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.

Comparison of calibration coefficients for a vinten ionization chamber simulated using four Monte Carlo methods.

The Vinten 671 ionization chamber (VIC) was modelled using Monte Carlo (MC) programs EGSnrc, Penelope, and TOPAS. Several national measurement institutes have VICs with well-characterized response relationships and have measured calibration coefficients for many radionuclides. Twelve radionuclides with various decay emissions were assessed as well as 14 monoenergetic photon sources and 10 monoenergetic electron sources.

Gravimetric deposition of microliter drops with radiometric confirmation.

A manual microliter gravimetric dispensing technique is demonstrated using a micropipettor modified for use with removeable microcapillaries. Liquid scintillation sources were prepared from a well-characterized Am reference solution, providing a radiometric check of dispensed masses. Further experiments confirmed controlled dispensing of drops onto gold foils with losses ≤0.

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 %.

Realization and dissemination of activity standards for medically important alpha-emitting radionuclides.

Interest in targeted cancer therapy with alpha-emitting radionuclides is growing. To evaluate emerging radiotherapeutic agents requires precise activity measurements for consistent dose-response relationships and patient-specific dosimetry. National metrology institutes around the world have reported on the development and comparison of activity standards for medically important alpha emitters.

Toward a New Primary Standardization of Radionuclide Massic Activity Using Microcalorimetry and Quantitative Milligram-Scale Samples.

We present a new paradigm for the primary standardization of radionuclide activity per mass of solution (Bq/g). Two key enabling capabilities are 4π decay-energy spectrometry using chip-scale sub-Kelvin microcalorimeters and direct realization of mass by gravimetric inkjet dispensing using an electrostatic force balance. In contrast to traditional traceability, which typically relies on chemical separation of single-radionuclide samples, 4π integral counting, and additional spectrometry methods to verify purity, the system described here has both 4π counting efficiency and spectroscopic resolution sufficient to identify multiple radionuclides in the same sample at once.

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.

Natural Uranium Radioactivity Solution Standard: SRM 4321d.

A new natural uranium solution standard has been produced and will be disseminated by the National Institute of Standards and Technology (NIST) as Standard Reference Material 4321d. The standard is certified for the massic activities of U, U, and U in solution, and it is based on isotopic mass data for the metallic Certified Reference Material (CRM) 112-A (originally issued as SRM 960) that was obtained from THE U.S.

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).

Monte Carlo modelling of live-timed anticoincidence (LTAC) counting for Cu-64.

The radionuclide copper-64 is a promising candidate for nuclear medicine, but its complex decay creates challenges in the primary standardization of its activity. Monte Carlo simulations of live-timed anticoincidence (LTAC) counting of Cu were used to calculate corrections to extrapolation intercepts, resulting in improved activity determinations. A small correction (-0.

Phase stability and lithium loading capacity in a liquid scintillation cocktail.

Liquid scintillation cocktails loaded with neutron capture agents such as Li are used in both neutron and neutrino detectors. For detectors designed to operate over extended timespans, long-term stability can be a concern. We demonstrate the identification of thermodynamically unstable emulsions as distinct from stable microemulsions, driving phase separation with centrifugation.

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.

Micellar phase boundaries under the influence of ethyl alcohol.

The Compton spectrum quenching technique is used to monitor the effect of ethyl alcohol (EtOH) additions on phase boundaries in two systems. In toluenic solutions of the nonionic surfactant, Triton X-100, EtOH shifts the boundary separating the first clear phase from the first turbid phase to higher water:surfactant ratios. In a commonly used scintillant, Ultima Gold AB, the critical micelle concentration is not shifted.

Comparison of (14)C liquid scintillation counting at NIST and NRC Canada.

An informal bilateral comparison of (14)C liquid scintillation (LS) counting at the National Research Council of Canada (NRC) and the National Institute of Standards and Technology (NIST) has been completed. Two solutions, one containing (14)C-labeled sodium benzoate and one containing (14)C-labeled n-hexadecane, were measured at both laboratories. Despite observed LS cocktail instabilities, the two laboratories achieved accord in their standardizations of both solutions.

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.

Two determinations of the (223)Ra half-life.

Ra-223 is an alpha-emitter that is being used as a bone-seeking radiotherapeutic agent. The relatively large uncertainty on its evaluated half-life (0.26%, Bé et al.

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.

Identification of phase boundaries in surfactant solutions via Compton spectrum quenching.

The critical micelle concentration and the phase boundary between isolated surfactant molecules and aggregates are probed via fluorescence spectroscopy and a Compton spectrum quenching technique for aqueous and toluenic solutions of Triton X-100 (TX-100). The internal fluorophore of TX-100 provides a convenient probe for the fluorescence measurements, and the appearance of redder bands in the fluorescence spectra and their relationship with aggregation (clustering of TX-100) phenomena is addressed. The Compton spectrum quenching approach makes use of quench indicating parameters (QIPs) commonly measured in liquid scintillation counting experiments.

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.