The cross sections for the $ \mathrm{Al}^{27}(p,3pn) $ and $ \mathrm{C}^{12}(p,pn)\mathrm{C}^{11} $ reactions are considered to be in error. The data are based on the 10.8-mb value for the $ \mathrm{Al}^{27}(p,3pn) $ cross section at 420 MeV. Figure 1 shows that the $ \mathrm{C}^{12}(p,pn)\mathrm{C}^{11} $ cross section is insensitive to the incident proton energy in the studied range. Similar results were found for other reactions, suggesting that the probability of ejecting a small number of nucleons from a small nucleus remains constant over a wide energy range. However, meson production increases with energy, becoming a probable process. In large nuclei, mesons may be reabsorbed, shifting the maximum in the energy deposition spectrum to higher values. In small nuclei, meson reabsorption is less important, so the cross sections for reactions in light nuclei remain almost unchanged. The conservation of isotopic spin is a key concept, and it is shown that the usual principle of invariance under isotopic spin rotation is not consistent with localized fields. Instead, a principle of isotopic gauge invariance is proposed, leading to the existence of a b field with properties similar to the electromagnetic field. The b field satisfies nonlinear differential equations, and its quanta have spin unity, isotopic spin unity, and electric charge $ \pm e $ or zero. The paper explores the mathematical formulation of isotopic gauge invariance, the quantization of the b field, and the properties of its quanta. The b field equations are derived, and the interaction of the b field with other fields is discussed. The quanta of the b field are shown to have spin and isotopic spin unity, and their electric charge is determined by the conservation of electric charge. The mass of the b quantum remains an open question, as it is not possible to determine it from the given information. The existence of the b field is consistent with experimental information if its mass is within a certain range.The cross sections for the $ \mathrm{Al}^{27}(p,3pn) $ and $ \mathrm{C}^{12}(p,pn)\mathrm{C}^{11} $ reactions are considered to be in error. The data are based on the 10.8-mb value for the $ \mathrm{Al}^{27}(p,3pn) $ cross section at 420 MeV. Figure 1 shows that the $ \mathrm{C}^{12}(p,pn)\mathrm{C}^{11} $ cross section is insensitive to the incident proton energy in the studied range. Similar results were found for other reactions, suggesting that the probability of ejecting a small number of nucleons from a small nucleus remains constant over a wide energy range. However, meson production increases with energy, becoming a probable process. In large nuclei, mesons may be reabsorbed, shifting the maximum in the energy deposition spectrum to higher values. In small nuclei, meson reabsorption is less important, so the cross sections for reactions in light nuclei remain almost unchanged. The conservation of isotopic spin is a key concept, and it is shown that the usual principle of invariance under isotopic spin rotation is not consistent with localized fields. Instead, a principle of isotopic gauge invariance is proposed, leading to the existence of a b field with properties similar to the electromagnetic field. The b field satisfies nonlinear differential equations, and its quanta have spin unity, isotopic spin unity, and electric charge $ \pm e $ or zero. The paper explores the mathematical formulation of isotopic gauge invariance, the quantization of the b field, and the properties of its quanta. The b field equations are derived, and the interaction of the b field with other fields is discussed. The quanta of the b field are shown to have spin and isotopic spin unity, and their electric charge is determined by the conservation of electric charge. The mass of the b quantum remains an open question, as it is not possible to determine it from the given information. The existence of the b field is consistent with experimental information if its mass is within a certain range.