Measurement and modeling of proton-induced reactions on arsenic from 35 to 200 MeV

Abstract

72 As is a promising positron emitter for diagnostic imaging that can be employed locally using a 72 Se generator. However, current reaction pathways to 72 Se have insufficient nuclear data for efficient production using regional 100-200 MeV high-intensity proton accelerators. In order to address this deficiency, stacked-target irradiations were performed at LBNL, LANL, and BNL to measure the production of the 72 Se/ 72 As PET generator system via 75 As(p,x) between 35 and 200 MeV. This work provides the most well-characterized excitation function for 75 As(p,4n) 72 Se starting from threshold. Additional focus was given to report the first measurements of 75 As(p,x) 68 Ge and bolster an already robust production capability for the highly valuable 68 Ge/ 68 Ga PET generator. Thick target yield comparisons with prior established formation routes to both generators are made. In total, high-energy proton-induced cross sections are reported for 55 measured residual products from 75 As, nat Cu, and nat Ti targets, where the latter two materials were present as monitor foils. These results were compared with literature data as well as the default theoretical calculations of the nuclear model codes TALYS, CoH, EMPIRE, and ALICE. Reaction modeling at these energies is typically unsatisfactory due to few prior published data and many interacting physics models. Therefore, a detailed assessment of the TALYS code was performed with simultaneous parameter adjustments applied according to a standardized procedure. Particular attention was paid to the formulation of the two-component exciton model in the transition between the compound and preequilibrium regions, with a linked investigation of level density models for nuclei off of stability and their impact on modeling predictive power. This paper merges experimental work and evaluation techniques for high-energy charged-particle isotope production in an extension to an earlier study of this kind.

Summary Report of the Technical Meeting on Nuclear Data for Medical Applications

“…Collaboration has been established between Brookhaven, Lawrence-Berkeley and Los Alamos National Laboratories to help address the data needs within the US DOE Isotope Program for emerging isotope production pathways, and measure (p,x) reactions relevant to isotope production from threshold to 200 MeV for both the primary isotopes of interest and their impurities. Results from the TREND collaboration have been published for 75 As(p,x) 68 Ge, 72 Se [31] and 93 Nb(p,x) 90 Mo [32,33] and their impurities, and results for the nat Tl(p,x) 202 Pb, nat Sb(p,x) 119m,121m Te, and nat La(p,x) 134 Ce reaction campaigns will be submitted shortly for publication. Each of these five campaigns have yielded measurements of 25-40 unique product channels spanning proton energies from 0 to 200 MeV, resulting in a significant amount of high-fidelity and internally consistent reaction data suitable for identifying and correcting deficiencies in the reaction modelling of these channels.…”

“…This modelling work has also revealed the potential dangers involved in the evaluation of a single reaction channel of interest: regardless of adopting a descriptive or predictive evaluation process, evaluations of experimental data based on a single reaction channel lead inherently to false minima for other channels that arise as a consequence of the constrained nature of the total cross section. This has a direct impact on neighboring reaction channels (such as for the production of contaminant radionuclides), and affects calculations in the planning of a production target [31,32]. Model-based evaluations should be performed simultaneously on as many strongly-fed reaction channels as possible, including notable contaminants, to ensure that the recommended cross sections are physically selfconsistent.…”

“…90 Mo is also completely immune to (n,x) production on 93 Nb, being produced only via the primary proton beam, whereby only the 90 Mo γ lines can be observed as daughter 90 Nb undergoes ε decay to stable 90 Zr. Our group has performed and published three measurements of this excitation function and all three studies observed competing reaction channels up to 200 MeV [31,32,33], with a further three imminent experiments along with additional EXFOR data already available that together lay considerable groundwork for undertaking a more comprehensive evaluation.…”