Actinium-225 photonuclear production in nuclear reactors using a mixed radium-226 and gadolinium-157 target.

BACKGROUND: Actinium-225 is one of the most promising radionuclides for targeted alpha therapy. Its limited availability significantly restricts clinical trials and potential applications of 225Ac-based radiopharmaceuticals. METHODS: In this work, we examine the possibility of 225Ac production from the thermal neutron flux of a nuclear reactor. For this purpose, a target consisting of 1.4 mg of 226Ra(NO3)2 (T1/2 = 1600 years) and 115.5 mg of 90 % enriched, stable 157Gd2O3 was irradiated for 48 h in the Breazeale Nuclear Reactor with an average neutron flux of 1.7·1013 cm-2·s-1. Gadolinium-157 has one of the highest thermal neutron capture cross sections of 0.25 Mb, and its neutron capture results in emission of high-energy, prompt γ-photons. Emitted γ-photons interact with 226Ra to produce 225Ra according to the 226Ra(γ, n)225Ra reaction. Gadolinium debulking and separation of undesirable, co-produced 227Ac from 225Ra was achieved in one step by using 60 g of branched DGA resin. After 225Ac ingrowth from 225Ra (T1/2 = 14.8 d), 225Ac was extracted from the 226Ra and 225Ra fraction using 5 g of bDGA resin and then eluted using 5 mM HNO3. RESULTS: Measured activity of 225Ac showed that 6(1) kBq or 0.16(3) µCi (1σ) of 225Ra was produced at the end of bombardment from 0.9 mg of 226Ra. CONCLUSION: The developed 225Ac separation is a waste-free process which can be used to obtain pure 225Ac in a nuclear reactor.

X-ray determination of the thickness of thin metal foils.

The interpretation of neutron cross section experiments depends upon an in-depth knowledge of the physical characteristics of the target sample. An x-ray image of an encapsulated metallic Eu sample used in a neutron cross section measurement showed a very non-uniform thickness as well as holes in the sample. In light of this problem it was found necessary to determine the thickness distribution in four thin metallic Eu samples without disturbing the encapsulation (and exposing the Eu to air). All four Eu samples were subsequently x-rayed along with a Sm step wedge. The gray levels in the Eu images were then compared to the Sm gray levels and, taking into account differences in the x-ray absorption and density of Eu and Sm, the sample thickness distributions were obtained for each Eu sample. This work demonstrates that a step wedge can be used to calibrate x-ray images to a thickness scale, and allows the thickness variation of the samples to be represented in a simple probability table for incorporation into the analysis of neutron experiments.

Nuclear reactor pulse calibration using a CdZnTe electro-optic radiation detector.

A CdZnTe electro-optic radiation detector was used to calibrate nuclear reactor pulses. The standard configuration of the Pockels cell has collimated light passing through an optically transparent CdZnTe crystal located between crossed polarizers. The transmitted light was focused onto an IR sensitive photodiode. Calibrations of reactor pulses were performed using the CdZnTe Pockels cell by measuring the change in the photodiode current, repeated 10 times for each set of reactor pulses, set between 1.00 and 2.50 dollars in 0.50 increments of reactivity.