Broad Energy Spectrum of Laser-Accelerated Protons for Spallation-Related Physics

A beam of MeV protons, accelerated by ultraintense laser-pulse interactions with a thin target foil, is used to investigate nuclear reactions of interest for spallation physics. The laser-generated proton beam is shown (protons were measured) to have a broad energy distribution, which closely resembles the expected energy spectrum of evaporative protons (below 50 MeV) produced in GeV-proton-induced spallation reactions. The protons are used to quantify the distribution of residual radioisotopes produced in a representative spallation target (Pb), and the results are compared with calculated predictions based on spectra modeled with nuclear Monte Carlo codes. Laser-plasma particle accelerators are shown to provide data relevant to the design and development of accelerator driven systems.

Figure 1

(a) Proton energy spectrum (laser protons, solid line) determined via measurements of ${}^{63}\mathrm{C}\mathrm{u}(p,n{)}^{63}\mathrm{Z}\mathrm{n}$ reactions in stacked Cu foils positioned behind a laser-irradiated $10\mu \mathrm{m}$ thick Al target (see text for details). (b) Calculated cross sections for proton production via spallation evaporation, EVAP, and spallation-intranuclear cascade plus evaporation, $\mathrm{I}\mathrm{N}\mathrm{C}+\mathrm{E}\mathrm{V}\mathrm{A}\mathrm{P}$, reactions in 0.8 GeV (dotted lines), 1.2 GeV (dashed lines), and 2.5 GeV (dash-dot-dotted lines) $p+\mathrm{P}\mathrm{b}$ interactions [15]. The calculated 1.2 GeV spectra (dashed lines) are shown normalized to the measured proton spectrum in (a); excellent agreement is observed with the evaporation spectrum for energies greater than 12 MeV.

Figure 2

Isotopic distributions of Bi residues in ${}^{\mathrm{n}\mathrm{a}\mathrm{t}}\mathrm{P}\mathrm{b}$ produced by protons with energy up to 50 MeV. The ratios of the yield of each isotope to the total Bi yield, as measured experimentally (white) and calculated (gray/black) using the experimental cross sections [20] and the experimental and theoretical proton spectra, are plotted.