Excitation function of Ge(p,xnyp) reactions and production of 68Ge

On Cyclotron-Based Production of Gallium-68 Isotope: A Computational Benchmark for the Production Yield & Shielding Considerations

Gallium-68 (68Ga) has played a relevant role for the novel studies in the nuclear medicine area. Its production has been made traditionally and initially using 68Ge/68Ga generators. These devices represent some flaws, namely, high costs, low activity per elution, and long-time waiting between elutions. In order to address these concerns, the cyclotron-based production of 68Ga has been recently investigated and has shown promising outcomes regarding the activity at the end of bombardment for both solid and liquid targets. Currently, the use of computational codes and theoretical calculations takes relevance when it comes to calculating relevant nuclear physics quantities such as the production yield and the ambient dose rate. These outcomes are important for having a proper understanding of all the reactions involved during an irradiation routine with protons on a target. In this work, we used important cad-based programs, Monte Carlo codes, and a deterministic calculator with the objective of making a full benchmark with a previous experimental research. We also calculated the shielding requirements for this kind of isotope production facility. The proposed shielding materials and their respective thickness showed to be sufficient to avoid high ambient dose rates outside the machine. For the production yield, we found out that a hybrid combination of Monte Carlo codes and subsequently a computation with a deterministic calculator gave us more precise results for the irradiation conditions considered here.

Radioarsenic: A promising theragnostic candidate for nuclear medicine

Molecular imaging is a non-invasive process that enables the visualization, characterization, and quantitation of biological processes at the molecular and cellular level. With the emergence of theragnostic agents to diagnose and treat disease for personalized medicine there is a growing need for matched pairs of isotopes. Matched pairs offer the unique opportunity to obtain patient specific information from SPECT or PET diagnostic studies to quantitate in vivo function or receptor density to inform and tailor therapeutic treatment. There are several isotopes of arsenic that have emissions suitable for either or both diagnostic imaging and radiotherapy. Their half-lives are long enough to pair them with peptides and antibodies which take longer to reach maximum uptake to facilitate improved patient pharmacokinetics and dosimetry then can be obtained with shorter lived radionuclides. Arsenic-72 even offers availability from a generator that can be shipped to remote sites and thus enhances availability. Arsenic has a long history as a diagnostic agent, but until recently has suffered from limited availability, lack of suitable chelators, and concerns about toxicity have inhibited its use in nuclear medicine. However, new production methods and novel chelators are coming online and the use of radioarsenic in the pico and nanomolar scale is well below the limits associated with toxicity. This manuscript will review the production routes, separation chemistry, radiolabeling techniques and in vitro/in vivo studies of three medically relevant isotopes of arsenic (arsenic-74, arsenic-72, and arsenic-77).

Systematics of (p,α) (p,nα), and (p,np) reaction cross-sections

Semi-empirical systematics of (p,alpha) (p,nalpha), and (p,np) reaction cross-sections were obtained at various incident proton energies from 17.9 to 28.5 MeV. Systematics are based on analytical formulas derived using the pre-equilibrium exciton model, evaporation model and semi-empirical mass formula. Parameters of systematics were fitted to the data obtained from the analysis of available measured cross-sections for (p,alpha) (p,nalpha), and (p,np) reactions.

Excitation functions of natGe(p,xn)71,72,73,74As reactions up to 100MeV with a focus on the production of 72As for medical and 73As for environmental studies

Excitation functions for the formation of the arsenic radionuclides (71)As, (72)As, (73)As and (74)As in the interaction of protons with (nat)Ge were measured from the respective threshold energy up to 100 MeV. The conventional stacked-foil technique was used and the needed thin samples were prepared by sedimentation. Irradiations were done at three cyclotrons: CV 28 and injector of COSY at Forschungszentrum Jülich, and Separate Sector Cyclotron at iThemba LABS, Somerset West. The radioactivity was measured via high-resolution gamma-ray spectrometry. The measured cross section data were compared with the literature data as well as with the nuclear model calculations. In both cases, the results generally agree but there are discrepancies in some areas, the results of nuclear model calculation and some of the literature data being somewhat higher than our data. The integral yields of the four radionuclides were calculated from the measured excitation functions. The beta(+) emitting nuclide (72)As (T(1/2)=26.01 h) can be produced with reasonable radionuclidic purity ((71)As impurity: <10%) over the energy range E(p) = 18-->8 MeV; the yield of 93 MBq/microAh is, however, low. The radionuclide (73)As (T(1/2)=80.30 d), a potentially useful indicator in environmental studies, could be produced with good radionuclidic purity ((74)As impurity: <11%) over the energy range E(p) = 30 --> 18 MeV, provided, a decay time of about 60 days is allowed. Its yield would then correspond to 2.4 MBq/microAh, and GBq amounts could be produced when using a high current target.

A new method for radiochemical separation of arsenic from irradiated germanium oxide

Radioarsenic labelled radiopharmaceuticals could be a valuable asset to Positron Emission Tomography (PET). In particular, the long half-lives of (72)As (T(1/2)=26 h) and (74)As (T(1/2)=17.8 d) allow to investigate slow physiological or metabolical processes, like the enrichment and distribution of antibodies in tumor tissue. This work describes the direct production of no-carrier-added (nca) arsenic isotopes *As, with *=71, 72, 73, 74 or 77, the reaction to [*As]AsI(3) and its radiochemical separation from the irradiated solid germanium oxide via polystyrene-based solid-phase extraction. The germanium oxide target, irradiated at a cyclotron or a nuclear reactor, is dissolved in concentrated HF and Ge is separated almost quantitatively (99.97%) as [GeF(6)](2-). [*As]AsI(3) is formed by addition of potassium iodide. The radiochemical separation yield for arsenic is >90%. [*As]AsI(3) is a versatile radioarsenic labelling synthon.

Cyclotron production of 67Ga(III) with a tandem natGe-natZn target

Production of 67Ga(III) at the National Accelerator Centre is by proton bombardment of a natZn target, and uses 15-20 h of cyclotron beam time per production. A study was undertaken to use a tandem natGe-natZn target to produce the same amount of 67Ga, but using less beam time (7-8 h). 67Ga(III) was separated from the tandem target material by a method based on acid dissolution of the target and chromatography on an organic polymer resin (Amberchrom CG-71cd) containing no ion exchange groups. The separated 67Ga(III) has high radionuclidic purity and complies with the British and US Pharmacopoeia requirements for chemical purity.