Collision damping in the pi 3He ->d'N reaction near the threshold

We present a simple quantum mechanical model exploiting the optical potential approach for the description of collision damping in the reaction π 3 He → d ′ N near the threshold, which recently has been measured at TRIUMF. The influence of the open d ′ N → NNN channel is taken into account. It leads to a suppression factor of about ten in the d ′ survival probability. Applications of the method to other reactions are outlined.