  Energy-sum and angular correlation spectra of $e^+e^-$ pairs produced in the
$^{3}$H(p,$\gamma$)$^{4}$He nuclear reaction have been studied at $E_p$=510,
610 and 900 keV proton energies. The main features of the spectra can be
understood by taking into account the internal and external pair creations
following the direct proton radiative capture by $^{3}$H. However, these
processes cannot account for the observed peak around 115$^\circ$ in the
angular correlation spectra. This anomalous excess of $e^+e^-$ pairs can be
described by the creation and subsequent decay of a light particle during the
direct capture process. The derived mass of the particle is
$m_\mathrm{X}c^2$=16.94$\pm0.12 (stat) \pm 0.21 (syst)$~MeV. According to the
mass and branching ratio ($B_x=5.1(13)\times10^{-6}$), this is likely the same
X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 052501 (2016)]
for describing the anomaly observed in the decay of $^8$Be.
