In essence it was suggested that may happen a reaction resumable in the following terms
p⁺ + e⁻ → n γ
Now we propose a chain of steps that joined together shrinks in the overall above reaction.
In the first stage a proton p⁺ decays with formation of a positron β⁺ (anti-electron, electron with a positive charge) and a meson π⁰ (pion)
p⁺ → β⁺ + π⁰
This process, although not yet been observed experimentally in laboratory, is granted and expected by current theories.
Meson π⁰ is unstable and can decay in two ways: either forming two photons γ or giving rise to a positron β⁺, an electron e⁻ and a photon γ.
π⁰ → 2 γ
π⁰ → β⁺ + e⁻ + γ
The process that completes the dematerialisation is the electron annihilation with formation of two photons γ
β⁺ + e⁻ → 2 γ
The following image graphically illustrates the listed steps.