Photon–photon coincidences for activity determination: I-125 and other radionuclides

A bilateral comparison between LNHB and PTB to determine the activity concentration of the same 125I solution

A bilateral comparison to determine the activity concentration of the same 125I solution was organized. As electron-capture radionuclide with a rather high atomic number, 125I must be regarded as difficult to measure. The situation is partly exacerbated by the fact that some established standardization methods, like photon-photon coincidence counting, can no longer be applied due to the unavailability of appropriate equipment and expertise. One aim of this work is to compare modern liquid scintillation counting methods for the standardization of 125I. Both participating metrology institutes have used their custom-built triple-to-double-coincidence ratio (TDCR) counters and the determined activity concentrations are in excellent agreement even though the ways to analyze the data and to compute counting efficiencies were widely independent. The results also agree with the outcome of 4π-γ counting that was carried out at LNHB. In both laboratories, the measurements were complemented by measurements with several secondary standardization methods which even allow to establish a link to the CCRI(II)-K2.I-125(2) comparison started in 2004. A good agreement between the TDCR results and the key comparison reference value of the 2004/2005 comparison was obtained.

64Cu production by 14 MeV neutron beam

64Cu is an emerging radionuclide of great interest in personalized nuclear medicine. It is produced by a cyclotron via the reaction 64Ni(p,n)64Cu. This production method increased during the last decades, because small biomedical cyclotrons can be easily installed close to the nuclear medicine department of a hospital. As a matter of fact, 64Ni is a very expensive target material. For this reason, an alternative 64Cu production method was investigated at ENEA by using the quasi-monochromatic 14 MeV fusion neutron beam made available at the Frascati Neutron Generator (FNG) located at the ENEA – Frascati Research Center. In particular, two nuclear reactions were studied: 65Cu(n,2n)64Cu and 64Zn(n,p)64Cu. The radiochemical analysis of the activated samples was performed at the ENEA-NMLNWM laboratory located in ENEA-Casaccia Research Center. The activity measurements were carried out at the ENEA-INMRI, located in the ENEA-Casaccia Research Center, with high metrological level conditions and by assuring their traceability to the 64Cu primary activity standard here developed and maintained. A prediction of the 64Cu production by means of the high-brilliance 14 MeV neutron source named Sorgentina is also discussed.

Standardization of 109Cd by two methods

¹⁰⁹Cd is quite a useful nuclide for the calibration of X-ray spectroscopy, gamma-ray spectroscopy or as an excitation source in X-ray fluorescence. In this work, 4π(PC)e-X coincidence counting and 4π(LS)ce counting were used to determine the activity of the ¹⁰⁹Cd solution. The two methods showed good agreement in their counting results. On the other hand, the mean value came from the results of the two methods was used to calibrate the well type ionization chambers to maintain the radioactivity measurement standard of ¹⁰⁹Cd at INER.

Investigation of γ-γ coincidence counting using the National Nuclear Array (NANA) as a primary standard

The National Physical Laboratory has recently been in the process of commissioning a multi-detector γ ray array - the National Nuclear Array (NANA). In this study we have sought to exploit the NANA and the excellent timing characteristics of its intrinsic LaBr₃(Ce) scintillation detectors for use as a primary standardisation system. For this initial investigation, the absolute standardisation of ⁶⁰Co has been performed by the γ-γ coincidence technique using NANA and the result compared to the established 4π(LS)-γ Digital Coincidence Counting (DCC) system. The effect of the angular correlation of the stretched E2 transitions emitted from the 4⁺→2⁺→0 states of ⁶⁰Ni on the activity determined by NANA was observed between the pairs of detectors. Corrections for these angular correlations were derived through Monte Carlo simulations. An activity per unit mass by NANA of 330.8 (10) kBqg^-1 for the ⁶⁰Co solution was determined. There was no significant statistical difference between the results of NANA and the 4π(LS)-γ DCC, with a relative difference of 0.04% observed. This study shows that NANA can be used as a primary standard.

Standardization of 125I and 109Cd by the photon-photon coincidence method in PTKMR-BATAN

A photon-photon coincidence system was constructed for the standardization of (125)I and (109)Cd in PTKMR-BATAN, Indonesia. Two NaI(Tl) detectors of 76 mm diameter × 6mm thickness with 0.5mm aluminum window were used, which were positioned approximately symmetrically to the source holder. The electronic chain was almost the same as for a 4πβ-γ system. The CANBERRA Multiport II multi channel analyzer was used for energy calibration and a Philips type PM3092 oscilloscope for visualization of the pulses. A polyethylene plastic was used as the source substrate for the (125)I and (109)Cd samples. The activity of a (125)I solution was measured by the photon-photon coincidence and the efficiency extrapolation method (Schrader and Walz, 1987), whereas the activity of a (109)Cd solution was determined by a tracer method using (125)I (Schrader, 2006). The result of the (125)I activity showed good agreement with the result of measurements using a calibrated ionization chamber, and the result of (109)Cd also showed good agreement with the measurements result using a LEGe detector.