Total d+d--> alpha + eta cross sections near threshold.

The total cross section for [eta] production in deuteron-deuteron interactions has been measured at four different kinetic energies, from 0.7 MeV to 3.7 MeV above threshold. The squared amplitude is consistent with a constant value of [vert bar][ital f][vert bar][sup 2]=(24.6[plus minus]1.2[plus minus]1.7) nb/sr close to threshold (14[lt][ital p][sub [eta]][lt]40 MeV/[ital c]). Assuming that the [pi][sup 0]-[eta] mixing reaction mechanism is dominant, this result allows a prediction of ([ital d][sigma]/[ital d][Omega])[sub [pi][sup 0]]=(8.3[plus minus]0.5 [plus minus]0.6) pb/sr for the cross section of the isospin-forbidden reaction [ital d]+[ital d][r arrow][alpha]+[pi][sup 0] at the [eta]-threshold energy.