Speaker
Description
Multihundred MeV proton accelerators are promising sites for the large scale production of medical radionuclides due to the high production rates enabled by their high-intensity beam capabilities and the long range of high-energy protons. However, the ability to reliably conduct isotope production at these accelerators and model relevant (p,x) reactions in the 100–200 MeV range is hampered by a lack of measured data. The current suite of predictive reaction-modeling codes is only accurate to within approximately 20% for (p,x) and (n,x) reaction channels where a large body of experimental measurements currently exist. In cases where few data exist, these codes often exhibit discrepancies anywhere within a factor of 2–50. In order to address this deficiency, stacked-target irradiations were performed at LBNL, LANL, and BNL, measuring proton-induced reactions on niobium, arsenic, and lanthanum targets from threshold to 200 MeV.
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 assessment has revealed a systematic trend in how residual product excitation functions for high-energy proton-induced reactions on spherical nuclei are miscalculated in the current exciton model scheme. Additionally, adjustments made to the TALYS ldmodel 4 (Goriely) and ldmodel 6 (HFB+Gogny) level densities illustrate the reliance of reaction modeling upon well-characterized models of the nuclear level density at high excitation energy [1, 2].
[1] M. B. Fox, A. S. Voyles, J. T. Morrell, L. A. Bernstein, J. C. Batchelder, E. R. Birnbaum, C. S. Cutler, A. J. Koning, A. M. Lewis, D. G. Medvedev, F. M. Nortier, E. M. O’Brien, and C. Vermeulen, “Measurement and modeling of proton-induced reactions on arsenic from 35 to 200 MeV,” Physical Review C, vol. 104, p. 064615, dec 2021.
[2] M. B. Fox, A. S. Voyles, J. T. Morrell, L. A. Bernstein, A. M. Lewis, A. J. Koning, J. C. Batchelder, E. R. Birnbaum, C. S. Cutler, D. G. Medvedev, F. M. Nortier, E. M. O’Brien, and C. Vermeulen, “Investigating high-energy proton-induced reactions on spherical nuclei: Implications for the preequilibrium exciton model,” Physical Review C, vol. 103, p. 034601, mar 2021.
