[en] The use of a detection system involving an assembly of four stainless steel plates for neutrino-deuterium exposures in the FNAL 15-foot bubble chamber is discussed. With the initial design, track and chamber fiducials were not in focus from all cameras. Modifications to the plates to overcome these difficulties are under consideration and to gauge the utility of the downstream array it is necessary to have reliable estimates of its γ and e^+-detection capabilities. A study of a trimmed downstream plate array, as currently envisaged at Fermilab, using the Monte Carlo technique is reported. To obtain the necessary data the following reactions have been simulated: (1) Photons from νsub(μ) + D₂ reactions exclusive channels. (2) Photons, e⁺s from νsub(μ) + D₂ reactions, inclusive channels. (3) Showering in plates, photon conversion in deuterium. (U.K.)