Standardization of 64Cu activity

Abstract

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.

Determination of photon emission probability for the main gamma ray and half-life measurements of 64Cu

“…The dilution schemes and methods used to prepare the sources are described in detail by Bergeron et al (2017). Table 2 provides a brief description of the sources used for the measurements described in this work.…”

“…The determination of the emission probabilities was performed using the primary 64 Cu source activity from the LTAC method (Bergeron et al, 2017) and well-characterized HPGe detectors. The masses of the solutions of the ampoules were 4.9893 g and 5.0466 g, with respective source activities of (1.512 ± 0.008) MBq and (1.369 ± 0.007) MBq at a reference time of 12:00 EST 4 March 2016, see Table 2.…”

“…Half-life measurements were performed using the dose vial source, V1, prepared during the November 2015 experiment (Bergeron et al 2017), in the Vinten 671 ionization chamber (Woods et al 1983) with a Keithley 6517A electrometer (collectively referred to as the “VIC”) with the standard dipper. Calibration factors for the VIC ( K VIC ) were determined and reported separately (Bergeron et al, 2017).…”

“…Calibration factors for the VIC ( K VIC ) were determined and reported separately (Bergeron et al, 2017). The measured current over the course of the half-life determination ranged from approximately 50 pA to 1 pA; this range includes a range change for the Keithley 6517A electrometer, but data acquired with a 18 F source over the same current range indicate that the system non-linearity is less than 6 × 10 −3 percent per pA (resulting in a 1.1 × 10 −7 % uncertainty on the half-life).…”

“…The National Institute of Standards and Technology (NIST) recently performed a new standardization for 64 Cu (Bergeron et al, 2017). In order to contribute to the current set of decay data measurements, the photon emission probabilities for the main gamma-rays and the half-life were determined as part of that work.…”