for commercially available reentrant ionization chambers (ICs) have been developed for RaCl solutions and Ra adsorbed onto CaCO microparticles in suspension in ampoules, vials, and syringes. Ampoules and vials give IC responses consistent with each other to <1%.

Primary standardization of Ra activity by liquid scintillation counting.

A standard for activity of Ra 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.

An update on 'dose calibrator' settings for nuclides used in nuclear medicine.

Background: Most clinical measurements of radioactivity, whether for therapeutic or imaging nuclides, rely on commercial re-entrant ionization chambers ('dose calibrators'). The National Institute of Standards and Technology (NIST) maintains a battery of representative calibrators and works to link calibration settings ('dial settings') to primary radioactivity standards. Here, we provide a summary of NIST-determined dial settings for 22 radionuclides.

A reference material for evaluation of Cs radiochronometric measurements.

A new nuclear forensic reference material has been characterized as a standard for radiochronometric determination of the model purification date for Cs sources. The purification date of a radioactive source is a potentially diagnostic nuclear forensic signature for determining the provenance of a radioactive material. Reference values have been measured for the attributes needed to use the Cs/Ba chronometer: the molality (reported here as nmol g) of Cs and of the radiogenic portion of Ba in the material (hereafter referred to as Ba*).

Two determinations of the Ge-68 half-life.

In nuclear medicine, Ge is used to generate Ga for imaging by positron emission tomography (PET) and sealed sources containing Ge/Ga in equilibrium have been adopted as long-lived calibration surrogates for the more common PET nuclide, F. We prepared several Ge sources for measurement on a NaI(Tl) well counter and a pressurized ionization chamber, following their decay for 110 weeks (≈ 2.8 half-lives).

Source self-attenuation in ionization chamber measurements of (57)Co solutions.

Source self-attenuation for solutions of (57)Co of varying density and carrier concentration was measured in nine re-entrant ionization chambers maintained at NIST. The magnitude of the attenuation must be investigated to determine whether a correction is necessary in the determination of the activity of a source that differs in composition from the source used to calibrate the ionization chamber. At our institute, corrections are currently made in the measurement of (144)Ce, (109)Cd, (67)Ga, (195)Au, (166)Ho, (177)Lu, and (153)Sm.

Impact of Recent Change in the National Institute of Standards and Technology Standard for 18F on the Relative Response of 68Ge-Based Mock Syringe Dose Calibrator Standards.

Unlabelled: As a result of a recent change in the National Institute of Standards and Technology (NIST) activity standard for (18)F, we have determined new relative response ratios for a (68)Ge solid epoxy mock syringe source used in activity calibrators as a long-lived substitute for (18)F. New standardized solutions of each radionuclide were used to determine the response ratios while maintaining traceability to national standards. This work updates our previously published data from 2010.

Secondary standards for ²²³Ra revised.

Dose calibrator dial settings reported by NIST in 2010 (ARI, v. 68, p. 1367) are now known to give erroneously low (by 10%) activity readings.

Dose calibrator manufacturer-dependent bias in assays of ¹²³I.

Calibration factors for commercial ionization chambers (i.e. dose calibrators) were determined for a solution of (123)I; the activity was based on the 1976 NBS standard.

A Review of NIST Primary Activity Standards for (18)F: 1982 to 2013.

The new NIST activity standardization for (18)F, described in 2014 in Applied Radiation and Isotopes (v. 85, p. 77), differs from results obtained between 1998 and 2008 by 4 %.

The NIST radioactivity measurement assurance program for the radiopharmaceutical industry.

The National Institute of Standards and Technology (NIST) maintains a program for the establishment and dissemination of activity measurement standards in nuclear medicine. These standards are disseminated through Standard Reference Materials (SRMs), Calibration Services, radionuclide calibrator settings, and the NIST Radioactivity Measurement Assurance Program (NRMAP, formerly the NEI/NIST MAP). The MAP for the radiopharmaceutical industry is described here.

The effect of impurities on calculated activity in the triple-to-double coincidence ratio liquid scintillation method.

In the triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting, unaccounted or improperly accounted impurities can result in lower-than-expected or higher-than-expected recovered activities, depending on the counting efficiency of the nuclide of interest, the counting efficiency of the radionuclidic impurity, and the amount of impurity present. We describe these general dependences using a simple model. The trends predicted by the model are tested experimentally using a series of mixed (241)Am/(3)H and (63)Ni/(3)H sources.

Development of a traceable calibration methodology for solid (68)Ge/(68)Ga sources used as a calibration surrogate for (18)F in radionuclide activity calibrators.

Unlabelled: We have developed a methodology for calibrating (68)Ge radioactivity content in a commercially available calibration source for activity calibrators in a way that is traceable to the national standard. Additionally, the source was cross-calibrated for equivalent (18)F content by direct comparison with the national standard for (18)F in the same geometry.

Methods: Sources containing standardized (68)GeCl(4) or (18)F-FDG solutions were prepared at the National Institute of Standards and Technology (NIST) with mock syringe blanks used in the construction of a commercially available epoxy-based (68)Ge calibration source.

Development of secondary standards for 223Ra.

Ra-223 is a bone-seeking alpha emitter currently being evaluated as a radiopharmaceutical. Concurrent with the primary standardization, NIST established that calibration factors currently used for radionuclide calibrators in the clinical setting give readings 5.7-8.

A performance evaluation of 90Y dose-calibrator measurements in nuclear pharmacies and clinics in the United States.

A blind performance test was conducted to evaluate dose-calibrator measurements at nuclear pharmacies in the United States (US). Two test-sample geometries were chosen to represent those used for measurements of 90Y-ibritumomab tiuxetan (ZEVALIN). The radioactivity concentration of test-samples was verified by the US National Institute of Standards and Technology.

Assessing the 210At impurity in the production of 211At for radiotherapy by 210Po analysis via isotope dilution alpha spectrometry.

A method for assessing the impurity 210At in cyclotron-produced 211At via isotope dilution alpha spectrometry is presented. The activity of 210At is quantified by measuring the activity of daughter nuclide 210Po. Counting sources are prepared by spontaneous deposition of Po on a silver disc.

The measurement of activity contained in a 32P stainless-steel stent by destructive assay.

Destructive assays of stainless-steel stents containing 32P were performed. Prior to assay, 24 stents were intercompared on a NaI(Tl) well-type crystal. A subset of stents were then digested in a suitable carrier solution by the addition of concentrated hydrofluoric acid.

The standardization of 188W/188Re by 4pi beta 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 4pi beta liquid scintillation counting with efficiency tracing using the CIEMAT NIST method. Confirmatory measurements were carried out with gamma-ray spectrometry using high purity germanium detectors and a 4pi gamma NaI(Tl) system. A calibration factor of 1.