Measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>(<i>γ</i>,p<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>H total cross section and charge symmetry

The absolute total cross section for the $^{4}\mathrm{He}$(\ensuremath{\gamma},p${)}^{3}$H reaction has been measured in the \ensuremath{\gamma}-ray energy region between 28.6 and 58.1 MeV with a monochromatic photon beam and a nearly 4\ensuremath{\pi} proton detector. The comparison of our results with the most recent data on the $^{4}\mathrm{He}$(\ensuremath{\gamma},n${)}^{3}$He total cross section provides a mean value of ${\mathit{R}}_{\ensuremath{\gamma}}$=\ensuremath{\sigma}(\ensuremath{\gamma},p)/\ensuremath{\sigma}(\ensuremath{\gamma},n) =1.01\ifmmode\pm\else\textpm\fi{}0.06 between 28.6 and 42.4 MeV and tends to exclude a strong isospin mixing in the $^{4}\mathrm{He}$ due to charge symmetry breaking of the nuclear force.