[en] An experiment was designed to investigate the possible enhancement of the convective heat-transfer coefficient by utilizing multiple, parallel jets in the cooling of a small heated surface, such as typically induced by an accelerated ion beam on a thin foil or specimen. The hot spot was provided using a small electrically heated plate. It was found that heat-transfer calculations by means of simple empirical methods based on dimensional analysis are not useful in this case and that advanced computational fluid dynamics (CFD) mod-elling is essential to interpret the results. It is shown that enhanced convective cooling can indeed be obtained with a multi-jet configuration as compared to a single-jet configuration but only under very selective conditions. An improperly designed multi-jet configuration can also provide significantly reduced cooling relative to the single-jet case and the estimation of the behavior of any particular jet geometry is eminently non-intuitive. CFD provides acceptable quantitative results and seem to be the only tool available to gain an understanding of these complex flows where simple models and “rules of thumb” cannot be relied upon. – LA-UR-18-29455

[en] ¹³⁴La emits positrons, enabling its use in positron emission tomography (PET) imaging in the form of an in vivo generator with its parent, ¹³⁴Ce. Due to similar ionic radius and coordination geometries, the ¹³⁴Ce/¹³⁴La pair can be used as a surrogate for ²²⁵Ac or ²²⁷Th (non-PET isotopes) in the investigation of novel alpha-emitting radiotherapeutics. This talk will focus on using the unique LANL capability at the Isotope Production Facility (IPF) at Los Alamos Neutron Science Center (LANSCE) to develop a production method for ¹³⁴Ce (t_1/2 = 75.9 h, daughter ¹³⁴La t_1/2 = 6.67 m, 2.7 MeV β+). In addition, the approach to scale-up for bulk ¹³⁴Ce production will be discussed. This process involves separation of microscopic amounts of ¹³⁴Ce from macroscopic quantities (g) of lanthanum target material. Particular attention is focused on the Ce-La separation development that relies on 'in-house' production of a ¹³⁹Ce tracer (t_1/2 = 137.6 d, 165.9 keV γ) via the ¹⁴¹Pr(n,3n)¹³⁹Pr→¹³⁹Ce reaction using the secondary neutron flux near a stack of IPF production targets

[en] ¹⁴⁹Tb represents a powerful alternative to currently used α-emitters: the relatively short half-life (T_1/2 = 4.1 h), low α-energy (3.97 MeV, I_α = 16.7 %), absence of α-emitting daughters and stable coordination via DOTA are favorable features for potential clinical application. In this letter, we wish to highlight the unique characteristics of ¹⁴⁹Tb for PET imaging, based on its positron emission (E_β+mean = 730 keV, I_β+ = 7.1 %) in addition to it’s a therapeutic value. To this end, a preclinical study with a tumor-bearing mouse is presented. The perspective of alpha-PET makes ¹⁴⁹Tb highly appealing for radiotheragnostic applications in future clinical trials.

[en] Highlights: • Degradation of proton beam energy within a target stack was monitored via product nuclide ratios. • Nuclear reactions employed included ^natNi(p,x)⁵⁷Co and ^natNi(p,x)⁵⁷Ni. • Natural nickel foils were used to determine proton beam energies ranging from 15 to 30 MeV. • Proton energies determined serve as a basis to optimize radionuclide production. -- Abstract: The degradation of proton beam energy within a target stack was monitored via product nuclide ratios at the Los Alamos Isotope Production Facility (LANL-IPF). Nuclear reaction channels employed as energy monitors included ^NatNi(p,x)⁵⁷Co and ^NatNi(p,x)⁵⁷Ni. Natural nickel foils (thicknesses 0.025 mm) were used to determine proton beam energies ranging from 15 to 30 MeV. Energy values were estimated from a fitted ⁵⁷Ni/⁵⁷Co production activity ratio curve, which, in turn, was calculated from formation cross section data. Isotope production yields in the low energy “C” slot at LANL-IPF are very sensitive to beam energy, and differences of several MeV can translate into a drastic effect on overall production yields and radiochemical purity. Proton energies determined in this target stack position using nickel foils will serve as a basis to optimize radionuclide production in terms of product yield maximization and by-product minimization.

[en] Highlights: • Protactinium-230 produced from proton irradiation of thin thorium targets at LANL-IPF. • Proton energy distribution through the targets determined from nickel monitor foil reactions and SRIM simulations. • Solid-phase extraction chromatography of ²³⁰Pa from the irradiated target matrix with high recovery. • Production yields of ²³⁰Pa exceeding the theoretical yields. - Abstract: Uranium-230 (t_1/2 = 20.8 d) is an alpha-emitting radionuclide that has potential application in targeted alpha therapy (TAT) of cancer. Its parent isotope ²³⁰Pa (t_1/2 = 17.4 d), can be produced by proton irradiation of thorium metal targets. Preliminary ²³⁰Pa production runs were performed at the Los Alamos National Laboratory Isotope Production Facility (LANL-IPF) using thin thorium metal targets and a proton beam energy of 15–30 MeV, followed by radiochemical separation of ²³⁰Pa from the irradiated target matrix. The measured ²³⁰Pa production yields were found to exceed the predicted values in most of the experiments that were performed. This data will inform further production efforts for providing ²³⁰Pa/²³⁰U for clinical trials.

[en] Introduction: "4"4Sc, a PET radionuclide, has promising decay characteristics (T_1_/_2 = 3.97 h, Eβ"+_a_v = 632 keV) for nuclear imaging and is an attractive alternative to the short-lived "6"8Ga (T_1_/_2 = 68 min, Eβ"+_a_v = 830 keV). The aim of this study was the optimization of the "4"4Sc production process at an accelerator, allowing its use for preclinical and clinical PET imaging. Methods: "4"4CaCO_3 targets were prepared and irradiated with protons (~ 11 MeV) at a beam current of 50 μA for 90 min. "4"4Sc was separated from its target material using DGA extraction resin and concentrated using SCX cation exchange resin. Radiolabeling experiments at activities up to 500 MBq and stability tests were performed with DOTANOC by investigating different scavengers, including gentisic acid. Dynamic PET of an AR42J tumor-bearing mouse was performed after injection of "4"4Sc-DOTANOC. Results: The optimized chemical separation method yielded up to 2 GBq "4"4Sc of high radionuclidic purity. In the presence of gentisic acid, radiolabeling of "4"4Sc with DOTANOC was achieved with a radiochemical yield of ~ 99% at high specific activity (10 MBq/nmol) and quantities which would allow clinical application. The dynamic PET images visualized increasing uptake of "4"4Sc-DOTANOC into AR42J tumors and excretion of radioactivity through the kidneys of the investigated mouse. Conclusions: The concept “from-bench-to-bedside” was clearly demonstrated in this extended study using cyclotron-produced "4"4Sc. Sufficiently high activities of "4"4Sc of excellent radionuclidic purity are obtainable for clinical application, by irradiation of enriched calcium at a cyclotron. This work demonstrates a promising basis for introducing "4"4Sc to clinical routine of nuclear imaging using PET

[en] PET is the favored nuclear imaging technique because of the high sensitivity and resolution it provides, as well as the possibility for quantification of accumulated radioactivity. "4"4Sc (T_1_/_2=3.97 h, Eβ"+=632 keV) was recently proposed as a potentially interesting radionuclide for PET. The aim of this study was to investigate the image quality, which can be obtained with "4"4Sc, and compare it with five other, frequently employed PET nuclides using Derenzo phantoms and a small-animal PET scanner. The radionuclides were produced at the medical cyclotron at CRS, ETH Zurich ("1"1C, "1"8F), at the Injector II research cyclotron at CRS, PSI ("6"4Cu, "8"9Zr, "4"4Sc), as well as via a generator system ("6"8Ga). Derenzo phantoms, containing solutions of each of these radionuclides, were scanned using a GE Healthcare eXplore VISTA small-animal PET scanner. The image resolution was determined for each nuclide by analysis of the intensity signal using the reconstructed PET data of a hole diameter of 1.3 mm. The image quality of "4"4Sc was compared to five frequently-used PET radionuclides. In agreement with the positron range, an increasing relative resolution was determined in the sequence of "6"8Ga<"4"4Sc<"8"9Zr<"1"1C<"6"4Cu<"1"8F. The performance of "4"4Sc was in agreement with the theoretical expectations based on the energy of the emitted positrons. - Highlights: • Six PET radionuclides ("1"8F, "6"4Cu, "1"1C, "8"9Zr, "6"8Ga and "4"4Sc) were produced at CRS ETH-PSI-USZ. • Preclinical PET was performed with Derenzo phantoms. • The FWHM values was determined for each radionuclide with the same preclinical PET scanner. • In agreement with decreasing positron energies, the image resolution increased: "6"8Ga<"4"4Sc<"8"9Zr<"1"1C<"6"4Cu<"1"8F. • The FWHM of the radionuclides, were in agreement with the theoretical predictions of Palmer et al. (2005).