Gamma rays produced by 1.75- to 4-MeV proton bombardment of thick aluminum targets

In the few-MeV energy range below the (p,n) threshold, gamma rays are produced from proton bombardment of aluminum via the 27Al(p,p′γ)27Al, 27Al(p,α,γ)24Mg, and 27Al(p,γ)28Si reactions. Thick-target γ-ray yield data are important for various applications, including radiation shielding near accelerators and γ-ray background interference in experiments that focus on other materials. We measured p+Al γ-ray spectra over the photon energy range 0.5–15 MeV and at 0° and 90° laboratory angle relative to the incident proton beam. In the experiment, mono-energetic proton beams of 1.75, 2, 2.5, 3, 3.5, and 4 MeV irradiated thick stopping targets of pure aluminum. The resulting gamma rays were detected by 7.62×7.62 cm2 NaI scintillation detectors. The spectra were unfolded using detector response functions calculated with the Monte Carlo code MCNP-4C. We report γ-ray spectra and tabulated γ-ray yields that can be used in applications that involve protons incident on thick aluminum targets at energies ⩽4 MeV.