Dùng hạt(alpha ) có động năng K bắn vào hạt nhân(_{7}^{14}N) đứng yên

(begin{array}{l}
tan {20^o} = frac{{{P_H}}}{{{P_X}}} Leftrightarrow {left( {tan {{20}^o}} right)^2} = frac{{{m_H}{K_H}}}{{{m_X}{K_X}}}\
to {K_X} = frac{{{m_H}{K_H}}}{{{m_X}{{left( {tan {{20}^o}} right)}^2}}} = frac{{{K_H}}}{{17{{left( {tan {{20}^o}} right)}^2}}}\
sin {20^o} = frac{{{P_H}}}{{{P_alpha }}} Leftrightarrow {left( {sin {{20}^o}} right)^2} = frac{{{m_H}{K_H}}}{{{m_alpha }{K_alpha }}}\
to {K_alpha } = frac{{{m_H}{K_H}}}{{{m_alpha }{{left( {tan {{20}^o}} right)}^2}}} = frac{{{K_H}}}{{4{{left( {sin {{20}^o}} right)}^2}}}
end{array})

(frac{{{K}_{H}}}{17{{left( tan {{20}^{2}} right)}^{2}}}+{{K}_{H}}-frac{{{K}_{H}}}{4{{left( sin {{20}^{o}} right)}^{2}}}=-1,21MeV) suy ra ({{K}_{H}}=1,746MeV)