Large-scale production of 88Y and 88Zr/88Y generators: A proof of concept study for a 70 MeV H- cyclotron.

The large-scale production of 88Y with proton-induced reactions has been investigated from the perspective of new generation 70 MeV H- cyclotrons. Tandem target configurations are presented for both the direct production of 88Y as well as for producing 88Zr/88Y generators. Based on the relevant excitation functions, physical yields have been derived for 88Y production with Y2O3/SrCO3 tandem targets and 88Zr production with Zr/Y2O3 tandem targets. Yields are presented for optimized targets (i.e. optimum yield) as well as for balanced thermal loads on the individual targets. Liquid 88Zr/88Y generators have been produced using both natural Zr and Nb target materials, the former for dedicated productions and the latter as a byproduct by processing spent irradiated Nb capsules which normally would constitute radioactive waste. These stock solutions, which contain both the target material and 88Zr precursor, are retained virtually unchanged after processing except for the removal of 88Y on AG MP-50 macroporous cation-exchange resin. Methods are presented for the preparation of Nb stock solutions in hydrofluoric acid and Zr stock solutions in sulphuric acid. It is shown that multi-Ci productions of 88Y are feasible at a 70 MeV cyclotron facility, suitable for the needs of fracking applications. In addition, 88Zr/88Y generators can provide 88Y with very high specific activity, suitable for labelling of biomolecules. LA-UR-20-24305.

Pairing of thorium with selected primary target materials in tandem configurations: Co-production of 225Ac/213Bi and 230U/226Th generators with a 70 MeV H- cyclotron.

Several radionuclide production facilities based on a new generation of high-current, 70 MeV H- cyclotrons have been established in recent years and a number of new facilities are either under construction or being planned. In this study, the feasibility to produce 225Ac/213Bi and 230U/226Th generators via Th + p reactions at such a facility has been investigated. From the perspective of production yields, it has been found useful to compare the relevant reactions on thorium with those on other targets regularly employed in this energy region, in particular the natMg(p,x)22Na, natGa(p,x)68Ge, and natRb(p,x)82Sr reactions that have been exploited with 66 MeV proton beams at iThemba LABS for many years. Therefore, various tandem configurations of thorium with magnesium, gallium and rubidium are discussed based on the relevant nuclear data. In a few cases, the available data were judged to be insufficient in this energy region. New experimental cross sections are presented for 225Ac, 225Ra, and 230Pa in Th + p reactions as well as 22,24Na in natMg + p reactions. Integral yields have been derived for those radionuclides of main interest. Production yields expected from extended 70 MeV proton bombardments, on selected tandem-target configurations, are presented for 22Na, 68Ge, 82Sr, 225Ac, and 230Pa. It is concluded that 225Ac/213Bi generators can, in principle, be added to a production programme based at a 70 MeV H- cyclotron facility as the production rate is of similar magnitude to those of other well-established radionuclides in this energy region. Also, radio-contaminant levels for 225Ac are similar to those found in higher proton-energy windows. The scope for 230U/226Th generators, via bulk production of the precursor 230Pa, seems to be more limited due to a lower yield but can nevertheless be produced in clinically relevant quantities.

Concurrent spectrometry of annihilation radiation and characteristic gamma-rays for activity assessment of selected positron emitters.

A method is described to determine the activity of non-pure positron emitters in a radionuclide production environment by assessing the 511keV annihilation radiation concurrently with selected γ-lines, using a single High-Purity Germanium (HPGe) detector. Liquid sources of 22Na, 52Fe, 52mMn, 61Cu, 64Cu, 65Zn, 66Ga, 68Ga, 82Rb, 88Y, 89Zr and 132Cs were prepared specifically for this study. Acrylic absorbers surrounding the sources ensured that the emitted ß+-particles could not escape and annihilate away from the source region. The absorber thickness was matched to the maximum ß+ energy for each radionuclide. The effect on the 511keV detection efficiency by the non-homogeneous distribution of annihilation sites inside the source and absorber materials was investigated by means of Monte Carlo simulations. It was found that no self-absorption corrections other than those implicit to the detector calibration procedure needed to be applied. The medically important radionuclide, 64Cu, is of particular interest as its strongest characteristic γ-ray has an intensity of less than 0.5%. In spite of the weakness of its emission intensity, the 1346keV γ-line is shown to be suitable for quantifying the 64Cu production yield after chemical separation from the target matrix has been performed.

Production of (28)Mg by bombardment of (nat)Cl with 200MeV protons: Proof-of-concept study for a stacked LiCl target.

A stacked target consisting of ten Al-encapsulated LiCl discs, for producing (28)Mg via the (nat)Cl(p,X)(28)Mg process in the energy region 50-200MeV, is described. This target was irradiated with a 200MeV beam at an intensity of 100nA, providing information on both yield and outscattering losses. Results of a Monte Carlo modelling of the beam and target, by means of the code MCNPX, are also presented. Similar Al-encapsulated LiCl discs were individually irradiated with 66MeV proton beams of 65 and 90µA, respectively, to study their behaviour under high-intensity bombardment. Once removed from the Al encapsulation, the (28)Mg can be separated from the LiCl target material efficiently, using a 12.5cm x 1cm(2) column containing Purolite S950 chelating resin. The eluate contains (7)Be but no other measurable radio-contaminants. The removal of the (7)Be contaminant is performed by cation exchange chromatography in malate media, with (28)Mg being retained by the resin and (7)Be eluted.

The production of 8²Sr using larger format RbCl targets.

The production of (82)Sr at iThemba LABS is performed by the proton bombardment of a RbCl target using the facility's Vertical-Beam Target Station (VBTS). (82)Sr is separated from the target material using a method based on target dissolution, using dilute ammonium chloride solution, and the use of chromatographic methods on Purolite S950 ion exchange resin. After performing a further purification step using AG MP-50 macroporous cation exchange resin, the result is a product with a high radionuclidic purity and negligible Rb and Fe impurity content.

The use of selective volatization in the separation of 68Ge from irradiated Ga targets.

Cyclotron-produced (68)Ge can be separated from its Ga target material by dissolving the target in aqua regia and collecting the volatile (68)Ge in a solution containing 1.0M NaOH and 2% Na2SO3. The solution is then acidified with HF before being loaded onto a column containing AG MP-1 anion exchange resin. The column is rinsed with dilute HF to remove any remaining impurities, before eluting the desired product with 0.1M HCl. A radiochemically pure product is obtained.

The production of (88)Y in the proton bombardment of (nat)Sr: New excitation and separation studies.

The cyclotron production of (88)Y at iThemba LABS is performed via the reaction (88)Sr(p,n)(88)Y. The yields obtained were inconsistent with nuclear data obtained from the literature and the excitation function of the nuclear reaction was re-measured, using a differentiation of thick-target production rate measurements. Ion exchange chromatographic methods are described to separate (88)Y from (nat)Sr target material using AG MP-1 resin and AG 50W-X4 resins, respectively.

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

Yield and purity of 82Sr produced via the natRb(p,xn) 82Sr process.

The recently reported cross-section data for the production of 82Sr via the natRb(p,xn) 82Sr process were evaluated. For the natRb(p,xn) 85Sr process, cross-sections were measured experimentally over the proton energy range of 25-45 MeV, a region where very few data existed. An evaluation of the recently published data on the formation of 85Sr was then also performed. From the recommended data curves, the integral yields of the desired radionuclide 82Sr and the impurity 85Sr were calculated. Yields were also determined experimentally over several energy ranges using thick natRbCl targets. The experimental and calculated yields were found to be in agreement within 15%. These integral tests add confidence to the evaluated cross-section data. For the production of 82Sr, an incident proton energy of 60 MeV or above is recommended; the 85Sr impurity then corresponds to <20%.

Comments on the feasibility of 61Cu production by proton irradiation of (nat)Zn on a medical cyclotron.

Feasibility of 61Cu production in high radionuclidic purity form via (nat)Zn(p,x) 61Cu nuclear process is discussed. Based on the experimentally available cross-sections of the (nat)Zn(p,x) 61Cu, (nat)Zn(p,x) 60Cu and (nat)Zn(p,x) 64Cu nuclear processes the usefulness of the (nat)Zn(p,x) 61Cu process for high-scale production is questionable in the 22 --> 12 MeV energy range.

Formation of short-lived positron emitters in reactions of protons of energies up to 200 MeV with the target elements carbon, nitrogen and oxygen.

Excitation functions were measured by the stacked-foil technique for proton induced reactions on carbon, nitrogen and oxygen leading to the formation of the short-lived positron emitters (11)C (T(1/2) = 20.38 min) and (13)N (T(1/2) = 9.96 min). The energy region covered extended up to 200 MeV. The product activity was measured non-destructively via gamma-ray spectrometry. A careful decay curve analysis of the positron annihilation radiation was invariably performed. The experimental results were compared with theoretical data obtained using the modified hybrid nuclear model code ALICE-IPPE for intermediate energies. The agreement was found to be generally satisfactory. The data are of importance in proton therapy.

Integral excitation functions for natKr + p up to 116 MeV and optimization of the production of 81Rb for (81m)Kr generators.

Effective cross-sections for the production of 79,81,81m,82m,83,84,84m,86Rb, (77,79,85m)Kr and 77,82Br in the bombardment of natKr with protons were measured from threshold up to 116 MeV. Thick-target production-rate curves based on the measured integral excitation functions were also derived for 81,82m,83,84,86Rb, and the optimum incident energy for the production of 81Rb/(81m)Kr, as a function of the target thickness in MeV, was determined. Geometry-dependent hybrid-model calculations performed by means of the computer code ALICE/85/300 were found to be in good agreement with the experimental results as well as the derived thick-target production-rate curves.

Production of 52Fe via proton-induced reactions on manganese and nickel.

Excitation functions for the production of 52Fe in the bombardment of Mn and Ni with protons were measured from threshold up to 200 MeV. Production rates of 52Fe as well as of its 55Fe and 59Fe impurities were also measured in specific energy windows ranging up to 100 MeV. The agreement with previous measurements, where available, is reasonably good, except that considerably higher 55Fe contamination levels than those recently reported below 70 MeV were obtained in the case of Ni. The experimental results were compared with theoretical calculations by means of the computer code ALICE/85/300. Overall agreement to within a factor of two was obtained, and the usefulness of the code in planning a radioisotope production process was demonstrated. Finally, practical production rates and impurity levels, obtained with a 66 MeV proton beam at high intensities (approximately 50 microA), are reported.